close

Вход

Забыли?

вход по аккаунту

?

The formation of excimer molecules in microwave discharges

код для вставкиСкачать
THE FORMATION OF EXCIMER MOLECULES IN
MICROWAVE DISCHARGES
T h e s is p r e s e n t e d by
T *G ,F rank MSc
to th e
U n i v e r s i t y o f S t . Andrews
i n a p p l i c a t i o n f o r t h e d e g re e o f
D o c to r o f P h ilo s o p h y
F e b r u a r y 1984
ProQuest Number: 10166274
All rights reserved
INFORMATION TO ALL USERS
The quality of this reproduction is d e p e n d e n t upon the quality of the copy subm itted.
In the unlikely e v e n t that the a u thor did not send a c o m p le te m anuscript
and there are missing pages, these will be noted. Also, if m aterial had to be rem oved,
a n o te will ind ica te the deletion.
uest
ProQuest 10166274
Published by ProQuest LLO (2017). C opyright of the Dissertation is held by the Author.
All rights reserved.
This work is protected against unauthorized copying under Title 17, United States C o d e
Microform Edition © ProQuest LLO.
ProQuest LLO.
789 East Eisenhower Parkway
P.Q. Box 1346
Ann Arbor, Ml 4 8 1 0 6 - 1346
I !
DECLARATION
I
h e re b y c e r t i f y t h a t t h i s t h e s i s h a s b e e n com posed by me,
r e c o r d o f work done by me,
and i s a
and h a s n o t p r e v i o u s l y b e e n p r e s e n t e d f o r
a h ig h e r d e g re e .
T h is
S t,
r e s e a r c h was c a r r i e d o u t i n th e P h y s ic a l S c ie n c e s L a b o r a to r y o f
S a l v a t o r ’ s C o lle g e ,
i n t h e U n i v e r s i t y o f S t . A ndrew s, u n d e r th e
s u p e r v i s i o n o f D r. M a itla n d ,
T .G .F ra n k
CERTIFICATE
I c e r t i f y t h a t T .G .F ra n k h a s s p e n t n in e te rm s a t r e s e a r c h work i n t h e
P h y s ic a l
S c ie n c e L a b o r a to r y o f
U n iv e rs ity o f S t.
S t.
S a lv a to r’s
C o lle g e ,
in
th e
A ndrew s, u n d e r my d i r e c t i o n , t h a t h e f u l f i l l e d t h e
c o n d i t i o n s o f O rd in a n c e N o ,16 ( S t ,
A ndrew s) and t h a t he i s q u a l i f i e d
to
in
s u b m it
th e
f o llo w in g
th e s is
a p p l i c a t i o n f o r th e D eg re e o f
D o c to r o f P h ilo s o p h y .
A, M a itla n d
R e s e a rc h S u p e r v is o r
AUTHOR’ S CAREER
B orn
i n 1946 i n P a ig n to n ,
C ounty
S e c o n d a ry
T o rq u a y ,
M odern
S tu d ie d f o r
U n iv e rs ity
In c lu d in g
D evon.
School
firs t
( 1 9 6 5 -1 9 6 8 ) .
S e c o n d a ry e d u c a t io n
and
In d u s trie s ,
up
to
1973*
P ost
in
P h y s ic s ,
em ploym ent
a p e r io d a s a d e v e lo p m e n t
e n g in e e r
in
at
th e
w ith
L a n c a s te r
London a r e a ,
Rank
P re c is io n
G ra d u a te C e r t i f i c a t e i n E d u c a tio n
o b t a i n e d a t L eed s U n i v e r s i t y ( 1 9 7 2 -1 9 7 3 ) .
From 1973 t o 1978 em ployed
a s a p h y s ic s t e a c h e r a t M organ Academy, D undee.
The
P a ig n to n
S o u th Devon T e c n ic a l C o lle g e ,
d e g re e ,
V a rio u s
at
O b ta in e d a n MSc.
P r i n c i p l e s o f I n s tr u m e n t D e sig n a t A b erdeen U n i v e r s i t y i n
T h is
one
year
c o u rse
in c l u d e d
th e
r e p o r t e d on t h e d e s ig n ,
c o n s tru c tio n ,
a u th o r
of
p lo ttin g
r e fra c tiv e
an
in s tru m e n t
fo r
in d e x i n g l a s s s a m p le s .
v e ry
From 1979
a u th o r h as s t u d i e d e x c im e r l a s e r s a t S t .
1979*
p re p a ra tio n of a t h e s i s .
th e s is
and
te s tin g
s m a ll
to
th e
in
by
The
th e
v a ria tio n s in
p rese n t
Andrews U n i v e r s i t y .
th e
ACKNOWLEDGEMENTS
I w ould l i k e t o th a n k D r. M a itla n d f o r h i s a s s i s t a n c e th r o u g h o u t t h i s
w o rk .
H is e n th u s ia s m e s p e c i a l l y
te c h n ic a l
is
v e ry
much
a p p re c ia te d .
The
a s s i s t a n c e r e c e i v e d i s g r a t e f u l l y ack n o w led g ed w ith th a n k s
t o R. McRaw,
M. R o b e r ts o n ,
O u tw ith
U n iv e rs ity
th e
of
J . S p ark ,
S t.
B. M cAndie,
A ndrew s,
and F . Akerboom.
th a n k s
a r e due t o th e
D i r e c t o r o f The A d m ira lty S u r f a c e W eapons E s ta b lis h m e n t and D r. L acey
of
th e
lik e
E s ta b lis h m e n t
fo r
t h e l o a n o f th e r a d a r s e t .
t o th a n k D r. McKeague o f UKAEA D ounreay f o r
th e
I w ould a l s o
lo a n
of
th e
o p t i c a l s p e c tru m a n a l y s e r .
I
am
case
g ra te fu l
fo r
my f i n a n c i a l s u p p o r t w hich was i n t h e fo rm o f a
s t u d e n t s h i p from t h e SRC i n c o l l a b o r a t i o n w ith B a r r and
S tro u d
L t d . . F i n a l l y , I w ould t o th a n k S a l l y F ra n k f o r h e r e n c o u ra g e m e n t and
s u p p o r t th ro u g h o u t t h e p e r io d o f t h i s w o rk .
Ab s t r a c t
ABSTRACT
The F o rm a tio n o f E xcim er M o le c u le s I n M icrow ave D is c h a r g e s
E x p e rim e n ta l and t h e o r e t i c a l a s p e c t s o f th e f o r m a tio n o f e x c im er
m o le c u le s
in gas d isc h a rg e s a re d e s c rib e d .
E x p e rim e n ta l s t u d i e s a r e
o f t h e e m is s io n s p e c tru m o f r a r e - g a s h a l i d e m o le c u le s ,
m icrow ave
la s e r s
d is c h a rg e ,
and
to
d is c h a rg e .
p ro d u c in g
and c o v e r a s p e c t s r e l e v a n t to r a r e - g a s
h a lid e
th e p o s s i b i l i t y o f pum ping t h e s e l a s e r s by m icrow ave
T here
r e c o rd in g .
p ro d u c e d i n a
The
is
a
p a rtic u la r
a p p a r a tu s
50kW p u l s e s o f
c o n s is ts
320ns
e m p h asis
of
an
d u ra tio n
on
gas
life tim e
a d a p te d 3om r a d a r s e t ,
at
IIO O pps,
a
h a lo g e n
c o m p a tib le g a s h a n d lin g s y s te m , and an o p t i c a l s p e c tru m a n a l y s e r w ith
a
r e c o r d in g f a c i l i t y .
T h is p r o v id e s a
v e ry
fle x ib le
sy ste m
w ith
w id e s p re a d p o t e n t i a l f o r s p e c t r a l s t u d i e s .
R e a c tio n k i n e t i c s a r e d e s c r i b e d u s in g r a t e e q u a ti o n s ,
in v o lv e
co m p e tin g f o r m a tio n and l o s s p r o c e s s e s .
e v a lu a te d
to
c o n s titu e n t
The
lo ss
p r o v id e
lim its
fo r
g a s e s u n d e r th e c o n d i t i o n t h a t
of
fre e
r e c o m b in a tio n
and
r e c o m b in a tio n
shown
upper
th a t
p r o p o rtio n a l
h a lo g e n s
g iv e s
d o m in a te d
th e
to
by
th e
th e
The
and th e s e
e q u a tio n s
p a r tia l p ressu res of
f o r m a tio n
is
d o m in a n t.
d i f f u s i o n i s com pared w ith l o s s by
d e lin e a tio n
of
d iffu s io n
r e g i o n s o f th e o p e r a t in g c o n d i t i o n s .
th re s h o ld
lin e w id th /
a re
pump
power d e n s i t y
in a
la s e r
and
I t is
is
and t h a t f o r a t y p i c a l e x c im e r l a s e r
t h i s r e q u ir e m e n t i s a t l e a s t lOkW cm
Ab s t r a c t
D iffu s io n
l o s s o f h a lo g e n s i n • t h e
e x p e r im e n ta l
a p p a r a tu s
is
e x p e c te d t o be h ig h due t o t h e u s e o f a s m a ll d i a m e t e r ( 2 mm) d i s c h a r g e
tu b e and a s t r o n g r e a c t i o n b e tw e e n t h e tu b e m a t e r i a l ( q u a r t z ) and f r e e
h a lo g e n s .
to
D e t a il e d c a l c u l a t i o n s o f t h e l o s s o f h a lo g e n s by d i f f u s i o n
th e tu b e w a l l u n d e r t h e p u ls e d c 'o n d itio n s o f t h e
p r o v id e d .
a
e x p e rim e n t
a re
The th e r m a l b e h a v io u r i s e v a lu a te d and p e r m i ts t h e u s e o f
te m p e r a tu r e d e p e n d e n t d i f f u s i o n c o e f f i c i e n t .
I t i s shown t h a t t h e
e x c e s s g a s te m p e r a t u r e , a t e q u i l i b r i u m , above t h e w a ll te m p e r a tu r e i s
in d e p e n d e n t
o f th e gas p r e s s u r e ,
b u t t h a t d i r e c t p r o p o r tio n a lity to
t h e d i f f u s i v i t y m eans t h a t t h i s e x c e s s t e m p e r a tu r e i s p r o p o r t i o n a l t o
th e
mean a b s o l u t e g a s te m p e r a t u r e .
o u ts id e
of
d isc h a rg e
lo w e s t
th e
p ressu res
in te r-p u ls e
and
d is c h a r g e tu b e c a n be v e ry e f f e c t i v e i n c o o lin g t h e
gas w ith in .
c o n trib u tio n s
F o rc e d c o n v e c tio n c o o lin g o f t h e
A t t h e e x p e r im e n ta l p u l s e r a t e ,
( 0 .1 A t)
o f a p u ls e
p e rio d .
th e
d isa p p e a r
te m p e r a tu r e
w e ll
b e fo re
and
th e
and f o r
th e
c o n c e n tra tio n
end
of
th e
At t h e h i g h e s t p r e s s u r e s (2 A t) t h e te m p e r a tu r e
c o n c e n t r a t i o n f a l l by a b o u t 25% i n t h e i n t e r - p u l s e
p e rio d .
At
e q u i l i b r i u m , th e mean c o n c e n t r a t i o n o f f r e e h a lo g e n t h a t r e s u l t s from
e ffe c tiv e
c o o li n g ( f o r c e d c o n v e c tio n ) i s
a p p r o x im a te ly
tw ic e
th a t
a c h ie v e d w ith o u t e f f e c t i v e c o o li n g ( f r e e c o n v e c t i o n ) .
The
d e s ig n
c rite ria
f o r s u i t a b l e m icrow ave d is c h a r g e c o u p le r s
a r e d e v e lo p e d fro m a c o n s i d e r a t i o n o f m icrow ave d i s c h a r g e s , m icrow ave
p r o p a g a t io n ,
and
m u lt i- e le m e n t
d i r e c t i o n a l c o u p le r s may be p a r t i c u l a r l y
th e
e le m e n ts
c o u p lin g
c a lc u la tio n
th e
a b s o rp tio n
a re
schem e i s d e r i v e d
g rad ed
fo r
s k in
d e p th .
a lo n g
th e
th e
c o u p lin g
It
i s shown t h a t
s u ita b le
if
c o u p lin g r e g i o n .
fa c to rs
of
A
e a ch
Ab s t r a c t
3
e le m e n t
n e c e ssa ry
v o lu m e.
T h is a p p ro a c h i s a p p l i e d t o a S c h w in g e r d i r e c t i o n a l c o u p le r ,
chosen
b ecause
to
it
g iv e
u n ifo rm
e x c ita tio n
of
p e r m its a d e m o u n ta b le s t r u c t u r e ,
th e
d isc h a rg e
and d e t a i l s o f
c o n s t r u c t i o n and p e rfo rm a n c e a r e p r o v id e d .
The
e x p e r im e n ta l w ork c o n s i s t s m a in ly o f an e x t e n s i v e programme
t e s t i n g m ix tu r e s o f a r a r e - g a s (X e,
K r,
o r A r) w ith a h a lo g o n d o n o r
(S F g , NFg, o r HCl) and a b u f f e r g a s (H e, Ne, o r A r ) ,
work
co n cern s
A rF,
X eC l,
v a ria b le s
and
XeF b u t some r e s u l t s a r e a l s o p r e s e n t e d f o r
and K rC l.
a re
m ea su rem e n ts
te m p o ra l
KrF
The m a j o r i t y o f
The s p e c tru m o f XeO i s o b s e r v e d .
m ix tu r e
ra tio
and
The
m ain
t o t a l p r e s s u r e and t h e p r i n c i p a l
a r e a v a i l a b l e e i t h e r from i n t e g r a t e d
s p e c tra
r e c o r d s o f t h e i n t e n s i t y a t t h e s p e c tru m p e a k .
or
from
The r e s u l t s
form
an e m p i r ic a l
o p t i m i s a t i o n s tu d y . One o f t h e aim s o f t h i s s tu d y
was
to
m ix t u r e
fin d
flu o re s c e n t
T hese
th e
e m is s io n ,
r a t i o s and t o t a l p r e s s u r e s f o r w hich t h e
f o r any g iv e n e x c im e r s y s te m ,
was a maximum.
r a t i o s and p r e s s u r e s c o u ld t h e n be u s e d a s a s t a r t i n g p o i n t i n
a tt e m p t s
donor
to o b ta in la s in g .
because
s tu d ie d
it
is
a
C o n s id e r a b le u s e w as made o f SFg a s
c h e ap
th e
a l t e r n a t i v e t o NF^ and h a s n o t b e e n
i n d e t a i l a s a d o n o r e ls e w h e r e .
R e s u lts a r e e x tr a c te d
from
t h e m ain body o f r e s u l t s i n o r d e r t o com pare t h e p e rfo rm a n c e o f t h e s e
two
is
d o n o rs and t o com pare th e p e rfo rm a n c e o f t h e t h r e e b u f f e r s .
shown c o n c l u s i v e l y t h a t g r e a t e r l i f e t i m e s a r e o b t a i n a b l e w ith SFg
b u t a t t h e c o s t o f lo w e r i n t e n s i t i e s .
lo w e r
and
It
I n t h e b u f f e r c o m p a r is io n much
f l u o r e s c e n t e m is s io n i s o b s e rv e d when Ar i s u s e d ,
KrF m i x t u r e s ,
and t h a t d i s c h a r g e s a r e
lO O T orr.
Below
t h e optim um d i l u t i o n s th e
s im ila r.
H ow ever,
a t h ig h e r d ilu tio n s in
o n ly form ed
i n b o th XeF
below
about
r e s u l t s f o r He and Ne a r e
XeF
and
KrF
m ix t u r e s ,
Ab s t r a c t
4
f l u o r e s c e n t i n t e n s i t i e s a r e s i g n i f i c a n t l y g r e a t e r , and d i s c h a r g e s may
be
o b ta in e d a t g r e a te r t o t a l p r e s s u r e ,
m ix tu r e s
w ith
Ne
b u ffe r.
In
XeF
i t i s fo u n d t h a t g a s l i v e s a r e 4 t o 8 tim e s a s lo n g w ith Ne
b u f f e r a s th e y a r e w ith He b u f f e r .
The
te m p o ra l r e c o r d s p r o v id e g a s l i f e i n f o r m a t i o n
r a n g in g
p u ls e s
from
300
to
10^
p u ls e s .
tim e ) was d e v e lo p e d u s in g a m o n o ch ro m ato r,
w id th
rem ove
p e rio d .
e n a b le d
of
o s c illo s c o p e .
to
th e
a
sy s te m
( 5ns
resp o n se
f a s t p h o t o m u l t i p l i e r , and
B ecau se o f t h e v e ry s m a ll r a t i o o f t h e
in te r-p u ls e
p e rio d
s c a le
* To r e v e a l b e h a v io u r o v e r fe w e r
and w i t h i n s i n g l e p u l s e s a h ig h s p e e d
s to ra g e
on
p u lse
a b la n k in g s y s te m was d e v is e d t o
t h e o v e r - b r i g h t b a s e l i n e o c c u r r in g
d u r in g
th e
in te r-p u ls e
The h ig h r e p e t i t i o n r a t e o f IIO Opps and much r e d u c e d volum e
gas l i f e
m a g n itu d e
s t u d i e s t o be c a r r i e d o u t i n tim e s w hich a r e o r d e r s
s m a l le r
th a n
th o s e
re q u ire d
u s in g
th e
c o n v e n tio n a l e x c im e r l a s e r sy ste m w ith much g r e a t e r v olum e.
lO pps o f a
1
INTRODUCTION............................................ .
2
RARE-GAS HALIDE EXCIMER LASERS
2 .1
2 .2
F o rm a tio n K i n e t i c s . .
Q uenching K i n e t i c s
H a lid e K i n e t i c s
B u f f e r Gas K i n e t i c s .
L a s e r O p e r a tio n
........................................... 11
.
. ........................
. . . . . . . . . .
B a s ic E q u a tio n s
H eat T ra n sp o rt
D iffu s io n
................... 65
................................................................... . . .
77
78
D is c h a r g e E x c i t a t i o n by DC P u l s e s ......................................
M icrow ave D is c h a r g e E x c i t a t i o n . . .
................................................. 80
M icrow ave D is c h a r g e C o u p le rs
4 .2 .1
4 .2 .2
4 .2.3
. ,
. . . . . . . .
89
The C o u p lin g P ro b lem .............................................................. . . . . .
89
M icrow ave D is c h a r g e C o u p le r D e sig n . . . .
................................. 94
P r e i o n i s a t i o n M ethods
..................................
98
C o m p ariso n o f M icrow ave and DC D is c h a rg e A p p a r a t u s ......................... 100
MICROWAVE APPARATUS........................ . ....................................
5.1
53
, 55
63
C om parison o f M icrow ave and DC D i s c h a r g e s ............................................... 78
4 .1 .1
4 .1 .2
4.3
. . . . .
52
H eat T r a n s p o r t .
.........................................................
65
D i f f u s i o n .................................................
73
C o n c lu s io n s
.............................................................................. . 7 5
MICROWAVE DISCHARGE EXCITATION
4 .2
.............................................. 52
.......................................................................
....................................................................
A p p l i c a t i o n t o th e E x p e r im e n ta l S i t u a t i o n
3 .2 .1
3 .2 .2
3 .2 . 3
4 .1
.4 6
D e r i v a t i o n o f t h e C a l c u l a t i o n M ethod .........................................................
3 .1 .1
3 .1 .2
3 .1 .3
3 .2
23
. . . .
................................................ 23
................................. .......................................... 27
............................................
.3 3
........................................
40
HALOGEN LOSS BY DIFFUSION TO THE WALL . . . .
3 .1
5
..................................................... 11
E xcim er K i n e t i c s ...................................................
2 .3
5
E xcim er M o l e c u l e s ........................ .... ............................................................. 11
R a r e - Gas H a lid e M o le c u le s ........................................................................... 14
R a re -G as H a lid e B - X E m is s io n F e a t u r e s
.................................... . 1 9
2 .2 .1
2 .2 .2
2 .2 .3
2 .2 .4
4
. . . . . .
M o le c u la r S t r u c t u r e and S p e c tr o s c o p y . . .
2 .1 .1
2 .1 .2
2 .1 .3
3
. .
The R a d a r S e t
5 .1 .1
5 .1 .2
5 . 1.3
,
104
.........................
G e n e ra l D e s c r i p t i o n .............................
S a f e t y ............................................
D e t a i l s o f th e M a g n e tro n C i r c u i t r y
104
........................
,1 0 4
,107
.1 0 9
5 .2
R ad ar S e t A d a p t a t i o n ..............................................................................................I l l
5 .2 .1
5 .2 .2
5 .3
A l t e r a t i o n s and A d d i t i o n s .............................
W aveguide A s s e m b l y ..................................................................
M icrow ave D is c h a rg e C o u p l e r s ..............................................................................113
T ra n s v e rs e -T u b e C o u p le r ................................ ........................................114
L o n g i tu d i n a l- tu b e C o u p le r
. . . . . .
....................................... .116
S c h w in g e r C o u p le r
. . . . . . . . . . . . .
.119
5 .3.1
5 .3 . 2
5 .3. 3
6
OTHER APPARATUS
6.1
6 .2
'EXPERIMENTS
...................................... .... .................................................................130
E x p e rim e n ta l M ethods ........................
7.1
E x p e rim e n ta l Programme . . . . .
7.2
RESULTS
8.1
8 .2
8.3
8 .6
.138
XeF M ix tu re s . . . . . . . . . . .
.....................................................141
KrF M ix tu re s
............................. 142
XeCl M ix tu re s
............................ . ,143
L a s in g A t t e m p t s ......................... ..................................................................... 144
M ix tu re s W ith No B u f f e r G a s .............................
.145
..................................
146
S in g le P u ls e B e h a v io u r... ............................. . . . . . . . . . .
.147
................................. . . . . .
.150
P u ls e E n v e lo p e R e c o rd s . . . . .
T em poral R e c o r d s ................................................
150
C o n s ta n t I n t e n s i t y
..................... 151
T h ree P r o c e s s b e h a v io u r . . . . . . . .
.......................... . . .
,1 5 2
I n t e n s i t y D u rin g E a r ly P u l s e s .........................
,153
U n b u ffe re d M ix tu r e s o f N i t r o g e n - T r i f l u o r i d e and K ry p to n .1 5 5
Donor C om parison
B u f f e r Gas Type
8 .6 .1
8 .6 .2
8.7
......................... . ................................. 1 37
............................................................
T em poral B e h a v io u r
8 .4 .1
8 .4 .2
8 .4.3
8 .4 .4
8 .4 .5
8 .4 .6
8 .4 . 7
8.5
. I 31
E m p ir ic a l P r e s e n t a t i o n o f R e s u l t s . , . . . .
, . . , . . . . 138
E xcim er S p e c t r a
...................... I . . . . . . .
. '.1 4 0
M ix tu re R a t io s and T o ta l P r e s s u r e
................................................. 141
8 .3.1
8 .3 . 2
8 .3 . 3
8 .3.4
8 .3 . 5
8 .4
. . . . . . . . .
................................................131
I n t e n s i t y v s Time R e c o rd in g
S p ectru m R e c o rd in g . . . . . . . . .
................................................134
P u ls e R e c o rd in g « . . . .............................................................................135
7 . 1.1
7 .1.2
7 . 1.3
8
........................................................................... 122
O p t i c a l S p ectru m A n a ly s e r
....................................................................122
Gas H a n d lin g S ystem
........................................................................ 125
P u ls e R e c o rd in g S y s t e m ...........................................
127
6.3
7
.111
.‘113
....................................................................................... 156
........................................ 158
B u f f e r s i n XeF M ix tu re s
B u f f e r s i n KrF M ix tu re s
.
..........................................
.1 5 8
.............................,159
C o l l i s i o n a l R e l a x a t io n
REFERENCES
.
.......................................................
....................161
167
Chapter 1
E xcim er
in te n s e
la s e r
la s e rs
firs t
i n tr o d u c e d
i n 1975 and s u b s e q u e n t
i n t e r e s t has b ro u g h t th e s e l a s e r s t o th e
fie ld
p u ls e d
when
t h e r e q u ir e m e n t
r a d ia tio n in
e n e rg ie s .
from
w e re
The
th e
firs t
ÜV
is
s p e c tru m
s u g g e s tio n
th e
at
h ig h
p u ls e
pow ers
and
f o r a l a s e r sy ste m u s in g e m is s io n
made i n I9 6 0 by H outerm ans ( I 9 6 0 ) .
s y s te m s ,
of
f o r e f f i c i e n t p r o d u c tio n o f
th e bound - f r e e e l e c t r o n i c t r a n s i t i o n o f an
was
fo re fro n t
e x c im e r
m o le c u le
Of t h e many p o s s i b l e e x c im e r
th e r a r e - g a s h a l i d e s a r e o u t s t a n d in g a s e f f i c i e n t e m i t t e r s
o f u -v r a d ia tio n .
T h is was f i r s t d e m o n s tra te d w ith ArCl by G olde and
T h ru sh
(1974) and w ith s e v e r a l
S e ts e r
(1 9 7 5 ).
L aser
xenon
m o n o h a lid e s
by
V e la zc o
and
a c t i o n from XeBr was d e m o n s tra te d so o n a f t e r
t h i s by S e a r l e s and H a r t ( 1 9 7 4 ) , from XeF, X eC l, and KrF by Ewing and
B rau
(1 9 7 5 )
and
e x p e rim e n ts
c o m m ercial
B rau and
Ewing
(1975 a ) .
t h e d e v e lo p m e n t o f e x c im e r l a s e r s
s y s te m s
m a n u f a c tu r e r s ,
a re
now
a v a ila b le
r e f l e c t in g th e
c u rre n t
from
F o llo w in g t h e s e e a r l y
has
at
in te re s t
been
su c h
th a t
l e a s t s e v e n m a jo r
in
th e s e
w id e ly
a p p l i c a b l e d e v ic e s .
The e a r l i e r r a r e - g a s h a l i d e l a s e r s w ere pumped by h ig h i n t e n s i t y
re la tiv is tic
th e
e l e c t r o n beams b u t now t h e m ost commonly u s e d m ethod i s
tra n s v e rs e
th e s e
DC
d is c h a rg e .
pum ping m eth o d s e x i s t s
d is c h a rg e .
A new and c h a l l e n g i n g a l t e r n a t i v e t o
in
th e
u tilis a tio n
of
a
m icrow ave
M icrow ave e x c i t a t i o n h a s b e e n a c h ie v e d by M endelsohn e t .
a l . (1 9 8 1 ) f o r a XeCl l a s e r and f u r t h e r d e v e lo p m e n t o f t h e same sy s te m
is
re p o rte d
re p o rte d
by
by W is o ff e t .
a l . ( 1 9 8 2 ) . . M icrow ave e x c i t a t i o n i s a l s o
C h r i s t e n s e n and
W aynant (1982) f o r a XeF
la s e r.
T hese
Chapter 1
6
a r e th e o u t s t a n d in g r e p o r t s o f m icrow ave e x c i t a t i o n o f e x c im e r l a s e r s
to d a te .
re a l
I n t h e d i s c u s s i o n s o f C h a p te r 4 ,
a d v a n ta g e s
e x c ita tio n .
la s e r
may
re s u lt
from
i t i s s u g g e s te d t h a t many
th e
use
of
th is
m ethod
of
I n p a r t i c u l a r t h e l a c k o f e l e c t r o d e s i n c o n t a c t w ith t h e
g a s e s may g iv e much l o n g e r l i f e t i m e s ,
t h e d is c h a r g e a p p a r a tu s
may be v e ry c o m p a c t, and g r e a t e r p u ls e d u r a t i o n s and p u l s e r e p e t i t i o n
ra te s
may
be
in v e s tig a tio n
m icrow ave
fe a s ib le .
A c c o r d in g ly
th is
o f t h e f o r m a tio n o f r a r e - g a s
d is c h a rg e
and
p e r m i ts
an
th e s is
h a lid e
assessm en t
co n cern s
m o le c u le s
of
in
an
a
t h e m icrow ave
d i s c h a r g e pum ping schem e.
O u ts id e
m icrow ave
th e f i e l d o f
d isc h a rg e s
h av e
e x c im e r
la s e rs ,
th e
a p p lic a tio n s
been
w id e s p re a d
and
t h e i r fu n d a m e n ta l
p ro p e rtie s
h a v e b e e n i n v e s t i g a t e d i n d e p th .
d is c h a rg e s
d e v e lo p e d
8 . C.Brown
and W .P .A llis
T e c h n o lo g y .
The
c o n d itio n s
of
Many
a fte r
in
m icrow ave
1945 w ith p i o n e e r in g w ork by P r o f e s s o r s
at
e a rlie r
In te re s t
fo r
th e
w ork
M a s s a c h u s e tts
was
c o n c e rn e d
In s titu te
m a in ly
f o r t h e i n i t i a t i o n o f breakdow n and w ith t h e
w ith
of
th e
in te ra c tio n
low pow er m icro w av es w ith g a s e s i o n i s e d by an a l t e r n a t i v e s o u r c e .
t e x t s a r e a v a i l a b l e c o v e r in g t h e s e t o p i c s .
breakdow n
e x a m p le,
p r o c e s s i s d e s c r i b e d i n d e t a i l by M acDonald (1 9 6 6 ) and
in te ra c tio n
o f m icro w av es
W h a rto n (1 9 6 5 ).
d is c h a rg e s
c h e m is tr y
For
H ow ever,
w ith
much
p lasm a
is
c u rre n t
c o v e re d
by
in te re s t
in
H eald
th e
th e
and
m icrow ave
c o n c e r n s a p p l i c a t i o n s su c h a s s p e c tru m s o u r c e s and p la sm a
w here m a in te n a n c e o f a s t a b l e ,
r e q u ir e m e n t.
u n if o r m ,
d is c h a r g e i s t h e
Chapter 1
It
i s shown i n S e c t i o n 2 .3 t h a t
c o n d itio n s
in
d e n s itie s
a ro u n d
ty p ic a l
ra re -g a s
o f a t l e a s t 10kW cm
to
a c h ie v e
th re s h o ld
h a l i d e e x c im e r l a s e r s ,
a re
re q u ire d
and
la s in g
pump pow er
th a t
v a lu e s
of
1MW cmT^ w ould be d e s i r a b l e f o r a m icrow ave a p p a r a tu s o f w ide
r a n g in g
e x c im e r l a s e r a p p l i c a t i o n .
le v e ls
is
lim ite d
m ic r o - s e c o n d ) ,
s u ffic ie n t
m eans
to
fa irly
C l e a r l y o p e r a t i o n a t t h e s e pow er
sh o rt
I t i s fo rtu n a te th a t
p u lse s
p u ls e d
( p r o b a b ly
m icrow ave
below
so u rc e s
pow er hav e b e e n d e v e lo p e d f o r u s e i n r a d a r s y s te m s .
a
of
T h is
t h a t m a g n e tro n s c a p a b le o f p r o v id in g t h e p u l s e pow er n e c e s s a r y
f o r e x c im e r l a s e r o p e r a t i o n a r e c o m m e rc ia lly a v a i l a b l e .
g o v e rn m e n t
In a d d itio n ,
s u r p l u s r a d a r s e t s may be a v a i l a b l e a t low c o s t .
p u rp o ses
of
th e
w ork
of
o b ta in e d
and a d a p te d a s d e s c r i b e d i n C h a p te r 5 .
For th e
t h i s t h e s i s a n a v a l X -band r a d a r s e t was
W hile t h i s p r o v id e d
a n a p p a r a tu s t h a t was c o n v e n ie n t, r e l i a b l e and c h e a p , t h e p u l s e pow er
of
50kW p ro v e d t o be i n s u f f i c i e n t t o o b t a i n l a s i n g fro m any
of
th e
from
th e
e x c im e r m o le c u le s i n v e s t i g a t e d .
The
h ig h
u tilis a tio n
T h is
is
e ffic ie n c y
of
e x c im e r
la s e rs
d e riv e s
o f a b o u n d - f r e e t r a n s i t i o n and fro m f a v o u r a b le k i n e t i c s .
e x p la in e d
in
C h a p te r 2 w here r a r e - g a s h a l i d e m o le c u le s a r e
d e s c r i b e d i n d e t a i l and r e l a t e d t o t h e m o le c u la r s p e c tr u m .
and
q u e n c h in g
a v a ila b le
p a rtia l
k in e tic s
a re
a ls o
k i n e t ic r a t e c o n s ta n ts
p ressu res
d is c u s s e d
e n a b le
and
lim itin g
F o rm a tio n
c o n tra s te d .
The
v a lu e s
th e
fo r
o f t h e g a s com ponents t o be d e r i v e d su c h t h a t t h e
q u e n c h in g r e m a in s n e g l i g i b l e .
Chapter 1
A m a jo r p ro b le m i n t h e o p e r a t i o n o f r a r e - g a s h a l i d e
th e
lim ite d
gas l i f e
and
fle x ib le
gas
r e p la c e m e n t.
p rese n t
lo ss
th a t o c c u rs.
h a n d lin g
th e
The g a s e s in v o lv e d a r e e x p e n s iv e
s y s te m s
a re
re q u ire d
to
d o n o r.
a p p a r a tu s
e s ta b lis h e d
in
fo r
c o llis io n s
The l i m i t e d l i f e t i m e i s m a in ly
h a lo g e n
e x p e r im e n ta l
re a c tio n
is
e n a b le
gas
The g r e a t c o n v e n ie n c e a f f o r d e d by a s e a l e d s y s te m i s a t
im p ra c tic a b le .
of
la s e rs
a
fre e
re s u lt
d ia m e te r
h a lo g e n s
in
th e
to
th e
T h is was e x p e c te d t o be r a p i d i n t h e
d e s c rib e d
2mm
due
h e re in
q u a rtz
and
a
ra p id
w h ere
d is c h a rg e s
tu b e .
s m a ll
a re
Thus a s t r o n g w a l l
life tim e
a c c u m u la tio n
of
a g a in s t
w a ll
s ta b le h a lid e s .
C h a p te r 3
d i s c u s s e s t h e d i f f u s i v e t r a n s p o r t o f p a r t i c l e s t o t h e tu b e
w a ll
a llo w s
and
fo r
th e
t e m p e r a tu r e
d e p e n d en c y o f t h e d i f f u s i o n
c o e ffic ie n t.
M icrow ave
C h a p te r 4 .
of
d isc h a rg e s
a re
com pared
w ith
DC
and
n o n -u n ifo rm
d is c h a rg e
s t a g e s o f a DC d i s c h a r g e p u l s e .
fav o u r
of
a p p a r a tu s
o b ta in e d
c o u p le r
lo o p s
m icrow ave
by
th e
decay
th a t
in to
h ig h ly
occur in th e l a t e r
H ow ever, a m ore p o w e rfu l a rg u m e n t i n
d is c h a rg e s
t h a t w av eg u id e
modes
a ris e s
tra n s m is s io n
from
th e
a ll o w s .
v e ry c o n v e n ie n t
The
m eans o f a m icrow ave d is c h a r g e c o u p l e r .
d e s ig n r e p l a c e s t h e m u l t i p l e p ro b le m ,
d e s ig n in g
in
I t i s p o i n te d o u t t h a t th e r a p i d f i e l d r e v e r s a l and l a c k
e l e c t r o d e s i n t h e m icrow ave c a s e p r e v e n t t h e
io n is e d
d is c h a rg e s
d isc h a rg e
is
The p ro b lem o f
i n DC d i s c h a r g e s ,
of
e l e c t r o d e g e o m e try and m a i n ta i n in g v e r y low im p ed an ce
i n a s tr u c tu r e c o n ta in in g
a
la rg e
h ig h
v o lta g e
in s u la to r.
C h a p te r 4 c o n s id e r s c o u p le r d e s ig n i n d e t a i l and i t i s shown t h a t t h e
S c h w in g e r
d ire c tio n a l
c o u p le r,
r e d e s ig n e d
w ith
g ra d e d
c o u p lin g
Chapter 1
.
e le m e n ts ,
p r o v id e s
c o u p le r .
an
a ttra c tiv e
p o s s ib ility
fo r
a
9
d isc h a rg e
D e t a i l s o f t h e c o n s t r u c t i o n and t e s t i n g a r e p r o v id e d .
The e x p e r im e n ta l work d e s c r i b e d i n C h a p te r 7 in v o lv e d t h e u s e o f
an o p t i c a l s p e c tru m a n a l y s e r (OSA),
w hich i s d e s c r i b e d i n C h a p te r 6 ,
t o g iv e p l o t s o f e m is s io n i n t e n s i t y ’( a t band c e n t r e ) a g a i n s t tim e and
to
p r o v id e
o p e ra tio n
160^
a
sp e c tru m
p l o t o f e x c im e r e m is s io n .
The OSA ra n g e o f
e x te n d e d from t h e UV t o t h e IR g i v in g a r e c o r d e d
in
w id th .
c o lle c tin g
I n m ost
cases
s p e c tru m
a s p e c tru m r e c o r d was o b t a i n e d by
t h e o u tp u t from 1000 p u l s e s .
In o rd e r
to
s tu d y
s in g le
p u l s e s o r th e f i r s t few p u l s e s o f a b u r s t o f p u l s e s f u r t h e r a p p a r a tu s
was
d e v e lo p e d and i s d e s c r i b e d i n C h a p te r 5 .
XeF^
X eC l,
K rF,
w ork
and XeO e m is s io n was a l s o o b s e r v e d .
ra re -g a s
h a lid e s
K rC l, and ArF w e re s t u d i e d d u r in g t h e e x p e r im e n ta l
The m o le c u le s w e re
i n d i s c h a r g e s i n m ix tu r e s o f t h e r a r e - g a s (X e,
d o n o r (NF^,
The
K r, o r A r ) , a h a lo g e n
SF^, o r H C l), and a b u f f e r g a s (H e, Ne, o r A r ) ,.
e m is s io n
i n t e n s i t i e s w e re
rec o rd e d f o r
h a lo g e n
d o n o rs o v e r a w ide r a n g e
th e d i f f e r e n t
o f m ix tu r e
p a r t i c u l a r g a s m ix tu r e was b e in g t e s t e d ,
form ed
ra tio s .
E xcim er
b u f f e r s and
W henever
a
s p e c t r a and tim e p l o t s w e re
r e c o r d e d f o r e a c h o f a b o u t 8 t o t a l p r e s s u r e s s u r r o u n d in g t h e p r e s s u r e
a t w hich maximum o u tp u t o c c u r r e d .
The
raw
d a ta
fro m t h e e x p e r im e n ta l w ork c o n s i s t e d o f o v e r 400
s h e e t s o f g ra p h p a p e r o b t a i n e d fro m t h e OSA and c o u ld n o t be i n c l u d e d
d ire c tly
tra c in g
The
in
th e
th e s is .
H ow ever,
some o f t h e d a t a was c o p ie d by
and p h o to - r e d u c e d t o e n a b le i t t o be p r e s e n t e d i n C h a p te r 8 .
tre n d s
i n i n t e n s i t y and g a s l i f e - t i m e i n r e s p o n s e t o c h a n g e s i n
th e p r i n c i p a l v a r i a b l e s ( g a s t y p e , m ix tu r e r a t i o , and t o t a l p r e s s u r e )
Chapter 1
10
a r e d i s c u s s e d i n c o n ju n c t io n w ith t h e p r e s e n t a t i o n o f t h e r e s u l t s .
The
how
volum e
of
u s e fu l th e
m icrow ave
in v e s tig a tio n .
c o u p lin g
tu b e ,
th e
a p p a r a tu s
t h e u s e o f t h e OSA.
(at
d isc h a rg e
be
fo r
th is
k in d
of
T h is was a d i r e c t r e s u l t o f t h e com pact and f l e x i b l e
1100
p p s)
w here
and
s m a ll
volum e
d isc h a rg e
A n o th e r o u t s t a n d i n g f e a t u r e i s t h a t
sy ste m a llo w e d g a s l i f e - t i m e
s t u d i e s t o be c a r r i e d o u t i n h a l f a
many
h o u rs w ould be r e q u i r e d i n a DC
pumped e x c im e r l a s e r w h ere p u ls e r a t e s a r e u s u a l l y a b o u t 1
p u lse p e r seco n d .
and
c o u ld
a rra n g e m e n t o f t h e w av eg u id e
and
m in u te
in
d a t a g e n e r a te d by t h i s w ork i s a n i n d i c a t i o n o f
The m icrow ave a p p a r a tu s p ro v ed t o be s im p le , s a f e ,
c o m p le te ly r e l i a b l e w ith no p a r t i c u l a r e n g in e e r i n g
c o n n e c tin g
c o n s tru c tio n
th e
of
m icrow ave
th e
d iffic u ltie s
s o u rc e t o t h e d i s c h a r g e c o u p le r o r i n
c o m p le te
s y s te m .
In th e
lig h t
of
th e s e
o b s e r v a t i o n s , t h e u s e o f a m icrow ave sy ste m o f t h e ty p e d e s c r i b e d c a n
be
h i g h l y recom mended f o r c r e a t i o n and s t u d i e s o f
m o le c u le s .
te rm s
The
in d ic a tio n s
a re
th a t
h a lid e
e x p a n s io n o f t h e sy ste m ( i n
o f pow er) c o u ld in d e e d p r o v id e a v a l u a b l e
e x c im e r l a s e r pump s o u r c e .
ra re -g a s
a lte rn a tiv e
as
an
Chapter 2
2
.
1
1
RARE-GAS HALIDE EXCIMER LASERS
2 .1
M o le c u la r S t r u c t u r e and S p e c tr o s c o p y
2 ,1 .1
E x c im e r M o le c u le s
The
e x c im e r
m o le c u la r
w ill
in te ra c tio n
p o te n tia l
m o le c u la r
w ith t h e n u c l e i a s c h a rg e
w hich
is
a
h e re
in
te rm s o f
s ta te .
p o te n tia l
c e n tre s
and
th e
n u c le a r
e le c tro n ic
f u n c t i o n o f t h e m o le c u la r s t a t e s .
a d i a b a t i c Coulomb p o t e n t i a l c u rv e c a n be draw n
and
fo r
A
each
F i g u r e 2 . 1 ( a ) show s a r e p r e s e n t a t i o n o f c u r v e s f o r
su c h m o le c u la r s t a t e s ,
lo w e s t
c o n s id e r e d
M o le c u la r p o t e n t i a l e n e rg y c o n s i s t s o f b o th a C oulom bic
e n e rg y
c o n tin u o u s
b in d in g
be
b in d in g a n d t h e c u rv e o f p o t e n t i a l e n e rg y a g a i n s t
s e p a ra tio n .
th re e
m o le c u le
th e
m id d le
re s p e c tiv e ly .
th e u pper g iv in g
and
a
p u re ly
re p u ls iv e
lo w e r c u r v e s g i v i n g w eak and s t r o n g
I t i s u s u a l t o ta k e t h e l o w e s t p o i n t
of
th e
c u rv e a s z e r o f o r t h e p o t e n t i a l e n e rg y o f t h e sy ste m and t h i s
a l s o g i v e s t h e g ro u n d s t a t e e q u i l i b r i u m i n t e r - n u c l e a r s e p a r a t i o n .
A
p o t e n t i a l d ia g ra m su c h a s t h a t shown i n F ig 2 . 1 ( a ) i s t y p i c a l
of
a
s t a b l e m o le c u le w h e re b in d in g i s s t r o n g i n t h e g ro u n d a s t a t e .
In
an e x c ite d s t a t e ,
d is s o c ia te
in
h o w e v e r,
c o llis io n s
t h e m o le c u le may be w e a k ly bound and
o r may be .unbound.
F o r c e r t a i n m o le c u le s
ENERGY
INTERNUCLEAR SEPARATION
Figure 2.1 (a )
R
Molecular p o te n tia l
excited s t a t e
ENERGY
ground s ta te
R
Figure 2.1(b) Excimer
potential
Chapter 2
12
th e o r d e r i n g o f t h e b in d in g s t r e n g t h s may be r e v e r s e d w ith r e s p e c t t o
th e
lo w e r
shown
m o le c u la r
s ta te s
i n F ig 2 . 1 ( b ) .
s ta te
but
is
e x h ib itin g
H ere th e m o le c u le i s
s tro n g ly
t h i s k in d
e x c im e r s .
g i v i n g a p o t e n t i a l d ia g ra m o f t h e ty p e
bound
of
in
an
b e h a v io u r
unbound
e x c ite d
have
in
th e
s ta te .
become
g ro u n d
M o le c u le s
w id e ly
known
as
I n t h e c h e m ic a l l i t e r a t u r 'e , h o w ev er, t h e terra 'e x c im e r* i s
re s tric te d
t o h o m o p o lar m o le c u le s ( a l s o known a s d im e rs ) w h e re a s t h e
terra ’ e x ip le x * i s u s e d w h ere h e t e r o p o l a r m o le c u le s a r e c o n c e rn e d .
s h o u ld a l s o be n o te d t h a t ,
in p ra c tic e ,
It
*excim er* m o le c u le s w i l l be
p r e s e n t i f lo w e r l e v e l s a r e s u f f i c i e n t l y w eakly bound t o e n s u r e r a p i d
c o llis io n a l
p o p u la tio n
s ta te .
e x c ite d
fo r
rem o v a l
is
w ith
p rim a rily
th e
in
c o n seq u e n c e
th a t
th e
m o le c u la r
t h e form o f th e s t r o n g l y bound e x c i t e d
I t i s c l e a r t h a t e l e c t r o n i c t r a n s i t i o n s from a s t r o n g l y bound
s t a t e t o a d i s s o c i a t i v e g ro u n d s t a t e p r o v id e good c a n d i d a t e s
V
l a s e r s s i n c e t h e p ro b le m o f a b s o r p t i o n by t h e r e v e r s e t r a n s i t i o n
i s rem oved.
An
id e a l
s in g le ,
m o le c u le
fo r
a
la s e r
sy s te m w ould h a v e a
s t r o n g l y bound e x c i t e d s t a t e t h a t ca n be pumped
e ffic ie n c y
s ta te .
e x c im e r
and
w ith
h ig h
a s i n g l e e l e c t r o n i c t r a n s i t i o n t o a r e p u l s i v e g ro u n d
T h is i d e a l i s m ost l i k e l y
d ia to m ic m o le c u le .
to
be
a p p ro a c h e d
by
a
s im p le
U n f o r tu n a t e l y t h e m o le c u la r b o u n d - f r e e e l e c t r o n i c
t r a n s i t i o n h a s a d raw b ack f o r l a s e r o p e r a t i o n i n t h a t th e s p o n ta n e o u s
e m is s io n
b a n d w id th
m a n ifo ld
o f t h e bound e x c i t e d s t a t e .
a
h ig h
th re s h o ld
is
v e ry
w ide due t o t h e r o t a t i o n a l - v i b r a t i o n a l
T h is w id e b a n d w id th r e s u l t s i n
pump pow er d e n s i t y f o r l a s i n g ( a s d e m o n s tra te d by
c a lc u la tio n
in S e c tio n 2 .3 ) .
v ib ra tio n a l
and
ro ta tio n a l
I n th e id e a l
le v e ls
,to
m o le c u le
re la x a tio n
of
t h e i r g ro u n d s t a t e s m u st be
Chapt er 2
13
p o s s ib le
on a t i m e - s c a l e t h a t i s s h o r t com pared w ith t h e s p o n ta n e o u s
e m is s io n
life tim e
m o le c u le s
and
th is
as lik e ly la s e r
a g a in i s p r e d i c t i v e o f s im p le d ia to m ic
c a n d id a te s .
The
ra re -g a s
m o n o h a lid e s ,
e s p e c i a l l y XeF, X eC l, KrF, and K rC l, g iv e a v e ry n e a r a p p ro a c h t o t h e
id e a l
m o le c u le w ith t h e r e s u l t t h a t r a r e - g a s h a l i d e l a s e r s
e x c im e r
la s e rs
d e v e lo p m e n t
been
w here
a re
from NeF,
The o t h e r r a r e - g a s h a l i d e s
XeBr
A rC l,
p re d is s o c ia tio n
and
A rF.
K rB r,
w h ere
F lu o re s c e n t
la s in g
has
e m is s io n h a s b e e n
and X el b u t n o t from ArBr and
p r o b a b ly t a k e s p l a c e .
K rI
I n a l l o f t h e e x c im e rs
t h a t have been s tu d ie d i n r e l a t i o n s h i p to l a s e r o p e ra tio n ,
is
th e
h a v e r e c e i v e d t h e m ost w id e s p re a d i n t e r e s t and
to d a te .
p ro d u c e d
o b s e rv e d
th a t
a re
ra d ia tio n
by m eans o f a n e l e c t r i c d i p o l e t r a n s i t i o n so t h a t t y p i c a l e x c i t e d
s ta te
l i f e t i m e s a r e a ro u n d 10 n s .
s ta te
life tim e
lO’"^ n s ) ,
bound
th e
d is s o c ia tiv e
s ta te ,
c o llis io n a l
F o r t h e c a s e o f a w eak ly
d i s s o c i a t io n ta k e s p la c e .
l a s e r s a re g e n e ra lly o p e ra te d a t p r e s s u re s o f
a tm o s p h e re ,
g ro u n d
w i l l be a b o u t one m o le c u la r v i b r a t i o n p e r io d (a ro u n d
p o p u la tio n in v e r s io n i s a s s u re d .
g ro u n d
e x c im e r
S in c e
w here
c o llis io n
f re q u e n c ie s
w ill
be
w e ll
S in c e
oyer
g re a te r
1
th a n
10^^ s ” ^ ,
l i f e t i m e s o f a ro u n d ICT^ n s can be e x p e c te d and p o p u l a t i o n
in v e rs io n
is
m o le c u le s ,
s till
m a in ta in e d .
The n a t u r e o f t h e r a r e - g a s h a l i d e
from w hich t h e i r s u i t a b i l i t y a s l a s e r
d e s c r i b e d i n t h e f o ll o w i n g s u b s e c t i o n s .
m ed ia
ste m ,
is
Chapt er 2
2 ,1 .2
14
R are-G as H a lid e M o le c u le s
The
e le c tro n ic
tra n s itio n
i n r a r e -g a s h a lid e s re s p o n s ib le f o r
t h e i r u t i l i s a t i o n i n l a s e r s i s c l o s e l y a l l i e d t o t h e b e h a v io u r o f t h e
is o la te d
r a r e - g a s f r a g m e n t.
u n re a c tiv e
e x c ite d
C
p 8
4
due t o a f u l l
I n t h e i r g ro u n d s t a t e s ,
o u te r
e le c tro n
s h e ll
ra re -g a se s a re
C p ^ ).
The
firs t
s t a t e o f a r a r e - g a s atom h a s a n o u t e r e l e c t r o n c o n f i g u r a t i o n
and,
b ecause th e r e
is
a lw a y s
a
p a rtic u la rly
la rg e
e n e rg y
d i f f e r e n c e b e tw e en a p s h e l l and t h e n e x t s s h e l l , t h i s e x c i t e d s t a t e
is
c l o s e r t o t h e i o n i s a t i o n p o t e n t i a l th a n t o t h e g ro u n d s t a t e .
a rg o n ,
fo r
g ro u n d
th e
e x a m p le,
th e f i r s t e x c ite d s t a t e i s
1 1 .5 eV a b o v e t h e
s t a t e w hich i s 73? o f t h e i o n i s a t i o n e n e r g y .
e x c ite d
a r g o n atom th e n t a k e s 4 .3 eV,
c a n be made h e r e i n t h a t p o ta s s iu m ,
ta b le ,
a ls o
io n is a tio n
has an is o l a te d ,
Io n is a tio n
of
An im p o r ta n t o b s e r v a t i o n
t h e n e x t e le m e n t i n t h e p e r i o d i c
s in g le ,
p o t e n t i a l o f 4 .3 eV.
In
o u t e r s e l e c t r o n and h a s a n
I t ca n t h e r e f o r e be
e x p e c te d
th a t
e x c ite d
a rg o n atom s w i l l b eh av e l i k e p o ta s s iu m ato m s e s p e c i a l l y when
fç rm in g
i o n i c bonds w ith o t h e r atom s
c o m p a ris o n
ca n
be
made
to
fo rm
and t h e a l k a l i - m e t a l t h a t f o llo w s i t i n
S in c e
th e
io n ic
b in d in g ,
h a lid e s
th e
by
g av e
and
i t i s p o s s ib le to
g a in
th e
p e rio d ic
ta b le .
u n d e r s t a n d in g
of
ra re -g a s
make p r e d i c t i o n s f o r t h e i r b e h a v io u r by c o m p a ris o n w ith
T h is a n a lo g y was u s e f u l l y
a p p lie d
and Ewing (1975 b) i n e a r l y s t u d i e s o f r a r e - g a s h a l i d e s and
r e a s o n a b ly a c c u r a t e p r e d i c t i o n s
sp e c tra .
a
form s t a b l e m o le c u le s w i t h t h e h a lo g e n s by
c o r r e s p o n d in g a l k a l i - h a l i d e .
B rau
Such
b etw een e a ch r a r e - g a s i n i t s f i r s t e x c i t e d
s ta te
a lk a li-m e ta ls
m o le c u le s .
of
ra re -g a s
h a lid e
e m is s io n
Chapter 2
.
1
5
D e s p ite t h e a p p a r e n t s i m p l i c i t y ' o f r a r e - g a s h a l i d e m o le c u le s ,
fu ll
u n d e r s ta n d in g
a c h ie v e d .
One
of
th e ir
rea so n
fo r
e m is s io n
th is
s p e c tra
is
th e
has
s till
g e n e ra l
a
to
be
d iffic u lty
of
q u a n t i f y i n g m o le c u la r s p e c t r a w h ere v i b r a t i o n a l and r o t a t i o n a l e n e rg y
s t a t e s add t o t h e e l e c t r o n i c s t a t e , ' I n g e n e r a l ,
be
its
r e g a r d e d a s in d e p e n d e n t.
own
p o te n tia l
d e g re e s
in te rv a ls
of
th e
F o r exam ple e ach e l e c t r o n i c
c u rv e ,
o f w e ll d e p th and
th e s e s t a t e s cannot
as
p r e v i o u s ly m e n tio n e d ,
w e ll
asym m etry.
v ib ra tio n a l
s ta te s
T h is
v a ry
s ta te
has
w ith v a r i o u s
m eans
th a t
c o n s id e r a b l y
th e
b e tw e e n
e l e c t r o n i c s t a t e s a n d , w i t h i n a g iv e n e l e c t r o n i c s t a t e , t h e i n t e r v a l s
w ill
be
u n e q u a l due t o th e a n h a rm o n ic v i b r a t i o n o f th e atom s i n t h e
a sy m m e tric
d e s c rib e d
p o te n tia l.
in
u n d e r s ta n d in g
m ore
T hese v i b r a t i o n a l and r o t a t i o n a l f e a t u r e s a r e
d e ta il
in S e c tio n 2 . 1 . 3 .
r a r e - g a s h a l i d e s p e c t r a a r i s e s from t h e
many e l e c t r o n i c m o le c u la r s t a t e s .
e x is ts
fo r
A n o th e r d i f f i c u l t y i n
th e
d e s c rip tio n
e x is te n c e
W hile a good t h e o r e t i c a l fram ew ork
of
m o le c u la r
s ta te s ,
p ro b le m s
i d e n t i f i c a t i o n and e n e rg y o r d e r i n g h a v e f r e q u e n t l y a r i s e n .
s ta te s
of
i n t h e b ound-bound t r a n s i t i o n o f XeF and XeCl
of
The lo w e r
g iv e
e x a m p les
w h ere th e s e p ro b le m s h a v e o c c u r r e d .
C a lc u la tio n s
o f th e r a r e - g a s h a lid e e le c tr o n i c s t a t e s have been
c a r r i e d o u t by many a u th o r s a n d , i n p a r t i c u l a r d e t a i l , by D unning and
Hay ( 1 9 7 8 ) and Hay,
in f o r m a t io n
re fe re n c e s.
d e s c rip tio n
c o n fig u ra tio n
e t,
on r a r e - g a s
As
a l,
(1 9 7 9 ).
h a lid e
m o le c u la r
r e f l e c t e d i n t h e s e w o rk s,
o f e x c im e r m o le c u le s
and
R hodes (1 9 7 9 ) a l s o g i v e s much
is
to
s ta te s
and
c ite s
many
th e f i r s t s te p in a f u l l
e s ta b lis h
th e
e le c tr o n ic
te rm sym bols f o r t h e g ro u n d s t a t e and t h e e x c i t e d
C hapter 2
16
s ta te s .
th e n
be
The n a t u r e and s t r e n g t h o f t h e b in d in g i n
be c h a r a c t e r i s e d .
th is
ra re -g a s
g e n e ra l
a re
a p p ro a c h .
In
become
th e
h a l i d e m o le c u la r s t a t e s ,
s im p lific a tio n
s ta te
Though many p ro b le m s s t i l l re m a in ,
s a id t h a t th e r a r e - g a s h a lid e s have
u s in g
each
use
w e ll
f o ll o w i n g
is
made
ca n
i t c o u ld
u n d e r s to o d
by
d e s c rip tio n
of
of
a
f o rtu ito u s
t h a t c a n be a p p l i e d i f a c c u r a t e n u m e r ic a l p r e d i c t i o n s
n o t re q u ire d .
The s i m p l i f i c a t i o n i s t o b a s e t h e a n a l y s i s on t h e
p o s s i b l e s t a t e s o f t h e a to m ic f r a g m e n ts a t i n f i n i t e s e p a r a t i o n .
T h is
i s j u s t i f i e d by t h e d o m in a n t r o l e o f t h e e x c i t e d r a r e - g a s atom i n t h e
m o le c u le
w ith i t s i n t e r a c t i v e o u t e r e l e c t r o n b e in g w e l l rem oved from
t h e atom i t s e l f .
C o n s id e r
ta k e n
in to
s u b s h e lls
f i r s t t h e c a s e w h ere s p i n - o r b i t i n t e r a c t i o n s
a c c o u n t. Ground
sy m b o ls
ra re -g a se s
n o m e n c la tu r e
1
f o ll o w s
H e rz b e rg
2
^ 3 / 2 1/ 2 *
and
not
th e ir
fu ll
(N o te ,
The
t h r o u g h o u t .)
L=1
g iv in g
p o s i t i v e r a r e - g a s and n e g a t i v e h a lo g e n i o n s
s im p ly i n te r c h a n g e d .
s ta te
p a ir w ill
be
I n c l o s e p r o x im ity ,
n e u tra l
g ro u n d
(u s u a lly
r e p u l s i v e ) w h ile t h e i o n p a i r w i l l
i o n i c b o n d in g .
S.
(1 9 5 0 )
s t a t e h a lo g e n s on t h e o t h e r hand h a v e 8 = 1 /2
t h e s e te rm sym bols a r e
th e
w ith
h a v e S=0 and L=0 g i v i n g t h e te rm sym bol
s p e c tro s c o p ic
Ground
s ta te
a re
s u b je c t
be
to
th e
c o v a le n t b o n d in g
s u b je c t
to
s tro n g
T h is i o n i c bond d e s c r i p t i o n i s d i r e c t l y a p p l i c a b l e t o
h a l o g e n - e x c i t e d r a r e - g a s bond by v i r t u e o f t h e h ig h e n e rg y ( n e a r
io n is a tio n )
of
th e
ra re -g a s
e l e t r o n e g a t i v i t y o f t h e h a lo g e n .
momentum
T h e refo re
(io n ic a lly
v e c to r
on
s ta te
and
th e
h ig h
The p r o j e c t i o n o f t h e t o t a l a n g u la r
t h e m o le c u la r a x i s ( A ) c a n h a v e v a l u e s 0 t o L.
t h e r e a r e two s t a t e s ,
bound)
e x c ite d
le v e l
and
A =0 and
th e
lo w e r
A=1 f o r
b o th
th e
upper
( c o v a l e n t l y bound) l e v e l .
Chapter 2
17
T hese s t a t e s a r e l a b e l l e d , 2^1'*^, 2^11, I^ Z * , and l^ flj r e s p e c t i v e l y ,
S p in -o rb it
c o v a le n t
e f f e c t s a r e p r i m a r i l y p r e s e n t f o r t h e h a lo g e n i n t h e
m a n ifo ld
la rg e s t e ffe c t,
2
Pgyg -
fo r
2
w ith
to
in a s p l i t t i n g o f th e
2
th e
FI s t a t e i n t o 2
2
4-
I n Xe ,
I n t h e m o le c u le t h i s
2
and 2 F^yg s t a t e s
Pgy 2 -
P .9 1 ) .
2
P^yg s p l i t t i n g o f t h e r a r e - g a s i o n ( e g ,
c lo s e
s e e R hodes
The c o rr e s p o n d in g s p l i t t i n g due t o t h e n e u t r a l h a lo g e n
t h e c o v a le n t bond i n c r e a s e s w ith t h e a to m ic num ber o f t h e h a lo g e n
but
i s g e n e r a l l y s m a l l e r th a n t h e r a r e - g a s c o n t r i b u t i o n i n t h e i o n i c
bo n d .
It
t h i s s p l i t t i n g am o u n ts t o 1 ,3eV .
The
i s due t o t h e
an e n e rg y d i f f e r e n c e t h a t h a s b e e n g e n e r a l l y shown t o be
1979»
in
w here r a r e - g a s h a l i d e s a r e c o n c e rn e d ,
s p l i t t i n g i n th e h e a v ie r o f th e r a r e - g a s io n s .
ex am p le,
re s u lts
and t h e r a r e - g a s i o n s i n t h e i o n i c m a n if o ld .
A ll
s i x m o le c u la r s t a t e s a r e shown s c h e m a t i c a l l y i n F ig 2 . 2 .
s h o u ld be n o te d h e r e t h a t w h ile t h e s im p le i o n i c u p p e r l e v e l
c o v a le n t
lo w e r
d e g e n e r a te
s ta te
of
b in d in g
th is
le v e l
L iu
io n ic
le v e l
b o n d in g
m odel s u c c e s s f u l l y p r e d i c t s t h e n e a r
3 - f o l d s p l i t t i n g o f t h e g ro u n d s t a t e
th e r a r e - g a s h a l i d e m o le c u le ,
and
firs t
fo u n d
d e ta ils
of
A c l e a r exam ple o f t h i s i s g i v e n by t h e bound lo w e r
i n XeF w hich was n o t p r e d i c t e d by e a r l i e r t h e o r y .
(1976)
e x c ite d
m ore d e t a i l e d m o d els o f t h e
a r e r e q u i r e d t o c o r r e l a t e o b s e r v a t io n s w ith t h e
s p littin g .
and
th a t
K ra u ss
and
t h e b in d in g c o u ld o n ly be p r e d i c t e d i f some
b o n d in g was m ixed w ith t h e lo w e r c o v a le n t bond i n t h e p r e s e n c e
o f a weak v a n d e r W aal’ s a t t r a c t i o n .
(01
R
Figure 2.2 Rare-gas halide molecular states and transitions
C hapter 2
Of
th e n in e c o n n e c tio n s b e tw e e n t h e t h r e e u p p e r and t h r e e lo w e r
s ta te s
AQ=0
d e s c rib e d above,
ru le ,
(Hay
tra n s itio n s
lo w e s t
o rd er
e t,
and
A,
o f e n e rg y .
2
2 Z
d e g e n e r a te
The
B,
T hese
s ta te s
1.979).
a re
a re
f o r t h e o t h e r s t a t e s i n a s c e n d in g
I
shown i n F ig 2 .2 w here t h e n e a r
in c l u d e d
in
th e
s i n g l e A. s t a t e .
is
due
tra n s itio n
o c c u rs.
at
th e
in te r-n u c le a r
Thus
when
in
s e p a ra tio n
tra n s itio n s
th e in te r - n u c le a r s e p a r a tio n ,
is of
m ore
or
le s s
c o n s ta n t
i n t e r n u c l e a r s e p a r a t i o n s i n v o lv e d .
c o n s id e ra b le
la s e rs
in
from
h ig h e r
e n e rg y
over
th e
ra n g e
t h e b l u e - g r e e n s p e c tr u m .
However,
la s in g
has
w ith t h e
th a n
B
th e
and
C
B - X
s ta te s ,
band
by
Due t o
th e
t h e D - X band i s s h o r t e r i n
an
am ount
a p p ro x im a te ly
to
U n f o r tu n a te ly
t h is t r a n s i t i o n i s u n lik e ly to
o p e ra tio n
it
as
re s u lt
a c h ie v e d f o r a C - A t r a n s i t i o n i n XeF o n ly .
r e m a in in g t r a n s i t i o n o f i n t e r e s t i s t h e D - X b a n d .
th e
pow er
t h i s e m is s io n band i s
th a t
of
of
The 0 - A t r a n s i t i o n h a s r e c e i v e d
a t t e n t i o n m a in ly b e c a u s e t h e r e i s a l a c k o f h ig h
been
th e
t h e t e r m i n a t i n g p o i n t (X
due t o a s t e e p lo w e r p o t e n t i a l c u r v e ,
w a v e le n g th
w hich
and t h e r e f o r e from
b ro ad ,
c lo s e n e s s
B - X,
o p e ra tio n .
at
occur
v e ry
The
th e
la s e r
v ib r a tio n a l le v e ls in th e upper e le c tr o n ic s t a t e ,
s ta te )
to
The
f o r t h i s n a rro w band w id th i s t h a t t h e lo w e r Z c u rv e i s
fla t
ra n g e
th e
T h is t r a n s i t i o n a l s o g i v e s t h e n a r r o w e s t e m is s io n
re la tiv e ly
a
fo r
C e tc ,
and i s c o n s e q u e n tly o f g r e a t e s t i n t e r e s t f o r
reaso n
th e
The s t a t e s in v o lv e d i n o b s e rv e d
r a r e - g a s h a l i d e e x c im e r e m is s io n
r “ Z tra n s itio n .
band
a l,
by
a r e l a b e l l e d i n s p e c t r o s c o p i c n o t a t i o n u s in g X
s ta te
s tro n g e s t
t h e r e a r e f i v e t r a n s i t i o n s a llo w e d
th a t
c o rr e s p o n d s
th e s p in - o r b it s p l i t t i n g o f th e r a r e -g a s
be
u se fu l
2
P s ta te .
fo r
la s e r
a p p e a r s t o be r a t h e r e a s i l y q u e n c h ed (R hodes 1979»
Chapter 2
19
P .9 2 ) ,
2 .1 .3
R are-G as H a lid e B - X E m is s io n F e a tu r e s
The
a re
f in e r d e t a i l s o f th e B - X r a r e -g a s h a lid e
e x p la in e d
e m is s io n
i n te rm s o f m o le c u la r v i b r a t i o n and r o t a t i o n i n t h e B
s ta te
and a l s o i n t h e X s t a t e f o r t h e c a s e s o f a bound lo w e r
T hese
fe a tu re s
F irs tly ,
b an d s
have
im p o r ta n t
consequences
fo r
le v e l.
l a s e r o p e ra tio n .
th e y e f f e c t t h e w id th o f t h e s p o n ta n e o u s e m is s io n band and
c o n s e q u e n tly
in flu e n c e
th e
t h r e s h o l d pump pow er d e n s i t y ,
th e fre q u e n c y d i s t r i b u t i o n
illu s tra te
To
th e im p o r ta n t d e t a i l s i n t h e B - X e m is s io n s p e c t r a ,
th e
o f a few
s p e c tra
shown
re p re s e n ta tiv e
below
w ere
cases
o b ta in e d
th e
la s e r
th e y
e m is s io n .
s p e c tra
of
and s e c o n d ly ,
w ill
from
be
th e
d e s c rib e d .
(T he
e x p e r im e n ta l
w ork
d e s c rib e d l a t e r i n th e t h e s i s ) .
XeF
The
s p e c tru m o f XeF i s d i s t i n g u i s h e d from
th e
o th e r
ra re -g a s
h a l i d e s by h a v in g s h a r p d e t a i l s o n b o th t h e b lu e and r e d s i d e s o f t h e
e m is s io n p e a k .
T h is i s due t o t h e s i g n i f i c a n t b in d in g (1100 cm*'^ ) i n
t h e lo w e r l e v e l , a s shown i n t h e a p p ro x im a te p o t e n t i a l d ia g ra m o f F ig
2 .3 ( a ) ,
th e
The p o s i t i o n o f th e c u rv e s i s su ch t h a t t r a n s i t i o n s from a l l
lo w e r
v ib ra tio n
le v e ls
of
th e
upper
s ta te
t e r m in a te
v ib ra tio n a l
l e v e l i n t h e lo w e r s t a t e below th e
It
s e e n i n F ig 2 . 3 ( a ) t h a t t h e lo w e r c u rv e d e p a r t s s t r o n g l y
can
be
d is s o c ia tio n
on a
from t h e sy m m e tric p a r a b o l i c s h a p e o f t h e u p p e r c u r v e .
v ib ra tio n
v ib ra tio n a l
in
th e
lo w e r
s ta te
is
th e re fo re
lim it.
The m o le c u la r
a n h a rm o n ic
and
th e
i n t e r v a l s g e t c l o s e r w ith i n c r e a s i n g v i b r a t i o n a l e n e r g y .
30000
290003532 A
3514 A
E
w
Laser
transitions
iv"=4
2
R(A)
3
Figure 2 . 3 ( a ) . X e F potentials and vibrational levels
43000
T
e
w
2
R(A)
Figure 2 3 (b ). Kr F potentials
Chapt er 2
20
The r e s u l t o f t h i s i s
th e
t h a t t h e s p a c in g o f t h e v i b r a t i o n a l f e a t u r e s i n
s p e c tru m i s som ew hat c o m p lic a te d a s ca n be s e e n i n t h e XeF B - X
s p e c tru m
of
a n a ly s e d
t h i s s p e c tru m and g i v e n t h e v i b r a t i o n a l a s s ig n m e n t shown i n
F ig
2 .4 .
F ig
The
d e g r a d in g
2 .4 .
T e llin g h u is e n ,
a d d itio n a l
peaks
th e
e t,
a l.
b lu e
(1 9 7 8 ) h a v e
or
r e d ( o r b o th )
o f t h e a s s i g n e d p e a k s a r i s e from m o le c u la r r o t a t i o n .
fin e
s tru c tu re
th is
s p e c tru m due t o p r e s s u r e
ro ta tio n a l
in flu e n c e
lo w e r
and
J.
of
ro ta tio n a l
s ta te s
a ffe c t
bands i s n o t g e n e r a lly r e s o lv a b le i n
and
th e
is o to p ic
s p e c tru m
b r o a d e n in g .
m a rk e d ly ,
H ow ever,
th e
b e in g o n t h e v i b r a t i o n a l f r e q u e n c i e s i n t h e
s ta te
The
g re a te s t
w e a k ly
bound
t h a t a r e a l t e r e d by t h e 'c e n t r i f u g a l d i s t o r t i o n ’ o f t h e
m o le c u la r p o t e n t i a l .
G e n e r a l ly ,
w ith
a
n o n - th e r m a l
c o n v e r s io n
e n e rg y .
H ow ever,
p a irs
e le c tro n ic
fo r
s ta te .
le v e l
is
s ta te s
p re c u rso rs
to
v ib ra tio n a l
s ta te s
r e s p e c tiv e ly ,
tra n s itio n s
from
in
th e
to
v ib ra tio n a l
a r e shown,
P.O .
upper
and
lo w e r
by e v a l u a t i o n o f t h e
e t.
a l.
1 9 7 8 ),
to
be
t h e lo w e s t v i b r a t i o n a l l e v e l o f t h e
The e x t e n t t o w hich t h e g a in f o r t r a n s i t i o n s from t h i s
b ro a d e n e d
is
a
d e te r m i n a n t o f t h e l a s i n g
re la x
to
th e
lo w e s t
s ta te .
Such r e l a x a t i o n m u st be
by c o l l i s i o n p r o c e s s e s i f i t i s t o com pete w ith
from
s p e c tru m
due
and d e p e n d s o n t h e e x t e n t t o w hich h ig h l y i n g v i b r a t i o n a l
can
in d u c e d
of
h o m o geneously
e ffic ie n c y
v ib ra tio n a l
th e
f a c t o r s ( T e llin g h u is e n ,
upper
s ta te s
of
fo rm ed
t h e r e l a t i v e p r o b a b i l i t i e s f o r t r a n s i t i o n s b e tw e e n
le v e ls ,
F ra n k -C o n d o n
g re a te s t
d is trib u tio n
o f t h e e x c e s s e n e rg y o f
d iffe re n t
decay
t h e B s t a t e s o f t h e r a r e - g a s h a l i d e w i l l be
th e B s t a t e .
s p o n ta n e o u s
C o n s e q u e n tly b o th t h e s p o n ta n e o u s e m is s io n
and t h e l a s i n g s p e c tru m a r e a f f e c t e d by
th e
p ressu re
and
m
<D
C
cn
GO
JD
GTS
CD
O
o
u
ol
CÛ
cn
—i
m
Chapt er 2
21
te m p e r a tu r e
o f t h e g a s m ix tu r e and t h e ty p e o f b u f f e r g a s u s e d .
For
e x a m p le, c o m p le te r e l a x a t i o n t o a th e r m a l d i s t r i b u t i o n i n t h e B s t a t e
is
a c h ie v e d
b u ffe r,
at
0 .5 atm
(R okni
w ith
1 9 7 8 ).
Ar b u f f e r and a t a ^ o u t 3 atm w ith He
H s ia
e t,
a l.
(1 9 7 9 )
re p o rt
ra is e d
t e m p e r a tu r e e x p e rim e n ts i n a XeF l a s e r and show a t r a n s i t i o n from t h e
3530 2
l a s i n g w a v e le n g th ( 0 - 3 )
to
th e
3510 2
la s in g
w a v e le n g th
(0 •» 2 ,1 “ 4) f o r a te m p e r a tu r e change from BOOK t o 450K.
If
th e
lo w e r
la s e r
l e v e ls o f th e X s t a t e ,
te rm in a tin g .
ra p id
(1 9 8 0 )
have
i n XeF,
w ere n o t rem oved,
How ever,
d is s o c ia tio n
le v e l
by
c o llis io n a l p ro ce sse s.
th e
lo w e r
life tim e
o f 4 - 6 n s .a tm w ith He a s
life tim e
is
in c re a s in g
p ressu re
te m p e r a t u r e .
le v e l
l a s e r a c t i o n w ould be s e l f
t h e s h a llo w w e l l d e p th o f t h e X
in v e s tig a te d
a ro u n d
nam ely t h e v " = 2 , 3 , and 4
15 n s ,
some
above
1 atm
s t a t e a llo w s
Fulgham
e t,
a l,
l e v e l d i s s o c i a t i o n and g iv e a
b u ffe r.
S in c e t h e u p p e r
im p ro v em en t
and
by
may
s ta te
be e x p e c te d by
in c re a s in g
th e
gas
A b s o r p tio n e x p e r im e n ts c a p a b le o f i n d i c a t i n g t h e lo w e r
p o p u l a t io n w ere n o t c a r r i e d o u t i n t h e e x p e r im e n ta l work t o be
re p o rte d .
The
f lu o r e s c e n t
s p e c tra ,
h o w ev er,
w ill
r e f l e c t th e
d i s t r i b u t i o n i n t h e u p p e r l e v e l v i b r a t i o n a l m a n if o ld .
XeDI.
A s p e c tru m o f XeCl i s
shown
F ig
2 ,5
w here
a s s ig n m e n ts h a v e b e e n ta k e n from T e l l i n g h u i s e n e t ,
p rese n c e
o f lo w e r l e v e l
b in d in g
w hich
“1
255 cm .
is
g iv e n
v ib ra tio n a l s ta te s
by
T e llin g h u is e n
th e
a l,
in d ic a te s
e t,
a l,
v ib ra tio n a l
(1 9 7 6 ).
lo w e r
The
le v e l
(1976)
as
Thus XeCl j o i n s XeF i n b e in g t h e o n ly e x c im e rs w ith bound
lo w e r l e v e l s , th o u g h i n t h e c a s e o f X eC l, t h e b in d in g i s so weak t h a t
under
u su a l o p e ra tin g c o n d itio n s c o l l i s i o n a l p ro c e s s e s w i l l keep th e
vD
r-~
CTs
fO
CJ
cz
OJ
{/)
_c
cnî
c
m
ai
E
o
c_.
o
to
. 1—
c:
QJ
£!
C
,E '
(/)
t/)
m
ml
c
o
o
ru
c_
JQ
E
D
c-
4
m
- —'
W
OJ
CM
in
o<C
c=)
<u
O
o
■
DQ
LJ
m
XI
tn
L_J
ai
X
m
CNJ
QJ
t—
ZJ
.S'!
;u-1
Chapter 2
.
2
2
lo w e r
p o p u l a t io n n e g l i g i b l y s m a l l.
B “ X
p o t e n t i a l c u rv e s o f XeCl g iv e th e t h r e e s t r o n g e s t t r a n s i s t i o n s
as
0 - 2 ,
0 " 1,
c o n d itio n s ,
ra p id
0 “ 3
in
The F ran k -C o n d o n f a c t o r s f o r t h e
oM èr
of
s tre n g th .
w hich g e n e r a l l y g iv e l a s i n g on a l l
v ib ra tio n a l
tra n s fe r
is
U nder
th re e
la s in g
tra n s itio n s ,
re q u ire d to ch an n el th e upper s t a t e
p o p u l a t i o n e n e rg y th ro u g h th e l a s e r t r a n s i t i o n s .
KrCl
is
and KrF
shown
The
The n a t u r e o f a bound » f r e e B - X t r a n s i t i o n s p e c tru m
c l e a r l y i n F ig s 2 .6 and 2 .7 f o r KrF and KrCl r e s p e c t i v e l y .
u n d u l a t io n s due t o v i b r a t i o n a l s t a t e s i n
s ta te
a re
th e
upper
e le c tro n ic
sm oothed o u t by t h e c o n tin u u m d e r i v i n g from t h e r e p u l s i v e
lo w e r s t a t e .
The c o r r e s p o n d in g p o t e n t i a l d ia g ra m f o r KrF i s shown i n
F ig 2 . 3 ( b ) .
ArF
The
s p u rio u s
ArF
s p e c tru m o f F ig 2 .8 i s i n c lu d e d h e r e
f e a t u r e s i n t h e s p e c tr u m .
I t seem s
lik e ly
d e t a i l o f t h i s s p e c tru m i s due t o s t r o n g a b s o r p t i o n .
( 1976) ,
f o r e x a m p le,
a t t r i b u t e s im ila r d e ta il in
s p e c tru m t o t h e Schum ann-Runge sy ste m o f 0 ^ .
a s a n exaittple o f
th a t
a ll
th e
Burnam and D jeu
th e
ArF
la s in g
ca
E
o
o»
OJ
o
- LA
g
m
V —
zc
tZ
i/)
S
ZJ
Cl
4—
U
QJ
ex.
</)
Y
00
u_
VD
CSÎ
o<C
O
•g
(U
trj
gi
IL ,
CÛ.
o C
o»
o
w
CN
E
o
o
un
o
o
o
un
T—
0.1
:n
_^
w
%:
E
r»
*1—
o
QJ
CL
m
><
ca
__,
Y
cxC
o
<o
csj
rsj
OJ
LL
Cl
g i
LL_
o<C
o>
o
o
Cvj
m
E
CxJ
CD
O
m
o<C
.
CD
CD
Ox
uy=>
uo
È
Z3
C-
4—
W
OJ
Ol
f/)
X
I
CD
LL,
<
CO
cxi
OJ
c _
.S ’
ijL.
Chapter 2
2 .2
23
E xcim er K i n e t i c s
The
h ig h
b o u n d -fre e
n a tu re
p a rtic u la rly
m o le c u le s
com pete
e ffic ie n c y
of
w ith
p o p u la tio n .
i m p o r ta n t
th e
f a v o u r a b le
a r e fo rm e d .
th e
of
exc.im er l a s e r s i s due n o t o n ly to t h e
la s in g
k in e tic
I t i s th e
f o r m a tio n
p ro ce sse s
Even s o ,
f o r m a ti o n
re a c tio n
lo s s
but
by
a ls o
w hich
to
th e
some
e x c im e r
t h e r e a r e many l o s s p r o c e s s e s
p u rp o s e
and
tra n s itio n
of
and
th is
p ro cesses
red u ce
c h a p te r
and
th a t
th e u p p e r s t a t e
to
th e ir
o u tlin e
th e
d e p en d en cy on
p r e s s u r e , g a s m ix tu r e r a t i o , and t h e k in d o f h a lo g e n d o n o r and b u f f e r
gas used.
2 .2 .1
F o rm a tio n K i n e t i c s
Gas
m ix tu r e s
fo r
rare -g a s
h a lid e
e x c im e r
la s e rs
g e n e ra lly
c o n s i s t o f t h r e e co m p o n en ts: a h a lo g e n b e a r in g m o le c u le , t h e r a r e - g a s
th a t
fo rm s
u s u a lly
m ix tu r e s
th e
e x c im e r ,
and
a b u ffe r gas (a ls o a ra re -g a s ) th a t
c o n s t i t u t e s o v e r 95^ o f t h e m ix tu r e .
re s u lts
d is c h a r g e
in
q u ite
c o m p lic a te d
w ith th e g e n e r a t i o n o f a
io n is e d s p e c ie s .
T a b le 2 .1 sh o w s,
la rg e
The u s e o f
k in e tic
v a rie ty
trip a rtite
p ro ce sse s
of
in th e
e x c ite d
i n g e n e r a l te r m s , t h e s p e c i e s and
r e a c t i o n s t h a t a r e c o n s id e r e d t o be im p o r ta n t i n e x c im e r l a s e r s .
s p e c ie s
c o n s is t
ra re -g a se s,
v a rio u s
of
m onatoraic
and
d ia to m ic
io n is e d
and
and
d i s s o c i a t io n p ro d u c ts .
The
e x c ite d
e x c i t e d t r i a t o m i c s p e c i e s w ith a h a lo g e n com ponent,
io n is e d
and
and
e x c i t e d s t a t e s o f t h e h a lo g e n m o le c u le and i t s
The r e a c t i o n s i n T a b le 2 ,1 a r e shown i n t h r e e
p r i n c i p a l s e c t i o n s : i n i t i a l e l e c t r o n im p a c t e x c i t a t i o n and i o n i s a t i o n
REACTION
SPECIES
(1)R +
(1 )R *
(1 )
(1)R?*
BR +
BR"*
TRIATOMIC
R?>(*
BRX""
HALIDE
M fX )M (X )-*
X
X
BX^'
INITIAL SPECIES BY
ELECTRON IMPACT
1, ( 1j2 ) Ê+R
R”+2 0
2 . (1) — . - " R ’Vs
3. (2)è+M(X)— H(X)“
4.
~®*M(X)
5.
’NlXl'^X^ 0
6.
— N(X)+X"
7.
-^N(X)+)#e
RARE-GAS HALIDE
FORMATION
METASTABLE CHANNEL
8 . R“+M(X)— RX*4N(X)
9, BR^'+MIXI— RX^NM+B
10. F?5 +M(Xh-RX%N(XkR
11. Xf+ R — R X 5X
IONIC CHANNEL
12.R%X+M— RX-ÎM
13.Rf+XTM-"-RX%R+M
EXCHANGE REACTION
14. BX®+ R — RXlB
INTERMEDIATE AND
2ND. STEP REACTIONS
15.(2)B**+ R— B+R++0
16.(2)
- “ BR'TE
17.
-»-R »+B 1
18.(12) R'" + e - - R + + 2 e
19.(1,2)R'+!f— (ÿ+R 4. e l
2011,2)R*+R*|— R?+R + e
21(1,2)R? R^— R9+2R+e
22.(1)R'!i-R+R— Rf +R
23.(1)R%R+R— R-; -f-R
24. R *+B +B -“ BR*4-B
25. R-^+B+B— BR-'+ B
26. B-^ + R — R ++ 2B
27.(1) R-^7 + 0 -— RG + R
HALIDE
28.
MIX)-""— M(X|29,
— N(X)“-^X
30.(1) M(X)+f?--“ X+N(X)-R
31. M(X) + X*— X*^
32. B'- + X ' — BX'-*
33. B**-i-M(X)— BX'4N(X)1
34.
4 -X -— BX« +B
35.
BX*'— B+X''
36, BX*(-R — R fB + X
R - r a r e -g a s , B - buffer gas, M (X )a n d N(X) - h a lid e s ,
X - h a l o g e n , M - th ird body
(1 ) Reactions involving R or B. (2 ) E lectro n reactions
Note s
1. B u f f e r gas always lig h t e r than excimer r a r e - gas.
2 , Ionic reactio n third body omitted in most cases.
3, NIX) usually s ub ject to f u r t h e r dissociation.
4. I m p u r i t y re a c tio n s may be important.
Table 2.1 General form ation reactions and r e a c tio n species
Chapter 2
of
24
t h e r a r e - g a s e s and t h e h a lo g e n d o n o r and i t s
p ro d u c ts ,
th e f i n a l
r a r e - g a s h a l i d e fo rm in g r e a c t i o n , and t h e many i n t e r m e d i a t e r e a c t i o n s
in c lu d in g
t r a n s f e r o f e x c i t a t i o n - a n d c h a rg e from
one
com ponent
to
a n o th e r.
The e f f i c i e n c y o f e x c im e r r e a c t i o n k i n e t i c s i s d e te r m in e d by t h e
quantum
e ffic ie n c y ,
w ith in
s in g le
b r a n c h in g i n t h e r e a c t i o n c h a in
re a c tio n s .
The
quantum e f f i c i e n c y ,
ra tio
o f t h e l a s e r p h o to n e n e rg y t o t h e
p lu s
any
a d d itio n a l
e x c ita tio n s ,
2 .2 .
It
a ro u n d
d e fin e d a s th e
p recu rso r
account
fo r
e n e rg y ,
in te rm e d ia te
T a b le
c a n be s e e n t h a t t h e u p p e r l i m i t f o r quantum e f f i c i e n c y i s
50%,
m ost
B ra n c h in g i n t h e r e a c t i o n c h a in r e p r e s e n t s a l o s s ,
or
o f e n e rg y t o t h e sy ste m and i s p r e s e n t i n t h e s im p l e s t
e ffic ie n t
re a c tio n s .
p a rtic le
to
b r a n c h in g
c a n be a s s e s s e d fro m t h e e n e rg y v a lu e s g iv e n i n
p a r tia l lo ss ,
and
q u a n titie s
in itia l
and
r e a c tio n
c h a in s
in
th e
fo rm
of
q u e n c h in g
The d e g r e e t o w hich any b ra n c h i s f a v o u r e d w i l l d epend on
d e n s i t i e s and r e a c t i o n r a t e s .
Some
i m p o r ta n t
ra te s
a re
g iv e n i n T a b le 2 .3 and i t i s n o te w o rth y t h a t t h e s e a r e f a s t r e a c t i o n s
r e s u ltin g in fre e lif e tim e s , fo r re a c ta n ts in ty p ic a l la s e r s , o f le s s
th a n
10 n s .
b ra n c h in g
B ra n c h in g w i t h i n a s i n g l e r e a c t i o n i s i n d i c a t e d by t h e
r a t i o w hich i s t h e r a t i o o f t h e p r o b a b i l i t y
of
p ro d u c in g
t h e r a r e - g a s h a l i d e t o t h e p r o b a b i l i t y o f an a l t e r n a t i v e o u tco m e.
is
a n o u t s t a n d in g f e a t u r e o f r a r e - g a s
ra tio s
and
h a lid e s
th a t
th e
It
b r a n c h in g
f o r t h e f o r m a tio n r e a c t i o n s ( 8 - 14 i n T a b le 2 .1 ) c a n be h ig h
a re e f f e c tiv e ly u n ity
X e C lfC lg ),
and
X e B rfB r^ ).
fo r
XeFCF^
The
and
o v e ra ll
NF^
d o n o r),
K rF C F ^),
l a s e r e f f i c i e n c y w i l l be
i n f l u e n c e d by t h e s e k i n e t i c e f f i c i e n c i e s and a l s o by q u e n c h in g o f t h e
ra re -g a s
h a lid e ,
d is c h a r g e i n e f f i c i e n c y ,
and o p t i c a l a b s o r p t i o n a t
Rare -Gases
Halogens
R
He
Ne
Ar
Kr
Xe
R+
24.6
21.6
15.8
14.0
12.1
FT" R"*
19.8
41.1 16.7
27.6 11.5
24.6 9.9
212 8.3
Rz
2.47
1.16
123
1.15
1.03
K d
Fg mass x10& "0
2.55 4 36 0.18 14 2.0
0.5 20 67 0.90 0.49 2.3
068 40 281 1.79 0.21 2.9
84 427 3.76 115 3.2
131 702 5B6 0.08 3.5
ENERGY-eV
REACTION
P2
P E
1.6
F"—
F+ e
3.5
F
F"^ e
17,4
SF^—te- S Fg"^' F
3.7
SF~— SFf+ F
1,5
1.4
Sp6^ ^ SF^"*" e
3.6
Sp5“^ SF^'*' e
SF.— SF^ e
16.6
2.35
NFg— NF^+ F
2.5
Cl2 " ^ Cl ■** Cl
4.43
HCl — H Cl
“ — SS».
Rare-gas
halides
Üuantum
efficiency
RX""
Ne F
ArCl
ArF
KrCl
KrF
XeCl
XeF
RX""
NeF
ArCl
ArF
KrCl
KrF
XeCl
XeF
XA Ehv
1080 11.5
1750 7.1
1930 6.5
2 22 0 5.6
2490 5.0
3080 4.0
3510 3.5
R"
0.53
0.45
0.41
0.40
0.36
0.33
0.29
R"
0.69
0.62
0.56
0.57
0.51
0.48
0.42
R j Rare-gas
R^^f^ met*astable
state
n - Refractive
index at ST P
T)-kg m**^at STP
K-DiffusivitycmV'^
1 3 1 2 (2 6 )].
d - Diameter -A
(Moore 1972)
cr
X- B-X wavelength
2.6
Efiy- Energy (eV)
T - B state lifetime
4 . 2 3x10""^^ cr'-Stimulated emission
cross section (cm?)
6.8 2x10"^^
11.0 5x10“^^ 0,032eV Xstate bond
15.0 4x10"^^ 0.14 eV
..
I.
R"^ - Ionic channel
“ Metastable channel
Table 2.2 Rare-Gas Halide Data
Metastable Channel
Rat e
crn^s"'’
R e a c tio n
X I + F2 —
X? + NFa —
X I + Ciz •—
F 75x10-11
XeF^'NFz 9x10^"
XeCftCl 72x10'i^
Xe +HCI —^ XeCl’‘+ H 56x10“'^
Kr + Fz — KrF’^ F 6 6 x10 ”11
l(« + MP3 - ^ K r F * 4 N f t 8.9x10-11
K? + Clz — KrCfiCl 73x1Q-il
75x10-11
A? + Fz - * - A r F « + F
Branching
ratio
1
1
1
0.6
0.9
(values fro m Rhodôs1979)
Ionic Channel
R 'i .
—
Rare Rate constant
gas
cm&s-1
Xe
Kr
Ar
Ne
He
R X '^ + M
M a x.e ff.2 -b o d y
constant.cm^s-i
6.7x10-2^ (<1 At.) 2.0x10-6(at1At]
8.9x10-26
,,
2.5x10-5
3.4x10-5
1. 2 x IQ-25
,,
5.6 X 1Q-2^(<2At.) 3.4x10-" (at 2 At)
6 .1x 10-26
,,
6.9x10-5
,,
(approximated from Flannery 1978)
Table 2.3 Excimer Formation Rates
1
Chapter 2
25
t h e l a s e r w a v e le n g th .
Of
th e
p o s s ib le
ra re -g a s
h a lid e
f o r m a tio n
c h a n n e ls ,
th e
f o ll o w i n g i s o u t s t a n d i n g i n s i m p l i c i t y and e f f i c i e n c y : e *{* R “ 4SK“ e
R** 4. M(X)
R
RX^ + N(X)
w here R i s t h e r a r e - g a s , M(X) an d N(X) a r e h a lo g e n b e a r i n g m o le c u le s ,
and
X i s t h e h a lo g e n ato m .
For
any
g iv e n
ra re -g a s
h a l.id e ,
th e
m e t a s t a b l e c h a n n e l h a s t h e h i g h e s t quantum e f f i c i e n c y , t h e m e t a s ta b le
ra re -g a s
b e in g t h e p r e c u r s o r o f lo w e s t e n e rg y .
t h e f o r m a ti o n r e a c t i o n i s f a s t ,
t o 10~^ cm ^s^l
In a d d itio n to t h is ,
w ith a r a t e c o e f f i c i e n t i n t h e ra n g e
a s shown i n T a b le 2 .3 »
T h is
i s because
th e
e x c i t e d r a r e - g a s i s n e a r i o n i s a t i o n and a n e l e c t r o n c a n t r a n s f e r t o a
h a lo g e n
form
atom i n t h e h a lo g e n b e a r i n g m o le c u le and ro n o v e t h e atom
th e
io n ic a lly
bound
rare -g a s
d e s c rib e d
as
(5 “ 10 X)
a t w hich th e y c a n ta k e p l a c e .
d e s ig n
'h a rp o o n in g *
d is c h a r g e pumped
(if
due
to
h a lid e .
ra re -g a s
it
is
th e
q u ite
I t is
h a lid e
f o r m a tio n
channel
d is c h a r g e
e f f i c i e n c y and m in im is e
Such
p o s s ib le
re a c tio n s
la rg e
to
a re
s e p a ra tio n s
c l e a r l y d e s i r a b l e bo
la s e rs
to
p ro m o te
th is
t o s im u l ta n e o u s l y m a in ta in
o p tic a l
a b s o rp tio n
and
e x c ite d
s t a t e q u e n c h in g ) .
In
e le c tr o n - b e a m pumped d e v ic e s t h e f r a c t i o n o f r a r e - g a s h a l i d e
f o r m a tio n
th a t
u n a v o id a b ly
ta k e s
s m a l l.
p la c e
T h is
is
th ro u g h
th e
m e ta s ta b le
because
th e
e l e c t r o n beam e n e rg y i s
u s u a lly
above 100 keV w ith t h e r e s u l t
s p e c ie s
a r e p ro d u c e d . A t y p i c a l
e 4- R —«0— 2 e + R
channel
t h a t h ig h d e n s i t i e s
io n ic r e a c tio n channel
of
is
io n ic
is
Chapter 2
26
e 4* M(X)
4,
„
R *}• X
w here
X
4* N(X)
iî
+ M «>=<s!E“ RX 4* M j
M is
a
r e c o m b in a tio n
th ird
body,
o f R^ and X
m ost
p r o b a b ly
th e
b u ffe r g as.
i n t h i s r e a c t i o n ca n o n ly
occur
The
if
th e
k i n e t i c e n e rg y g e n e r a te d by t h e p a r t i c l e s ’ a p p ro a c h i s rem oved.
happens
when t h e o r b i t i n g p a i r c o l l i d e w ith a n e u t r a l b a c k g ro u n d g a s
atom (M ),
can
T h e refo re,
a t low p r e s s u r e ,
th e
e ffe c tiv e
a
tw o-b o d y
ra te
c o n s ta n t
p a r tic le d e n s ity .
maximum
in
th e
in te rm e d ia te
p re ssu re .
c a lc u la tio n s
of
w ill
T h e refo re,
e ffe c tiv e
T h is
F la n n e r y
is
and
I n t h i s re g im e ,
v a ry i n v e r s e l y a s t h e
i t f o ll o w s t h a t t h e r e w i l l
tw o-body
ra te
d e m o n s tra te d
in
c o n s ta n t
th e
num ber
show ing
at
an
th e o re tic a l
Yang (1978) f o r e x c im e r f o r m a tio n i n
m ix tu r e s o f a s i n g l e r a r e - g a s w ith a f l u o r i n e d o n o r.
re s u lts ,
th e
A t h ig h p r e s s u r e , h o w ev er, t h e a p p ro a c h
th e io n s i s im peded by t h e m o b i l i t y o f t h e i o n s .
th ird -b o d y
be
t h e th r e e - b o d y r a t e c o n s t a n t
be e x p r e s s e d a s t h e p r o d u c t o f a tw o-body r a t e c o n s t a n t and
t h ir d - b o d y p a r t i c l e d e n s i t y .
of
T h is
T h e ir g r a p h i c a l
v a r i a t i o n o f t h e r a t e c o n s t a n t a g a i n s t b a c k g ro u n d
d e n s ity (o n
two
s c a le
ran g e s),
a re
shown
in
F ig
2 .9 .
C o rre s p o n d in g a p p ro x im a te r a t e c o n s t a n t s a r e g i v e n i n T a b le 2 , 3 .
A lth o u g h
ra tio s
th e
i o n i c f o r m a ti o n r e a c t i o n s may h av e h ig h b r a n c h in g
and f a s t r a t e s ,
in
th e
p resen ce
of
a d e q u a te
t h ir d - b o d y
p ressu re,
t h e a t t a i n a b l e k i n e t i c e f f i c i e n c i e s a r e lo w e r th a n i n t h e
m e ta s ta b le
c h a n n e l.
th a t
th e
io n ic
The e n e rg y l e v e l s shown i n T a b le
quantum
e ffic ie n c y
m e t a s ta b le quantum e f f i c i e n c y .
re a c tio n s
m e ta s ta b le
2 .2
in d ic a te
i s l im it e d to a b o u t 70% o f th e
I n a d d i t i o n a much g r e a t e r v a r i e t y o f
ta k e p l a c e when t h e i n i t i a l f o r m a tio n i s i o n i c r a t h e r th a n
w ith
a
re s u ltin g
lo s s . of
e n e rg y .
D e s p ite
th e s e
CO
CA
E
o(U
LL.
•|w «
"U)
c
cu
*D
fU
on
vi
>
fO
c
QJ
U
cu
w
o
c
o
m
c
Ici
E
o
w
cu
cd
CA
c>i
cu
c_
3
.sn
u_
Chapter 2
27
in e ffic ie n c ie s ,
e ffic ie n c ie s
la rg e ly
beam
pum ping
th a n d o e s d is c h a r g e pum ping.
from
d is c h a rg e s .
e le c tro n
s till
y ie ld s
h ig h e r
The r e a s o n s f o r t h i s stem
t h e d i s c h a r g e i n s t a b i l i t i e s w hich d e v e lo p i n DC p u ls e d
H ig h e s t
e ffic ie n c ie s
fo r
e x c im e r
la s e rs
have
been
a c h ie v e d by c o m b in in g e-beam and d i s c h a r g e pum ping.
The
r o l e o f t h e h a lo g e n d o n o r and b u f f e r g a s i n t h e k i n e t i c s o f
r a r e - g a s h a l i d e l a s e r s i s i m p o r ta n t and c o m p lic a te d .
a c tiv ity
T h e ir q u e n c h in g
w i l l be a p p a r e n t i n t h e f o ll o w i n g s e c t i o n and t h e re m a in in g
d e t a i l s o f t h e i r b e h a v io u r i s p r e s e n t e d i n s e c t i o n s 2 . 2 . 3 and 2 . 2 , 4 .
2 .2 .2
Q uenching K i n e t i c s
In
rem ove
ra re -g a s h a lid e la s e r s ,
th e
p re c u rso rs
e x c im e r
m o le c u le
v a r i o u s r e a c t i o n s ta k e p la c e
and
a ls o
th e
io n ic
i n d i r e c t c o m p e t it io n w ith f o r m a tio n
and m e t a s t a b l e
re a c tio n s .
may
c o n s e q u e n tly be l o s t v i a a r a d i a t i v e t r a n s i t i o n .
a re
v e ry im p o r ta n t and p a r t l y d e te r m in e t h e p r e s s u r e and
th e
c o n s titu e n t
q u a n tita tiv e
gases.
D e s p i te
th is ,
much
i n f o r m a t i o n on q u e n c h in g r e a c t i o n s
of
is
w hich
E nergy
Such r e a c t i o n s
th e
not
ra tio s
of
n e c e ssa ry
a v a ila b le ,
m ost o f th e p u b lis h e d d a t a b e in g c o n f in e d t o XeF and KrF l a s e r s .
The g e n e r a l r e a c t i o n s ,
w here p u b lis h e d i n f o r m a t i o n e x i s t s ,
f o r e x c im e r q u e n c h in g by tw o -b o d y r e a c t i o n s ,
RX* + M(X)
*
RX + R
*
RX + B
,
a re
Chapter 2
28
e x c im e r q u e n c h in g i n th r e e - b o d y r e a c t i o n s ,
RX* + B 4- B
RX
RX
ij
ÎÎ
4- R 4* R
4- R 4* B
RX* 4. M (X )
-Î- R ,
m e t a s ta b le q u e n c h in g i n th r e e - b o d y r e a c t i o n s ,
R
a
4* B 4- B
R
R
4- R 4" R
%
4* R 4- B
,
and i o n q u e n c h in g i n t h r e e - b o d y r e a c t i o n s ,
R
'I* B 4* B
R* + R + R
R ^ 4- R 4- B .
A c o l l e c t i o n o f q u e n c h in g r a t e c o n s t a n t s f o r some p a r t i c u l a r c a s e s o f
th e s e
re a c tio n s
rep re sen t
g iv e n
of
th e
T a b le 2 ,4 and a lth o u g h t h i s d o e s n o t
of
th e
lite ra tu re
it
is
fa irly
t h e f a c t t h a t q u e n c h in g s t u d i e s h a v e b e e n c a r r i e d
f o r o n ly a s m a ll f r a c t i o n . o f t h e g a s c o m b in a tio n s t h a t h a v e b e e n
u s e d f o r e x c im e r l a s e r s .
have
in
a n e x h a u s t i v e summary
r e p re s e n ta tiv e
out
is
I t i s n o te d , i n p a r t i c u l a r ,
b e e n c a r r i e d o u t u s in g SF^,
e x p e r im e n ta l
w ork
d e s c rib e d
t h a t no s t u d i e s
th e donor used i n th e m a jo rity
in
th is
th e s is .
re s e rv a tio n s
th e s ig n if ic a n c e o f th e a v a ila b le d a ta i s
and
re la te d
may
be
to
of
D e s p ite t h e s e
c o n s id e r a b l e
t h e t r e n d s d e m o n s tra te d i n t h e e x p e rim e n ts
d e s c r i b e d i n C h a p te rs 7 and 8 .
I
tD
C
ro
Os
S;
CO
cu
*a
o
JC
cc
o
e
o
g :
o
CO
cu
"c
_K:
o
q;
I I
.2
m
o
CO
as
r - \—
CT\ -—c_
"— ' o
c
CO
ro
L.
hun
CD
CM
'k
o
ca
m
CNJ
<SJ
V—
sà
m
m
CM
m
CNI
<
CD
CO
crv
CO
OJ
X
o
u
ro
cc
cu
'
04
O
O
<u
ZC
o
CA
Ln
X nn
I
mtn
E
•M—
*
vO
CO
CD
*
u_ un
£_ tn
»
LU
m
cz
•'Η
«
<
<
ro
CC
m
X
a .
\—
CD
CM
s
vO
§
LU LU i n
z
S
nro m
o CD
o
z
01
E
.£
Lc
tj
c
OJ
3
O
m sa
o CD
2
CO
<: X
<N
r-
H
2 2
Ln Ln
â
cvi
CA
C 'j
Oi
X X
CN
OJ
S
sa
X
Csl CN CNl
z
2
in
sO
CM
tn 2
s
CD
CD
O
CD no g
vO
lC
Z
X
•è* i x:
t
tj i
CM
1 X X x“ X X <
OJ
«hr
-d '
OJ
-o "O
^
I
cvj m
.§
I
CO
«^nw
c
ZD
<1CN
OJ
jd
ro
t—
Chapter 2
The
m e t a s ta b le
29
n e t f o r m a tio n r a t e o f
channel
w ith
e x c im e r
lo ss
by
m o le c u le s
s p o n ta n e o u s
v ia
th e
2 -b o d y
decay
and
2 -b o d y
q u e n c h in g , and w ith no o t h e r p r o c e s s e f f e c t i v e , i s g i v e n by
d n ^ /d t = k^ngRg - k^n^n^ - n ^ / t ^
'
(1 )
w h ere th e sym bols a r e a s f o ll o w s :
“3
n^ - e x c im e r number d e n s i t y i n cm
n^ -
“3
m e t a s ta b le r a r e - g a s d e n s i t y i n cm
n^ -
d o n o r m o le c u le d e n s i t y i n cm” ^
“ q u e n c h in g p a r t i c l e d e n s i t y i n cm” ^
-
f o r m a tio n (h a rp o o n r e a c t i o n ) r a t e c o n s t a n t
i n cm s ”
kg -
2 -b o d y q u e n c h in g r a t e c o n s t a n t i n
t^ -
e x c im e r s p o n ta n e o u s e m is s io n l i f e t i m e i n s .
A ssum ing
t h a t th e c o n s titu e n t gas d e n s it ie s
cm^s” ^
s ta y
c o n s ta n t
on
t ir a e s c a le o f i n t e r e s t and t h a t s t i m u l a t e d e m is s io n i s n e g l i g i b l e ,
th e
th e
s o l u t i o n t o (1 ) i s
= k^n^n^d - exptC-kgn^ - 1 / t g ) ) / ( k g n ^ + l / t ^ )
.
(2)
T h is h a s t h e maximum v a lu e
= k ^ n^n^/C k^n^ + 1 / t ^ )
w ith a c h a r a c t e r i s t i c r i s e tim e g i v e n .by
(3 )
Chapter 2
t(ris e )
E q u a tio n
a
ty p ic a l
ris e
and
30
= - ( ln ( 1 - 1 /e ))/(k g ii^ + l / t ^ )
.
(4 )
(4 ) h a s a maximum v a lu e when th e q u e n c h in g i s s m a ll and f o r
e x c im e r
life -tim e
o f 10 n s i s a b o u t 5 n s .
T h is maximum
tim e i s s h o r t e r th a n t h e u s u a l pum ping p u l s e d u r a t i o n s
much
a p p a r a tu s
s h o rte r
th a n
th e
m icrow ave
p u lse s
( 3 2 0 n s ) u s e d i n t h i s s tu d y so t h a t
(50 n s )
o f th e e x p e r im e n ta l
th e
e x c im e r
d e n s ity
g iv e n by (3 ) may be u s e d i n m o st c a s e s .
For
2 -b o d y
q u e n c h in g
of
th e
e x c im e r
by
t h e h a lo g e n d o n o r,
e q u a ti o n (3 ) becom es
n^ = k^ngUg/Ckgng + l / t ^ )
T h is
.
(5 )
e x p r e s s i o n h a s a maximum v a l u e ,
a t h ig h d o n o r
c o n c e n tra tio n s ,
g i v e n by
( 6)
>
w here
we
c o n s ta n t.
h av e
assum ed
th a t
t h e m e t a s ta b le d e n s i t y ,
To a c h ie v e s a y 90$ o f t h i s
v a lu e ,
th e
n^,
re m a in s
re q u ire d
donor
d e n s i t y i s g iv e n by
“ 9 / bgkg
«
(7)
T h is v a lu e c o u ld be i n t e r p r e t e d a s t h e minimum d o n o r d e n s i t y r e q u i r e d
fo r
th e e x c im e r d e n s i t y t o h a v e a v a lu e t h a t i s n o t l i m i t e d
by
th e
Chapter 2
donor
and
31
d e n s ity .
On t h i s b a s i s ,
t h e minimum p a r t i a l p r e s s u r e s f o r Fg
NF^ c o r r e s p o n d in g t o t h e c o n s t a n t s i n
(F g ,X e F ),
0 ,0 9 atm
( F g ,K r F ) ,
T a b le
0 .0 4 atm
2 .4
a re
(F g ,A ^ F ),
0 .0 6 atm
and
1 ,4 atm
(NF ,X e F ).
If
2 -b o d y q u e n c h in g by a
c rite rio n
w ould
s p o n ta n e o u s
be
th a t
th e
ra re -g a s
is
q u e n c h in g
l o s s w hich i s u n a v o id a b le .
c o n s id e r e d ,
s h o u ld
be
a
u se fu l
l e s s th a n th e
The q u e n c h in g l o s s i s
equal
t o t h e s p o n ta n e o u s l o s s when t h e f o llo w in g i s s a t i s f i e d ;
^3^4 ~
w here
»
(8 )
n^ i s t h e r a r e - g a s num ber d e n s i t y and
i s t h e q u e n c h in g r a t e
c o n s t a n t f o r t h e r a r e - g a s a c t i n g on t h e e x c im e r m o le c u le .
d e n s ity
n^^
c o n v e r te d
c a lc u la te d
can
now be r e g a r d e d a s t h e maximum r a r e - g a s d e n s i t y and
to a
on
The num ber
p a rtia l
th is
p ressu re.
Maximum
p a rtia l.
p ressu res
b a s i s f o r 2 -b o d y r a r e - g a s q u e n c h in g o f e x c im e rs
a r e shown i n T a b le 2 . 5 ( a ) ,
Some
T a b le 2 , 4 ,
v a lu e s o f t h e 3 -b o d y q u e n c h in g r a t e c o n s t a n t s a r e shown i n
I f 3 -b o d y q u e n c h in g and s p o n ta n e o u s d e c a y a r e r e g a r d e d a s
t h e o n ly l o s s e s , e q u a ti o n (1 ) c a n be w r i t t e n t o g iv e
d n ^ /d t = k^ngn^ - k^n^n^n^ - n ^ / t ^
w h ere
k
3
i s t h e 3 -b o d y q u e n c h in g r a t e c o n s ta n t an d n_ and n , a r e t h e
b
o
ra re -g a s d e n s itie s .
be
(9 )
I f a s i n g l e r a r e - g a s i s i n v o lv e d , n^ and n^ w i l l
eq u al to th e t o t a l r a r e - g a s d e n s ity .
In
th is
case
a
p a rtia l
Quenchant
25
8.3
He
Ne
Kr
3 .4
0.086
1.9
Xe
Ar
Table 2.5 (a)
Ne
+ Ar
4» Kr
4- Xe
+ Ne
4* Ar
+ Fz
+ Ar
Table 2. 5( b)
Quenchant
and 3 r d . - body
Ar
Kr
Xe
Xe
Xe
+ Ar
+ Kr
+ Xe
He
+ Ar
Table 2 ,5 ( c )
3.2
2 -body Excimer Quenching
Quenchant
and 3rd.-body
Ne
Ar
Kr
Xe
Xe
Xe
Xe
Kr
K rF *
X eF*
XeF*
K rF *
4.5
2.5
Product of 2 -body
maximum pressures
1.5
0.48
0,6
0.12 At2
0.71
0.16
0.0006
0.31 n
0.006 M
•
0 .2 4 A t^
At?
,1
11
3 -bod y Excimer Quenching
Kf'
( Fzl
4 .5
2.5
Product of 2-body
Kr®
Xe®
Xe®
(NF3 ) ( F 2 ) {NF 3 } maximum pressures
8
4.7,
14
23
3.6
2 .2
14Af2 38Af2
9 .8 „ 27 „
2 .2
0.16
At?
,,
3-body H efastable Quenching
Table 2.5 Quenching-Maximum P a rtia l Pressures (At)
Chapter 2
p ressu re
32
ca n
be fo u n d f o r t h e r a r e - g a s w h ere t h e q u e n c h in g l o s s and
s p o n ta n e o u s l o s s o f t h e e x c im e r a r e e q u a l.
c o u ld
As b e f o r e ,
be r e g a r d e d a s a u s e f u l maximum and v a lu e s f o r c a s e s w ith r a t e
c o n s t a n t s i n T a b le 2 .4 a r e g iv e n i n T a b le 2 . 5 ( b ) .
3 -b o d y
be
th is p ressu re
q u e n c h in g i s due t o two r a r e - g a s e s ,
If,
h o w ev er,
a maximum v a lu e c a n o n ly
fo u n d f o r th e p ro d u c t o f t h e p a r t i a l p r e s s u r e s o f t h e two
Such
th e
g ases.
v a lu e s a r e a l s o shown i n T a b le 2 .5 ( b ) a lo n g w i t h v a lu e s f o r t h e
p ro d u ct
o f th e maximum p r e s s u r e s o f t h e two g a s e s
fro m
th e
2 -b o d y
q u e n c h in g d a t a f o r c o m p a ris o n .
Some d a t a i s a v a i l a b l e on t h e q u e n c h in g o f m e t a s t a b l e p r e c u r s o r s
in
2 -b o d y and
r a t e o f change
d U g /d t = M -
w h ere
th e
3 -b o d y
3 -b o d y r e a c t i o n s . I n t h e
ab sence o f o th e r e f f e c t s
o f t h e m e t a s ta b le d e n s i t y i s g i v e n by
k^ngUg - k^ngC^n^ ,
(1 0 )
sy m b o ls r e t a i n t h e i r p r e v io u s m eaning an d w h e re
m e t a s ta b le q u e n c h in g r a t e c o n s t a n t and M i s
p r o d u c tio n
th e
ra te .
S in c e
it
th e
kj^ i s
th e
m e ta s ta b le
i s d e s i r a b l e t h a t q u e n c h in g s h o u ld n o t
com pete
w ith e x c im e r f o r m a tio n ,
p a rtia l
p ressu res
maximum
quenchant
and
t h ir d - b o d y
a r e ta k e n a s th o s e r e q u i r e d t o make t h e q u e n c h in g
l o s s r a t e e q u a l t o t h e e x c im e r f o r m a tio n r a t e u s in g
= V 5 “6 •
V a lu e s
o b ta in e d
(1 1 )
o f maximum q u e n c h a n t and t h ir d - b o d y p a r t i a l p r e s s u r e s c a n
i f a v a lu e f o r n^ i s a ssu m e d .
donor d e n s ity ,
Minimum v a l u e s f o r n^ ,
be
th e
w ere c a l c u l a t e d ab o v e ( i n te rm s o f p a r t i a l p r e s s u r e ) .
Chapter 2
33
By u s in g t h e s e and m e t a s t a b l e q u e n c h in g r a t e c o n s t a n t s from T a b le 2 .4
we
g e t th e v a lu e s shown i n T a b le 2 . 5 ( c ) .
As b e f o r e ,
th e c a se s o f a
s i n g l e r a r e - g a s and two r a r e - g a s e s a r e d e a ].t w i t h .
Q uenching
of
io n ic
m e t a s ta b le q u e n c h in g .
ra re -g a s
p re c u rso rs
w i l l be a n a lo g o u s t o
How ever, t h e c o m p le x ity o f t h e i o n i c f o r m a ti o n
r a t e c o e f f i c i e n t and l a c k o f know ledge o f i o n d e n s i t i e s mean t h a t th e
s im p lifie d
a n a l y s i s o f q u e n c h in g p r e s e n t e d above c a n n o t
be
a p p lie d
and no o t h e r a n a l y s i s w i l l be a tte m p te d h e r e .
2 .2 .3
H a lid e , K i n e t i c s
The r o l e s o f t h e h a lo g e n d o n o r and i t s p r o d u c t s i n d i s c h a r g e s i n
ra re -g a s
th e
h a l i d e g a s m ix tu r e s a r e v a r i e d and c r u c i a l
flu o re s c e n t
e ffic ie n c y .
in.
d e te r m in in g
The e l e c t r o - n e g a t i v i t y o f t h e h a l i d e s
r e s u l t i n t h e i r h a v in g a l a r g e i n f l u e n c e on d is c h a r g e s t a b i l i t y ;
a ls o
have
fast
re a c tio n s .
re a c tiv e
u s a b le
th e
re a c tio n
Of s p e c i a l
ra te s
im p o rta n c e
in
b o th
in
f o r m a ti o n
th e
p rese n t
th e y
and q u e n c h in g
s tu d y
is
th e
n a t u r e o f t h e h a lo g e n s w hich r e s u l t i n t h e e v e n tu a l l o s s o f
d onor m o le c u le s .
e le c tro n
d is c h a r g e
is
lo s t,
r e s u l t i n g i n a runaw ay
The h a lo g e n s a r e l o s t by t h e f o r m a ti o n o f h i g h ly s t a b l e
form ed fro m t h e o r i g i n a l d o n o r c o n s t i t u e n t atom s o r ,
im p o rta n tly ,
d is c h a r g e
h a lo g e n s
th e s t a b i l i s i n g e f f e c t o f
c u r r e n t i n DC d i s c h a r g e s o r l a r g e r e f l e c t i o n s i n m icrow ave
d is c h a rg e s .
compounds
a tta c h in g
As t h i s h a p p e n s ,
by r e a c t i o n w ith w a l l m a t e r i a l s .
tu b e s o f s m a ll d ia m e te r w e re u se d
m ore
I n t h e p r e s e n t s tu d y ,
so
th a t
th e
lo ss
of
h a lo g e n s i n w a l l r e a c t i o n s was f a s t ; c o n s e q u e n tly , e f f e c t i v e g a s l i f e
Chapter 2
34
m e a su re m e n ts
w o rk .
c o n s titu te d a
la rg e
p ro p o rtio n
of
th e
e x p e r im e n ta l
I n a c t i v e l a s e r s t h e h a lo g e n d o n o r and i t s p r o d u c t s may r e d u c e
t h e l a s e r p e rfo rm a n c e by a b s o r b in g a t t h e l a s e r w a v e le n g th .
T h is and
o t h e r c o n s i d e r a t i o n s r e s u l t i n t h e r e b e in g v e ry few h a lo g e n compounds
w hich
a re s u ita b le d o n o rs.
d ia to m ic
h a lo g e n s ,
NF^,
The m ost f r e q u e n t l y u s e d d o n o rs a r e
and HCl,
e x te n s iv e ly b ecause i t i s cheap,
an
e x c im e r c o n t e x t .
SFg.
it
I n t h e p r e s e n t w ork SF^ was u se d
s t a b l e , and r e l a t i v e l y u n s tu d i e d i n
I n a few c a s e s NF^ was u s e d f o r c o m p a ris o n w ith
The d o n o r u s e d f o r XeCl and KrCl was HCl.
d is c u s s io n ,
th e
In
th e
f o ll o w i n g
F^ i s i n c l u d e d b e c a u s e o f i t s w id e s p re a d u s e and b e c a u s e
w i l l be fo rm ed when t h e
o th e r
flu o rin e
d o n o rs,
NF^
and
SF^
d i s s o c i a t e in th e d is c h a r g e .
F lu o rin e
M o le c u la r
flu o rin e
i s p r o b a b ly t h e b e s t d o n o r f o r KrF and
ArF l a s e r s th o u g h s l i g h t l y i n f e r i o r t o NF^ f o r u s e i n XeF l a s e r s .
g iv e s
8,
r a p i d f o r m a ti o n r a t e s b o th by t h e m e t a s t a b l e c h a n n e l ( r e a c t i o n
T a b le 2 .1 ) and t h e i o n i c c h a n n e l ( r e a c t i o n 1 2 ,
io n ic
channel
e le c tro n
fo r
It
5
f o r m a tio n
ra te
T a b le 2 . 1 ) .
i s a c t u a l l y d e te r m in e d by t h e s lo w e r
d i s s o c i a t i v e a tta c h m e n t r a t e w hich i s a b o u t 7x10™^^
eV
th e r m a l
e le c tro n s .
The
cm^s ^
The r a p i d f o r m a ti o n r a t e s w ith
as
d o n o r a r e m atch ed by r a p i d q u e n c h in g o f t h e e x c im e r by F^ a s shown i n
T a b le
of
2 .4 ,
I f d o n o r c o n c e n t r a t i o n s a r e h ig h enough f o r e q u a ti o n (6 )
S e c t i o n 2 . 2 . 2 t o a p p ly ,
m e ta s ta b le
d e n s ity
and 0 .4 : 1 f o r A rF.
t h e r a t i o o f t h e e x c im e r d e n s i t y t o
i s l i m i t e d t o 2 ,1
: 1 f o r XeF,
th e
1 .2 ; 1 f o r E rF ,
Chapter 2
For
35
e a ch r a r e - g a s f l u o r i d e m o le c u le ,
g e n e r a te d
w ith t h e
h i g h e s t when
re s u lt
th a t
th e
i s u s e d a s t h e d o n o r.
h a lo g e n s ,
a re e f f e c tiv e ly
lo s t
two
flu o rin e
d e n s ity
and t h e o t h e r
r e a c t i o n s i n v o lv i n g t h e f r e e
a to m s , t h e g a s l i f e w ith F^ a s d o n o r i s l i k e l y t o be p o o r.
c o n s id e ra tio n
c o llis io n
ra te
c o n c e r n in g
life
is
th e
F o r e x a m p le,
e s ti m a t e d v a lu e o f 10
F 4 F
The m ajo r
c o m p a ris o n o f t h e w a l l
r a t e w ith t h e F -r F r e c o m b in a tio n r a t e .
i s q u i t e s lo w .
w here
gas
a re
of fre e flu o rin e is
S in c e f l u o r i n e ,
v ia
atom s
The r e c o m b in a tio n
Jo h n so n and H u n te r (1 9 8 0 ) g i v e an
orn^s"^ f o r t h e r e a c t i o n
M—
Fg + M
M i s a th ird -b o d y .
,
The f l u o r i n e l o s s r a t e w i l l be
tw ic e
th e
r e c o m b in a tio n r a t e o f f o r m a ti o n o f F^ and i s t h e r e f o r e g iv e n by
d n ^ / d t = 2 k g (n ^ )^ n g
,
(1 )
w here n^(cm ^) i s t h e f l u o r i n e num ber d e n s i t y , n ^ ( cm "^) i s t h e b u f f e r
gas d e n s ity ,
and k^ i s t h e r a t e c o n s t a n t .
S u b s t i t u t i o n o f t h e above
v a lu e f o r k^ g iv e s
d n ^ /d t = 2x10” ^ ^ (n ^ )^ n g
If
it
is
assum ed
th a t
cm^^s"^
each
.
(2 )
f l u o r i n e atom t h a t c o l l i d e s w ith t h e
c o n t a i n e r w a l l i s l o s t t h e r e , t h e d i f f u s i o n l o s s r a t e i s g iv e n by
Vp = Dn^/A^
,
(3 )
Chapter 2
w here
. 3
(om °^s” ‘ ) i s t h e d i f f u s i o n
volum e w ith n e g l i g i b l e end a r e a s ( a lo n g t h i n
e x a m p le ) , A
i s g iv e n by
(T he
d iffu s io n
th e
c y lin d ric a l
w here
c h a ra c te ris tic
D
and
= ( r / 2 . 405)2
th e
ra te ,
c o e ffic ie n t
l\
A
lo ss
6
d iffu s io n
le n g th .
For a
tu b e
fo r
,
(4)
r i s t h e tu b e r a d i u s and 2 .4 0 5 comes from t h e B e s s e l f u n c t i o n .
d e r i v a t i o n s o f e q u a ti o n s (3 ) and (4 ) a r e g i v e n by M cD aniel
Mason
1 9 7 3 ).
The
d iffu s io n
and
c o e f f i c i e n t f o r f l u o r i n e can be fo u n d
from t h e e q u a ti o n
D = 3(8kT/iTmg)"^^^/32nga2g
,
(5)
w hich i s e q u a ti o n (2 8 ) o f S e c t i o n 3 . 1 . 1 .
d e n s ity ,
ra^
g a s - h a lo g e n
th e
b u ffe r
gas
H e re ,
m o le c u la r
c o l l i s i o n d ia m e te r .
m a ss,
n^ i s t h e b u f f e r g a s
and o.^ ^ t h e b u f f e r
U sing v a lu e s fro m T a b le
3 .1
fo r
f l u o r i n e w ith h e liu m a s b u f f e r a t 300K g i v e s
D = 2.7x10^^/ng
cra^s” ^
(6)
w ith Ug i n cm” ^ . S u b s t i t u t i n g e q u a t i o n s (4 ) an d (6 ) i n t o (3 ) g i v e s
Vjj = 1 .ô x IO ^ ^ n ^ /r^ n ^
w here
be
cm^^s"^
,
“3
r i s i n cm and n.^ i s i n cm .
(7 )
The d i f f u s i o n l o s s r a t e can now
com pared w ith t h e r e c o m b in a tio n l o s s r a t e by c o m p a rin g
e q u a ti o n s
Chapter 2
(7 )
37
and
(2 ).
E q u a tin g t h e s e and u s in g t h e e x p e r im e n ta l tu b e r a d i u s
o f 0 .1 cm and c o n v e r t in g t o p a r t i a l p r e s s u r e g i v e s
^He^F
w here
4.1x10™^ atm ^
P„ and P_ a r e
he
r
re s p e c tiv e ly .
s tra ig h t
T h is
(8 )
th e
h e liu m
fu n c tio n
and
is
flu o rin e
p lo tte d
in
l i n e d e l i n e a t e s t h e r e c o m b in a tio n and
re g io n s .
p a rtia l
F ig
p ressu res
2 .1 0
w here th e
d iffu s io n
d o m in a te d
A lso shown on t h i s g ra p h i s a r e g i o n t h a t c o v e rs t h e ra n g e
o f b u f f e r g a s - F^ m ix tu r e r a t i o s commonly u s e d i n e x c im e r l a s e r s .
The e x p e r im e n ta l work was c o n d u c te d o v e r r a n g e s o f p r e s s u r e s and
m ix tu r e s
t h a t f a l l i n b o th t h e r e c o m b in a tio n d o m in a te d and d i f f u s i o n
d o m in a te d
la rg e
r e g i o n s o f F ig 2 .1 0 .
number
d iffu s io n
of p u ls e s ,
H ow ever,
i n t h e lo n g te r m ,
a fte r a
t h e h a lo g e n p o p u l a t io n w i l l be d e p l e t e d by
e v e n i f t h e d i f f u s i o n r a t e i s s lo w .
The
d e ta ils
of
th e
d i f f u s i o n p r o c e s s i n t h e s h o r t te rm a r e d is c u s s e d i n C h a p te r 3 .
N itr o g e n
T riflu o rid e
The
re m o v a l o f a f l u o r i n e atom from NF^ t a k e s
2 .5 eV com pared w ith 1 .6 eV f o r F^ (T a b le 2 . 2 ) .
of
th is ,
t h e m e t a s t a b l e e x c im e r f o r m a tio n r e a c t i o n s a r e s lo w e r f o r
NFg a s d o n o r th a n f o r F ^ .
by
NF^
ra tio
is
H ow ever,
f o r XeF a t l e a s t ,
t h e q u e n c h in g
a l s o c o n s id e r a b l y s lo w e r th a n q u e n c h in g by F ^ .
o f t h e e x c im e r d e n s i t y t o t h e m e t a s ta b le d e n s i t y ,
fro m (6 ) o f S e c t i o n 2 . 2 . 2 ,
th e
P o s s ib l y a s a r e s u l t
h ig h e r
fo r
NF^
c a lc u la te d
i s 5 .6 f o r XeF w ith NF^ d o n o r com pared t o
r a t i o 2 .1 w ith F^ a s d o n o r.
e ffic ie n c y
Thus t h e
T h is p r e d i c t s
a
h ig h e r
f o r m a tio n
and i t seem s l i k e l y t h a t t h i s i s t h e r e a s o n f o r
la s in g e f f i c i e n c i e s t h a t a re re p o rte d
when
it
is
u se d
to
RECOMBINATION
or
DOMINATED
-I—
00
00
LU
CE:
CL
D IFFU SIO N
COMMON
MIXTURE
RATIOS
DOMINATED
-3
LU
LU
(X.
10
-
HELIUM
' FIGURE
P A R T I A L P R ESS URE
2.10 Fluorine recombination
(At)
He
and d iffu s io n
Chapter 2
38
rep lace
i n XeF l a s e r s .
N i t r o g e n t r i f l u o r i d e h a s b e e n u s e d i n KrF l a s e r s ,
la se rs,
and r e a c t i o n k i n e t i c s h a v e b e e n s t u d i e d by
(1 9 7 7 )»
Shaw and J o n e s (1 9 7 7 )»
e t.
a l,
(1981).
re a c tio n
of
Kr
a s w e l l a s XeF
Chow
e t,
S m ith and H u e s t i s ( 1 9 8 1 ) ,
a l,
and Tang
I n Chow (1 9 7 7 ) i t i s s u g g e s t e d t h a t t h e f o r m a t i o n
w i t h NF^ i s t w i c e a s f a s t a s t h e r e a c t i o n w i t h NF^
and
t h a t th e in c r e a s e i n l a s e r o u tp u t t h a t o ccurs d u rin g
100
sh o ts
th e
i s due t o t h e i n i t i a l i n c r e a s e i n NF^ d e n s i t y .
firs t
From t h i s
i t fo llo w s t h a t th e rec o m b in a tio n r e a c t i o n
NP + NF
NgFg
w i l l be i m p o r t a n t a s w e l l a s t h e r e a c t i o n
NFg *s- F *}* M
NF^ + M
*
A lth o u g h t h e r e a c t i o n r a t e f o r NF 4- NF i s n o t known,
i t i s su g g ested
i n Chow (1977) t h a t t h e above r e a c t i o n i s t h e m ost l i k e l y and rem o v e s
m ost
o f t h e NF b e tw e e n l a s e r p u l s e s .
h a s b e e n fo u n d t o be 2 .3 x 1 0
-31
The 3 -b o d y r e c o m b i n a t i o n
5 -1
cm s
w i t h 1 Atm o f Ne a s b u f f e r (Tang
1 9 8 1 ) , d e c r e a s i n g t o a b o u t h a l f t h i s v a l u e w i t h 4 Atm o f Ne,
about
200
tim es
fa ste r
ra te
T h is i s
th an th e F + F re c o m b in a tio n r a t e w ith th e
r e s u l t t h a t t h e f r e e f l u o r i n e d e n s i t y , and h e n c e t h e d i f f u s i o n l o s s ,
w ill
be
less
when
NF^
is
u s e d i n s t e a d o f F^ a s t h e d o n o r .
T h is
c o r r e l a t e s w i t h t h e i n c r e a s e d g a s l i v e s t h a t a r e r e p o r t e d f o r NF^.
S u lp h u r
H e x a flu o rid e
S ulp h u r
h ex aflu o rid e
is
seldom
used
as
a
Chapter 2
39
f l u o r i n e d o n o r i n e x c im e r l a s e r s and c o n s e q u e n t l y t h e k i n e t i c s o f SF^
i n t h i s c o n te x t have r e c e iv e d l i t t l e
is
g rea ter
th an
th at
a tte n tio n .
NF^ ; e n e r g i e s
of
g rea ter
req u ired
t o rem ove a f l u o r i n e atom from SF^.
u n lik e ly
to
shown
t h a n 3 . 7 eV a r e
F o r t h i s r e a s o n SF^ i s
g i v e good b r a n c h i n g r a t i o s f o r e x c im e r f o r m a t i o n i n t h e
m e ta s ta b le ch a n n el.
is
The s t a b i l i t y o f SF^
by
The r e a c t i o n r a t e o f Kr
V e la z c o
e t,
a l,
(1976)
w i t h SF^,
to
be
f o r e xam ple,
n e g lig ib ly sm a ll.
However, s t r o n g l a s i n g w i t h SF^ a s a d onor h a s b e e n o b s e r v e d by R o th e
and G ib s o n (1977) w i t h t h e i m p l i c a t i o n t h a t f o r m a t i o n m ust t a k e p l a c e
v ia
io n ic sp e cie s.
T h i s seem s r e a s o n a b l e
in
view
e l e c t r o n a f f i n i t y o f S F ^ ( 1 ,4 eV) and F ( 3 . 5 e V ) .
in
of
stro n g
E l e c t r i c a l breakdow n
SFg h a s b e e n s t u d i e d e x t e n s i v e l y due t o i t s u s e a s a n
in su la to r.
th e
e le c tric a l
I m p o r t a n t r e a c t i o n s a r e g i v e n by
SF g 4- e
SF g
«3» 8Fg 4- F
,
a s d i s c u s s e d by F e h s e n f e l d ( 1 9 7 0 ) , and
o
4- M —
SF^ 4* M
F
4- SF^ —
D
SF— 4* F 4* M
b
F
4" SFj^ 4- M
D
a l.
(1 975).
These r e a c t i o n s ,
c o u p le d
t h e o b s e r v a t i o n t h a t s i x f l u o r i n e atom s a r e a v a i l a b l e from ea ch
d o n o r m o l e c u l e , s u g g e s t t h a t F and F
is
,
SF^ 4- F
a s d i s c u s s e d by McGeehan e t .
w ith
,
used as a donor.
d e n s i t i e s w i l l be h i g h when SF^
G e n e r a l l y how ever t h e r e i s
little
in fo rm a tio n
a v a i l a b l e t o s u g g e s t w hich o f t h e p o s s i b l e r e a c t i o n s and s p e c i e s w i l l
/
Chapter 2
40
be p r e s e n t i n r a r e - g a s h a l i d e g a s d i s c h a r g e s w i t h SF^ a s d o n o r .
2 .2 .4
B u f f e r Gas K i n e t i c s
B uffer
rare-g as
h a lid e
ex ceed in g
Ne
or
g a se s have g e n e r a l l y
gas
m ix tu res
found
Ar)
has
d isc u ssio n
be
n ecessary
in
The t y p e o f b u f f e r g a s (He,
b e e n fo u n d t o be i m p o r t a n t f o r d i s c h a r g e s t a b i l i t y ,
e fficie n cy ,
of
to
w i t h optimum q u a n t i t i e s o f t e n
95^ o f t h e t o t a l g a s c o n t e n t .
flu o re sc e n c e
w ill
lase r
been
and l a s i n g e f f i c i e n c y .
In
th e
fo llo w in g
th e im p o rta n t f u n c tio n s of th e b u f f e r g a s,
Xe and Kr
be i n c l u d e d b e c a u s e i n some o f t h e e x p e r i m e n t a l work no
buffer
g a s was u s e d a n d , s i n c e Xe o r Kr a r e t h e n t h e m a j o r i t y g a s , t h e y m ust
perform
th e fu n c tio n s of th e b u ffe r g as,
A c o lle c tio n of
d a ta
for
r a r e - g a s e s i s g i v e n i n T a b le 2 . 2 ,
E lectro n
d e te rm in e
of
th e
E nergv
The
b u ffer
g a s t y p e and i t s p r e s s u r e
t h e E/N v a l u e ( r a t i o o f e l e c t r i c f i e l d t o number
d isch arg e
d istrib u tio n .
v ario u s
D istrib tio n
w hich
is
a
d e te rm in a n t
d e n sity )
o f th e e l e c t r o n energy
The d i s t r i b u t i o n i n t u r n a f f e c t s t h e r a t e a t w hich t h e
e x c i t a t i o n s and i o n i s a t i o n s t a k e p l a c e .
In th e e x p erim en tal
m icrow ave a p p a r a t u s t h e p u l s e pow er, P, was 50 kW and t h i s i s r e l a t e d
t o t h e e l e c t r i c f i e l d a t t h e w a v e g u id e c e n t r e , E, by
h ,(p
. . .,/E ,)\ 1 / 2
P = B a b ( 1 - ( f^ /f) ^2 )\ 1 / 2 ,/4
a-"'
w here
a
and
p e rm e ab ility
b
are
th e
w a v e g u id e
and p e r m i t i v i t y o f
free
d im en sio n s,
space,
f^
pLg and
is
th e
a re th e
c u t-o ff
Chapter 2
.
frequency,
g iv es
in
t h e g u i d e f r e q u e n c y ( s e e H arvey 1 9 6 3 ) .
T h is
a n e l e c t r i c f i e l d o f 6 . 7 kVcmT^ f o r t h e w a v e g u id e (WG 16)
used
our
v a lu e
and
f
is
e x p erim en ts.
The d i s c h a r g e c o u p l i n g s t r u c t u r e r e d u c e s t h i s
by a f a c t o r o f a b o u t 7 and t h e p r e s s u r e
m a j o r i t y o f e x p e r i m e n t s was 0 ,1 t o 2 a tm .
v a lu e s
was
m icrow ave
E/N
1 ,8 x 1 0 ” ^*^
to
in
i n h e liu m ,
rare-g ases
are
for
th e
d istrib u tio n
argon,
(1979) and r e p r o d u c e d i n F i g 2 . 1 1 ,
th e
used
fo r
cases
th e
of
For c a se s o f poor c o u p lin g ,
E l e c t r o n e n e rg y
d isch arg es
range
The r e s u l t a n t r a n g e o f E/N
3,6x10*”^^ Vcm*"
to d isc h a rg e c o u p lin g .
v a lu e s r e s u l t .
v a lu e s
of
41
for
good
lo w e r
v a rio u s
E/N
and n e o n a r e g i v e n by Sze
The m e t a s t a b l e and i o m .c e n e r g i e s
in d ic a te d
on t h i s d ia g r a m and t h i s e n a b l e s
c e r t a i n q u a l i t a t i v e o b s e r v a t i o n s t o be made w i t h r e s p e c t t o d i s c h a r g e
1
s t a b i l t y and m e t a s t a b l e e x c i t a t i o n e f f i c i e n c y .
D isch arg e i n s t a b i l i t y
j
t h e form o f a runaw ay g ro w th o f e l e c t r o n d e n s i t y and c u r r e n t i s a
I
in
m a jo r
lim ita tio n
d e v ic e s,
th e
in
e x c im e r
resu lt
is
la se r
d isch arg es.
secondary
e m issio n
In
at
DC d i s c h a r g e
th e
e le c tro d e s
acco m p a n ie d by a r c f o r m a t i o n w hich r e s u l t s i n a low im pedance t h a t i s
not
m atc h ed t o t h e s u p p ly n e tw o r k .
lo c a lise d
o p tic a l
arcs
d isch arg e
c o n ta i n m e n t
th a t
term in a te s
its
th e
d ischarge
th is
p ro b le m
is
to
u s e a s a medium g i v i n g u s e f u l
g a i n and c a u s e s e l e c t r o d e damage a t t h e a r c i n g p o i n t s .
m icrow ave
e le c tro n
b o th
The d e c a y o f
not
as
In a
s e v e r e owing t o t h e
of th e d isch arg e i n a d i e l e c t r i c tu b e .
However,
h ig h
d e n s i t i e s a g a i n r e s u l t i n a n unm atched l o a d w i t h t h e r e s u l t
a l a r g e p r o p o r t i o n o f t h e i n c i d e n t m icrow ave power i s r e f l e c t e d
b a c k fro m a d i s c h a r g e t h a t i s l o c a l i s e d w i t h i n a s m a l l p o r t i o n o f t h e
d isch arg e
tu b e.
d istrib u tio n
is
C learly ,
i f t h e h i g h e n e rg y wing o f
too
past
far
th e
th e
e le c tro n
i o n i s a t i o n en erg y o f th e heavy
r a r e - g a s p r e s e n t , t h e n t h e t e n d e n c y t o i o n i s a t i o n i n s t a b i l i t y w i l l be
I
^ :7 N “ 6x-10^>£^
Xe*9 K? ^ 1 2
Electron Energy (eV)
Electron
15
Energy Distribution (from Sze
Chapter 2
%2
in creased .
namely
In p ra c tic e ,
h a lo g e n s,
re la tio n sh ip
or
b e tw e e n
circ u m sta n c e s
h o w e v e r, t h e p r e s e n c e o f a t t a c h i n g s p e c i e s ,
e a sily
io n ise d
im p u ritie s
w ill
E/N and t h e o n s e t o f i n s t a b i l i t y .
a lte r
th e
Under t h e s e
t h e c u r v e s o f F i g 2 .1 1 may n o t be v e r y r e l e v a n t and
a
m ore d e t a i l e d a n a l y s i s , l i k e t h a t g i v e n i n J o h n s o n ( 1980) f o r e x a m p le,
may be r e q u i r e d .
Therm al
th a t
E ffe c ts
high
rise s
The h i g h pump powers u se d i n
gas tem p eratu res a re p o s s ib le .
and,
low
i n some c a s e s , f a s t g a s c i r c u l a t i o n .
tem p eratu re
r i s e s may be f a v o u r a b l e i n some c a s e s ,
u ltim a te ly
g iv e
tem p eratu re
r i s e s d u rin g th e d is c h a rg e w i l l d i s t u r b
unw anted
therm al
la se rs
In p ra c tic e ,
a r e l i m i t e d by s h o r t p u l s e o p e r a t i o n ,
ra te s,
e x c im e r
mean
tem p eratu re
p u lse
re p e titio n
A lth o u g h m o d e r a te
larg e r is e s w ill
p o p u la tio n s.
A ls o ,
th e
larg e
re fra c tiv e
i n d e x i n t h e o p t i c a l p a t h and a f f e c t t h e beam q u a l i t y .
Gas
h e a t i n g o c c u r s t h r o u g h e l a s t i c c o l l i s i o n s b e tw e e n e n e r g e t i c
e l e c t r o n s and n e u t r a l s .
The r e l a x a t i o n t i m e ,
t^ , fo r e le c tro n s (see
Haydon 1964) i s g i v e n by t h e a p p r o x i m a t i o n
t
e
w h e re
= M/2mv
0
M is
,
th e
m o le c u la r
t h e b a c k g ro u n d g a s ,
freq u en cy
per
e le c tro n s
t o come t o t h e r m a l e q u i l i b r i u m w i t h t h e b a c k g ro u n d g a s
absence
T h is
e l e c t r o n - b a c k g ro u n d
g iv es
o f an e x t e r n a l f i e l d .
be fo u n d from t h e r e l a t i o n
th e
gas
m i s th e
m ass,
e le c tro n .
th e
of
e le c tro n
th e
and
mass
c o llisio n
c h a r a c t e r i s t i c t im e f o r
in
The mean c o l l i s i o n f r e q u e n c y c a n
Chapter 2
43
Vq = NQV ,
w h e re
N
is
th e
b a c k g ro u n d
e l e c t r o n - b a c k g ro u n d
th e
gas
mean e l e c t r o n s p e e d .
f o r th e v a lu e of t ^ ,
1964)
gas
p a rticle
d e n sity ,
Q
is
atom c o l l i s i o n c r o s s ~ s e c t i o n ,
To o b t a i n a n o r d e r o f
a cro ss - se c tio n of 3
w i t h a n e l e c t r o n e n e r g y o f 5 eV.
x
and V i s
m a g n itu d e
1
th e
e stim a te
ra^ i s u s e d (Haydon
W ith 1 atm
of
b u ffer
gas,
t h i s g iv e s th e fo llo w in g v a lu e s ;
f o r h e liu m
t ^ = 3 x 10
f o r neon
t = 2 x 10
e
f o r arg o n
t ^ = 3 x 10
T h is
in d ic a te s
-9
»8
-8
th a t
sec ,
s e c , and
sec .
gas
h e a tin g ,
w ith
e fficie n cy ,
may t a k e p l a c e e v e n d u r i n g
p a rtic u la rly
w ith
h e liu m
as b u f f e r .
a
a
co n seq u e n tia l lo s s of
sh o rt
In a d d itio n ,
d isch arg e
p u lse,
i t seems l i k e l y
t h a t lo n g p u ls e s (>100 ns) w i l l r e s u l t i n o p t i c a l d i s t u r b a n c e s cau sed
by
s p a tia l
irre g u la ritie s
of
i r r e g u l a r i t i e s i n r e f r a c t i v e in d ex .
gas
h e a tin g
w hich
resu lt
in
For a gas t h e d e n s it y i s r e l a t e d
t o t h e r e f r a c t i v e i n d e x by t h e G l a d s t o n e - D a l e la w
n - 1 / p = c o n s t a n t = A n/A p .
S in ce
f o r a s m a l l h e a t i n g i r r e g u l a r i t y t h e change i n d e n s i t y w i l l be
p ro p o rtio n a l
re fra c tiv e
are
to
th e
d e n sity
itse lf,
th e
re su lta n t
i n d e x w i l l be p r o p o r t i o n a l t o ( n ~ 1 ) ,
change
in
V a lu e s o f ( n ~ 1)
shown i n T a b le 2 , 2 and i n d i c a t e t h a t o p t i c a l d i s t u r b a n c e s may be
e x p e c te d to i n c r e a s e w ith i n c r e a s i n g r a r e - g a s ato m ic m ass.
Chapter 2
44
The
and
e x h ib it c o n sid e rab le v a r i a ti o n .
ra te
th e
v a l u e s o f d i f f u s i v i t y f o r r a r e - g a s e s a r e g i v e n i n T a b le 2 , 2
of
S in c e t h e d i f f u s i v i t y g i v e s t h e
h e a t tr a n s p o r t per u n i t tem p eratu re g r a d ie n t,
i t in d ic a te s
r a t e a t w hich h e a t i n g i r r e g u l a r i t i e s w i l l d i s a p p e a r .
v a l u e f o r h e liu m may be b e n e f i c i a l f o r two r e a s o n s .
add
t o t h e a d v a n ta g e t h a t h e liu m a l r e a d y h a s
q u a lity
a id
in
a lo n g d is c h a r g e p u ls e .
in te r - p u l s e c o o lin g .
ex p erim en ts
d e scrib ed
T his
in
is
th is
fo r
S e c o n d ly ,
F irstly ,
h ig h
i t w ill
m a in ta in in g
beam
use of t h i s gas w i l l
p a rtic u la rly
th e sis
The
because
im p o rta n t
of
in
th e
th e s m a ll tube
d i a m e t e r s and t h e h i g h r e p e t i t i o n r a t e s u s e d ( 1 1 0 0 p p s ) .
R e d i s t r i b u t i o n o f V i b r a t i o n a l L e v e l s As h a s b e e n d e s c r i b e d i n S e c t i o n
2 . 1 .3 ,
th e
la sin g
e fficie n cy
of
e x c im e r
lase rs
w i l l h ave some
d e p e n d en c e on t h e r a t e o f r e d i s t r i b u t i o n o f v i b r a t i o n a l s t a t e s i n t h e
upper
sta te
m an ifo ld .
It
is
req u ired
t h a t t h i s p r o c e s s be f a s t
enough t o p r e v e n t a n o n - e q u i l i b r i u m d i s t r i b u t i o n w i t h a d e f i c i e n c y i n
th e
le v e l
upper
lase r
le v e l.
i s a lso re q u ire d .
c o llisio n s
b e tw e e n
c o llisio n
I n XeF,
B oth
th e
of
r a p i d re m o v a l o f t h e bound l o w e r
th ese
process
are
prom oted
e x c im e r m o le c u le and b u f f e r g a s a to m s .
frequency per
e x c im e r
m o le c u le
(u sin g
th e
by
The
app ro x im ate
t h e o r y g i v e n i n Moore 1972) i s g i v e n by
?
1/0
z = NTtd ( 8 k T / ( i l l ) ^
w here
z
d e n sity ,
is
th e
,
c o llisio n
freq u en cy ,
d i s th e c o l l i s i o n d iam e te r,
1 atm o f b u f f e r g a s a t 3 0 0 K,
N i s t h e b u f f e r g a s number
and p.
th e red u ced m ass.
and u s i n g 3 S f o r d ,
For
and t h e b u f f e r g a s
Chapter 2
45
atoDiic m ass f o r |i
f o r He,
Ne,
a s ro u g h a p p r o x i m a t i o n s , t h e c o l l i s i o n f r e q u e n c i e s
and Ar b u f f e r s a r e 9 «5x10^^ , 4 . 3 x 1 0 ^ and 3 .0 x 1 0 ^ ^ s ’"^ ,
re sp e c tiv e ly .
These c o r r e s p o n d t o l i f e t i m e s b e tw e e n c o l l i s i o n s t h a t
a r e 50 t i m e s l e s s t h a n e x c im e r s p o n t a n e o u s d e cay l i f e t i m e s .
th e
c o l l i s i o n r a t e j u s t g i v e n w i l l be l a r g e r
tra n sitio n
ra te
induced.
T his
e n e rg y l e v e l s a r e s e p a r a t e d
0 .0 2 6 eV
in
0 .0 2 6 eV.
XeCl,
w h ile
req u ired
o u tsta n d in g
fo r
th e
by 0 .0 3 7 eV i n XeF, 0 .0 5
th e
c h a ra c te ristic
used
to
eY i n KrF,
en erg y
p red ict
adeq u ate upper s t a t e r e l a x a t i o n ,
u n c e rta in tie s in th e c o llis io n process.
t h i s i s th e f a s t r e la x a tio n
r e p o r t e d f o r Ar b u f f e r
w hich
to
i s t h o u g h t t o be due
v ib ra tio n a l
i s b e c a u s e t h e e x c im e r v i b r a t i o n a l
W hile t h e s e d a t a c o u ld be
pressures
th an
However,
th e fo rm a tio n
An
at
and
300K i s
th e
b u ffer
th e re are
exam ple
of
on XeF ( H s i a 1979)
ofth e
in te rm e d ia te
s p e c i e ArXeF .
Q uenching
rare-g as
A c tiv ity
In fo rm a tio n
on
th e
q u e n c h in g
i s g i v e n i n T a b le 2 . 4 which h a s b e e n u s e d t o c a l c u l a t e
p a r t i a l p r e s s u r e l i m i t s shown i n T a b l e 2 . 5 .
and Ne a p p a r e n t l y
p r e s s u r e h a s t o be c o n s i d e r a b l y
q u e n c h in g r a t e .
to ta l
slo w e r,
and KrF t o
o f Xe on XeF i n d i c a t e s
th an
0.1 atm
for
th a t
a
low
I n g a s m i x t u r e s w i t h no b u f f e r g a s , t h i s becomes t h e
gas p re ssu re lim it .
how ever,
le ss
th e
For 2 - b o d y q u e n c h in g , He
p o se no p ro b le m s b u t Ar may quench XeF,
a l e s s e r e x t e n t . The h i g h q u e n c h in g r a t e
Xe
a c t i v i t y of th e
Q uenching o f
KrF
by Kr
is
very
much
and t h e r e f o r e KrF o p e r a t i o n w i l l n o t h a v e t h e same
l i m i t a t i o n s im posed by
q u e n c h in g t h a t XeF h a s .
Chapter 2
46
From
occur
t h e i n f o r m a t i o n on 3-b o d y q u e n c h in g ,
g iv in g
F irstly ,
Kr p a r t i a l p r e s s u r e i n a KrF m i x t u r e h a s t o be
m ix tu re s,
p ressure
For
S e c o n d ly ,
le ss
th an
i f Ne b u f f e r i s u s e d w i t h XeF
e x a m p le ,
i f t h e Ne p r e s s u r e i s
l i m i t i s a b o u t t h e same a s t h a t r e q u i r e d
q u e n c h in g l i m i t ; i e .
by
1 atm t h e Xe
th e
2-body
i t m ust be below a b o u t 0 . 1 atm .
L aser O p e ra tio n
The
pump
e m issio n
an
e x a m p le s
t h e p r o d u c t o f t h e Xe and Ne p a r t i a l p r e s s u r e m ust be l e s s
2
0 .1 2 atm ,
2 .3
two
more s t r i n g e n t c o n d i t i o n s t h a n t h e 2 - b o d y l i m i t a t i o n s .
0 . 4 8 atm f o r low q u e n c h in g .
th an
o n ly
E/N
a
o p tic a l
d e n s i t y r e q u i r e d t o o b t a i n e x c im e r f l u o r e s c e n t
h a s m e r e ly t o be s u f f i c i e n t t o m a i n t a i n t h e d i s c h a r g e
v a lu e
o p e ra tio n ,
g iv e
power
high
enough
fo r
m e ta sta b le
p ro d u ctio n .
sm all
sig n a l
g a in
th at
w ill
g iv e a n e t g a in a g a in s t th e
l o s s e s due t o a b s o r p t i o n i n t h e l a s e r g a s and r e f l e c t i o n and
th e r e l a t i v e l y high
w a v elen g th ,
re su lts
w hich
For l a s e r
h o w ever, t h e p o p u l a t i o n i n v e r s i o n h a s t o be s u f f i c i e n t t o
t r a n s m i s s i o n l o s s e s a t t h e m i r r o r s a n d / o r windows.
th a t
w ith
and
broad
o p tic a l
band
lo ss,
c o u p le d
I t i s shown below
w ith
th e
sh o rt
e m is s io n o f r a r e - g a s h a li d e e x c im ers,
i n a v e ry h ig h th re s h o ld v a lu e f o r th e
w ill re s u lt in la s e r o s c illa tio n .
pump
power
d e n sity
T h i s h i g h power r e q u i r e m e n t
h a s i m p o r t a n t c o n s e q u e n c e s f o r t h e d e s i g n o f t h e pumping s y s te m .
Chapter 2
4?
The i m p o r t a n t a b s o r p t i o n p r o c e s s e s i n r a r e - g a s h a l i d e l a s e r s a r e
p ro b ab ly
io n s,
of
p h o to d isso c ia tio n
of
h a lid e s
and r a r e - g a s d im er p o s i t i v e
p h o to d e ta c h m e n t o f n e g a t i v e h a l o g e n i o n s ,
e x c ite d
d iffic u lty
d u rin g
lac k
rare-g as
atom s and m o l e c u l e s (Rhodes 1 9 7 9 ) «
i n d e t e c t i n g a b s o r b i n g s p e c i e s and
Due t o t h e
m e a s u r in g
a b so rp tio n
s h o r t h i g h power p u l s e s t h e r e i s c o n s i d e r a b l e u n c e r t a i n t y and
o f in fo r m a tio n c o n cern in g
summary
fo u n d
from e x p e r i m e n t a l work o r c a l c u l a t e d on
Gower
e t,
a b so rp tio n
A lth o u g h
k in e tic
(1978)
carefu l
se le c tio n
1979)
c r o s s s e c t i o n s t h a t have been
F^
as
th e o re tic a l
of
donor
donor
and
and
ca n l e a d t o much s m a l l e r a b s o r p t i o n
e ffic ie n c y i s reduced.
Rhodes
grounds.
v a l u e s o f 1 - 2% cm ^ f o r t r a n s i e n t
g iv es
i n a XeF l a s e r u s i n g
a
p ressures
p h o to ab so rp tio n
B rau (in
a
a l.
of
a b so rp tio n .
g iv es
v a lu e
and p h o t o i o n i s a t i o n
He
as
b u ffer.
r a r e - g a s e s and t h e i r
(R hodes
I t seems l i k e l y ,
1979)î
th erefo re,
o f 1 ^ em"^ a b s o r p t i o n w i l l be a u s e f u l l o w e r l i m i t
to
th e
th a t a
ap p ly .
F o r a common e x c im e r l a s e r o f a b o u t 1m l e n g t h t h i s g i v e s a r o u n d t r i p
lo ss
o f 200%.
T h is c l e a r l y i s
much
g rea ter
m irro r
lo sse s
case.
I n t h e d i s c h a r g e tu b e o f t h i s w ork,
a ro u n d
10 cm
ex p e cte d .
th an
any
rea so n a b le
w hich w ould t h e r e f o r e h a v e a s u b o r d i n a t e r o l e i n t h i s
so
th a t
t h e d i s c h a r g e l e n g t h was
a ro u n d t r i p a b s o r p t i o n l o s s o f 2 0 % m ig h t be
By u s i n g a s m a l l o u t p u t c o u p l i n g f r a c t i o n ,
m irro r l o s s e s
a r e k e p t w e l l below t h i s l o s s v a l u e and may s t i l l be ig n o re d *
T h resh o ld
and
hence both
e m issio n
l a s i n g may be a p p r o a c h e d by i n c r e a s i n g t h e pump power
th e
in te n s ity .
upper
L aser
sta te
p o p u latio n
and
th e
s p o n ta n e o u s
o s c i l l a t i o n b e g i n s when t h e s p o n ta n e o u s
e m i s s i o n i n t e n s i t y a lo n g t h e c a v i t y a x i s c a u s e s s u f f i c i e n t s t i m u l a t e d
Chapter 2
48
e m issio n
to
c o m p e n sa te f o r t h e o p t i c a l l o s s e s .
s p o n ta n e o u s
o p tic a l
The
e m issio n
a x is
to
th a t
tra v e ls
s u ffic ie n tly
round
p a ra lle l
to
th e
c o m p le te a r o u n d t r i p o f t h e c a v i t y i s v e r y s m a l l .
s tim u la te d e m issio n a t th r e s h o ld i s
m e r e ly
The f r a c t i o n o f t h e
rep la ce s
a lso
v ery
sm all
as
th is
t h e f r a c t i o n o f t h e s p o n ta n e o u s i n t e n s i t y l o s t i n a
t r i p o f th e c a v ity .
T herefore,
t h e t h r e s h o l d pump
power
is
t h a t r e q u i r e d t o f e e d t h e t o t a l s p o n t a n e o u s e m i s s i o n t h a t o c c u r s when
th e
r o u n d t r i p l o s s from t h e c a v i t y i s e q u a l t o t h e ro u n d t r i p g a i n .
R e g a r d in g
t h e lo w e r l a s e r p o p u l a t i o n a s e f f e c t i v e l y z e r o ,
th e sm all
s i g n a l g a i n c o e f f i c i e n t i s g i v e n by
Y^(V) = N0 (V)
,
w here Y^(v) i s t h e f r e q u e n c y d e p e n d e n t s m a l l s i g n a l g a i n c o e f f i c i e n t ,
N
is
th e
dependent
upper
s t a t e p o p u l a t i o n d e n s i t y and
s tim u la te d e m issio n
s ig n a l g a in to th e lo s s ,
N = 1(V)/0(V)
l( v )
c ro ss-se c tio n .
o(v)
i s th e freq u e n c y
E q u a tin g
, g iv es th e th re sh o ld p o p u latio n
.
T h i s p o p u l a t i o n i s l o s t t o s p o n ta n e o u s e m i s s i o n a t t h e r a t e
d N /dt
th e
= l(v )/to (v )
w here t i s t h e u p p e r s t a t e l i f e t i m e .
sm all
Chapter 2
If
49
th e
pump power i s c o n v e r t e d t o s p o n ta n e o u s e m i s s i o n w i t h an
e f f i c i e n c y e , t h e t h r e s h o l d pump power d e n s i t y i s g i v e n by
P =
(d N /d t)h v /e
(1)
= h v l(v )/eto (v )
w here h v i s t h e p h o to n e n e r g y .
V a lu e s o f t h e p r o d u c t t o ( v ) h a v e b e e n
m e a s u re d f o r some o f t h e e x c i m e r s .
and
XeCl a r e
resp e c tiv e ly .
fo llo w in g
way.
term s
th e
of
E in ste in
g iv en
in
For
R hodes(1979)
A lte rn a tiv e ly ,
ot
e xam ple,
v a l u e s f o r XeF, KrF,
as
17,
v a lu e s
The s t i m u l a t e d e m i s s i o n r a t e
stim u la te d
64,
and
50
S
^ns
may be c a l c u l a t e d i n t h e
may
be
expressed
in
e m i s s i o n c r o s s - s e c t i o n o r i n te rra s o f t h e
B c o e f f ic ie n t (th e s tim u la te d
e m issio n r a t e
c o e ffic ie n t).
T his y i e l d s th e r e l a t i o n s h i p
B = 0(v)c/hvg(v)
w here
g(v) i s th e l i n e shape f u n c tio n .
The B c o e f f i c i e n t i s r e l a t e d
t o t h e A c o e f f i c i e n t ( s p o n t a n e o u s e m i s s i o n r a t e c o e f f i c i e n t ) by
A = B8 iC h v ^ /c ^ ,
(see
f o r exam ple V e rd e y en 1 9 8 1 ) .
S ince th e
A
r e c i p r o c a l o f t h e s p o n ta n e o u s e m i s s i o n l i f e t i m e ,
c a n be combined t o g i v e
o(v)t
= X \ ( v ) / 8 tc
.
c o e ffic ie n t
is
th e
t h e s e two e q u a t i o n s
Chapter 2
50
The a p p r o x i m a t e l i n e v / i d t h i s g i v e n by
Av= 1 /g ( v ) = cA X /??
which g i v e s
o ( v ) t = X ^/ S n cA X
.
( 2)
S u b s t i t u t i o n i n (1) y i e l d s
P = 8nl(v)hc^AX/eX^
.
(3)
The
l i n e w i d t h f o r XeF i s d i f f i c u l t t o a s s e s s b u t t h e s p e c t r a o f F i g s
2 .6
and
2 .5
f o r KrF and XeCl i n d i c a t e FWHM l i n e w i d t h s o f a b o u t 3 oS
and 2oS r e s p e c t i v e l y .
6o2^ns
for
XeCl
T h i s g i v e s v a l u e s f o r Ot o f 1? S ^ n s f o r KrF and
w hich
compare
w ell
w ith
th e v a lu e s above.
The
h i g h e s t pump power d e n s i t y r e q u i r e d i s f o r ArF( o t = I p S ^ n s ) w h i l e t h e
lo w e st
is
cm” ^
for
XeF( o t = 64 % ^n s).
U sing
l o s s g i v e s t h r e s h o l d pump power
th ese
v a l u e s i n (1 ) w i t h
d e n s i t i e s o f 8 . 8 x 1 G ^/e Wm” ^
0
«9
and 8 .5 x 1 0 / e Wm
f o r XeF and ArF r e s p e c t i v e l y .
The
efficien cy
m eta sta b le
w ith
above i s t h e p r o d u c t o f t h e e f f i c i e n c y o f
p r e c u r s o r p r o d u c t i o n by t h e
efficie n cy ,
XeF
used
d ischarge
and
th re sh o ld
quantum
i f p e r f e c t e x c im e r f o r m a t i o n k i n e t i c s a r e a ssum ed.
t h e quantum e f f i c i e n c y i s 0 . 4 2 and m e t a s t a b l e s may
an
th e
e fficie n cy
of
a ro u n d
20%
(Rhodes
1979).
pump power d e n s i t y f o r XeF o f a ro u n d 10^^ Wm” ^
a s a minimum v a l u e ,
be
For
produced
T h is g i v e s a
(lOkWcm™^)
A p r a c t i c a l l a s e r d e s i g n w ould n e e d t o a l l o w f o r
Chapter 2
h ig h
51
o u tp u t
c o n d itio n s
power
c o u p lin g
such
and
th e
lik e ly
occu rren ce
of
n o n - o p tia u m
a s h i g h o p t i c a l a b s o r p t i o n i n impulse g a s e s .
d e n s i t y o f p e r h a p s lOOkWcm
may t h e n be
req u ired .
A pump
If,
in
a d d i t i o n , o p e r a t i o n w i t h a s h o r t w a v e l e n g t h e x c i m e r , s u c h a s ArF, was
a
d e sire d o p tio n ,
(IMI'/cm
w ould
pump
be
power
d e sira b le .
d e n sitie s
a
fac to r
l a s e r s i s n o t p r e c l u d e d by any i n t r i n s i c
c le a rly
p rev en ted
th e
10
larg e r
Thus w h i l e c o n t i n u o u s o p e r a t i o n o f
e x c im e r
by
of
p ro p erty ,
it
is
power r e q u i r e m e n t and t h e a t t e n d a n t h e a t
d i s p o s a l p r o b le m .
To s u m m a ris e ,
req u irem en t
d ra m a tic
th e
a
d e v e lo p m e n t
T his i n d i c a t e s th e
of
,s h o r t
w av elen g th
lase rs.
a c c o m p a n ie s
In a d d itio n ,
broad
and h i g h o p t i c a l a b s o r p t i o n o f e x c im e r e m i s s i o n r e s u l t s i n
pump
fo llo w s
fu n c tio n of th e lin e w id th /X ^ .
in c re a se in d i f f i c u l t y of l a s e r o p e ra tio n th a t
lin e w id th
hig h
is
i t h a s b e e n shown above t h a t t h e l a s e r pump power
power
th a t
re q u ire m e n ts
d e n sity
d e v e lo p m e n t
re q u iren e n ts
of
s y s te m s
of
w ith
at
l e a s t lOkWcra*"^.
sm a lle r
power
It
su p p ly
w ould i n v o l v e e f f o r t s t o g i v e h i g h e f f i c i e n c i e s i n v e r y
s m a l l a c t i v e v o lu m e s .
Chapter 3
3
52
HALOGEN LOSS. BY DIFFUSION TO THE WALL
In
th e
m icrow ave
d isc h a rg e a p p a ra tu s a sm all bore tu b e,
i n t e r n a l d i a m e t e r , was u s e d t o c o n t a i n t h e d i s c h a r g e v o lu m e.
stro n g
re a c tio n
is
to
2 mm
S in ce a
be e x p e c t e d b e tw e e n a f r e e h a l o g e n atom and
s i l i c o n from t h e q u a r t z t u b e , i t i s i m p o r t a n t t o c o n s i d e r t h e l o s s o f
h a lo g e n
re su ltin g
d escrib ed
sh o rt
is
from
d iffu sio n
to
th e w a ll.
T h is d i f f u s i o n i s
i n th e f o llo w in g w ith th e d i f f u s a n t produced i n r e p e t i t i v e
p u lses
a c co m p a n ie d by h e a t p r o d u c t i o n .
tre a te d f i r s t
to
allo w
c a lc u la tio n
of
The t h e r m a l b e h a v i o u r
tem p e ra tu re
dependent
d iffu sio n .
3 .1
D e r i v a t i o n o f t h e C a l c u l a t i o n Method
The
p r im a r y
s im p lific a tio n s
are
th a t
th e
p u lse d u ra tio n i s
assum ed t o be n e g l i g i b l e compared w i t h t h e p e r i o d b e tw e e n t h e p u l s e s ,
and
th an
t h a t t h e t h e r m a l c a p a c i t y o f t h e c o n t a i n i n g t u b e i s much g r e a t e r
th a t of th e gas.
The l a t t e r s i m p l i f i c a t i o n
p e rm its
th e
tu b e
h e a t i n g t o be t r e a t e d s e p a r a t e l y from t h e g a s h e a t i n g .
Two
heat
lo ss
processes
are
d escrib ed ;
f r e e c o n v e c t i o n and
f o r c e d c o n v e c t i o n . U nder f r e e c o n v e c t i o n , h e a t i s l o s t from t h e o u t e r
su rface
of
c o n v e c tio n
th e
tube
5 /ii
a t a r a t e p ro p o rtio n a l to T
,
w h ile fo rc e d
i s re g a rd e d as h o ld in g th e o u te r s u r f a c e o f th e
room t e m p e r a t u r e .
tu b e
at
Chapter 3
3 .1 .1
. 5
3
B asic E q u a tio n s
The f u n d a m e n ta l e q u a t i o n s g o v e r n i n g d i f f u s i o n i n i s o t r o p i c m ed ia
are
f = -D g r a d C
'
(1 )
and
a c / a t = d iv (D g r a d C ) ,
w here
and
(2 )
C i s th e p a r t i c l e c o n c e n tra tio n ,
f
area.
th e
norm al
p a rticle
f lo w
D th e d if f u s io n
c o e ffic ie n t
i n number p e r u n i t tim e p e r u n j.t
F o r h e a t t r a n s p o r t by c o n d u c t i o n i n b o t h t h e g a s and t h e t u b e
w a l l we c a n w r i t e
C = phT ,
and
D = K/ph ,
w here
T
c a p a c ity ,
is
th e
tem p eratu re,
h th e s p e c if ic h e a t
and K t h e t h e r m a l c o n d u c t i v i t y o f t h e g a s ( o r t h e
I t i s usual to w rite
k = K/ph
p th e d e n s ity ,
w a ll).
Chapter 3
w here
54
k
i s known a s t h e d i f f u s i v i t y .
e q u a tio n
The s o l u t i o n o f t h e d i f f u s i o n
(2 ) i s d i s c u s s e d i n d e p th by Crank (1 9 5 6 )
and,
for
heat
c o n d u c t i o n , by C a rs la w and J a e g e r ( 1 9 5 9 ) .
The
p a r t i c u l a r s o l u t i o n o f (2) r e q u ir e d h e re i s f o r c y l i n d r i c a l
g e o m e try
w ith
tem p e ra tu re
tre a te d
dependence
fo r
of
th e
th e
rad ia l
d iffu sio n
c o o rd in a te
and
by s e p a r a t i n g t h e tim e b e h a v i o u r i n t o
c o n sta n t
d iffu sio n
tem p eratu re
each
v a ria tio n
and
The
d i f f u s i v i t y w i l l be
sm all
e le m e n t s
w ith
The n e c e s s a r y c h a n g e s due t o
w i l l be i n s t e p s p r o v i d i n g an a v e r a g e v a l u e t o a s s i g n t o
tim e
e le m en t.
d iffu sio n
d iffu siv ity .
o n ly .
T h is means t h a t a s o l u t i o n o f ( 2 ) f o r c o n s t a n t
c o e ffic ie n t
can
be
used,
thus
av o id in g
c o n s id e r a b l e -
m ath em atical c o m p le x ity .
For
th e
c y lin d ric a l
case
o f a c o n s t a n t d i f f u s i o n c o e f f i c i e n t and by u s i n g
c o o rd in a te s w ith r a d i a l v a r i a ti o n
o n ly ,
e q u a tio n
(2)
becomes
a c / a t = D (ô ^ C /ô r^
It
w ill
be
u sefu l
(1 /r)ô C /a r)
,
to use th e fo llo w in g d im e n s io n le ss v a r i a b l e s i n
t h i s e q u a tio n ;
r = r/a
t = D t / a ^ , C = ,C /C q f o r d i f f u s i o n , and
t = k t/a
2
(3)
and T = T/T^ f o r h e a t t r a n s p o r t ,
Chapter 3
w here
. 5
a i s t h e i n n e r tu b e w a l l r a d i u s ,
d iffu san t
re su ltin g
from
0^ i s
th e
5
c o n c e n tra tio n
a s in g le e x c ita tio n p u lse ,
and
of*
i s th e
room t e m p e r a t u r e ( 2 9 3 K ) .
3 .1 .2
Heat T ra n sp o rt
The a p p r o p r i a t e d i m e n s i o n l e s s form o f (3 ) i s
ô f / ô t = Ô^T/ôr^ + ( 1 / r ) Ô T / ô r
For
ty p ic a l
e q u a tio n
o b tain ed
d iv id e d
in v o lv e s
(4)
c o n d itio n s
len g th y
th e
in to
a n a ly tic
su m m a tio n s .
u sin g th e f i n i t e d i f f e r e n c e
v a ria b le s
te m p o r a l
b o u n d a ry
.
S o lu tio n s
method
a number o f i n t e r v a l s .
so lu tio n
(C r a n k
are
In th e fo llo w in g ,
5 t,
resp e c tiv e ly .
The
fin ite
th is
th erefo re
1956)
i and j g i v e t h e number o f s p a t i a l i n c r e m e n t s ,
in cre m e n ts,
of
w ith
r
th e in te g e r
5 r,
and
d iffe re n c e
r e p r e s e n t a t i o n s o f th e d e r i v a t i v e s app ro x im ate to th e f o llo w in g ,
(a^T/apZ)
= (T
1+1, J
- 2T, . + T
1-I,j
= (V l.j (a î/a ? ),_ j =
A l s o , we h av e
- T ,^ j)/5 t
.
.
.)/(5r)^ ,
(5)
(G)
(7)
Chapter 3
56
r = i5 r
,
( 8)
S u b s t i t u t i n g t h e s e i n t o (5 ) g i v e s
T, . ,
= T. .+ 5tt(2i+l)T. ,
1;J+1
IjJ
. - ItiT. , + (2i-1)T. , .]/2i(5r)^ .
1+1,0
1,0
1 ™1 , 0
....(9 )
T h is
e q u a t i o n g i v e s a f o r m u l a w hereby t h e r a d i a l d i s t r i b u t i o n o f t h e
d im e n sio n le ss
tem p eratu re
can
be
c a lc u la te d
fo r
i n t e r v a l s s t a r t i n g fro m an i n i t i a l d i s t r i b u t i o n .
th e
v a lu e
th ree
of
p o in ts
are
and l a r g e r r a d i u s .
in crem ent
p re v io u sly .
T h is f o r m u l a c a n n o t be u s e d ,
of
th re e
c o n d itio n s
may
th erefo re,
f o r th e
I n a d d i t i o n , t h e s e end p o i n t s
may be i n c o n t a c t w i t h h e a t s o u r c e s , o r s i n k s .
v a rie ty
These
t h e c u r r e n t p o i n t and i t s n e ig h b o u r s a t s m a l l e r
two end p o i n t s o f t h e r a d i u s v a r i a b l e .
great
I t c a n be s e e n t h a t
t h e m ain v a r i a b l e a t a g i v e n p o i n t i s c a l c u l a t e d from
s p a t i a l v a l u e s one tim e
sp a tia l
s u c c e s s i v e tim e
o ccu r,
S in ce,
i n g e n e r a l .,
a
i t w i l l be n e c e s s a r y t o
e l a b o r a t e t h e model u s e d h e r e t o p e r m i t c a l c u l a t i o n o f t h e s e t e r m i n a l
v a lu e s.
For
th e tu b e ,
t h e l a r g e t h e r m a l c a p a c i t y means t h a t c o n d i t i o n s
i n th e gas w i l l have s t a b i l i s e d b e f o r e th e tube te m p e ra tu re s t a r t s to
rise .
As
a consequence,
t h e h e a t f l o w i n g i n t o t h e i n n e r tu b e w a l l
c a n be r e g a r d e d a s c o n s t a n t , sm o o th , and e q u a l t o t h e a v e r a g e r a t e a t
which
th e gas i s h e a te d .
c a n be w r i t t e n
F o r t h e p r e s e n t c i r c u m s t a n c e s e q u a t i o n (1)
Chapter 3
57
£ = -.DôC/ôr
;
w hich i n d i m e n s i o n l e s s v a r i a b l e s o f h e a t t r a n s p o r t i s
q = (-KT / a ) a T / 6 r
,
(1 0 )
w here q i s e n e rg y p e r u n i t a r e a p e r u n i t t i m e .
The f i n i t e d i f f e r e n c e
r e p r e s e n t a t i o n o f (1 0 ) i s
= -aq/K T o
For
th e
in n er
tu b e
w a ll,
•
(1 1 )
th e
term T. , i n (1 1 ) and (9 ) w i l l be
3.“ I
f i c t i t i o u s and m ust be e l i m i n a t e d from ( 9 ) and (1 1 ) t o g i v e
T, . , = T. , + (25t/(5r)^)CI. ,
1 , J+1
J
. - T. . + (2i-1)5raq/2iKT.]
1+ ‘ , J
^I J
.
u
( 12)
For
th e o u te r tube w a l l,
q is
th e
heat
lo ss
ra te
and
T^^^
is
e lim in a te d to g iv e
T.1 , J + | = T. . + (25t/(5r)^)[T
;J
- T.1 , J, - (21+1)6raq/2iK?n]
U
■
..(13)
Under f o r c e d c o n v e c t i o n , t h e o u t e r w a l l t e m p e r a t u r e i s c o n s t a n t a t T^
and
(1 3 ) i s n o t u s e d .
F o r f r e e c o n v e c t i o n from a h o r i z o n t a l t u b e o f
d i a m e t e r d, q i s g i v e n by
Chapter 3
58
q =
,
w here AT
is
(1 4 )
t h e d i f f e r e n c e b e tw e e n t h e s u r f a c e t e m p e r a t u r e and room
•“2
I f d i s i n cm and q i s i n Worn
th e
t e m p e r a t u r e and H i s a c o n s t a n t .
v a lu e
o f H,
g i v e n by Zemansky ( 1 9 5 7 ) ,
i s 4 .2 x 1 0
I n (1 3 ) we c a n
now r e p l a c e q u s i n g (1 4 ) and t h e n by w r i t i n g
AT=T. _. - To
,
we g e t
(2 i+ 1 ) 0 ra H T ^ ^ ^ ( T
U
If
f a i r l y h ig h
ra d ia tiv e
heat
te m p e ra tu re s
lo ss
w ill
. - 1 )^'^^10” \ d * ^ ''^ ]
If J
are
become
ex p ected
on
im p o rta n t.
th e
In
.
(1 5 )
tube
th a t
su rface,
case
th e
tem p eratu res,
be
S t e f a n - B o l t z m a n n r a d i a t i o n law
q = OE(T^ - Tq )
w ill
r e p l a c e e q u a t i o n (1 4 ) o r ,
added t o i t .
fo r in te rm e d ia te
Chapter 3
.5 9
We now c o n s i d e r t h e t h e r m a l b e h a v i o u r o f t h e g a s .
gas
In itia lly
c o o l i n g b e tw e e n p u l s e s i s l e s s t h a n t h e t e m p e r a t u r e r i s e
by t h e p u l s e s .
v a lu e
It
th e
caused
The mean t e m p e r a t u r e t h e r e f o r e r i s e s up t o a c o n s t a n t
w here t h e i n t e r - p u l s e c o o l i n g and t h e p u l s e h e a t i n g a r e e q u a l .
is
assum ed t h a t ,
due t o t h e l a r g e t h e r m a l c a p a c i t y o f t h e t u b e ,
th e
t e m p e r a t u r e r i s e o f t h e tu b e i s n e g l i g i b l e i n t h e tim e t a k e n f o r
th e
mean
term ,
equal
tem p eratu re
t o become c o n s t a n t .
T herefore,
th e gas te m p e ra tu re a t th e in n e r tube w a ll
to
room
tem p eratu re.
I n th e long term ,
is
in th e s h o rt
c o n sta n t
and
th e e q u ilib riu m gas
t e m p e r a t u r e b e h a v i o u r c a n s im p l y be s u p e rim p o s e d on t h e s l o w l y r i s i n g
w all
tem p e ra tu re .
p a rtic u la rly
d iffu siv ity
th e
gas.
when c o o l i n g i s by
fo r
larg e
free
rise s
in
c o n v e ctio n ,
th e
tem p e ra tu re ,
change
in
w ith te m p e ra tu re w i l l a l t e r th e e q u ilib r iu m b eh a v io u r o f
T his can
e q u ilib riu m
However,
be
b e h a v io u r
tak en
in to
at
few
a
account
d isc re te
by
re c a lc u la tin g
in te rv a ls
d u rin g
th e
th e
tem p e ra tu re r i s e of th e tu b e .
By
so
sym m etry,
t h e t e m p e r a t u r e g r a d i e n t a t t h e tu b e a x i s i s z e r o
t h e te rm ( 1 / r ) ô T / ô r i n e q u a t i o n (4) i s i n d e t e r m i n a t e .
d iffe re n c e
r e p r e s e n t a t i o n on t h e a x i s i s g i v e n
by
The f i n i t e
C ra n k (1 9 5 6 )
but
w i t h o u t a d e r i v a t i o n ; we s h a l l now d e r i v e i t . T h e t e m p e r a t u r e g r a d i e n t
i s r e p r e s e n t e d by T a y l o r ’ s s e r i e s a s
(ÔÎ/Ô?)- = (bT/d?)^
I
cU vJU o
+ rCa^ï/aÿZ)
+ ............ e tc
c iX J L o
F o r s m a l l r , ,ô T /ô r = 0 and (1 6 ) a p p r o x i m a t e s t o
.
(16)
Chapter 3
60
From (1 7 ) and (4) we g e t
ôT/bb = z a ^ T / a p f
when
r i s sm a ll.
(1 8 )
U sin g i = 0 o n t h e a x i s ,
th e
fin ite
d ifferen ce
r e p r e s e n t a t i o n s ( 4 ) and (6 ) g i v e , a f t e r r e a r r a n g i n g ,
If
d e ta ile d
tim e
b eh a v io u r
is
not re q u ire d f o r th e tu b e,
a
s im p l e e q u i l i b r i u m a n a l y s i s c a n be u s e d by s e t t i n g
ÔT/Ôt = 0
i n e q u a t i o n (4 ) t o g e t
Ô^T/Ôr^ + ( 1 / r ) Ô T / ô r = 0 .
(20)
T his e q u a tio n has th e g e n e ra l s o l u t i o n
T = A 4- B ln r
U sing T = T^, r = b / a a t t h e o u t e r w a l l , a n d e q u a t i o n ( 1 0 ) , t h e r a d i a l
v a r i a t i o n o f f a t e q u i l i b r i u m i s g i v e n by
T = T^^ « ( q a / K T Q ) l n ( r a / b )
.
(2 1 )
Chapter 3
The
61
e q u ilib riu m
tem p eratu re
d i f f e r e n c e b e tw e e n t h e i n n e r and o u t e r
t u b e w a l l i s t h e n g i v e n by
T^ - T^ = - ( q a / K T o ) l n ( a / b )
A lte rn a tiv e ly ,
tem p eratu re
tem p eratu re.
w ith
we
tim e
.
can
by
(2 2 )
c a lc u la te
v a ria tio n
of
tu b e
t r e a t i n g t h e tu b e a s a m ass w i t h u n i f o r m
T h is a p p r o x i m a t i o n i s a p p r o p r i a t e when t h e r i s e i n mean
tem p e ra tu re
is
tu b e
The r a t e a t w hich t h e mean
w a ll.
th e
larg e
com pared w i t h t h e t e m p e r a t u r e d r o p a c r o s s t h e
tu b e
tem p eratu re
rise s
is
g i v e n by
d T y d t = (P - A^q)/mo
,
(2 3 )
w here P i s t h e h e a t s u p p l y r a t e , A^^ i s t h e t u b e o u t e r s u r f a c e a r e a , q
i s t h e h e a t l o s s r a t e g i v e n by ( 1 4 ) , m i s t h e t u b e m ass, and c i s t h e
s p e c i f i c h e a t c a p a c ity o f th e tu b e m a t e r i a l .
S u b s t i t u t i n g f o r q from
(1 4 ) w i t h A t = T^ - Tq and s e p a r a t i n g t h e v a r i a b l e s g i v e s
‘t
0
dt =
T h is
^ [ m o d 1 / * /( P d 1 / * - A^H(T^ - T Q )5 /4 )]
i n t e g r a l can
be
e v a lu a te d
u sin g
.
sta n d a rd
(2 4 )
in te g ra l
ta b le s.
However, h a v in g r e g a r d t o t h e a p p r o x i m a t i o n s i n v o l v e d i n d e r i v i n g t h e
e q u a t i o n , n u m e r i c a l i n t e g r a t i o n o f (2 4 ) i s a d e q u a t e .
Chapter 3
62
The v a r i a t i o n o f d i f f u s i v i t y w i t h t e m p e r a t u r e w i l l be c o n s i d e r e d
fo r
th e
case
th e
a p p r o p r ia te ap p ro x im atio n f o r a
re se rv o ir.
m o le c u la r
o f p r e s s u r e b e in g i n d e p e n d e n t o f t e m p e r a t u r e w hich i s
The
th erm al
tube
of
gas
c o n n ected
to
a
c o n d u c t i v i t y o f a g a s v a r i e s w i t h t h e mean
s p e e d and i s t h e r e f o r e
p ro p o rtio n a l
to
T
1/ 2
.
The
gas
d e n s i t y i s p r o p o r t i o n a l t o P/T and t h e r e f o r e t h e d i f f u s i v i t y i s g i v e n
by
q / p
k = K /pc = c o n s t a n t x T
/P
.
(2 5 )
From g a s k i n e t i c t h e o r y (Moore 1 9 7 2 ) , we h ave
K = mcCp/8^'^^TCd^
/ li:m )
c = (8 k ^Tj /p
B
, and
,
w here m i s t h e p a r t i c l e m ass,
c i s t h e mean t h e r m a l s p e e d , Cp i s t h e
sp e c ific
is
heat
B o ltz m a n n ’ s
c a p ac ity ,
c o n sta n t,
d
th e
c o llisio n
d iam e te r,
and T t h e a b s o l u t e t e m p e r a t u r e .
k^
is
In a d d itio n ,
t h e d e n s i t y o f a g a s i s g i v e n by
p= N^mP273/T
w here
is
,
L o sch m id t’ s
number and P t h e p r e s s u r e i n a tm o s p h e r e s .
Combining t h e s e e q u a t i o n s , (2 5 ) becomes
Chapter 3
63
As s t a t e d p r e v i o u s l y , t h e t e m p e r a t u r e u s e d i n t h i s e q u a t i o n w i l l be a
mean v a l u e and s u b j e c t t o p i e c e - w i s e v a r i a t i o n o n l y .
I t i s im p o rta n t
t o n o t e t h a t t h e d i f f u s i v i t y and t h e t e m p e r a t u r e r i s e due t o a s i n g l e
h e a tin g
p u lse
th ese
are
both
in v e rs e ly p ro p o rtio n a l to p re ssu re .
d e t e r m i n e t h e h e a t g a i n and
e q u ilib riu m
mean
gas
lo ss
tem p eratu re
rate s
fo r
th e
S in c e
gas,
th e
w i l l be i n d e p e n d e n t o f p r e s s u r e .
T h is i s d e m o n s t r a t e d i n e q u a t i o n (3 7 ) b e lo w .
3 .1 .3
D iffu sio n
In
o b ta in in g
s im p lific a tio n s
q u a n tity
s o lu tio n s
a r e made:
to
th e
d iffu sio n
p ro b le m
th ree
( a ) e a c h e x c i t a t i o n p u l s e ad d s a c o n s t a n t
to th e d if f u s a n t p a r t i c l e c o n c e n tra tio n ,
(b) th e d i f f u s a n t
c o n c e n t r a t i o n i s z e r o a t t h e w a l l due t o a s t r o n g w a l l r e a c t i o n ,
(c)
th e w a ll r e a c tio n i s
process
th e
o n ly
lo ss
p rocess.
The
and
d iffu sio n
i s t h e n d e s c r i b e d by e q u a t i o n s (9 ) and (1 9 ) w i t h c r e p l a c i n g
f and w i t h
t = D t/a
An
2
app ro x im ate e x p r e s s io n f o r th e d i f f u s i o n
d e riv e d u sin g k i n e t i c th e o ry ,
n^
and
n^
are
th e
D
can
be
Jo st(1 9 5 2 ) g iv e s
D = ( 3 /3 2 ( n ^ + n g )o ^ g )(8 k T /T t} i)'^ ^ ^
w here
c o e ffic ie n t
number
,
.d e n s itie s
(2 7 )
o f t h e d i f f u s a n t and
Chapter 3
ba c k g ro u n d
64
gas,
i s th e c o l l i s i o n d iam e te r , f o r
th e
two
gas
s p e c i e s and p i s t h e r e d u c e d m ass d e f i n e d by
When
t h e d i f f u s a n t i s i n s m a l l c o n o ë n t r a t i o n s and t h e b a c k g ro u n d g a s
i s l i g h t su c h t h a t U g » n ^ and m2 <<m^ e q u a t i o n
D = ( 3/ 3 20^ 0 ^2 ) ( 8 k T / n * 2 ) 1 / 2
( 2.7 ) becomes
^
(28)
T h is e q u a t i o n can be r e w r i t t e n i n m ore c o n v e n i.e n t form u s i n g
Hg = n^P273/T
w here
,
n^ i s L o s c h m i d t ’ s num ber,
and
su b stitu tin g
B o ltz m a n n ’ s c o n s t a n t u s i n g MKS u n i t s .
( 26)
e q u iv a le n c e
of
p a rticle
fo r th e d i f f u s i v i t y ,
compared
w ith ( 2 9 ).
v a lu e
for
We g e t
D = ( T ^ / Z / p ) ( 7 . 6 x 1 0 - 4 1 / 0 2 ^ ^ 1 / 2 ) ^ 2 ^ -1
The
th e
^
(29)
and t h e r m a l d i f f u s i o n a l l o w s e q u a t i o n
o b ta in e d fo llo w in g
M o o re (1 9 7 2 ),
to
be
S u b s t i t u t i n g v a l u e s f o r n^ and k^ i n (2 6 ) g i v e s
th e ex p re ssio n
k = ( T 3 / 2 / p ) ( g . 1 x 1 0 * 4 1 /4 2 ^ 1 /2 ) ^^2^-1 ^
w hich com pares f a v o u r a b l y w i t h ( 2 9 ) .
be
used
E q u a t i o n (2 9 ) w i l l ,
th e re fo re ,
t o c a l c u l a t e D f o r t h e c a s e .of f l u o r i n e d i f f u s i n g i n h e liu m
Chapter 3
65
t h a t i s c o n sid e re d i n S e c tio n 3 .2 .2 .
3 .2
A p p lic a tio n to th e E x p erim en tal S i t u a t i o n
3 .2 .1
Heat T ra n sp o rt
The
T able
t u b e u s e d i n t h e e x p e r i m e n t a l work was o f f u s e d q u a r t z
and
3 .1 g i v e s t h e d a t a r e q u i r e d by t h e c a l c u l a t i o n t o f o l l o w .
The
m icrow ave
a p p a ra tu s
absorbed
by
d e liv e re d
17.6 ¥
av erag e
pow er.
The
power
t h e g a s i s e s t i m a t e d t o be a t l e a s t 10 W s o t h i s i s t h e
v a l u e we s h a l l u s e .
For fo rc e d c o n v e c tio n ,
in itia l
d im e n sio n le ss
tem p eratu re
was
fo u n d
w hich
e q u a t i o n s (9 ) and ( 1 2 ) a r e r e q u i r e d . The
tem p e ra tu re
at
a t i = 20 r e m a i n s a t 1 ,
th a t
th e
c a lc u la tio n
l e a d s t o 4 ,0 x 1 0 * ^ f o r 6 t .
th ese
p o in ts
is
1 and t h e
The v a l u e o f 5 r i s 0.1
was s t a b l e when
and
it
Ô t / ( Ô r ) ^ was 0 . 4
I n e q u a t i o n (1 2 ) t h e v a l u e
of
th e
terra
( ( 2 i - 1 )/2 i)(6 raq /K T Q )
becomes 1.7 1 6 x 1 0
be
-3
when i = 1 0 .
fo u n d a t s u c c e s s i v e tim e
c e rta in
number
of
tim e
The t e m p e r a t u r e d i s t r i b u t i o n c a n now
in te rv a ls,
in crem en ts,
c o n v e r t e d t o a c t u a l tim e by u s i n g
each
j.
c o rre sp o n d in g
D im en sio n le ss
to
t im e
a
is
Microwave Pulses
Pulse
duration
320ns
Pulse
interval
0.909ms
Pulse
power
50 kW
Mean
power
Pulse
Tube
17.6 W
energy
16.0 mJ
(fused quartz)
I D
2.0 mm
OD
4.0mm
Length
200mm
Inner wall
area
12.6 cm?
Outer wall area
25.1 cm^
Volume
0.628 cm^
Quartz
volume
1.89cm^
Mass
4.15 g
Density
2 2 0 4 kg
Thermal conductivity
1.SWm~i{<~i
Specific heat capacity
780Jkg-iK"i
D i f fu s iv i t y
8.7% 10""^m^s"i
Helium
Collision
diameter [from Moore 1972] 0,2 nm
Mass
6.68x10"^*^ kg
Specific heat capacity (Cp)
5 2 5 4 J kg~i K'“i
Density (STP)
0.179 kgm-3
Fluorine
Collision
diameter
Mass
Table 3.1 Values for diffusion calculation
'^0.23nm
1117x10-2* kg
C hapter 3
66
t = k t/a ^ = 0 . 87t
and t e m p e r a t u r e i n d e g r e e s K e l v i n i s o b t a i n e d from t h e e q u a t i o n
T = TTq
T h is
c a l c u l a t i o n and a l l e n s u i n g c a l c u l a t i o n s w e re c o m p le te d u s i n g a
H e w le tt-P a ck a rd
HP41CV
program m able
c a lc u la to r.
The
r e s u lts for
v ario u s
tim e i n t e r v a l s and i n t h e l o n g te rm l i m i t a r e shown
3 . 1( a ) .
, "The
e q u ilib riu m .
shown
in
tem p eratu re
drop
acro ss
th e
tu b e
is
in
3«7^C
at
tim e
is
A p l o t of th e in n e r w a ll tem p eratu re a g a in s t
F ig
3 .2 (a )
F ig
w hich shows t h a t 90^ o f t h e t o t a l r i s e t a k e s
p l a c e i n 0 . 7 s ( 7 7 0 m icrow ave p u l s e s ) .
When
be
used
t h e t u b e i s c o o le d by f r e e c o n v e c t i o n ,
when
i z 20.
The l a s t
te rm
in
e q u a t i o n (1 5 ) m ust
th is
e q u a tio n has
th e
c o e ffic ie n t,
( ( 2 i + 1 ) / 2 i ) ( 5 r a H T j / 4 / K d ‘*/4.jQ“ 4
w hich
h a s t h e v a l u e 1 .4 9 x 1 0 ^ .
v a r i o u s tim e i n t e r v a l s ,
in
The
tem p eratu re
and t h e e q u i l i b r i u m d i s t r i b u t i o n ,
F ig 3 .1 ( b ) ( w ith d i s c o n t i n u i t i e s i n th e
te m p e ra tu re
fin ite
d istrib u tio n s
tem p e ra tu re
a r e shown
a x is).
d r o p a c r o s s t h e t u b e a t e q u i l i b r i u m i s s t i l l 3.7*^C.
d i f f e r e n c e m ethod i s
c a lc u la tin g
th e
q u ite
slo w
d e ta ile d
fo r
tim e
th is
c a lc u la tio n
in ste a d
of
sp a tia l
t e m p e r a t u r e d i s t r i b u t i o n t h e .tim e b e h a v i o u r o f
at
The
The
so
b e h a v i o u r o f t h e w hole
th e
sp a tia l
0736s
0368s
0184 s
0092s
Figure 3.1(a) Tube temperature - forced convection
-Temperature in degrees-Kelvin
I
1*5
RADIUStmm)
gure _3..1( b) .„Tube temperature % freeze on ve c 1 1on ...
c
o
w
-a» OJ
u.
CL
QJ
o
o
TD
W
o
o
w
LJ
eu
Uî
JQ
c
CD
m
en
<0
CD
m
m
m
ZJ
en
LU
~-4-^
JO
CD
o
w
c
Cl
*D
CD
CD
m
CD
en
Chapter 3
mean
in
57
t e m p e r a t u r e i s fo u n d fro m (2 3 ) and ( 2 4 ) .
The r e s u l t s a r e shown
F i g 3 . 2 ( b ) w hich shows t h a t 90‘S o f t h e t o t a l r i s e o f 200^0
p lace
in
130 s e c o n d s .
tak e s
I n o r d e r to d em o n strate t h a t th e c a l c u l a t i o n
b a s e d on s p a t i a l mean t e m p e r a t u r e i s a d e q u a t e , c a l c u l a t i o n s u s i n g t h e
f i n i t e d i f f e r e n c e m ethod f o r t h e i n n e r and o u t e r w a l l t e m p e r a t u r e s a t
t h r e e r e p r e s e n t a t i v e t i m e s a r e a l s o ’shown i n F i g 3 « 2 ( b ) .
To
su m m a rise ,
t h e t e m p e r a t u r e o f t h e i n n e r w a l l r i s e s by 3*7^0
to
e q u ilib riu m
i n about 1second w ith fo rc e d c o n v e c tio n
by
2 00^0 t o e q u i l i b r i u m i n a b o u t 200 s e c o n d s w i t h
c o o l i n g when t h e h e a t i n p u t
In
d ilu te d
th e
ex p erim en tal
w i t h h e li u m ,
m ix tu re .
is
free
c o o l i n g and
c o n v e c tio n
10 W.
w ork,
g a s m i x t u r e s w e re m ost f r e q u e n t l y
th is gas o fte n c o n s titu tin g over
90^
of
th e
C o n seq u en tly , a r e a s o n a b le a p p ro x im a tio n i s to c o n s id e r th e
t h e r m a l b e h a v i o u r t o be t h a t o f p u r e h e li u m .
F or an av erag e a b so rb ed
power o f 10 W, e a c h p u l s e d e p o s i t s 9 * 1 x 1 0 " ^ J i n t o t h e h e l i u m .
fo llo w in g ,
0 .1 atm
r e s u l t s w i l l be o b t a i n e d f o r 2 atm ,
to ta l pressure.
1 atm ,
In th e
0 . 5 a tm , and
The t e m p e r a t u r e r i s e f o r a s i n g l e m icrow ave
p u l s e a t e a c h o f t h e s e p r e s s u r e s i s 8 .3 ° C , 1 6 .5 ^ C , 33«1°C, and 165°C,
re sp e c tiv e ly .
p art
g a s w i l l be l o s t from t h a t
o f t h e t u b e i n w h ic h t h e d i s c h a r g e o c c u r s by e x p a n s i o n and w i l l
retu rn
d u rin g
because
gas
D u rin g t h e h e a t i n g p u l s e ,
th a t
th e in te r - p u l s e co o lin g .
T his e f f e c t i s ig n o re d h e re
o f th e d i f f i c u l t y i n d e te rm in in g th e th erm al h i s t o r y o f
lea v e s
C o n s e q u e n tl y ,
and
retu rn s
to
th e
tu b e
th e
d u rin g a p u lse c y c le .
t h e c a l c u l a t i o n f o r t h e lo w e r p r e s s u r e s ,
p a rtic u la rly
a t 0 . 1 atm , w i l l p r o b a b l y u n d e r e s t i m a t e t h e r e s u l t i n g t e m p e r a t u r e s .
C hapter 3
In
68
c a lc u la tin g
sequence,
we u s e
b e h a v io u r
over
th e
th e
many
gas
tem p eratu re
su p e rp o sitio n
p u lses
re su ltin g
p rin c ip le .
from
The
a p u lse
tem p e ra tu re
ca n be fo u n d by a d d in g s e c t i o n s o f t h e
b e h a v i o u r t h a t would f o l l o w a s i n g l e p u l s e a s d e s c r i b e d b e lo w .
th e
at
re su lts
A ls o ,
a t a g i v e n p r e s s u r e c a n be r e s c a l e d t o g i v e t h e r e s u l t s
o t h e r p r e s s u r e s and t o
allo w
fo r
changes
in
(1 9 )
are
d iffu siv ity
and
d e n sity .
R e su lts
c o n sta n t
u sin g
i n n e r tu b e w a l l
d im e n sio n le ss
u n if o r m
e q u a tio n s
( 9)
and
tem p e ra tu re
of
293K
o b tain ed
(w h ic h
The
v a l u e s a r e shown i n F i g 3 * 3 .
a p p ly in g
sequence,
S i m p s o n 's
,
and
w ith
d i s t r i b u t i o n i s c a l c u l a t e d f o r a t o t a l o f 400
and r e s u l t s e x t r a c t e d
c a lc u la tio n
in
a s i n g l e h e a t i n g p u l s e w hich g i v e s a n i n i t i a l
d i s t r i b u t i o n of 2 .0 (d im e n sio n le ss tem p eratu re)
in crem en ts
1.0
/
fo rm ),
5 t / ( 5 r ) ^ z 0 .2 5 .
is
w ith a
at
a
se le c tio n
of
in te rm e d ia te
F o r e a c h d i s t r i b u t i o n s e l e c t e d from t h e
t h e s p a t i a l mean t e m p e r a t u r e T^ i s
R u le
to th e s p a ti a l d i s t r ib u t io n .
fo u n d
by
T hese v a l u e s
a r e p l o t t e d i n F i g 3 . 4 w hich p r o v i d e s t h e b a s i c t e m p e r a t u r e b e h a v i o u r
th a t
w ill
The
be
used
i n o u r s u b s e q u e n t d i s c u s s i o n s and c a l c u l a t i o n s .
' l e a s t s q u a r e s ' b e s t a p p r o x i m a t i o n t o an e x p o n e n t i a l
curve
fo r
th is d a ta i s
\
= 0 .9 7 3 e r ° '° 1 * 5 j
w here
of
T^
(30)
i s t h e d i m e n s i o n l e s s s p a t i a l mean t e m p e r a t u r e on t h e s c a l e
0 to 1 ,
C a lc u la tio n s
and j i s t h e number o f i n c r e m e n t s o f d i m e n s i o n l e s s t i m e .
u sin g
th is
e q u a t i o n d e v i a t e by no more t h a n 2.5% from
initial temperature
RADIUS
Fjgure 3.3 Gas temperature vs Radius. Time intervals in
_ .
calculation increment steps.
_ „
.i.
25
T 3aniva3dW3i
Chapter 3
th e
^9
d a ta in F ig 3 .4 .
tem p e ra tu re
resid u al
from
th e
su p e rp o sitio n
p rin c ip le ,
th e
mean
a f t e r many p u l s e s (T^) c a n be r e g a r d e d a s t h e sum o f t h e
t e m p e r a t u r e s o f ea ch i n d i v i d u a l p u l s e .
th e
d iv id e d
By
area
under
T his
is
o b tain ed
t h e c u rv e i n F i g 3 , 4 (by i n t e g r a t i o n o f ( 3 0 ) )
by t h e number o f c a l c u l a t i o n i n c r e m e n t s ,
n,
i n a m icrow ave
i n t e r » p u l s e p e r i o d ; we g e t
= 67.1 (1 -
H ere
th e
th e
.
(31)
t e m p e r a t u r e i s a n a v e r a g e b o th s p a t i a l l y and t e m p o r a l l y i n
s e n s e t h a t t h e p u l s e e f f e c t s h a v e b e e n sm oothed o u t .
A ls o i t i s
n o t e d t h a t t h i s i s a d i m e n s i o n l e s s v a l u e on a s c a l e o f 0 t o 1 w h e re 1
rep re sen ts
th e tem p eratu re r i s e p e r p u lse .
t h i s becomes t h e e q u i l i b r i u m v a l u e ,
= 67.1/n
For l a r g e
v a lu e s
of
j
g i v e n by
.
(32)
The t e m p e r a t u r e r i s e , Tp, due t o a m icrowave p u l s e o f e n e r g y E i s
Tp = EK/vpCp
.
(3 3 )
F o r h e liu m we g e t
p = 0.179X 273P/T
,
and u s i n g d a t a from T a b le 3 ,1 we g e t
Tp = 5 . 6 4 x 10"^T/P
,
(34)
Chapter 3
70
w here T i s t h e mean a b s o l u t e t e m p e r a t u r e .
of
pressures,
w i t h T = 293K a r e
shown
V a lu e s f o r Tp,
in
T a b le
3 .2 .
a t a range
R e c a llin g
p rev io u s e q u a tio n s
Ôt = a ^ 5 t / k , 5 t = 2.5x10*"^, and
k = 2 . 7 8 X 1 0 " ^ T ^ ^ ^ /P ,
(e q u a tio n
(2 6 )
w i t h v a l u e s from T a b le 3 . 1 ) t h e tim e p e r c a l c u l a t i o n
i n c r e m e n t i s g i v e n by
Ôt = 0 .0 9 0 P /T ^ ^ ^ 8
.
\
The i n c r e m e n t s i n a m icrow ave i n t e r ~ p u l s e p e r i o d a r e t h e n g i v e n by
n = 1 .0 1 x 1 0 " ^ T 3 /2 / p
and
^
v a l u e s f o r a mean t e m p e r a t u r e o f 293K a r e g i v e n
(3 5 )
in
T a b le
3 .2 ,
Com bining (35) and (3 2 ) g i v e s
T^ = 6 .6 4 x 1 o 3 p / T 3 /2
To
convert
,
(3 6 )
t h i s t e m p e r a t u r e T^ t o t e m p e r a t u r e i n d e g r e e s c e n t i g r a d e
ab o v e t h e w a l l t e m p e r a t u r e we u s e (3 4 ) t o g e t
T^ = 3 7 5 /T ^ ^^ °C
.
(3 7 )
Pressure (Atmospheres)
0.1
0 .5
1.0
2.0
mean
wail
cooling
gas
tempera- lonvGction
tempera­
ture -K tur e-K type
Mean gas temperature rise per pulse
Tp ( K )
from equation (34)
16.5
8 .3
2! 93
293
177
35.4
17.7
8 .9
314
293
232
46.4
23.3
11.6
411.5
393
287
57.5
28J
14.4
509.6
49 3
165
33.1
Gas temperature
forced
free
calculation increments - n
from equation ( 3 5 )
507
101
50.7
25.3
2 93
293
562
112
56.2
28.1
314
293
843
169
84.3
4 2.2
411.5
393
1160
232
116
58.1
509.6
493
forced
fre e
Diffusion calculation increments per pulse. *- n
from
equation ( 4 2 )
366
73.2
36.6
18.3
293
293
406
81.2
4 0.6
20.3
314
293
609
122
60.9
30.5
411.5
393
8 40
168
84.0
424
509.6
493
forced
free
Equilibrium mean concentration Ce/Co (=EJ
from equation (43)
0.17
0.83
1.65
3.31
314
293
0.11
0.55
1.10
2.20
411.5
393
0,08
0.40
080
1.60
509.6
493
forced
free
Table 3.2 Summary of temperature and diffusion calculation r e s u l ts
Chapter 3
T h is
71
i m p o r t a n t r e s u l t shows t h a t
s p a tia l
th e
(w ith
independent
o f t h e g a s p r e s s u r e b u t d e p e n d e n t on t h e
tem p eratu re
of
gas.
For
a
and
of
e q u ilib riu m
th e
a v e ra g in g
tem p eratu re
w all
tem poral
th e
gas
at
s m o o th in g )
is
mean
a b so lu te
t e m p e r a t u r e o f 293K>
th is
e q u a t i o n i s s a t i s f i e d by t h e v a l u e
.
Tg = 21°C
U sin g
a new v a l u e f o r t h e mean t e m p e r a t u r e o f 314K,
new v a l u e s from
e q u a t i o n s (3 4 ) and (3 5 ) a r e found and a p p e a r i n T a b le 3 . 2 ,
E q u a tio n
(3 1 )
can
be
used,
w ith
v a lu e s
of
n and Tp from
T a b le 3 . 2 , t o p l o t t h e s p a t i a l - t e m p o r a l , mean t e m p e r a t u r e a g a i n s t tim e
(o r
number
3 .5 .
a
3 .6 .
in te r-p u lse
shown
p e r i o d a f t e r e q u i l i b r i u m and t h i s i s shown i n
To o b t a i n t h e l o n g te r m f o r c e d c o n v e c t i o n b e h a v i o u r ,
eq u ilib riu m
F ig
m icrow ave p u l s e s ) and t h e s e r e s u l t s a r e shown i n F i g
F i g u r e 3 , 4 c a n be a d a p t e d t o g i v e t h e t e m p e r a t u r e b e h a v i o u r i n
s in g le
F ig
of
t e m p e r a t u r e r i s e o f 21^0 h a s t o be added t o t h e c u r v e o f
3 . 2 ( a ) f o r t h e i n n e r t u b e w a l l t e m p e r a t u r e and g i v e s
in
th e
F ig
3 .7 (a ).
The
th e
curve
c o rr e c tio n re q u ire d fo r th e a d d itio n a l
3 .7 ° C due t o t h e w a l l t e m p e r a t u r e i s n e g l i g i b l e .
Under
c o n d itio n s of f r e e
c o n v e ctio n ,
w h e re
th e
in n er
t e m p e r a t u r e r i s e s t o 493K, c o r r e c t i o n s w i l l be s u b s t a n t i a l .
in te rm e d ia te
t e m p e r a t u r e o f 393K,
v alu e
T^ = 18.5^C
,
w all
U sin g an
e q u a t i o n (37) i s s a t i s f i e d by t h e
tn
00
O)
oo
=3
CL
>
w
v»_
o
-
1/1
CL?
JD
3
Cl
O
CD
m
fD
CL
<
LA
O
<
CD
O
( lie« 8Aoqe) ]
3yniVd3dW 3i
l--yr 4
T|—r:
100-
fi - 0.5 At
equilibrium mean temperature '
TIME
j-
j;:~i 0.9 09 ms
I.
:
P-Flgure 3.6 Mean temperature vs. time during an inter - p u ls e
^ L _ : _ ^ _ _ _ _ p e r i o d - at equilibrium - (wall -2 93 K ).
r- - ;
II
r
o
>
(/)
"O
:o
w
LU
LU
œ
-Q
CL
O.
<z>
rsi
Db 3dniVd3dW3i
o
00
or
O
LJ
LU
1 EL
O
LU
'CD
u
cr.
LU
GE
<D
LU
!rm
o
:-T-- .
I
-O
m
T 'c T '3 m iV d 3 d W 3 I
:
en
C hapter 3
7^
w h i l e f o r M93K i t i s s a t i s f i e d by
T = 1 6 .6 ^ 0
e
The
mean
a b so lu te
tem p eratu res
o f th e gas a t w a ll te m p e ra tu re s o f
393K and 493K a r e 411.5K and 5 0 9 . 6K,
now
be
used
for
T a b le 3 . 2 ,
re sp e c tiv e ly .
These v a l u e s c a n
i n (3 4 ) and (3 5 ) t o p r o v i d e f u r t h e r v a l u e s o f n and Tp
The t e m p e r a t u r e b e h a v io u r i n
a
sin g le
p e r i o d w i t h a w a l l t e m p e r a t u r e o f 493 i s shown F i g 3 . 8 .
a d d in g 21°C,
in te r-p u lse
F in a lly ,
by
1 8 . 5 ° C, and 16.6°C t o t h e c u r v e o f F i g 3 . 2 ( b ) a t 293%,
393%, and 493%, r e s p e c t i v e l y , t h e c u rv e f o r t h e mean g a s t e m p e r a t u r e ,
in
th e lo n g term ,
w ith f r e e c o n v e c tio n c o o lin g i s , o b t a i n e d
in
F ig
su m m a ris e d .
The
3 .7 (b ).
The
gas
d iffe re n c e
c o n ta in s
te rm
tem p eratu re
b eh av io u r
can
i n t h e r m a l c a p a c i t y b e tw e e n
now
th e
be
tu b e
and
th e
gas
it
means t h a t t h e g a s r e a c h e s a q u a s i - e q u i l i b r i u m i n t h e s h o r t
d u rin g
w h ic h
th e
tem p eratu re
e q u ilib riu m
i s a b o u t 21^0 w h i l e g a s a t 200^0 r i s e s by o n l y 1 6 .5 °C t o
goes
The
number
of
gas
th e
a p p ro x im ate ly
For
The
tem p eratu re
rem a in s
c o n sta n t.
eq u ilib riu m .
room
tu b e
tem p e ra tu re
p u lses
rise
per
p u lse
fo rced
about
40°C
c o n v e c tio n
c o n v e c tio n
to
th e
th e
e q u ilib riu m
rise
to
to
2 atm .
and t h e r a t e o f c o o l i n g b e tw e e n
i s g r e a t e r f o r b o t h l o w e r p r e s s u r e s and h i g h e r
W ith
to
m icrow ave p u l s e s t o r e a c h e q u i l i b r i u m
from 1 t o 10 a s t h e p r e s s u r e i n c r e a s e s from 0 ,1 atm
tem p eratu re
rise
tem p eratu res.
i n n e r t u b e w a l l t e m p e r a t u r e r i s e s by..,
in
about
e q u ilib riu m
1 second
w h ile
under
free
i s a b o u t 216°C and t h i s t a k e s
-
...
O .SA t
•1 6 .6
0.909ms
ii; .Figure 3.8 Mean temperature vs. time during an
inter-pulse-period (wall - 493 K )----- =
C hapter 3
about
73
200 se conds»
about
25^0
and
resp e c tiv e ly .
T h e r e f o r e t h e f i n a l mean
235^0
F in a lly ,
tube o u t e r w a ll i s ,
fo r
forced
and
gas
free
tem p eratu res
c o n v e c tio n
are
c o o lin g
t h e h e a t l o s s by r a d i a t i o n a t 235°C fro m t h e
by S t e f a n * s Law, a b o u t 0.3W and i s t h e r e f o r e n o t
an i m p o r t a n t l o s s p r o c e s s i n t h i s c a s e .
3 .2 .2
D iffu sio n
H aving
s y s te m
we
d e te r m i n e d t h e t e m p e r a t u r e c o n d i t i o n s p r e v a i l i n g i n
can
now c o n s i d e r t h e d i f f u s i o n o f f l u o r i n e ,
h e liu m ~ flu o rin e donor m ix tu re , to th e tube w a l l s .
th a t
th ro u g h th e
I t w i l l be assum ed
e a ch m icrow ave p u l s e c o n t r i b u t e s a c o n s t a n t c o n c e n t r a t i o n 0^ o f
flu o rin e
th e
th e
by d i s s o c i a t i o n o f a d onor m o l e c u l e .
The tim e b e h a v i o u r o f
s p a t i a l d i s t r i b u t i o n f o l l o w i n g a s i n g l e m icrow ave p u l s e i s g i v e n
d ire c tly
by e q u a t i o n s ( 9 ) and (1 9 ) a s shown i n
tem p eratu re
0 - Cq,
sc ale
(1 ~ 2)
S im ila rly ,
rep laced
F ig 3 .4 g iv e s th e
a g a in st
d im e n sio n le ss
p u lse.
The
mean
is
tim e
on
c o n c en tra tio n
a
3.3
w here
th e
by t h e c o n c e n t r a t i o n s c a l e
sp a tia l
sc ale
a fte r
B’i g
0 many
mean
c o n c en tra tio n
fo llo w in g à s in g le
p u lses
is
fo u n d
by
r e - w r i t i n g (31) i n t h e form
= 6 7 .1 ( 1 “
,
(3 8 )
The e q u i l i b r i u m v a l u e from (3 2 ) i s
= 6 7 . 1/ n
.
(3 9 )
Chapter 3
E q u a tio n
th e
(2 9 )
f o r th e d i f f u s i o n c o e f f i c i e n t i s e v a lu a te d w ith
h e liu m a to m ic m ass and
as
t h e mean f l u o r i n e - h e l i u m d i a m e t e r ,
u s i n g v a l u e s from T a b le 3 , 1 , t o g i v e
D = 2 .0 1 x 1 0 " ^ T ^ ^ ^ /P mfs°1
,
(4 0 )
U sing 6 t = 2,5x10**^, we g e t
5 t = a^Ôt/D = 0 .1 2 P / T 3 / 2 s
and
th e
number
^
(4 1 )
o f c a l c u l a t i o n i n c r e m e n t s p e r m icrow ave i n t e r - p u l s e
p e r i o d becomes
n = 7 . 3 X 10” ^T^'^^/P
.
(4 2 )
V a lu e s o f n when T = 293K a r e g i v e n i n T a b le 3 . 2 ,
Combining (3 9 ) and
(4 2 ) g i v e s t h e e q u i l i b r i u m c o n c e n t r a t i o n a s
c ^ = g u P x i o ^ p /T ^ / z
,
(4 3 )
The e q u i l i b r i u m t e m p e r a t u r e r i s e when t h e w a l l t e m p e r a t u r e i s 293% i s
21°C.
th e
U sing T = 314K i n (4 3 ) a t t h e f o u r p r e s s u r e s o f i n t e r e s t g i v e s
e q u i l i b r i u m c o n c e n t r a t i o n s f o r t h e 293K w a l l t e m p e r a t u r e .
appear
in
T a b le 3 . 2 .
To
o b tain
th e
c o n c e n t r a t i o n i n c r e a s e w i t h p u l s e number,
is
te m p o ra l-sp a tia l
and
e q u a tio n
F ig
3*9»
W ith
( 38) i s th en used.
forced
c o n v e ctio n ,
mean
a mean t e m p e r a t u r e o f 3 1 4K
u s e d i n (42) ( t h e c o r r e s p o n d i n g v a l u e s o f n a r e
3 .2 )
These
g iv en
in
T a b le
These r e s u l t s a r e p l o t t e d i n
th e
e q u ilib riu m
mean
gas
j-r r i
NUMBER OF PULSES
0 Oi s
F.igure 3.9„„TemporaL~spatial mean concentration vs.
— number of pulses (wall -2 93 K , gas - 3 1 4 K )
rf : -1
Chapter 3
75
t e m p e r a t u r e r i s e s by a f u r t h e r 3 .7 ° C .
d iffu sio n
i s s m a l l and c o n s e q u e n t l y i t
c o n v e ctio n ,
has
a
The e f f e c t o f t h i s r i s e on t h e
h o w ever,
per
e q u ilib riu m
effect
m icrow ave
on
th e
d iffu sio n .
in te r-p u lse
p erio d
t h e i n t e r m e d i a t e t e m p e r a t u r e 4 11.5K ,
The
(mean) c o n c e n t r a t i o n b e h a v i o u r i n a
lo n g
th e
free
The
and
th e
c a lc u la tio n
lo n g
terra
tem p eratu re,
and r e c o r d e d i n T a b le 3 . 2 .
sin g le
in te r-p u lse
p e rio d
te r m e q u i l i b r i u m i s shown f o r f o r c e d and f r e e c o n v e c t i o n
c o o lin g i n F ig 3 ,1 0 .
in
Under
mean c o n c e n t r a t i o n a r e c a l c u l a t e d f o r t h i s
and
a fte r
n e g le c te d .
t h e mean g a s t e m p e r a t u r e r i s e s t o 5 0 9 . 6K w hich
c o n sid e rab le
in cre m e n ts
is
lo n g
F i n a l l y , F i g 3.1 1 shows t h e mean c o n c e n t r a t i o n ,
te r m ,
a g a in st
tim e
for
f r e e and f o r c e d c o n v e c t i v e
c o o lin g .
3 .2 .3
-C-O-aclusiong.
In
th e p re c e d in g s e c t i o n s ,
sp e c ific
ex p erim en tal
lim ita tio n s.
d if f u s io n th eo ry i s
s itu a tio n
under
v ario u s
W it h in t h i s c o n t e x t s e v e r a l c l e a r
a p p lie d
to
a
a p p r o x i m a t i o n s and
tren d s
emerge
and
t h e s e a r e l i s t e d b e lo w .
1. Forced
can
c o n v e c t i o n c o o l i n g o f t h e o u t e r w a l l o f t h e d i s c h a r g e tu b e
be v e r y e f f e c t i v e i n k e e p i n g t h e t e m p e r a t u r e o f t h e
gas
w ith in
t h e t u b e low .
2 . The
mean
e sta b lish e d
gas
tem p eratu re
a fte r
l o n g te r m e q u i l i b r i u m h a s b e e n
i s i n s e n s i t i v e to p r e s s u r e s w ith in th e ran g e c o n s id e re d .
T h is i s d e m o n s t r a t e d by e q u a t i o n ( 3 7 ) , d e r i v e d a b o v e , w hich i n d i c a t e s
th a t
t h e e q u i l i b r i u m mean t e m p e r a t u r e o f t h e g a s above t h e mean w a l l
mean
{concentration
-n
o
lA t
5At
1.1A H
Forced convection
1 At
lA t
Free convection
iF-igune 3.10 Mean concentration- v s _ t i m e - during- a
microwave
inter ~ pulse period.
:- -
Forced convection
Free convection
IM E ~ s e c o n c
f ig u r e 3.11 Temporal - spatial mean concentration
vs
C hapter 3
76
t e m p e r a t u r e i s d e p e n d e n t o n l y on t h e mean a b s o l u t e t e m p e r a t u r e o f t h e
gas.
3 , The
tem p e ra tu re
d ifferen ce
2 atm
mean
b e tw e e n
and
th e
p a rtic le
b eh a v io u r
c o n c e n tra tio n s
at
d u i'in g t h e i n t e r ^ p u l s e p e r i o d .
show
d u rin g
m arked
0.1 atm and t h e b e h a v io u r a t
In p a rtic u la r,
a t 0.1 atm t h e
t e m p e r a t u r e and c o n c e n t r a t i o n i n c r e m e n t s i m p a r t e d by e a ch p u l s e
h a v e b e e n removed by t h e end o f t h e i n t e r - p u l s e p e r i o d .
2 atm
a
th e
However,
at
mean t e m p e r a t u r e and c o n c e n t r a t i o n o n l y f a l l by a b o u t 25%
th e in te r - p u l s e p e rio d .
T h is a s p e c t i s shown
in
F ig s
3 .6 ,
3 . 8 , and 3 . 1 0 .
4 . The , mean
e q u ilib riu m
c o n c e n t r a t i o n d e p e n d s s t r o n g l y on p r e s s u r e
and t e m p e r a t u r e and i s t h e r e f o r e d e p e n d e n t on c o o l i n g .
T h is i s shown
c l e a r l y i n F i g 3 .1 1 w here t h e mean c o n c e n t r a t i o n a t 2 atm i s 20 t i m e s
th e
mean
(co o lin g )
mean
mean
c o n c e n tra tio n
and
at
0 .1 atm
fo r
f r e e c o n v e c t i o n (n o c o o l i n g ) .
both
fo rced
c o n v e ctio n
At a l l p r e s s u r e s ,
th e
c o n c e n tr a tio n w ith fo rc e d c o n v e c tio n i s a p p ro x im ate ly tw ice th e
c o n c e n tra tio n
th at
occurs
e s ta b l is h e d w ith f r e e c o n v e c tio n .
a fte r
therm al
e q u ilib riu m
is
C hapter 4
4
.
77
MICROWAVE DISCHARGE EXCITATION
Microwave
a p p lic a tio n s
re a c tio n
d i s c h a r g e s i n g a s e s h a v e fo u n d w i d e s p r e a d u s e i n s u c h
as th e e x c ita tio n
c h a m b e rs .
of
However,
sp e ctral
so u rces
and
c h e m ic a l
t h e m icrow ave d i s c h a r g e r e p r e s e n t s a
r a d i c a l d e p a r t u r e from t h e m ore u s u a l m ethods ( s u c h a s e-beam o r f a s t
d isch arg e)
rep o rts
(Handy
used
to
pump
o f g a s l a s e r s e x c i t e d by
and
B ra n d e lik
1 9 7 8 ),
(Ahmed and K ocher 1 9 6 4 ) ,
C l,
S,
Si
d isso c ia tio n
e t.
r a r e - g a s h a l i d e e x c im e r l a s e r s .
a l,
d ischarge
m icrow ave
d isch arg e
(B ran d e lik
and
in clu d e
Ar ( P a i k and C re e d o n 1 9 7 8 ) ,
CS^ and 0^ ( S u a r t e t .
S m ith
1980),
a l,
and
P re v io u s
1972),
00^
He - Me
B r,
C,
m icrow ave d r i v e n
o f t h e f l u o r i n e d o n o r i n t h e c h e m ic a l HP l a s e r ( B e r t r a n d
1978) .
The
f i r s t s u c c e s s f u l a p p l i c a t i o n o f a m icrowave
t o pump a n e x c im e r l a s e r (XeCl) was a c h i e v e d
M endelsohn
e t.
a l,
(1981).
m icrow aves
f o r p r o v i d i n g t h e h i g h pump power
in
1981
by
The a d v a n t a g e s and d i s a d v a n t a g e s o f
e x c im e r l a s e r s a r e d i s c u s s e d b e lo w .
d e n sity
req u ired
fo r
Chapter 4
4,1
78
C om parison o f M icrowave and DC D i s c h a r g e s
4 .1 .1
I n pumping by DC p u l s e s ,
through
used
t h e a c t i v e medium.
m ethod
fo r
e le c tro n -b ea m
ex p en siv e.
fo r
a c a p a c i t o r bank i s d i s c h a r g e d r a p i d l y
T h is i s c u r r e n t l y
pumping
e x c im e r
th e
la se rs,
m ost
fre q u e n tly
E lectro n -b eam
s t a b i l i s e d DC d i s c h a r g e s y s te m s a r e l a r g e r ,
However,
and
and
m ore
e v e n th o u g h DC d i s c h a r g e s y s te m s a r e p r e f e r r e d
sm a ll s c a le e x p e rim e n ts,
such l a s e r s
s till
have
c o n sid e ra b le
d e s i g n p ro b le m s w hich l a r g e l y ste m from t h e h i g h pump power d e n s i t i e s
req u ired
glow
for
20kV
are
( a b o u t IMV/cm ^ ) ,
The p la s m a im pedance d u r i n g
th e
u niform
phase
o f a h i g h power p u l s e d d i s c h a r g e i s a ro u n d 0 . 5 Q ,
Thus,
o o
t y p i c a l l a s e r a c t i v e volum es ( a b o u t 10 cm ) v o l t a g e s o f a ro u n d
are req u ired .
a b o u t 10
( T y p i c a l v a l u e s o f E/N o f r a r e - g a s h a l i d e l a s e r s
“5
2
Vcm ) .
I t h a s b e e n b e e n fo u n d t h a t ,
because
of
th e
h i g h p r e s s u r e s i n v o l v e d , t h e s p a t i a l and t e m p o r a l u n i f o r m i t y r e q u i r e d
fo r
e f f i c i e n t l a s e r e x c i t a t i o n c a n o n l y be a c h i e v e d u n d e r
c o n tro lle d
d isc h a rg e
and
rath e r
u n ifo rm ity
lim ite d
and
circ u m stan c e s.
sta b ility
are
The
d isc u sse d
c a re fu lly
p ro b le m s
of
d e ta il
by
in
L e v a t t e r and L i n (1980) w h e re t h e r e q u i r e m e n t s f o r v e r y s h o r t v o l t a g e
rise
tim es
fo rm a tio n
d e n sity
sp read in g
homogeneous
p re io n isa tio n
a
fila m e n ta ry
(strea m er)
of
a p p lic a tio n
low
and
are
e m p h a s is e d .
fo llo w in g
th e
o f a h ig h v o lta g e p u lse i s a n a tu r a l consequence o f
th e
of
seed
e le c tro n s
and
th e
d isc h a rg e
The
low
lev el
t h a t r e s u l t s from t h e h i g h g a s p r e s s u r e .
of d iffu siv e
In th e
e le c tro n
Chapter 4
79
av ala n c h es
th a t
f o l l o w t h e a p p l i c a t i o n o f an e l e c t r i c f i e l d a t h i g h
E/N v a l u e s a p o i n t i s r e a c h e d w here t h e m a g n itu d e o f t h e s p a c e c h a r g e
fie ld
at
th e
a p p lie d
fie ld
spacecharge
th a t
h e a d o f t h e a v a l a n c h e a p p r o a c h e s t h e m a g n itu d e o f t h e
( ’B a e t h e r
fie ld
c rite rio n ’ ,
a c c e le ra te s
th e
see
R aether
1940).
T h is
d e v e lo p m e n t o f t h e a v a l a n c h e s o
s t r e a m e r f o r m a t i o n t i m e s a r e Very much l e s s t h a n t h e tim e f o r a
sin g le
e le c tro n
tim e ).
to
tra v e l
acro ss
t h e i n t e r e l e c t r o d e gap ( t r a n s i t
I n He a t l a t m and a t y p i c a l E/N v a l u e o f
1 .5x1C"’^^Vcm^
th e
e l e c t r o n d r i f t v e l o c i t y i s a b o u t 2x10^cm s ^ g i v i n g a t r a n s i t tim e o f
1|ls f o r a 2 cm g a p .
S tream er fo rm a tio n ,
t im e s a s s h o r t a s 10
w ill
s.
h o w ever,
may t a k e p l a c e i n
T h i s s u g g e s t s t h a t s h o r t v o l t a g e r i s e t im e s
be r e q u i r e d i f t h e d i s c h a r g e i s t o be u n i f o r m a t h i g h p r e s s u r e .
E x p e r ie n c e
has
shown
th a t
a
u niform
glow
d i s c h a r g e c a n o n l y be
o b ta in e d a t h ig h p r e s s u r e i f p r e i o n i s a t i o n produces a d e q u a te , u n ifo rm
s e e d e l e c t r o n d e n s i t i e s and o n l y i f t h e v o l t a g e r i s e t i m e i s l e s s t h a n
about 20ns.
U n le s s
th e v o lta g e p u lse i s k ep t
d isc h a rg e
in sta b ility
m easures.
Thus,
by
runaw ay
fa ll
cu rren t
damage.
a lm o s t
io n isa tio n
o n ly
be
fo re sta lle d
sh o rt
(<50ns),
by t h e p r e c e d i n g
a r e l a t i v e l y s t a b l e d is c h a r g e w i l l e v e n tu a ll y decay
g r o w th ,
i n t h e E/N v a l u e .
e le c tro d e
due
w ill
d e lib e ra te ly
e n tire ly
a f a l l i n p la s m a im p e d a n ce and h e n c e a
U ltim a te ly ,
C urrent
to
a r c s w i l l form which w i l l c a u s e
s t a b i l i t y on t h e s e s h o r t tim e s c a l e s i s
b a la n c e
b e tw e e n
and e l e c t r o n l o s s by a t t a c h m e n t .
e le c tro n
p ro d u ctio n
T herefore,
by
t h e c u i 'r e n t
g r o w th a c co m p a n ie s a f a l l i n t h e a t t a c h m e n t r a t e d u e , f o r e x a m p le, t o
a
fa ll
sp a tia l
in
d e n sity .
In a d d itio n to c u rre n t i n s t a b i l i t y ,
i r r e g u l a r i t i e s w i l l c a u s e h e a t i n g i r r e g u l a r i t i e s w hich
slig h t
w ill
C hapter 4
80
e v e n t u a l l y c a u s e t h e s p a t i a l h o m o g e n e ity t o be l o s t ,
th e
d e v e lo p m e n t o f a r c s .
th u s e n co u rag in g
Therm al i n s t a b i l i t y i s d i s c u s s e d by
Jacob
and Mani (1975) who g i v e r e f e r e n c e s t o o t h e r a s p e c t s o f h i g h p r e s s u r e
d isc h a rg e i n s t a b i l i t i e s .
To
su m m a ris e ,
homogeneous
rise tim e s
In
DC d i s c h a r g e pumping o f e x c im e r l a s e r s
p re io n isa tio n
and v o l t a g e p u l s e s i n e x c e s s o f 20kV w i t h
below a b o u t 2 0 n s and d u r a t i o n s o f l e s s t h a n
a d d itio n
p ro p o rtio n s
to
th is,
gas
m ix tu re
about
1 0 0 n s,
r a t i o s m u st be l i m i t e d t o t h e
t h a t p e rm it an e l e c t r o n av a la n c h e
c o n tro lle d s t a b i l i t y .
req u ires
yet
g iv e
a tta c h m e n t
I t s h o u l d be n o t e d how ever t h a t im provem ent i n
one o f t h e s e c o n d i t i o n s may a ll o w a r e l a x a t i o n i n a n o t h e r .
4 ,1 .2
M icrowave D i s c h a r g e E x c i t a t i o n
As
perform
th e
w i t h DC d i s c h a r g e e x c i t a t i o n ,
m icrowave e x c i t a t i o n
e le c tr o n te m p e ra tu re w h ile
b e s t E/N
sta b ility ,
im p o rta n t
w ill
be
p ro v id e
pum ping.
lim ite d
mode
of
to
t h e d u a l t a s k o f d r i v i n g e l e c t r o n a v a l a n c h e s and m a i n t a i n i n g
in e la stic
m e ta sta b le prod u ctio n ) a re ta k in g p la c e .
th e
has
v a lu e
fo r
m eta sta b le
c o llisio n s
(p a rtic u la rly
The p r o b le m s o f m a i n t a i n i n g
p ro d u ctio n
w h ile
m ain ta in in g
u n i f o r m i t y and e f f i c i e n c y a r e s t i l l p r e s e n t b u t t h e r e a r e
d i f f e r e n c e s w hich w i l l be d i s c u s s e d b e lo w .
u sefu l
first
to
c o n sid e r
However,
w h e t h e r a m icrow ave s y s te m c a n
t h e E/N v a l u e s and power d e n s i t y r e q u i r e d f o r e x c im e r
The
power
w h ic h
ca n
be
tra n sm itte d
lase r
by a w a v e g u id e i s
by breakdow n o f t h e g a s w i t h i n t h e w a v e g u id e .
a re c ta n g u la r g u id e,
it
In
th e
TE^^
th e e l e c t r i c f i e l d i s p a r a l l e l to th e
Chapter 4
na rro w
81
w a l l and i s maximum a t t h e g u i d e
recommended
of
th a t
c e n tre .
It
is
g e n e ra lly
w a v e g u id e e l e c t r i c f i e l d s a r e l i m i t e d t o a q u a r t e r
t h a t v a l u e a t w hich breakdow n o c c u r s i n
a ir
at
STP,
However,
g r e a t e r f i e l d s a r e o b t a i n e d i f t h e w a v eguide s u r f a c e i s smooth and i f
th e g u id e i s p r e s s u r is e d .
w a v e g u id e
Adding g a s e s su c h a s SF^ t o t h e g a s o f t h e
a l s o g i v e s i n c r e a s e d breakdow n f i e l d s .
Thus t h e breakdow n
”1
f i e l d f o r a i r OOkVcm ) may be a p p ro a c h e d o r e x c e e d e d .
F ie ld v a lu e s
“1
o f aro u n d lOkVcra
a r e t y p i c a l i n DC s y s te m s b u t s u c h a v a l u e w i l l be
d iffic u lt
t o a c h i e v e u s i n g m ic ro w a v e s .
T h is i s
because
th e
g u id e
e l e c t r i c f i e l d i s r e d u c e d by t h e c o u p l i n g s t r u c t u r e w hich d i s t r i b u t e s
th e
f i e l d over th e len g th o f th e d isch arg e tu b e .
tube
of
len g th
For
20.cm and X-band (3cm) m ic ro w a v e s ,
f i e l d i s a t l e a s t a f a c to r of 10.
a
d isch arg e
th e re d u c tio n in
I t t h e r e f o r e seems t h a t s u c c e s s f u l
l a s i n g ca n o n l y be a c h i e v e d when t h e w aveguide h a s i t s
power h a n d l i n g
c a p a b i l i t y im p ro v e d .
It
w i l l be r e c a l l e d t h a t a pump power d e n s i t y o f 2MlVcm ^
r e a l i s t i c aim f o r an e x c im e r l a s e r .
th at
w ill
th e
m a g n e tro n
have t o be lOkW i n t h e m o st o p t i m i s t i c c a s e and p r o b a b l y
IMlf
more r e a l i s t i c a l l y .
are
a v a ila b le
p ow ers
a
sin c e i t i s u n lik e ly
d i s c h a r g e t u b e v olum es w i l l be much below 1 cm ,
power
a
T herefore,
is
up
to
M a g n e tro n s o p e r a t i n g a t X-band
600kW
w ith
fre q u e n c ie s
SF^ i n t e r n a l i n s u l a t i o n .
H ig h e r
ca n be o b t a i n e d a t l o w e r f r e q u e n c i e s b u t h e r e t h e b e n e f i t s o f
larg e r
w a v eguide
w i l l h ave t o be w eighed a g a i n s t t h e c h e a p e r and
more compact X-band s y s t e m s .
Chapter 4
82
The o b v io u s d i f f e r e n c e b e tw e e n a m icrowave and a DC d i s c h a r g e i s
th a t
in
t h e e l e c t r i c f i e l d o f t h e l a t t e r i s m o d u la te d a t h i g h f r e q u e n c y
th e form er.
th at
An im m e d ia te and m o st s i g n i f i c a n t r e s u l t o f t h i s
t h e s t r e a m e r breakdow n w hich i s so d i f f i c u l t t o p r e v e n t i n h i g h
power
DC
d isch arg es
d isc h a rg e .
much
cannot
occur
in
th e
eq u iv a len t
strin g e n t
demands
p re io n isa tio n .
sh o rt
m icrow ave
T h is i s b e c a u s e t h e f i e l d r e v e r s a l tim e ( a b o u t 10
l e s s t h a n t h e s t r e a m e r f o r m a t i o n tim e (<10 ^ s ) .
th e
In
is
fo r
However,
rise tim e s
sin c e
sh o rt
T h is
“ 10
s) i s
rem oves
p u l s e r i s e t i m e s and homogeneous
i t w i l l r e m a in n e c e s s a r y t o e x p e c t
fa irly
t h e o v e r a l l p u l s e w i l l be o f s h o r t d u r a t i o n .
a d d i t i o n some l e v e l o f p r e i o n i s a t i o n may be d e s i r a b l e f o r r e a s o n s
g i v e n b elow .
A n o th e r r e s u l t o f t h e h i g h f r e q u e n c y m o d u l a t i o n i s t h a t
th e
d i s c h a r g e may be c o n t a i n e d i n a d i e l e c t r i c t u b e .
th e
lo n g
T h is
p rev en ts
te rm d e c a y i n t o a r c s t h a t o c c u r s i n a DC d i s c h a r g e and may
l e a d t o lo w e r l e v e l s o f c o n t a m i n a t i o n .
The
la se r
m ain d i f f i c u l t i e s o f o p e r a t i n g a
e x c ita tio n
d isch arg e
of
at
su ffic ie n t
len g th
w ith
An
for
in sig h t
in to
efficie n t
c o u p lin g
of
th e
A f u r t h e r p ro b le m a r i s e s i n t h a t
optimum e x c i t a t i o n c o n d i t i o n s f o r
d isc h a rg e.
d isch arg e
h ig h p r e s s u r e a r e th o se o f o b t a in in g a un ifo rm
m icrow ave power i n t o t h e d i s c h a r g e .
th e
m icrow ave
reliab le
in itia tio n
of
th e
t h e s e d i f f i c u l t i e s ca n be g a i n e d by a
s i m p l i f i e d c o n s i d e r a t i o n o f t h e p r o p a g a t i o n o f m ic ro w a v es i n a p lasm a
i n t e r m s o f e l e c t r o n d e n s i t y , e l e c t r o n - atom c o l l i s i o n f r e q u e n c y and
t h e m icrowave f r e q u e n c y .
C hapter 4
.
The
m icrow ave
fie ld
can
be
rep resen ted
as
83
a
p lane
e l e c t r o m a g n e t i c wave t r a v e l l i n g i n t h e z - d i r e c t i o n a s
w here y i s t h e com plex p r o p a g a t i o n c o e f f i c i e n t and i s g i v e n by
Y = a + j(3
w here a
be
and (3 a r e t h e a t t e n u a t i o n and p h a s e c o e f f i c i e n t s .
These c a n
e x p r e s s e d i n te r m s o f t h e a t t e n u a t i o n i n d e x and r e f r a c t i v e i n d e x ,
X and |i ,by
a = x w /o
and
P = M-tO/c
.
In th e absence o f c o l l i s i o n s ,
90^
f r e e e le c tr o n s o s c i l l a t e a t a phase of
t o t h e a p p l i e d f i e l d and t h e r e f o r e do n o t
ste a d y
sta te .
r a n d o m is e d
c o llisio n s
do
occur
th e
by t h e c o l l i s i o n s and t h e e l e c t r o n s g a i n
c o n tin u o u sly .
o sc illa tio n
in -p h a se
When
g a in
As
th e
c o llisio n
in th e d riv in g
d rift
v e lo c ity
fie ld
freq u en cy
is
in creases.
en erg y
in
th e
e l e c t r o n m o ti o n i s
k in e tic
en erg y
in c re a se s th e e le c tro n
in c re a sin g ly
damped
as
th e
The e q u a t i o n o f m o tio n f o r a n
e l e c t r o n i n t h e d r i v i n g f i e l d E w i t h o o l l i s i o n a l dam ping i s
C hapter 4
84
mx = - e E “ vmx
w here
x i s th e d isp la c em e n t,
Vmx t h e damping
c o l l i s i o n f r e q u e n c y f o r momentum t r a n s f e r .
te r m
and
v
is
th e
T h is h a s t h e s t e a d y s t a t e
so lu tio n
X = eE/DK0(C0 - j v )
w here
(1 )
t h e s u b s t i t u t i o n o f jW f o r ô / ô t h a s b e e n
used.
The
complex
c o n d u c t i v i t y i s t h e n g i v e n by
G
= J /E = -n ex /E = n e^ (v -
w here
J
is
frequency
th e
cu rren t
jU J )/m (w ^
d e n sity
-fV ^ )
(2 )
and n t h e e l e c t r o n d e n s i t y .
o f o s c i l l a t i o n o f f r e e e l e c t r o n s i n a p la s m a ,
th e
The
plasm a
f r e q u e n c y Wp, i s g i v e n by
(T he
e l e c t r o n d e n s i t y o b t a i n e d from t h i s e q u a t i o n i s t h e c r i t i c a l o r
p la s m a d e n s i t y ) .
o = e jjL)p(
V
S u b s t i t u t i o n i n (2) t h e n g i v e s
“• jw ) /( w ^ + v ^ )
.
(4 )
85
Chapter 4
It
and
i s shown i n H eald and W harton (1965) t h a t
d ie le c tric
co n d u c tiv ity
a lso
be
process
c o n sta n t
may
be
combined
th e
in
o r a complex d i e l e c t r i c c o n s t a n t .
a
c o n d u c tiv ity
sin g le
com plex
The same p r o c e s s may
a p p l i e d t o t h e r e f r a c t i v e i n d e x and a b s o r p t i o n i n d e x .
o f s u b s t i t u t i o n and e x t r a c t i o n o f r e a l and
im a g in a ry
By a
p arts
( n o t r e p e a t e d h e r e ) t h e r e f r a c t i v e i n d e x and a t t e n u a t i o n in d e x c a n be
expressed as fo llo w s:
w 2 \2
1n
Si
w
W
COL
X = W
The
1
0)
!(’
as
V
1
(5 )
7
4 0)
Ill
V
(6)
0)4v2 0)
2
W
')
W(?
OJ/
a t t e n u a t i o n c o e f f i c i e n t c a n be
d efin ed
a)p2
used
to
g iv e
a
sk in
d e p th
t h e d i s t a n c e t r a v e l l e d i n t h e p la s m a f o r a 1 / e r e d u c t i o n
i n t h e e l e c t r i c f i e l d s t r e n g t h by
5 = 1 / a = c/xco
(7)
T h i s e q u a t i o n i s a p p l i c a b l e f o r m icrow aves i n c i d e n t on a w e l l d e f i n e d
p lasm a
p la s m a .
b o u n d a ry
and
fo r
a homogeneous e l e c t r o n d e n s i t y w i t h i n t h e
Under t h e s e c o n d i t i o n s t h e power r e f l e c t i o n and t r a n s m i s s i o n
c o e ffic ie n ts are
r = ( (1 - n ) ^ +X^) / C( 1
and
( 8)
Chapter 4
86
t = 1 - r = 4 p / ( ( 1 4- | l ) ^ + X ^ )
re sp e c tiv e ly .
F in a lly ,
(9 )
t h e power a b s o r p t i o n i s g i v e n by
P =
(1 0 )
w here
is
th e
r e a l p a r t o f t h e c o n d u c t i v i t y and
i s th e lo c a l
f i e l d a m p litu d e .
E q u a tio n s
of
Wp
(o r
(7) - (1 0 ) c a n now be e v a l u a t e d u s i n g t y p i c a l
e le c tro n
d e n s i t y ) and
9x10^ Hz ( 5 . 7 x 1 0 ^ ^ r a d s ” ^ ) ,
c o llis io n
fie ld
frequency
v
v a lu e s
w i t h a m icrow ave f r e q u e n c y
To e s t i m a t e t h e e x p e r i m e n t a l
range
t h e r a n g e o f E/N v a l u e s h a s t o be f o u n d .
a t t h e w a v e g u id e c e n t r e c a n
be
fo u n d
from
th e
of
of
The
fie ld -p o w er
r e l a t i o n f o r a w a v e g u id e (H a rv e y 1963) which i s
2
P = E^abd - fg /f)
1/2
/1510
w h e re
P
fie ld
a m p l i t u d e i n t h e TE^^ mode,
f^
is
T his
i s t h e t r a n s m i t t e d pow er,
th e
c u to ff
frequency,
by
pressure
th e
2 .1 1 .
in
th e
ap p a ra tu s
c o u p l e r t o p e r h a p s 0.7kVcm” ^ ,
w hich
Mean
e le c tro n
w ill
be
For th e ex p erim en tal
r a n g e 0 .0 1 - 2 . 0 atm t h e r a n g e o f E/N v a l u e s w i l l
2 .6 x 1 0 ^^ - 1 ,3 x 1 0 ^^Vom ^ .
v a lu e s
a and b a r e t h e g u i d e d i m e n s i o n s ,
and f i s t h e t r a n s m i s s i o n f r e q u e n c y .
g i v e s a b o u t 7kVcm*^ f o r E^
reduced
E^ i s t h e s p a t i a l maximum o f t h e
e n e rg ies
c a n be gau g ed from t h e e l e c t r o n d i s t r i b u t i o n s
at
g iv en
These r a n g e from a b o u t 2eV (He) t o a b o u t 12eV ( N e ) ,
th en
be
t h e s e E/N
in
F ig
C u rv e s o f
C hapter 4
S?
c o llisio n
frequency
M acD onald(1966)
c o llisio n
to ta l
and
a g a in st
e le c tro n
reproduced
in
energy
F ig
4 .1 ,
are
g iv en
T a k in g t h e r e q u i r e d
f r e q u e n c y f o r momentum t r a n s f e r t o be r e a s o n a b l y n e a r
c o l l i s i o n fre q u e n c y g iv e n i n P ig 4 .1 ,
t o t h e above e l e c t r o n e n e r g y r a n g e i s 7x10
by
th e
th e ran g e co rre sp o n d in g
11
13-1
-
1x10 ' s
T a k in g i n t e r v a l s o f v i n pow ers o f 1 0 , v a l u e s o f X> |1 * and 5 a r e
p lo tte d
a g a in st
e le c tro n
d e n sity
scale s.
The r e f l e c t i o n c o e f f i c i e n t r
F i g u r e 4 . 3 ( b ) shows a p l o t o f p.,
in
X»
F ig
is
4 .2
u sin g
p lo tte d
in
lo g a rith m ic
F ig
4 .3 (a ).
and r f o r t h e p a r t i c u l a r c a s e
V = 5.7x10^ ^ s “ ^ w hich i s t h e m icrow ave f r e q u e n c y i n r a d s*”^ .
of
th ese
d e n sity
graphs
a
dashed
lin e
On a l l
i s drawn t o i n d i c a t e t h e e l e c t r o n
a t w hich t h e p la s m a f r e q u e n c y
is
equal
to
th e
m icrow ave
freq u en cy .
In sp e c tio n
change
of
th e
graphs
and p r e c e d i n g e q u a t i o n s r e v e a l s t h e
i n t h e p r o p a g a t i o n c h a r a c t e r i s t i c s t h a t o c c u r when e i t h e r t h e
c o llisio n
freq u en cy
or
th e
p la s m a
freq u en cy
passes
th ro u g h th e
m icrow ave f r e q u e n c y .
I n p a r t i c u l a r i t c a n be s e e n t h a t f o r any g i v e n
c o llisio n
above t h e m icrow ave f r e q u e n c y ,
d e n sity
freq u en cy
in cre ase s
tra n sp a re n t
d e p th .
co n sid e red
be
gas
b ein g
p la s m a
opaque
changes
w ith
These c h a n g e s a r e more a b r u p t
freq u en cy
causes
to
th e
h ig h
at
from
as th e e l e c t r o n
b e in g
r e f l e c t i o n and s m a l l s k i n
or
below
which i s e q u a l t o t h e m icrow ave f r e q u e n c y .
th e
c o llisio n
I f th e case i s
w here a s t r o n g m icrow ave f i e l d i s i n c i d e n t on a
t h e g a s t o breakdow n,
th a t
th e
rem a in in g
gas
and
i t c a n be s e e n t h a t t h e d i s c h a r g e w i l l
l o c a l i s e d i n a s h a l l o w s k i n d e p th w here t h e m ic ro w a v es
and
re la tiv e ly
volume w i l l be s h i e l d e d .
m eet
th e
Even i f t h e
25“
20
“
15-
I
u
Qj
to
a\
I
O
CL
7>
ELECTRON
Figure 4.1
ENERGY ( e V )
Ratio of electron collision
elect ron energy m rare
pressure
vs
lnqhuisen_1_9l6.l
-1-
- - refractive index {jj )
r
—
Wp =W
attenuation index ( x )
collision frequency v~s
skin-depth
5 -cm
to
Figure 4.2 Refractive index () j ), attenuation index (% ), and skin-depth ( 5 )
vs electron density IOe-cnr^ ).Microwave frequency 96Hz.
0
"
Figure A»..3 (a) Reflection coefficient vs electron density
-I"
Figure 4.3 (b)
jj,x,5,àn d r
vs
Pe . ‘V= (J-5.7xlO'*^
Chapter 4
88
a b so rp tio n
th e
was l i n e a r t h e r e w ould s t i l l be an e x p o n e n t i a l
e le c tro n
in te re stin g
w ill
d e n s i t y i n t h e m icrow ave p r o p a g a t i o n d i r e c t i o n .
t o n o t e t h a t i n t h e above c o n t e x t t h e
a u to m a tic a lly
reg io n ,
be
near
th e
th is
fre q u e n c ie s
g iv es
n^
as
( V>W) t h e e l e c t r o n
e le c tro n
c r i t i c a l v a lu e ,
f o r low c o l l i s i o n f r e q u e n c i e s (v<CO),
freq u en cy
d e cay
d e n sity
F o r t h e X-band
w ill
r e f l e c t i o n c o e f f i c i e n t ap p ro ach es u n i ty .
I t is
in th e d isch arg e
a ro u n d 4x10^^cm ^ ,
d e n sity
in
radar
At h i g h c o l l i s i o n
sta b ilise
w h e re
th e
T h is o c c u r s when
u)p - vw
a s ca n be s e e n
from e q u a t i o n s ( 5 ) and ( 6 ) .
F o r an e l e c t r o n
10eV
and a g a s p r e s s u r e o f 1 atm t h e c o l l i s i o n f r e q u e n c y
2x10
8
for
d e n sity
v a lu e
He
and
w ill
Ne
and a b o u t 1x10 “ s
th e re fo re
i n A r.
energy o f
is
about
The e l e c t r o n
be a p p r o x i m a t e l y 1,5x10^^cm ~^ i n He and
Ne and TxlO^^om*^ i n Ar.
The
p re c e d in g
d iffic u lty
su ita b le
parag rap h s
c le a rly
d e m o n s t r a t e t h e f u n d a m e n ta l
o f u s i n g m ic ro w a v es t o g e n e r a t e a l o n g u n i f o r m
fo r
d iffic u ltie s
la se r
e x c ita tio n .
in p ra c tic a l
c o u p lin g
The
m an ifestatio n
stru c tu re s
are
f o l l o w e d by some s p e c i f i c d e t a i l s o f c o u p l e r d e s i g n .
now
d isc h a rg e
of
th ese
d iscu ssed
C hapter 4
4 .2
89
Microwave P i s c h a r g e C o u p l e r s
4 ,2 .1
The C o u p lin g P roblem
The
m icrow ave
u niform
c o u p lin g o f
th is
d ischarge
th e
th e
co u p le r
m icrow ave
d isch arg e
h a s t o p r o v i d e e f f i c i e n t and
power
a d d itio n
to
se p a ra te
problem i s d i s c u s s e d f i r s t .
to
th e
d isch arg e.
In
m ust be i n i t i a t e d and t h i s r a t h e r
The p roblem e x i s t s b e c a u s e
of
t h e d i f f e r e n c e b e tw e e n t h e e l e c t r i c f i e l d r e q u i r e d t o c a u s e breakdow n
and t h a t r e q u i r e d t o m a i n t a i n i t ,
reason
10™^
for
th e
The
th e d i f f e r e n c e i s t h a t a t h ig h e l e c t r o n d e n s i t i e s (above
tim es th e c r i t i c a l
d iffu sio n
th e l a t t e r b e in g th e s m a lle r .
d e n sity
(see
MacDonald
1 9 6 6 ))
a m b ip o lar
d o m in a te s and r e d u c e s t h e e l e c t r o n d i f f u s i o n and t h e r e f o r e
e le c tro n lo ss r a te .
In th e absence o f s u f f i c i e n t seed e le c tr o n s
t h e breakdow n f i e l d w i l l become v e r y h i g h ,
t h e r e w i l l be s t a t i s t i c a l
d e l a y s i n t h e o c c u r r e n c e o f b reakdow n, s p a t i a l , u n i f o r m i t y may d e v e l o p
s lo w ly ,
and
th e
g r o w th
of
e l e c t r o n d e n s i t y w i l l be s lo w .
These
p ro b le m s w i l l be p a r t i c u l a r l y i m p o r t a n t w here s h o r t r e p e t i t i v e p u l s e s
a re used,
in
as i n th e case under c o n s id e r a tio n h e re .
I t was e x p l a i n e d
S e c tio n 4 .1 .2 t h a t th e u ltim a te u n ifo rm ity of a p ulsed
d isch arg e
However
is
e s t a b l i s h i n g and n o t d e p e n d e n t on p r e i o n i s a t i o n .
e v e n i f f i e l d s w e l l above t h e m a in te n a n c e f i e l d s
p re io n isa tio n
v a ria tio n s
im provem ent
w asted
se lf
w ill
s till
are
used,
be o f v a l u e i n rem o v in g s t a t i s t i c a l p u l s e
and l o w e r i n g t h e d i s c h a r g e f o r m a t i o n
s h o u ld
m icrow ave
tim e.
The
la tte r
i n c r e a s e t h e e f f i c i e n c y s i n c e t h e r e w i l l be l e s s
energy i n th e e a r l y p a r t o f th e p u ls e .
S y ste m a tic s t u d i e s of
Chapter 4
90
t h e u s e o f p r e i o n i s a t i o n i n a h i g h power m icrow ave d i s c h a r g e h a v e n o t
been
c a rrie d out
g rea ter
M endelsohn
e t.
a l.
(1981)
s t a b i l i t y and r e p r o d u c i b l i t y w i t h i t s u s e .
th erefo re,
t o be c o n c l u s i v e
p re io n isa tio n
re p e titiv e
th e
a lth o u g h
req u ired .
about
th e
lev el
I t is d iffic u lt,
and
u n ifo rm ity
of
In a d d it io n i t i s n o ted t h a t f o r th e r a p id
p u l s e s o f t h e e x p e r i m e n t a l work t h e i o n i s a t i o n
in te r-p u lse
rep o rted
p e r i o d may be s i g n i f i c a n t .
su rv iv in g
T herefore p r e io n is a tio n
may be much more e f f e c t i v e f o r t h e f i r s t p u l s e t h a n f o r t h e f o l l o w i n g
p u lses.
P r a c t i c a l s u g g e s t i o n s f o r p r e i o n i s a t i o n m ethods a r e g i v e n i n
th e next s e c tio n .
The
d i f f i c u l t i e s o f u s i n g a m icrow ave s y s te m t o e x c i t e a
lase r
d i s c h a r g e stem from t h e n o n - l i n e a r a b s o r p t i o n e f f e c t s d e s c r i b e d above
and t h e f a c t t h a t t h e m icrow ave r a d i a t i o n i s d e l i v e r e d by a w a v e g u id e
of
sm all
dim ensions(23rara x 10mm, X -band)
w h ile
th e
a c tiv e
la se r
volume n e e d s t o be long(>200mm) The f i r s t o b s e r v a t i o n t o make i s t h a t
th e
w aveguide
a p e rtu re
a
in e ffe c t,
f i l l e d by t h e p la s m a .
sh o rt,
m icrow ave
m u s t,
high
d e n sity ,
w ith
h ig h
T herefore
1 " 5mm
can
are
req u ired
p ra c tic a l
volume
re fle c tio n .
p a r t i c u l a r l y in co n v e n ien t s in c e ,
volum es
T his i s to p r e v e n t th e o c c u rre n c e o f
one s k i n d e p th p la s m a ,
s o u r c e end o f t h e g a s
sh o rt-circu it
h ave o n l y a s m a l l f r a c t i o n o f i t s
and
Such
lo c a lis e d a t th e
c re a tin g
a
a
w a v e g u id e
req u irem en t
a s h a s b e e n shown,
is not
sm all d isc h a rg e
i n o r d e r t o o b t a i n h i g h pump power d e n s i t i e s .
d isc h a rg e
tu b e
d im e n s io n s
w ill
p robably
be
i n d i a m e t e r and 200 - 400mm i n l e n g t h and t h e d i s c h a r g e tu b e
be c o n v e n i e n t l y p l a c e d w i t h i n t h e w a v eguide o r i n some
w a v e g u id e s t r u c t u r e .
k in d
of
C l e a r l y t h e n t h e s k i n d e p t h d o e s n o t h ave t o be
g r e a t e r t h a n t h e t u b e l e n g t h b u t m ust be r a t h e r g r e a t e r t h a n t h e t u b e
Chapter 4
91
d ia m e te r to e n su re t r a n s v e r s e u n ifo r m ity .
I t w i l l be u s e f u l t o r e f e r
to a lo n g itu d in a l s k in d e p th , i n th e fo llo w in g , as th e c h a r a c t e r i s t i c
a b so rp tio n
re la te d
of
len g th
th e
d ischarge
tu b e.
T h is l e n g t h w i l l be
t o t h e o r d i n a r y s k i n d e p th by a f u n c t i o n i n v o l v i n g t h e r a t i o
th e
d ischarge
c ro ss-se c tio n a l
w hich
a lo n g
area.
c ro ss-se c tio n a l
area
A f u r th e r ex p la n a tio n
to
is
th e
g iv en
w a v egu ide
in
F i g 4 .4
p ro v id e s a d ia g ra m a tic r e p r e s e n t a t i o n o f th e lo n g it u d in a l s k in
d e p th .
In
t e r m s o f m icrow ave e n g i n e e r i n g t h e d i s c h a r g e h a s t o a c t a s a
m atched
lo ad .
That
is
it
m u st
beh a v e
as a l o s s y d i e l e c t r i c o f
su fficie n t
e x t e n t t o g i v e t o t a l a b s o r p t i o n and i t
a lte r
w a v e g u id e
th e
Such
im p e d a n c e ,
th e
m a t c h in g ,
g u id e
w a v e g u id e
in te rio r.
not
unduly
o th erw ise r e f l e c t i o n s w i l l o ccu r.
a l o a d would c o n s i s t o f a w a l l
acro ss
m ust
of
In
re sistiv e
order
to
m aterial
o b tain
p laced
im pedance
t h e w a l l m ust be i n c l i n e d t o l i e a t a s m a l l a n g l e t o
a x is.
A
d isch arg e
tu b e
w ith in
th e
t h e g u i d e would h a v e t o be
i n c l i n e d t o t h e a x i s f o r t h e same r e a s o n .
C o n sid er
p erp en d icu lar
th rough
now
to
a
th e
w a v e g u id e
te rm in a te d
by
a
p lan e
end
w a ll
a x i s w i t h a d i s c h a r g e tu b e e n t e r i n g t h e g u i d e
a h o l e i n t h e end w a l l c e n t r e and l e a v i n g t h e g u i d e
th rough
th e
s i d e w a l l some d i s t a n c e away a lo n g t h e g u i d e .
th e
a b s e n c e o f a d i s c h a r g e and w i t h o u t r e f l e c t i o n from t h e end w a l l )
alo n g
at
th e
t u b e a x i s w i l l v a r y a s a q u a r t e r s in e - w a v e w i t h a maximum
t h e end w a l l and a minimum a t t h e s h o r t w a l l .
p ro je c tio n
mode.
The RMS f i e l d ( i n
T h i s i s s im p l y t h e
o f t h e t r a n s v e r s e f i e l d p r o f i l e i n t h e g u i d e f o r t h e TE^^
I n t h i s c o n f i g u r a t i o n t h e d e c r e a s e i n power a lo n g t h e
g u id e,
microwave
propagaMon
Skin depth ( 6 ) in a plasma fil le d waveguide , c ro s s -s e ction A
Skin depth (D) in a plasma filled t u b e , cross-section a
D = f (5,a/A)
Figure 4.4 Longitudinal skin depth (D) in a par tia lly filled waveguide
Chapter 4
92
due t o a b s o r p t i o n by t h e d i s c h a r g e ,
may be c om pensated by t h e e f f e c t
of
t h e i n c l i n a t i o n o f t h e tu b e to w a rd s a p o s i t i o n o f
In
a
p ra c tic a l
c o n v e n ie n tly
th e
w av e s.
pressure
so
th a t
prevent
u n a b s o rb e d
th e
energy
occurrence
of
may p a s s t o a
re fle c tio n
and
T h e re w i l l m ost c e r t a i n l y be a r e g i o n o f r e l a t i v e l y
( < 0 ,5 atm)
u n ifo rm ity ,
h ig h er
t h e d i s c h a r g e tu b e e n t r y p o i n t s may be more
work)
l o a d and t h u s
sta n d in g
fie ld .
p l a c e d a t w aveguide bends ( a s i n t h e d e v i c e use d d u r i n g
ex p erim en tal
m atched
low
d ev ic e
h ig h er
p erhaps
p ressures,
w here
at
th e
how ever,
th is
arrangem ent
e x p e n se
i t can be
w ill
g iv e
good
of e f f i c i e n t a b so rp tio n .
ex p ected
th a t
d e c ay
At
to
a
l o c a l i s e d h i g h d e n s i t y p lasm a w i l l s t i l l o c c u r .
It
would
gu id e*
may
be
d e sira b le
t o f i n d a n a l t e r n a t i v e t o t h e *tube i n
c o u p l i n g s t r u c t u r e so t h a t u n ifo rm h i g h
be
power
o b tain ed .
range
at
a l l p o in ts,
th e
d isc re te
d isch arg e
fie ld
in
th e
a c tiv e
d isc h a rg e
and would g i v e e f f i c i e n t c o u p l i n g ,
p f plasm a c o n d i t i o n s .
p lac in g
d isch arg es
An i d e a l s t r u c t u r e would d i s t r i b u t e t h e microwave
i n su c h a way t h a t t h e
c o n sta n t
pressure
One a p p ro a c h t o such a s y s te m ,
tu b e
e le m e n t s g r a d e d s o
over a
th a t of
i n an a u x i l i a r y g u i d e and c o u p l i n g v i a
as
to
g iv e
c o n sta n t
power
co u p lin g
t h r o u g h e a ch e le m e n t , i s d e s c r i b e d i n d e t a i l i n t h e n e x t s e c t i o n .
th e
r e m a in i n g p o s s i b i l i t i e s ,
m ost
p r o m i s in g .
resonant
stru c tu re ,
lite ra tu re .
in d ic a tio n s
su ite d
The
to
T h is
o th er
a
method
slow -w ave s t r u c t u r e s a r e
m a jo r
method
d e n sitie s
perh ap s
Of
th e
c o u p l i n g m ethod i s t o u t i l i s e a
fre q u e n tly
en co u n tered
in
th e
i s g i v e n no f u r t h e r a t t e n t i o n h e r e a s t h e
in th e l i t e r a t u r e suggest th a t these
low
was
and
sh o rt
s e n s itiv e to d isch arg e c o n d itio n s .
d e v ic e s
tu b e l e n g t h s ,
are
best
and a r e r a t h e r
C hapter 4
93
T h e re
in te re st
a r e two k i n d s o f
for
h e lic a l
th e p re s e n t a p p lic a tio n ;
s t r u c t u r e t h a t i s used i n
Open slow™wave s t r u c t u r e s ,
by
slow™wave
a
d isc h a rg e
stro n g
frin g e
th a t
may
be
of
open p e r i o d i c a r r a y s and t h e
tra v e llin g ^ w av e -tu b e
a m p lifie rs.
such as th e l i n e a r s tr a p p e d b a r d e s c r ib e d
B o s i s i o ( 1 9 ? 2 ) and t h e m eander
p ro v id e
stru c tu re
fie ld
lin e
used
a d ja c e n t
by
to
G o l d s b o r o u g h ( 1965)
th e
s tru c tu re .
The
tu b e c a n be p l a c e d i n t h i s f i e l d w i t h s u i t a b l e i n c l i n a t i o n
t o im prove u n i f o r m i t y ,
B o s i s i o ( 1972) u s e d two s t r u c t u r e s i n p a r a ] . l e i
but
w i t h opposed p r o p a g a t i o n d i r e c t i o n s t o g i v e im p ro v e d u n i f o r m i t y .
The
t r a v e llin g ™ w a v 6“ tu b e
w ith in
h e l i x c o n s i s t s o f a h e l i c a l w ire suspended
a co n d u c tin g tu b e .
d ischarge
tube
to
be
The
d e v ic e
is
o p e n -e n d e d
p lac e d a x i a l l y w ith in i t .
a llo w in g
a
U n fo rtu n a tely th e
r a d i a l f i e l d v a r i a t i o n i s q u i t e c o m p l i c a t e d and i n c l i n i n g t h e t u b e t o
th e
h e lix
u n ifo rm
d isch arg e.
stru c tu re s
g ra d u a lly
T h is
w ould
An i n t e r e s t i n g p o s s i b i l i t y w i t h t h e s e
be
to
slow -w ave
v a r y a s u i t a b l e d i m e n s io n o f t h e s t r u c t u r e
a lo n g i t s l e n g t h i n o r d e r t o
giv e
a
u n ifo rm
d isc h a rg e.
c o u ld be a c h i e v e d m o st r e a d i l y i n t h e h e l i x s y s te m by a g r a d u a l
red u c tio n
co n c ern in g
'open*
a x i s may n o t be a p a r t i c u l a r l y s u c c e s s f u l way t o o b t a i n a
in th e h e lix
p itc h
or
d iam e te r.
A
fin a l
o b se rv a tio n
t h e s e two t y p e s o f slow -w ave s t r u c t u r e s i s t h a t w h i l e t h e
s y s te m may r e q u i r e s h i e l d i n g i n h i g h
power
w o rk,
it
does
p r o v i d e a n e x c e l l e n t s y s te m f o r e x p e r i m e n t a l work w i t h e a s e o f a c c e s s
and a n unimpeded v iew o f t h e d i s c h a r g e .
C hapter 4
4 .2 .2
94
Microwave D i s c h a r g e C o u p le r D e s ig n
In
w hich
t h i s s e c t i o n th e d e sig n d e t a i l s a re d e riv e d f o r a c o u p le r in
th e
d i s c h a r g e tu b e i s p l a c e d i n a n a u x i l i a r y g u i d e c o u p le d by
a p e r t u r e s t o t h e p r im a r y g u i d e ,
( I t i s p o in te d o u t t h a t t h i s c o u p le r
was d e s i g n e d and c o n s t r u c t e d to w a r d s t h e end o f t h e e x p e r i m e n t a l work
and
was u s e d f o r a s m a l l number o f t h e e x p e r i m e n t s o n l y . ) The
b a sic
c o n c e p t b e h in d t h i s d e s i g n i s t h a t t h e f r a c t i o n o f t h e m ain w a v e g u id e
power
c o u p le d by e a c h s u c c e s s i v e a p e r t u r e c a n be made t o i n c r e a s e s o
th at
equal
w ill
be e x c i t e d by e q u a l i n t e n s i t i e s a t a s e r i e s o f p o i n t s a lo n g i t s
len g th .
pow ers
If
a r e c o u p le d by e a c h e le m e n t .
th ese p o in ts a re c lo s e ,
Thus t h e d i s c h a r g e
compared w i t h t h e l o n g i t u d i n a l
s k i n d e p t h , a h i g h d e g r e e o f u n i f o r m i t y may be a c h i e v e d .
e x p r e s s e d i n a d i f f e r e n t way.
I f t h e d i s c h a r g e t u b e i s s im p l y p l a c e d
a x i a l l y i n t h e m ain w a v e g u id e ,
lo n g itu d in a l
h o w e v e r,
sectio n s
s k i n d e p t h s somewhat g r e a t e r t h a n t h e t u b e l e n g t h .
lo n g itu d in a l
sp acin g
of th ese s e c tio n s .
because
th e
c o n d itio n
u n i f o r m i t y can o n l y be a p p ro a c h e d f o r
t h e power i s d i v i d e d and t h e t u b e e x c i t e d
th e
T h is c a n be
power
is
in
many
If,
sh o rt
s k i n d e p th need o n l y be g r e a t e r t h a n t h e
A n o th e r a s p e c t o f t h i s
d iv id e d
w here a l l t h e power
th e
d isch arg e
in te ra c ts
w ith
d e sig n
is
th a t
c a n n o t d e cay t o t h e
a
v ery
sm all
d e n sity
p la s m a .
se ctio n
w i l l be t h o s e o f h i g h e r power a n d / o r p r e s s u r e com pared
hig h
The c o n d i t i o n s w h e re t h i s d e c a y d o e s o c c u r i n e a ch
t h e s im p l e t u b e - i n - g u i d e s t r u c t u r e .
w ith
Chapter 4
A
sc h em a tic
4 .5 (a )
be
95
of
th e
co u p lin g
d e v i c e i s shown i n F i g
and t h e t h r e e ways i n w h ic h t h e m ain and a u x i l i a r y g u i d e s may
jo in e d
c o u p lin g
takes
d ia g ra m
is
shown
in
F ig
4 .5 (b ).
I t ca n be shown t h a t w h e re a
e le m e n t b e tw e e n g u i d e s i s p e r f e c t l y m atched (no
p lace)
d ire c tio n a l
(H a rv e y
req u ired ,
co u p le r.
th e
ra d ia tio n
1963).
in to
th e
a u x ilia ry
T herefore,
sin c e
re fle c tio n
g u id e
good
m a tc h in g
is
t h e c o u p l i n g d e v i c e i s s im p ly a m u l t i - e l e m e n t d i r e c t i o n a l
Many d e s i g n s e x i s t f o r s u c h d i r e c t i o n a l c o u p l e r s b u t
equal
siz e d
h ere.
C o u p lin g e l e m e n t s a r e u s u a l l y ro u n d h o l e s o r s l o t s ,
h a v in g
i s p u rely
w ith
e lem en ts r a t h e r th a n th e grad ed s iz e d e le m e n ts req u ired ,
broader
frequency
c h a ra c te ristic s.
S lo ts
w e re
th e l a t t e r
th erefo re
c h o s e n f o r t h e c o u p l i n g e l e m e n t s b e c a u s e t h e y w ould be l e s s s e n s i t i v e
to
d im e n sio n a l
was
irre g u la ritie s.
t h a t o f F ig 4 . 5 ( b ) ( i i i ) .
rev erse
d ire c tio n a l
a v a ila b le
The w aveguide c o n f i g u r a t i o n c h o s e n
T his i s
th e
form
of
th e
S o h w in g e r
c o u p l e r f o r w hich d e s i g n i n f o r m a t i o n i s r e a d i l y
( ’ The M icrowave
E n g in e e r s *
Handbook’
1962).
A
u sefu l
f e a t u r e o f t h i s d e s i g n i s t h a t t h e a u x i l i a r y g u i d e may be c o n s t r u c t e d
i n two h a l v e s a l l o w i n g s i m p l e d i s a s s e m b l y and a c c e s s t o t h e d i s c h a r g e
tu b e.
T h is
c u rre n ts
and
p o ssib ility
a rise s
because
i n t h e TE^^ mode t h e w a l l
i n t h e b ro a d w a l l do n o t c r o s s t h e l o n g i t u d i n a l c e n t r e l i n e
r a d i a t i o n w i l l n o t o c c u r a t a j o i n t a lo n g t h i s l i n e .
S in ce t h i s
j o i n t i s a d j a c e n t t o t h e d i s c h a r g e t u b e , a s shown i n F i g 4 . 5 ( b ) ( i i i ) ,
sm all
spacers
in
th e
jo in t
w i l l a l l o w t h e a c t i v e d i s c h a r g e t o be
o b serv ed w ith o n ly s l i g h t r a d i a t i o n le a k a g e .
discharge
tube
auxiliary guide
input power
main guide
coupling element
Figure 4 .5 ( a) Coupler
schematic.
auxiliary guide
discharge
tube
joint
coupling
element"
main guide
(i)
(in
(iii)
Figure 4 . 5 ( b ) Waveguide configurations
Schwinger coupler
C hapter 4
In
spaced
96
m u l t i - e l e m e n t d i r e c t i o n a l c o u p l e r s t h e e l e m e n t s h av e
by
an
d ire c tio n a l
to
be
odd number o f q u a r t e r - w a v e l e n g t h s f o r t h e a r r a y t o be
and w e l l m a tc h e d .
The e le m e n t s i n t h e S c h w in g e r c o u p l e r
a r e l o n g i t u d i n a l s l o t p a i r s and t h e c o u p l i n g f a c t o r i s r e l a t e d t o t h e
len g th
by d e s i g n c u r v e s g i v e n i n *The Microwave E n g i n e e r s ’ H andbook’
( 1962)
and
reproduced
in
F ig
4.6
which
a lso
c o n ta in s
a l l th e
r e m a in i n g d e s i g n d e t a i l s ,
A
fo r
f o r m u la i s now d e r i v e d w h ic h w i l l e n a b l e t h e c o u p l i n g
each
e le m e n t
t o be c a l c u l a t e d .
facto r
The f o l l o w i n g l i s t d e f i n e s t h e
q u a n t i t i e s and sy m b o ls t o be u s e d ;
F - c o u p l i n g f a c t o r - c o u p le d p o w e r /u n c o u p le d power
“ i n p u t pow er, r e s i d u a l pow er, r e s p e c t i v e l y (m a in g u i d e )
p - power c o u p le d by e a c h e le m e n t
r , n , T “ s u b s c r i p t s d e n o t i n g r - t h and n - t h e le m e n t s and t o t a l
The h i g h e s t c o u p l i n g f a c t o r ,
th e
lo n g est
T herefore
w ill
be
slo t
th at
t h a t o f t h e l a s t e l e m e n t , i s l i m i t e d by
c a n be accommodated and c a n n o t be i n f i n i t e .
t h e r e i s a l i m i t t o t h e t o t a l c o u p le d
power
sin c e
an u n a v o i d a b l e r e s i d u a l power i n t h e m ain g u i d e .
above d e f i n i t i o n s we c a n w r i t e
Fn = P/F%
F t = np/Pj^
and
th ere
U sing t h e
SCHWINGER REVERSED DIRECTIONAL COUPLER
ASPECT RATIO 2 : 1
•ia .
-i-i 1-
ix tr
J-J.
. 44.
50
-UU
—
--t-t-
45
!•->•
:VtT
40
r
U -4 .
.l _ j .1
"U
-I'T
L-U
'0
t-r
0
Z
5
D
:iir
8
4i-ti
o.ns
i_u
a -l.
TERMINATED
0.040
H-H
END
30
tow
4--»
H IG H
:l D .
COUPLED
SAMPLE
20
M A IN
G U ID E
0
0.1
Figure 4.6
0,2
0.3
0.4
0,5
Coupler design data (from The Mkrov/ave Engineer;
Handbook 1962)
C hapter 4
w hich g i v e t h e r e l a t i o n
= nF^
(1)
The c o u p l i n g f a c t o r o f t h e r ~ t h e le m e n t i s g i v e n by
F^ = P/CP^ “ r p )
U sin g
P j = np - Pj,
and t h e f i r s t e q u a t i o n above g i v e s
F^ = F/(F^(n - r) - 1)
.
(2)
E q u a tio n s
(1 ) and (2 ) g i v e t h e b a s i s o f t h e d e s i g n p r o c e d u r e .
is,
to ta l
th e
c o u p lin g
fac to r
ap p ro p riate
The
to
(2 ).
m u lti-e le m en t
u n ifo rm ity
to ta l
The
th a t
of
th e
are
le n g th .
f a c t o r c a n be s e t by c o n s i d e r a t i o n o f t h e
la st
e le m en t,
th e
th e d is c h a r g e tu b e l e n g th ,
c o u p lin g f a c t o r s o f
e q u a tio n
to
co u p lin g
T hese
th e
rem ain in g
e q u a tio n s
d ir e c tio n a l c o u p le r.
th a t
th e
That
ca n
number
e lem en ts
and t h e e le m e n t s p a c i n g .
e lem en ts
be
of
a p p lie d
The a p p r o x i m a t e
are
to
fo u n d
any
u sin g
k in d o f
c o n d itio n s
fo r
e le m e n t s p a c i n g be somewhat l e s s t h a n t h e
The u n a b s o r b e d power i n b o th g u i d e s s h o u l d be c a r r i e d
m atched l o a d s t o p r e v e n t r e f l e c t i o n and s t a n d i n g w aves o c c u r r i n g .
p h y s i c a l d i m e n s io n s o f t h e S c h w in g e r r e v e r s e d i r e c t i o n a l c o u p l e r
was
c o n stru c te d
d u rin g
ex p erim en tal
c o n s tru c tio n a l d e t a i l s in S e c tio n 5 .3 .
work a r e g i v e n w i t h i t s
Chapter 4
4 .2 ,3
98
P r e i o n i s a t i o n Methods
It
th e
has been p o in te d o u t i n s e c t i o n 4 .2 .1
h ig h
p ressure
m icrow ave
d isch arg es
of
th a t p re io n isa tio n
in te re st
in
may l e a d t o
g rea ter
p u l s e t o p u l s e u n i f o r m i t y and im prove t h e s p a t i a l u n i f o r m i t y
of
d isc h a rg e.
th e
may
I n a d d i t i o n t o t h i s t h e d i s c h a r g e f o r m a t i o n tim e
be r e d u c e d l e a d i n g t o im proved e f f i c i e n c y .
lev e l
and
S in ce
u n ifo rm ity of p r e io n is a tio n a re u n lik e ly
s im p l e m ethods n eed o n l y be c o n s i d e r e d .
th e
d e ta ile d
t o be c r i t i c a l ,
Methods r e q u i r i n g e l e c t r o d e s
i n t h e d i s c h a r g e volume o r u t i l i s i n g s e p a r a t e d i s c h a r g e c i r c u i t r y a r e
th erefo re
not d isc u sse d .
m icrow ave
Thus
an
a u x ilia ry
d riv e n
by t h e
method
a lth o u g h th e use o f a r a d i o - a c t i v e
low
power
d isc h a rg e
p u l s e i s l i k e l y t o p r o v i d e t h e m ost u s e f u l
so urce
may
a lso
be
of
source
has c e r ta in c le a r
so urce
s tre n g th
in te re st.
The
u tilisa tio n
of
a
ra d io -a c tiv e
a ttra c tio n s.
In p a r tic u la r ,
sin c e
ac c u ra te ly
m ea su red and i t s
irra d ia n c e
c a re fu lly
c o n t r o l l e d , i t c o u ld
in v e stig a tio n s.
p re io n isa tio n
In
a d d itio n
be
to
th e
very
th is
of
th e
u sefu l
th e
can
d ischarge
in
p ro b le m
be
tube
ex p erim en tal
of tim in g th e
r e l a t i v e t o t h e m icrow ave p u l s e i s c o m p l e t e l y
ab sen t.
C l e a r l y t h e s e a t t r a c t i o n s h a v e t o be w eighed a g a i n s t t h e h a n d l i n g and
management
p ro b le m s
of
u sin g
ra d io -a c tiv e
so u rces.
The
m a jo r
p r a c t i c a l p ro b le m s a r e t h e d i f f i c u l t y o f p r e v e n t i n g t h e o c c u r r e n c e o f
a d i s c h a r g e w i t h i n t h e w a v e g u id e , e x t e r n a l t o t h e d i s c h a r g e t u b e , and
of
p lac in g
tra n sm issio n .
t h e s o u r c e s o t h a t i t d o e s n o t p e r t u r b t h e t h e m icrow ave
C hapter 4
99
An a u x i l i a r y d i s c h a r g e o b t a i n e d i n a q u a r t z t u b e a d j a c e n t t o t h e
m ain
tu b e can be s im p l y p r o v i d e d .
little
T h is d i s c h a r g e w i l l have t o c a u s e
p e r t u r b a t i o n i n t h e g u i d e and a b s o r b a s m a l l amount o f
so t h a t o v e r a l l e f f i c i e n c y i s n o t u n d u ly r e d u c e d .
p ro d u ctio n
q u artz
e f f i c i e n c y w i l l n eed t o be h i g h .
tube
co n ta in in g
x e non
c o n s i d e r a b l e UV r a d i a t i o n .
th e
m ost
fa v o u ra b le
e x p erim en tally .
and
p lac e d
ra d ia tio n
w ill
is
at
at
A
low
power
I n a d d i t i o n t h e UV
sm all
bore
(< 1mm)
pressure
w ill
p ro v id e
The b e s t p r e s s u r e f o r r a p i d breakdow n and
lo c a tio n
fo r
th e
tube
may
be
found
I f t h e tu b e i s s h o r t e r t h a n t h e m ain d i s c h a r g e tu b e
th e
end
o p p o site
to
th a t
i s in c id e n t i t i s p o ssib le th a t
a t which t h e m icrow ave
th e
a u x ilia ry
d isch arg e
e x t i n g u i s h a s t h e m ain d i s c h a r g e becomes f u l l y d e v e l o p e d .
t h e a b s o r p t i o n o f t h e m icrow ave power by t h e m ain
That
d ischarge
may
r e s u l t i n a f i e l d i n t h e v i c i n i t y o f t h e a u x i l i a r y t u b e t h a t i s below
its
m a in te n a n c e t h r e s h o l d .
a b so rp tio n
Under t h e s e c i r c u m s t a n c e s a h i g h e r power
by t h e a u x i l i a r y d i s c h a r g e may be p e r m i t t e d s i n c e i t w i l l
be a c t i v e o n l y b r i e f l y .
The
n o t i o n o f a p r im in g d i s c h a r g e t h a t becomes s c r e e n e d by
th e
m ain d i s c h a r g e l e a d s t o a p r e i o n i s e r d e s i g n o f g r e a t s i m p l i c i t y w here
th e
a u x ilia r y d isc h a rg e tak e s p lace a c ro s s th e
The
fo rm a tio n
se rie s
form
w a v e g u id e
in te rio r.
o f t h i s d i s c h a r g e i s s t i m u l a t e d by p l a c i n g a s p i k e o r
of sp ik e s,
i n s i d e t h e w a v e g u id e ,
t h a t cause a d isc h a rg e
to
b e tw e e n a w a v e g u id e b r o a d w a l l and t h e s p i k e s and p a s s o v e r t h e
su rface
of th e d isc h a rg e tu b e.
lo cated
w e ll
away
from
T h is
d isch arg e
w ould
have
to
be
t h e m icrow ave i n p u t end s o t h a t s u b s e q u e n t
e x t i n c t i o n w ould be e n s u r e d .
T h i s m ethod and t h e m ethod u t i l i s i n g a n
Chapter 4
100
a u x ilia ry
d i s c h a r g e t u b e w e re u s e d i n t h e e x p e r i m e n t a l work a l t h o u g h
s y s t e m a t i c e v a l u a t i o n s w e re n o t c a r r i e d o u t .
D e ta ils o f th e p h y sic a l
c o n s tru c tio n of th e p r e io n is e r s appear in S e c tio n 5 ,3 ,
4 ,3
C om parison o f M icrowave and DC D i s c h a r g e A p p a r a tu s
As a c o n c l u s i o n t o t h e p r e s e n t c h a p t e r t h e d i f f e r e n c e s b e tw e e n a
m icrow ave d i s c h a r g e a p p a r a t u s and a DC d i s c h a r g e a p p a r a t u s ,
for
pumping
a p p a ra tu s
e x c im e r
la se rs,
a re h ig h lig h te d .
w i l l be d i v i d e d i n t o f i v e s e c t i o n s .
s u p p l y and p u l s e f o rm in g c i r c u i t ,
d isc h a rg e
c o n ta in er,
su ita b le
F o r c o n v e n ie n c e t h e
These a r e
th e
power
t h e p u l s e t r a n s m i s s i o n s y s te m , t h e
t h e o p t i c a l c om ponents,
and t h e g a s
h a n d lin g
s y s te m .
T h e re
i s no p a r t i c u l a r d i s t i n c t i o n t o be made b e tw e e n t h e power
s u p p l i e s f o r t h e two s y s t e m s .
p u lse
th e
However,
i t has been p o in te d o u t t h a t
r i s e t im e s h a v e t o be v e r y s h o r t (< 10ns) i n DC s y s te m s w h e r e a s
absence o f
d isch arg e
T h is
th e
means
tendency
to
rise
t im e s
th at
form
fila m e n ts
in
a
o f aro u n d 5 0 n s w i l l be a d e q u a t e .
d i f f e r e n c e i s c r i t i c a l s i n c e t h e s w i t c h i n g tim e o f
d is c h a rg e ' sw itc h e s
is
lim ite d
m icrow ave
to
a ro u n d
15ns.
s im p le
gas
T herefore
fo r
e f f i c i e n t DC s y s te m s r a i l - g a p s w i t c h e s o r h y d r o g e n t h y r a t r o n s h a v e t o
be
has
used
for
The im pedance o f t h e p u l s e f o rm in g n e tw o rk
t o m atch t h a t o f t h e d i s c h a r g e i n DC s y s te m s o r t h e m a g n e tro n i n
m icrow ave
larg e r
th is
sw itc h in g .
s y s te m s ,
th e
th an th e form er.
im pedance
ad d s
la tte r
b e in g
a b o u t a n o r d e r o f m a g n itu d e
The e x i s t e n c e o f t h e s w i t c h i n g
c o n sid e rab ly
e le m e n t
in
t o t h e d e s i g n d i f f i c u l t i e s i n DC
C hapter 4
101
s y ste m s.
C o n n e c t io n s
e le c tro d e s
In
in
b e tw e e n t h e p u l s e f o rm in g n e tw o rk and t h e d i s c h a r g e
DC s y s te m s h a v e t o m a i n t a i n t h e low s o u r c e im p e d a n c e .
p a rtic u la r,
low
t h e t r a n s m i s s i o n s y s te m (an d s w i t c h ) h a v e t o be o f a
in d u ctan ce
to
perm it
r a p i d c u r r e n t r i s e tim e s . . T his r e q u i r e s
t h a t c u r r e n t l o o p a r e a s be a s s m a l l a s p o s s i b l e .
However, t h e u s e o f
h i g h v o l t a g e s and h i g h g a s p r e s s u r e s means t h a t t h e e l e c t r o d e s i n t h e
d i s c h a r g e h e a d h a v e t o be s e p a r a t e d by s u b s t a n t i a l i n s u l a t o r s s o t h a t
t h e r e q u i r e m e n t f o r s m a l l c u r r e n t l o o p s h a s t o be com prom ised.
d iffic u ltie s
h ig h
a r e c o m p l e t e l y a b s e n t i n a m icrow ave s y s te m
freq u en cy
m o d u la tio n
a llo w s
w a v e g u id e
tr a n s m is s io n sy stem s.
m icrow ave
s y s te m
in
th e
use
of
These
w here
s im p l e
and
I t i s an o u t s t a n d i n g f e a t u r e
th e
c h e ap
of
a
t h a t t h e u s e o f w aveguide a l l o w s g r e a t f l e x i b i l i t y
th e p lac in g of th e d isch arg e r e l a t i v e to
p u lse
fo rm in g
n e tw o rk .
lase r
h e a d a r e i n t i m a t e l y c o n n e c t e d f o r m in g
th e
power
su p p ly
and
I n DC s y s te m s t h e p u l s e f o r m in g n e tw o rk and
a
re la tiv e ly
im m obile
s tru c tu re .
It
i s p o s s i b l e t h a t t h e u l t i m a t e a d v a n ta g e i n u s i n g a m icrow ave
d ischarge
d ie le c tric
lev el
gas
f o r pumping a n e x c im e r l a s e r w i l l d e r i v e from t h e u s e o f a
tu b e
for
th e
c o n ta in m e n t o f th e d is c h a r g e .
o f c o n t a m i n a t i o n may be r e a l i s e d and w i t h i n c r e a s e d
life
th e
cost
o f gas rep lacem en t reduced.
Thus a low
e ffe c tiv e
I t s h o u l d be n o t e d
th a t
t h i s p o s s i b i l i t y h a s n o t b e e n i n v e s t i g a t e d i n d e p th th o u g h
work
of
th is
th e
t h e s i s a l l o w s c e r t a i n l i m i t e d c o n c l u s i o n s t o be draw n
for
a q u a rtz d isc h a rg e tu b e .
th e
e le c tro d e s
and
I n DC s y s te m s t h e c o n t a m i n a t i o n due t o
in su la tin g
m aterial
th a t
fo rm
th e d isch arg e
C hapter 4
102
cham ber may r e d u c e t h e g a s l i f e
t o j u s t a few p u l s e s .
d iffic u lty
sp e cia l
are
e le c tro d e s
and PTFE f o r t h e i n s u l a t o r .
ex p en siv e.
has
In
order
t o be l a r g e .
have
m a te ria ls
req u ired
such
To combat t h i s
a s monel f o r t h e
Both o f t h e s e m a t e r i a l s
are
to g iv e lo n g t r a c k in g d i s t a n c e s th e i n s u l a t o r
In a d d itio n to t h i s th e e le c tr o d e s
and
in su la to r
t o be s e c u r e l y b o l t e d t o g e t h e r a g a i n s t t h e g a s p r e s s u r e w i t h no
p o ssib ility
of lea k s.
The f i n a l s t r u c t u r e i s t h u s i n e v i t a b l y
b u lk y
and e x p e n s i v e i n m a t e r i a l s and m a n u f a c t u r i n g c o s t s .
The
in
o p t i c a l c om ponents and g a s h a n d l i n g s y s te m s w i j l be s i m i l a r
t h e two s y s te m s e x c e p t t h a t when f a s t g a s f lo w s a r e r e q u i r e d
sm all
bore
c re a te
th e
of
th e
d isch arg e
a severe lim ita tio n .
th e
tu b e i n t h e m icrow ave a p p a r a t u s w i l l
One f i n a l p o i n t o f c o m p a r is o n
is
th a t
e x p o s u r e o f t h e l a s e r h e a d i n a DC s y s te m com pared w i t h t h e w e l l
c o n t a i n e d t u b e i n t h e m icrow ave s y s te m means t h a t i n t h e f o r m e r t h e r e
i s a h a z a r d due t o t h e p r e s e n c e o f h i g h v o l t a g e s and t h a t h i g h l e v e l s
of
r a d i a t e d r a d i o n o i s e w i l l be e m i t t e d .
a tta c h e d
box
c irc u itry
a d d in g
h ave
co n sid e rab ly
The
lase r
head
and
its
t h e r e f o r e t o be c o n t a i n e d i n a l a r g e m e t a l
to
th e
b u lk
and
in co n v en ien ce
of
th e
stru c tu re .
To sum m a rise ,
d riv e
tube
i f i t c a n be shown t h a t a m icrow ave d i s c h a r g e can
an e x c im e r l a s e r s u c c e s s f u l l y ,
w ith in
compact
a
of
sm all
low
com pared
w ith
co n ta m in a tio n
a
DC
ad d s
s y s te m .
much
The
m icrow ave d i s c h a r g e pumping f o r e x c i m e r s .
to
h ig h
th e
u n ifo rm ity
p o ssib le
a d d itio n a l
t o t h e i m p o r ta n c e o f
in v estig a tin g
th is
d isch arg e
w aveguide o f f e r s a n a p p a r a t u s w hich i s o u t s t a n d i n g l y
and s i m p l e
p o ssib ility
th e use o f a
In a d d itio n
w i t h a m icrow ave d i s c h a r g e
C hapter 4
103
sh o u ld
g i v e h i g h beam q u a l i t y and
u sefu l
as
th e re fo re
make
th e
s y s te m
a n o s c i l l a t o r p r o d u c i n g r a d i a t i o n f o r a m p l i f i c a t i o n i n by
c o n v e n tio n al
be
may
DC p u l s e d d i s c h a r g e s .
The a d d i t i o n a l c o s t t h a t h a s
to
c o n s i d e r e d f o r a m icrow ave s y s te m i s t h a t o f t h e m agnetron, and o f
p ro v id in g
a p r e s s u r i s e d w a v e g u id e .
n o tw ith stan d in g
re la tio n
ap p a ra tu s
h ig h
w ould
th e
success
or
t o e x c im e r l a s e r pumping,
make
it
a
F in a lly i t i s p o in te d
out
th a t
f a i l u r e o f t h e m icrow ave s y s te m i n
th e ad v an tag es o f th e
m icrow ave
s t r o n g c o n t e n d e r f o r u s e i n a w ide v a r i e t y o f
power g a s d i s c h a r g e a p p l i c a t i o n s .
I n p a r t i c u l a r such a
s y s te m
be h i g h l y s u i t a b l e f o r u s e a s a s p e c t r a l s o u r c e p r o v i d i n g h i g h
energy p u ls e s a t h ig h r e p e t i t i o n r a t e s .
Chapter 5
5
104
MICROWAVE APPARATUS
5.1
The R a d a r S e t
5 .1 .1
i2enej£al^l}asiy2J4>J^^^
The
of
radar
m icrowave
s e t t h a t was s u b s e q u e n t l y a d a p te d f o r t h e g e n e r a t i o n
d isch arg es
(A8WE “ P o r ts m o u th )
in d o o r
(T he
d e sig n
c o n sid e ra b ly ).
in te n d e d
th e
as
redundant
from
e q u ip m e n t.
th e
Royal
Navy
I t h ad b e e n u se d f o r
of
th is
I t o p e r a t e s i n t h e X - band
48 m i l e s f o r l a r g e f e a t u r e s .
set
se ctio n
model
may
of
precede
th is
freq u en cy
and
d a te
was
a n a v i g a t i o n a i d f o r s m a l l s h i p s w i t h an u l t i m a t e r a n g e
but
in stru c tio n s,
th ese
w ere
S e v e r a l m anuals w e r e o b t a i n e d
m ain ly
concerned
w ith
w ith
o p e ra tio n a l
i n s t a l l a t i o n i n s t r u c t i o n s , and p a r t s l i s t s .
The b r i e f
d e s c r i b i n g t h e i n t e r n a l o p e r a t i o n o f t h e s y s te m c o n t a i n e d no
d ia g r a m s
in fo rm a tio n
they
o b tain ed
l a b o r a t o r y t e s t i n g o n l y and was b r o u g h t i n t o s e r v i c e i n a b o u t
1964.
of
as
was
of
p arts
or
w irin g .
It
seems
lik e ly
th a t
d e ta ile d
would r e s i d e w i t h t h e m a n u f a c t u r e r s (H u ghes) b u t w h e t h e r
would p r o v i d e su c h i n f o r m a t i o n was n o t
sp e c ific a tio n s
in v e stig a te d .
G eneral
o f t h e s e t a r e g i v e n i n T a b le 5 .1 w h ich i n c l u d e s some
d i m e n s io n s t o g i v e a n i n d i c a t i o n o f t h e s i z e o f t h e s y s te m .
F r e quency/Wavelengt'h
9410MHz / 3.186cm
Power Output
50kW ( p e a k )
Puise R epetition r a t e
1100 Hz
Puise Length
17 0 o r 3 2 0 ns
Interm ediate
60 MHz
Frequency
Receiver Bandwidth.
12MHz
Power Requirement
220V
D C , 2kW
Components
T ran s m itt er - Receiver
4 0 x 4 6 x 2 3 (cm) , 42 kg
Azimuth - Range In d ic a to r
56 X 43 x69
,
50
Indicator Control
4 3 X 36x19
,
20
36 X 31 X 13
,
10
Motor Generator
30 x 30 x 9 0
,
132
Aerial
2 0 0 cm long
,
51
Power
Motor
Supply
Starter
Interconnecting
Table
Unit
5.1
Radar
40 X 35 X 20
Cables
set
spec i f ication
j
16
C hapter 5
105
The
com ponents o f
screened,
t h e s y s te m
m u lti-w ire
c a b le s
are
p lu s
in te rc o n n e c te d
w ith
heavy,
some c o a x i a l s i g n a l c a b l e .
The
c o n n e c t i n g a r r a n g e m e n t s f o r t h e f u l l y o p e r a t i o n a l s y s te m a r e shown i n
F ig 5 .1 .
The f u n c t i o n s
o f ea ch com ponent a r e a s f o l l o w s
T ra n s m itte r - R e c e iv e r
th e
w a v e g u id e .
G en erates
m icrow ave
pu3.ses w hich a r e f e d
C o n ta in s a high v o lta g e g e n e r a to r ,
to
p u lse g e n e ra to r,
m a g n e tro n , t r a n s m i t - r e c e i v e c e l l , and d e t e c t i o n s y s te m ,
Azjj&uth. r . R.angLe
In d ic a to r
Radar
d is p la y w ith r a d i a l l y sw ept s ig n a l
lin e ,
.In d ic a to r
C o n t r o l U n i t A c t s a s a c e n tr a ] , t e r m i n a l b l o c k
and h a s
a
f a c i l i t y f o r s w i t c h i n g b e tw e e n two d i s p l a y u n i t s .
Power
th e
S u p p lv
P ro v id e s
n e a r l y a l l o f t h e DC v o l t a g e r e q u i r e m e n t s o f
s y s te m and i s a n i n t e r c o n n e c t i o n
c o n tro l
and
th e d is p la y .
p o in t
b e tw e e n
th e
in d ic a to r
The o p e r a t i o n a l s w i t c h e s a r e i n s t a l l e d on
th is u n it,
Mo_tor
G en erato r T h is i s
a
220V DC
m o to r
in
tandem
w ith
an
AC
g e n e r a t o r and c o n v e r t s t h e DC s u p p l y t o 180V, 1100Hz, AC.
Mo-tor
B ta rte r
T h re e
o p e r a t i o n a l u n i t s a r e housed w i t h i n t h i s u n i t ;
( a ) a s w i t c h i n g s y s te m t o p r e v e n t t h e DC power s u p p l y b e i n g p r e s e n t e d
w ith
a
v ery
p rev en ts
th e
low
im p e d a n ce when s w i t c h i n g on,
( b ) s w i t c h i n g w hich
t h e o u t p u t AC fro m b e i n g c o n n e c t e d t o t h e r a d a r l o a d
m o to r
g e n e ra to r
has
reached
at
l e a s t h a lf speed,
u n til
and ( c ) a
r e g u l a t o r f o r t h e AC o u t p u t ,
AÊJCiâX.
C om prises a s i x f o o t e n d - f e d s h u n t
slo tte d
w a v e g u id e
in
a
p e r s p e x h o u s i n g , a e r i a l r o t a t i o n m o to r , a c t i v i t y s e n s o r , and a r o t a r y
w aveguide j o i n t .
25 0 V AC
220 V
MOTOR
DC
GENERATOR
SUPPLY
MOTOR
STARTER
INDICATOR CONTROL U N I T
POWER
SUPPLY
I—
I____
AZIMUTH-RANGE
INDICATOR
50 Ohm
TRANSMITTER
/RECEIVER
AERIAL
coaxial cable
MulLi - wire harness
Wave guide
Figure 5.1
Connection diagram
Chapter 5
106
2P>.QJLP.Ç, Su p.pJ.y
The
r e c t i f i e r f o r c o n v e r t i n g s i n g l e p h a s e m a in s t o 220V DC
n o t p a r t o f t h e s u p p l i e d s y s te m .
9A
r u n n i n g c u r r e n t and
p e rio d .
A
cu rren t
DC
be
to
th e load;
d m 'in g
t h e m otor
g e n e ra to r
was
I t was a t y p e o f v a r i a b l e s u p p l y t h a t
t h e r e v e r s e p r o c e d u r e b e in g
fo u n d
sta rtin g
London) was u se d w i t h a
i n c r e a s e d fro m z e r o t o t h e o p e r a t i n g v o l t a g e a f t e r
It
su p p ly
The 220V DC s u p p l y h a s t o p r o v i d e a
s u p p l y ( S e r v i c e T r a d in g Co.
c a p a c i t y o f 10A.
to
o ff.
21A
was
f o l l o w e d when
has
c o n n e c tio n
sw itc h in g
t h a t by c a r r y i n g o u t t h i s p r o c e d u r e s l o w l y t h e
c u r r e n t d u rin g th e s t a r t i n g p e rio d
of
th e
m o to r
g e n e ra to r
c o u ld be k e p t below IDA,
As
a
d riv in g
p relim in ary
t o a d a p tin g th e r a d a r s e t to th e f u n c tio n of
a d i s c h a r g e t h e s y s te m was s e t
fu n c tio n in g .
up
and
of a sin g le f a u lt.
o p e ra tio n
of th e i n d i c a t o r s e l e c t i o n sw itch and,
triv ia l,
Had
c irc u it
fo r
n o rm al
The s e t was fo u n d t o be i n good w o r k in g o r d e r w i t h t h e
e x c ep tio n
was
teste d
T h is was fo u n d t o
be
due
to
fau lty
a lth o u g h th e f a u l t
c o n s i d e r a b l e d i f f i c u l t y was e n c o u n t e r e d i n t r a c i n g i t .
d ia g r a m s b e e n a v a i l a b l e t h i s t a s k ,
and t h e p ro b le m s o f
u n d e r s t a n d i n g t h e o p e r a t i o n o f t h e s y s te m , would h a v e b e e n s i m p l i f i e d
c o n sid e rab ly .
The
te stin g
showed
t h a t t h e w hole s y s te m w a s . q u i t e
cumbersome and n o i s y , and g e n e r a t e d h e a t t o t h e e x t e n t t h a t o p e r a t i o n
in
a
sm all
d e sira b le
lab o ra to ry
was
q u i te u n p le a sa n t.
I t t h e r e f o r e seemed
t o remove a s much o f t h e unw anted p a r t s o f t h e
p o s s i b l e a s d e s c r i b e d i n S e c t i o n 5 . 2 be lo w .
s y s te m
as
Chapter 5
5 .1 .2
107
S a fety
In
w o rk in g
in
c lo se
p r o x i m i t y t o m icrow ave r a d i a t i o n c a r e f u l
a t t e n t i o n h a s t o be p a i d t o t h e h a z a r d s o f t h e r a d i a t i o n .
w a r n in g s
c o n ta in e d
in
th e
radar
set
m anuals
w e re
The h a z a r d
very
b rie f,
c o n s i s t i n g o f t h e f o l l o w i n g two s e n t e n c e s : -
R a d i a t i o n h a z a r d s may r e s u l t from e x p o s u r e t o t h e main
beam
of
th e
rad ar
a e ria l
at
a
d ista n c e
of
six
i n c h e s ( 1 5.24cm) o r l e s s from t h e c e n t r a l f r o n t p e r s p e x f a c e
o f th e a e r i a l .
N ever
lo o k
down
a
w a v e g u id e
from
which power i s b e i n g
ra d ia te d .
S in ce
a l o n g p e r i o d o f w o rk in g
m ore
c lo se
a p p a ra tu s
was
ra d ia tio n
hazards
was
ra d ia tio n
hazards
and g i v e s many r e f e r e n c e s .
in
e n v isa g e d ,
in
so u g h t,
t h e USSR a r e q u i t e d e t a i l e d ,
band
and
ex p osure
t im e .
At
d e ta ile d
p ro x im ity
w ith
th e
i n f o r m a t i o n on m icrow ave
H arv e y (1 9 6 3 )
d iscu sses
The s t a n d a r d s a d o p te d
g iv in g c o n s id e ra tio n
to
9410MHz
are
th e
m icrow ave
lim its
frequency
10p.W/cm^
( c o n t i n u o u s e x p o s u r e d u r i n g a n a v e r a g e w o rk in g d a y ) , 100j.iW/cra^ ( f o r 2
ex posure
day).
These,
t o g e t h e r w i t h t h e w i d e l y a c c e p t e d s h o r t p e r i o d maximum
2
1 OmW/cm ,
w ere a d o p te d a s t h e maximum v a l u e s d u r i n g e x p e r i m e n t a l
of
w ork.
per
d ay ),
and ImW/cm
2
hours
(1 5 - 20 m in u t e e x p o s u r e p e r
Chapter 5
108
The
m icrow ave r a d i a t i o n was c o m p l e t e l y c o n t a i n e d i n a w aveguide
s tru c tu re
tu b e.
except
at
th e
two
a p e rtu re s th a t c a rr ie d th e d isch arg e
I n o r d e r t o c h e c k f o r l e a k s a t w aveguide j o i n t s and t o m e a s u re
th e
e x te n t
th e
tu b e
w avelength
c o u ld
to
which a d i s c h a r g e c o u ld c o u p le r a d i a t i o n o u t th r o u g h
a p e rtu re s
m icrow ave
sh o rt-c irc u it
be d e t e c t e d
w ith in
pressure
( < 1 0 T o rr )
c e n tim e tre s
more
th an
t h e w a v e g u id e .
th e
d e te c tio n
mount was u t i l i s e d .
g iv in g
in te n sity
th ese
a
lu m in o u s
a
diode
in
a
q u a rte r
No l e a k s a t any j o i n t
th o u san d th
of
th e
However,
i t was fo u n d t h a t a t low
gas
ex ten d ed
d isch arg e
a lo n g
th e
d i s c h a r g e tu b e o u t s i d e t h e w a v e g u id e .
co n d itio n s
th e
maximum
d isch arg e
was
about
power
d e te c te d
in te n sity
c lo se
a
few
Under
to
a t w e n t i e t h o f t h e w aveguide i n t e n s i t y .
th e
U sing
t h e mean m icrow ave o u t p u t power o f 7W and t h e i n v e r s e s q u a r e la w , t h e
minimum
safe
d istan ce
fo r
a
r a d i a t i o n i n t e n s i t y o f 10 Wom
2
(th e
c o n t i n u o u s e x p o s u r e l i m i t ) i s 53cm,
In
ru n n in g
p ra c tic e ,
s a f e c o n d i t i o n s w e re a s s u r e d d u r i n g
f o r two r e a s o n s .
F irstly ,
ex p erim en tal
t h e o p e r a t o r was a b l e t o c o n t r o l
t h e a p p a r a t u s and t a k e m ea s u re m e n ts a t a d i s t a n c e o f o v e r 2m from t h e
d isch arg e tube.
used
S e c o n d ly , i n a l l e x p e r i m e n t s t h e m icrow ave power was
i n s h o r t b u r s t s ( o f t e n 1 second) w ith
m in u te )
b e tw e e n b u r s t s .
long
p e rio d s
(about
1
D u rin g t h e few e x p e r i m e n t s when l o n g e r ' o n '
t im e s w ere u s e d t h e a u t o m a t i c r e c o r d i n g f a c i l i t y e n a b l e d t h e o p e r a t o r
t o s t a n d 5m from t h e a p p a r a t u s o r l e a v e t h e room.
Chapter 5
5 .1 .3
109
D e t a i l s o f t h e M agnetron C i r c u i t r y
The
p a rts
m icrow ave
may
th e
d isch arg e
su rro u n d in g
o p e ra tio n
of
radar
set
a p p lic a tio n
c irc u itry .
of
w ere
p rin c ip a l
th e
i n t e r e s t f o r th e
m a g n e tro n
and
th e
The f o l l o w i n g d e s c r i p t i o n o f t h e s e and t h e i r
i s d e r i v e d from t h e s c a n t , d e t a i l s g i v e n i n t h e m an u a ls and
t h e r e f o r e be i n a c c u r a t e i n c e r t a i n d e t a i l s .
However,
th e b a sic
p r i n c i p l e s a r e c l e a r and c o u ld be a p p l i e d t o a s e p a r a t e p u r p o s e b u i l t
s y s te m ,
A l i k e l y a r r a n g e m e n t f o r t h e m a g n e tro n c i r c u i t and t h e w aveform s
at
v a r i o u s p o i n t s i n i t a r e shown i n F i g 5 . 2 .
a f t e r p a ssin g a f i l t e r ,
to
g i v e ” 8 .2kV .
se ctio n s
(lo n g
p o te n tio m e te r,
T h is c h a r g e s
one
s u p p ly ,
and t r a n s f o r m e r i s r e c t i f i e d
sectio n
p u ls e ) o f a d e la y l i n e .
to a p u lse g e n e ra tin g c i r c u i t .
The 180V RMS
(sh o rt
p u lse)
or
two
The 180V s u p p l y i s a l s o f e d
D u r in g t h e e a r l y p a r t o f t h e p o s i t i v e
h a l f c y c l e t h e s a t u r a b l e r e a c t o r e x h i b i t s a h i g h im p e d a n ce and a l l o w s
th e
c a p a c i t o r t o be c h a r g e d .
c ritic a l
v alu e
d isch arg ed
a p p e a rin g
th e
th e
re a c to r
Vihen t h e
re a c to r
im p e d a n ce
drops
th rough th e tra n s fo r m e r p rim ary .
cu rren t
reaches
and t h e c a p a c i t o r i s
The h i g h v o l t a g e
t r i g a t r o n v a l v e which t h e n d i s c h a r g e s t h e d e l a y l i n e
t h e d e la y l i n e talc es p l a c e i n t h e
su p p ly
th e
p u lse
on th e tra n s fo rm e r secondary a c ts as th e t r i g g e r p u lse f o r
th r o u g h
p u l s e t r a n s f o r m e r g e n e r a t i n g 17kV a t t h e m a g n e tro n c a t h o d e .
of
a
d u rin g
w h ic h
p u lse c i r c u i t .
n e g a tiv e
h a lf
c y c le
a
C h a r g in g
of
th e
c i r c u i t o p e r a t i o n i s p r e v e n t e d by t h e d i o d e i n
The m a g n e tro n h e a t e r c u r r e n t i s s u p p l i e d v i a t h e
b i f i l a r secondary o f th e p u lse tra n s fo r m e r .
DELAY
LINE
0; 180V
TRIGATRON
MAGNETRON
TRIGGER PULSE
GENERATOR
CIRCUIT
180V rms Supply
8.2 kV
WAVEFORMS (1100Hz)
Figure 5.2 Magnetron circuit (modulator)
Chapter 5
In
110
p ro v id in g
in v estig a tio n s
o f tim e.
at
a h ig h
of
r e p e t i t i o n r a t e t h i s s y s te m e n a b le d t h e
g a s l i f e - t i m e s t o be c a r r i e d o u t i n s h o r t
p e rio d s
In a d d itio n th e i o n i s a t i o n s u rv iv in g th e i n te r - p u l s e perio d
a high r e p e t i t i o n r a t e i s
p re io n isa tio n .
req u ired
However,
su ffic ie n t
to
g iv e
e ffe c tiv e
p u lse
i f g r e a t e r f l e x i b i l i t y o f p u ls e tim in g i s
t h e r e a r e t h r e e m ain ways i n w hich t h e p r e s e n t sy ste m c o u ld
be a d a p t e d ;
( a ) The m a g n e tro n c o u ld be d r i v e n from a s e p a r a t e s y s te m e n t i r e l y .
( b ) The
d e la y
lin e
c o u ld
be
connected to p o in t C i n F ig 5 ,2 ,
charged
from
a
n e g a t i v e DC s u p p l y
The p u l s e c i r c u i t c o u ld be f e d w i t h
a p o s i t i v e (p e rh a p s slo w ly r i s i n g ) p u ls e a t i t s i n p u t,
( c ) The
180V
g e n e ra to r,
c o n n e c tio n
in p u t,
o r p e rh ap s j u s t th e in p u t to th e t r i g g e r p u lse
c o u ld be i n t e r r u p t e d
to
be made
for
by
c irc u itry
sin g le
whole
th a t
c y c le s.
would
en a b le
T h is w ould be
a c h i e v e d u s i n g t h y r i s t o r s ( o r a t r i a c ) and a n i n t e g r a t e d c i r c u i t z e r o
v o lta g e sw itc h .
The
a d v a n ta g e
e q u ip m e n t
o p erated
of
u sin g
(c)
w ould be t h a t a minimum o f a d d i t i o n a l
would be r e q u i r e d w h i l e ( b ) would e n a b l e t h e s y s te m t o
w ith o u t
th e
e n c um berance
of
th e
be
r a d a r power g e n e r a t i n g
s y s te m and t h e o t h e r p a r t s and c a b l e s r e q u i r e d f o r i n t e r c o n n e c t i o n .
Chapter 5
5 .2
111
JRa d a r S e t A d a p t a t i o n
5 ,2 .1
A l t e r a t i o n s and A d d i t i o n s
The
r a d a r a e r i a l was n o t r e q u i r e d f o r e x p e r i m e n t a l work and was
t h e r e f o r e d i s c o n n e c t e d a t t h e f i r s t w aveguide j o i n t on t h e o u t s i d e o f
th e
tra n sm itte r u n it.
c o n siste d
d e te c to r
ae rial
of
th e
The
e le c tric a l
m o to r s u p p l y ,
T his o u tp u t,
to
th e
a e rial
co n n e ctio n s f o r th e r a d a r a c t i v i t y
and a d i r e c t i o n s e n s o r ,
m o to r.
c o n n e ctio n s
and a n e l e c t r i c a l o u t p u t from
th e
o b t a i n e d from an a d d i t i o n a l w in d in g on
t h e m otor a r m a t u r e ,
vzas o f 115V, 3 - p h a s e , 50Hz and was u se d t o d r i v e
th e
in
d isp lay
co o lin g
sweep
s y n c h ro n is m
fan in th e tr a n s m itte r
o p e ra tio n
of
th is
a s se m b ly
and
D isc o n n e c tio n
fan
a ll o w e d
of
th e
th e
to
w ith
u n it.
m otor
run
th e
In
was
a e r i a l and t o f e e d a
order
to
e x tra c te d
d u rin g
o p e ra tio n
m ain ta in
th e
fro m t h e a e r i a l
of
th e
s y s te m .
r e m a i n i n g w i r i n g h ad no d e l e t e r i o u s e f f e c t on
t h e f u n c t i o n i n g o f t h e s y s te m .
The
rad a r d isp lay
D isc o n n ec tio n
of
was
a lso
not
req u ired
and
th e w irin g h a rn e s s c o n n e ctin g i t
u n it
m icrowave
re ta in
was
housed
However,
th e
t h e r a n g e change s w i t c h w hich g a v e a c h o i c e o f
p u l s e l e n g t h s o f 170ns o r 3 2 n s ,
S i n c e i t was d e s i r a b l e t o
t h e s e two p o s s i b l e p u l s e l e n g t h s t h e w i r i n g f o r t h e s w i t c h i n g
tra c e d .
c o n ta c t
reaoved.
t o t h e s y s te m had
no u n d e s i r e d e f f e c t on t h e g e n e r a t i o n o f r a d a r p u l s e s .
d isp la y
was
of
I t was fo u n d t h a t s w i t c h i n g
a
liv e
to o k
place
by
momentary
w i r e t o one o f two o t h e r w i r e s d e p e n d in g on t h e
Chapter 5
112
p u lse le n g th re q u ire d .
th e
power
su p p ly
T e r m i n a l s f o r t h e s e t h r e e w i r e s w e re fo u n d i n
u n it
and
a
s e p a ra te n o n -la tch in g ,
s i n g l e po le
c h a n g e - o v e r s w i tc h was c o n n e c te d t o them t o r e p l a c e t h e s w i t c h o n t h e
d isp lay u n it.
A f t e r rem o v a l o f t h e a e r i a l and t h e d i s p l a y ,
a tta c h e d
t o a r o b u s t b u t m ovable t a b l e .
a p p a ra tu s
to
to
t h e t r a n s m i t t e r was
T h is e n a b l e d t h e
d ischarge
be o p e r a t e d i n a r e m o te and v a r i a b l e p o s i t i o n r e l a t i v e
t h e r e m a in i n g r a d a r e q u ip m e n t.
To c o m p le te t h i s
fle x ib ility
it
was
d e s i r a b l e t o a l l o w t h e o p e r a t o r t o s w i t c h t h e m icrow ave power on
and
o f f from
o p e ra tio n a l
used
anyw here
s w itc h e s
in
w e re
th e
v ic in ity
of
th e
a p p a ra tu s.
The
h o u s e d on t h e power s u p p l y u n i t and w e re
w i t h t h e 220V DC s u p p l y i n t h e
fo llo w in g
way.
The
ru n /sto p
s w i t c h on t h e power s u p p l y was l e f t p e r m a n e n t l y i n t h e ’ run* p o s i t i o n
and
t h e o p e r a t i o n o f t h e s y s te m i n i t i a t e d by t u r n i n g t h e
s lo w ly
up
to
220V
as
d escrib ed
in
S e c tio n
DC
5 .1 .1 .
su p p ly
A fter th is ,
g e n e r a t i o n o f m icrow ave p u l s e s i s i n h i b i t e d f o r two m i n u t e s u n t i l t h e
o n /stan d b y
th e
sw itc h
t h e power s u p p l y becomes e f f e c t i v e and a l l o w s
m icrow ave p u l s e g e n e r a t i o n t o be s w i tc h e d on and
Thus
it
sw itc h
off
at
w ill.
was r e q u i r e d t o c o n n e c t a s w i t c h i n p a r a l l e l t o t h e s ta n d b y
a t t h e end o f a l o n g c a b l e s o t h a t re m o te s w i t c h i n g w ould
p e rm itted .
p u lses
about
on
In
a d d itio n
t o t h i s i t was r e q u i r e d t h a t t h e m icrow ave
c o u ld be s w i t c h e d on f o r b u r s t s o f
1
second.
T h is
be
a
c o n sta n t
d u ratio n
of
was a c h i e v e d by u s e o f a m o n o s ta b le c i r c u i t
t h a t c o u ld be t r i g g e r e d by a p u s h - b u t t o n s w i t c h , a l s o a t t h e end o f a
long
c a b le ,
A
shown i n F i g 5 . 3 .
c o m p le te
d ia g r a m
o f t h i s s w itc h in g arrangem ent i s
mo no s ta b le / a stable
"AAAr
555
1 kn
TIMER
single
shot
fr e e
running
10jj F
O.OIjj F
remote sho rt
burst switch
remote o n / o f f
switch
standby
switch rad ar power
supply
Figure .5.3 Additional rad a r s e t switchina
Chapter 5
113
5 .2 .2
The
r a d a r t r a n s m i t t e r o u t p u t w aveguide
m icrow ave
d ischarge
in co rp o rate d
w aveguide
was
co n n ected
to
th e
c o u p l i n g d e v i c e w i t h a w a v eguid e s t r u c t u r e t h a t
several
c om ponents
in te rc o n n e c te d
w ith
sta n d a rd
ty p e WG16 ( i n t e r n a l d i m e n s io n s 0 . 9 x 0 . 4 i n c h e s ) .
The whole
a s s e m b ly i s shown s c h e m a t i c a l l y i n F i g 5 . 4 , m i s s i n g o u t t h e b e n d s and
tw ists
req u ired
to
place
th e
co u p le r
and
d isch arg e
tu b e
in a
co n v e n ie n t p o s i t i o n .
The
iso la to r
was
used
in
th is
a s se m b ly
r e f l e c t e d s i g n a l s r e t u r n i n g t o t h e m a g n e tro n .
sig n a l
prevent
larg e
Any r e s i d u a l r e t u r n i n g
c o u ld be d e t e c t e d a t d e t e c t o r 1 and ro n o v ed by a d j u s t m e n t
E - H tu n er 1 .
used
to
of
R e f l e c t i o n from t h e c o u p l e r , whose m a g n itu d e c o u ld be
t o ju d g e t h e d e g r e e t o w hich m icrow ave power was b e i n g a b s o r b e d
in th e d isc h a rg e,
a tte n u a to r
m in im is e d
was i n d i c a t e d by d e t e c t o r 2 a f t e r r e d u c t i o n by t h e
p rec e d in g i t .
by
The r e f l e c t i o n from t h e d i s c h a r g e c o u ld be
a d j u s t m e n t o f E - H t u n e r 2 o r by t h e a d j u s t a b l e s h o r t
c irc u it.
5 .3
M ic n o w a v e .D is c h a rg e C o u p l e r s
T h re e m icrow ave d i s c h a r g e c o u p l e r s w e re u s e d d u r i n g e x p e r i m e n t a l
w ork.
D u rin g
tra n sv e rse -tu b e
work
used
ex p e rim e n tal
a
p r e l i m i n a r y t r i a l s and d e v e lo p m e n t o f t h e a p p a r a t u s a
c o u p l e r was u s e d w h i l e t h e m ain body o f e x p e r i m e n t a l
lo n g itu d in a l-tu b e
work
a
co u p le r
c o u p le r,F o r
based
on
th e
some o f t h e c o n c l u d i n g
S c h w in g e r
reverse
ADJUSTABLE SHORT CIRCUIT
DISCHARGE TUBE .
MICROWAVE DISCHARGE COUPLER
DETECTOR
ISOLATOR
ATTENUATOR
E-H TUNER
E-H TUNER
DETECTOR 1
ATTENUATOR
LOAD
DIRECTIONAL COUPLER
RADAR
TRANSMITTER
Figure
5A Waveguide
assembly
Chapter 5
114
d ire c tio n a l
co u p le r
co u p le r
was
used.
S in ce
th e
t h e o r e t i c a l a s p e c ts of
d e s i g n w e re d i s c u s s e d i n C h a p t e r 4 a b o v e ,
th e
d e sc rip tio n s
below w i l l be l i m i t e d t o t h e p h y s i c a l a s p e c t s w i t h a b r i e f summary o f
t h e p e rf o r m a n c e o f each d e v i c e .
5 .3 .1
T r a n s v e r s e - T u b e C o u p le r
A
The
c r o s s - s e c t i o n a l view o f t h i s c o u p l e r i s shown i n F i g
q u artz
d i s c h a r g e tu b e p a s s e s c e n t r a l l y t h r o u g h t h e n arrow w a l l s
o f t h e w a v e g u id e, p e r p e n d i c u l a r t o t h e w aveguide a x i s .
th e
w aveguide
tu b e
of
are
passes.
c o n n e ctio n
two
So ld ered o n to
s c r e e n i n g t u b e s th ro u g h w hich t h e d i s c h a r g e
The 2mm ID d i s c h a r g e t u b e c a r r i e d two
stu b s
and had two ro u g h windows form ed on t h e e n d s .
t h e tu b e had t o
w a v e g u id e .
5 .5 (a ),
The
tak e
c o u p le r
p lace
w ith
th e
tube
in
fo r
gas
C o m p le tio n
p lace
in
th e
was c o n n e c t e d t o t h e a s s e m b ly shown i n P i g
5 .4 .
The
p h y sic a l
stra ig h tfo rw a rd ,
in
c o n stru c tio n
of
th is
c o u p le r,
c a u s e d two m ain d i f f i c u l t i e s .
th ough
F irstly ,
s i t u o f t h e q u a r t z g l a s s w a r e was q u i t e d i f f i c u l t .
w aveguide
p refe ra b le.
a llo w in g
easy
S e c o n d ly ,
th e
tu b e
s y s te m
was
by
connected
gas
co m p atib le
e l a s t o m e r ) t u b e w hich i n q u i t e s t i f f .
care
t h e a s s e m b ly
d e m o u n ta b le
r e p l a c e m e n t and i n s p e c t i o n would h a v e b e e n
co m p atib le
great
h a n d lin g
A
q u ite
len g th s
of
to
v ito n
T his
th e
h a lo g e n
(a h a lo g e n
m eant
th at
had t o be t a k e n t o p r e v e n t t h e d i s c h a r g e t u b e from b e in g
b r o k e n e i t h e r d u r i n g c o n n e c t i o n o f t h e v i t o n t u b e o r by some movement
o f t h e v i t o n tu b e a t a l a t e r d a t e .
LJ
CÛ
JC
w
CQ
u
JD
CL
CQ
m
W
u
w
c_
w
u
o
JC
fD
cn
m
m
_o
6■
on
LL_
OI
*0.
<c
g
LJ
O)
3
on
cn
.o
_c
u
I
m
c
3
LJ
m
‘on
tc
LJ
LJ
o
<
LJ
z
"O
JC
LJ
ru
LO
cn
LH
a»
ru
C -.
3
CT
LL.
*o
LJ
Chapter 5
115
T his
d isc h a rg e
p rin c ip a l
p ro v id e
tu b e
e x p erim en ts,
th e
o b tain ed
firs t
arrangem ent
was
not
f o r th e rea so n s g iv en
d e m o n stra tio n
th a t
employed
below ,
e x c im e r
but
sp e ctra
for
th e
it
d id
c o u ld
w i t h m icrow ave p u l s e s o b t a i n e d from t h e a d a p t e d r a d a r
The
i n t e n s i t y o f e m i s s i o n and i t s
up
of
th e
o p tic a l
e x p e rim e n tal
h an d lin g
rec o rd in g
procedures.
s y s te m
w e re
be
se t.
tim e behavioui'* e n a b l e d t h e s e t t i n g
s y s te m
A ls o
th e
e sta b lish e d
and
fu ll
and
th e
fo rm u la tio n
of
req u irem e n ts fo r th e gas
th e
a p p a ra tu s
d e v e lo p e d
a c co rd in g ly .
In
was
term s
of
d i s c h a r g e p e rf o r m a n c e t h e t r a n s v e r s e t u b e c o u p l e r
i n f e r i o r to l a t e r d e s ig n s i n alm o st a l l r e s p e c t s .
n o tic e a b le
It
was
m o st
t h a t a d i s c h a r g e o c c u r r e d s p o n t a n e o u s l y f o r j u s t a n a rro w
r a n g e o f m i x t u r e s and p r e s s u r e s .
However,
t h e d i s c h a r g e c o u ld o f t e n
be i n i t i a t e d by means o f a T e s l a c o i l .
The r a n g e o f c o n d i t i o n s w h e re
th is
th an
m ethod was s u c c e s s f u l was
breakdow n i n i t i a t i o n ,
su rv iv e
w id er
in d ic a tin g
th e i n te r - p u l s e p erio d to
th a t
allo w
th o se
fo r
su fficie n t
s p o n ta n e o u s
i o n i s a t i o n can
sp o n ta n e o u s
breakdow n
to
o ccur.
O b serv atio n s
of th e ou tp u t of th e r e f l e c t i o n d e te c to r ( d e te c to r
2 i n P i g 5 . 4 ) w ere u s e d t o i n d i c a t e t h e a b s o r p t i o n p e r f o r m a n c e o f t h e
d isch arg e.
ju d g e d
th e
used
D e sp ite th e la c k o f c a li b r a t io n ,
t h e a b s o r p t i o n c o u ld be
t o be c o n s i d e r a b l y p o o r e r i n t h e t r a n s v e r s e c o u p l e r
lo n g itu d in a l
c o u p le rs.
to d istin g u is h
re fle c tio n s
from
b e tw e e n
The
th an
in
a p p a r a t u s o f F i g 5 ,4 c o u ld n o t be
re fle c tio n s
th e a d ju s ta b le s h o rt.
from
However,
th e
d isch arg e
and
i t was fo u n d t h a t
Chapter 5
th e
116
p o s itio n s of th e
in itia tio n
and
sh o rt
optimum
w e re
d iffe re n t
a b so rp tio n .
for
optimum
ease
of
The p o s i t i o n o f t h e s h o r t a l s o
had t o be a d j u s t e d f o r optimum a b s o r p t i o n when t h e t o t a l p r e s s u r e was
changed.
T h is
req u irem en t
fo r
retu n in g
m e a su rem e n ts
w e re made r e l a t i n g t o g a s l i f e ,
req u ired
ea ch
at
ex p erim en tal
pressure;
m eant
th a t i f in te n sity
two g a s
s a m p le s
w e re
one t o o p t i m i s e m a tc h in g
( a b s o r p t i o n ) an d one f o r t h e i n t e n s i t y / l i f e t i m e m e a s u re m e n t.
F i n a l l y i t was o b s e r v e d t h a t a s t h e p r e s s u i ’e was I n c r e a s e d above
h a l f a n a tm o s p h e re t h e d i s c h a r g e became i n c r e a s i n g l y l o c a l i s e d on t h e
in p u t sid e of th e d isc h a rg e tu b e ,
and t h a t t h i s was acco m p a n ie d by a
c o n tin u o u s i n c r e a s e i n th e r e f l e c t i o n s i g n a l .
th e
o th e r s above,
T h is o b s e r v a tio n ,
a r e b ro a d ly c o n s i s t e n t w ith
th e
d isc u ssio n s
and
of
C h ap ter 4 .
5 .3 .2
L o n g itu d in a l- tu b e C oupler
The
lo n g itu d in a l-tu b e
c o u p le r
is
shown
in
F ig 5 .5 (b )
c ro ss-se c tio n
t a k e n a lo n g t h e d i s c h a r g e t u b e a x i s .
se ctio n s
shown i n o r d e r t o i n d i c a t e t h e i n c l i n a t i o n o f t h e tu b e
to
are
t h e w aveguide a x i s .
Two
in a
tra n sv e rse
The d i s c h a r g e t u b e e n t e r s t h e g u i d e
at
bend
and a t t h e s h o r t - c i r c u i t t e r m i n a t i o n (w h ich i s a d j u s t a b l e ) .
th is
means t h e l e n g t h o f i n a c t i v e g a s on t h e o p t i c a l
s m a ll.
sm all
The
m icrow ave
leakage
fo il.
is
By
kept
a t t h e e n t r y p o i n t s was fo u n d t o be
b u t c o u ld be r e d u c e d f u r t h e r by w ra p p in g t h e
alum iniiun
a x is
th e
e n try
areas
in
O b s e r v a t i o n h o l e s w e re d r i l l e d a t 2cm i n t e r v a l s o n
t h e n a rro w w a l l c e n t r e l i n e and t h e r a d i a t i o n l e a k a g e was checked and
Chapter 5
117
fo u n d t o be u n d e t e c t a b l e .
A lth o u g h
th e
m ajo rity
of
t h e e x p e r i m e n t a l work was c o n c e r n e d
w i t h e x c im e r f l u o r e s c e n c e e m i s s i o n ,
to
some c o n c e r t e d e f f o r t s w ere made
o b t a i n e x c im e r l a s e r a c t i o n u s i n g t h i s c o u p l e r .
lo ss
c a v i t y w ere u s e d f o r t h e s e a t t e m p t s ,
one
Two t y p e s o f low
u tilisin g
B rew ster
a n g l e d windows, t h e o t h e r p l a c i n g t h e l a s e r m i r r o r s i n d i r e c t c o n t a c t
w ith
th e g as.
windows,
I n t h e B r e w s t e r window
had t o be c o m p le te d i n s i t u .
shown
in
shown
i n F ig 5 .6 ,
F ig 5 . 5 ( b ) .
near
th e
th e
tube,
The tu b e e n d s f o r t h i s c a s e
are
I n t h e w in d o w le s s s y s te m l a s e r m i r r o r m ounts,
w ere c o n s t r u c t e d s o t h a t t h e m i r r o r s u r f a c e s w e re
t o t h e d i s c h a r g e tu b e e n d s a s p o s s i b l e i n o r d e r t o m in im is e
le n g th o f in a c tiv e gas in th e o p tic a l p a th .
a d ju ste d
in
» o * -rin g s.
h a lo g e n
d ischarge
and g a s c o n n e c t i o n s form ed a s i n g l e q u a r t z g l a s s s t r u c t u r e
w hich
as
s y s te m
th is
mount
by
means
of
M i r r o r a li g n m e n t i s
s c re w s
The m a t e r i a l s i n c o n t a c t w i t h t h e g a s
c o m p a tib ility .
In
and
c o m p ressib le
w ere
chosen
th e m a jo rity of th e e x p erim en ts,
fo r
w h e re
l a s e r m i r r o r s w e re n o t r e q u i r e d , t h e same m i r r o r m ounts w e re u s e d b u t
w i t h c a lc iu m f l u o r i d e windows i n s t e a d o f l a s e r m i r r o r s .
The good p e rf o r m a n c e o f t h i s c o u p l e r was d e m o n s t r a t e d d u r i n g t h e
e x p erim en tal
below
programme w here d i s c h a r g e s w ere o b t a i n e d fro m p r e s s u r e s
0.0 1 atm
up
t o o v e r 2 atm d e p e n d in g o n t h e m i x t u r e u s e d .
In
m ost g a s m i x t u r e s h i g h a b s o r p t i o n c o u ld be o b t a i n e d o v e r a t l e a s t 70%
o f t h e p r e s s u r e r a n g e f o r w hich a d i s c h a r g e was p r e s e n t .
th e lo w er p r e s s u r e s i n a ra n g e ,
5 .4 )
to ta l
was
req u ired
pressure.
to
re tu n in g (u sin g E - H
However, a t
tu n e r 2 o f F ig
o b t a i n good a b s o r p t i o n f o l l o w i n g a change i n
Good u n i f o r m i t y was
lim ite d
to
a
much
narrow er
(If
N
V)
Zf
M0.1
W
QJ
m
u
to
\ \ \.
c
CU
c
o
Ë
cu
4ro
U
cn
cn
c
c:
«5—
c ’(/)
o
o
I
<
ZD
(U
c
d
o
w
(/)
O
CO
I
(
o
E
f-
c.
3T
c
tn
cu
cn
c n ID
cu
OJ ID
m to
c n CO
c
n
Ccn
c_ m c_ c c
o _c o —
c_ LU
71
C - LJ
c_ (O
11
c-<
in
C- a
CD L J a
'd
I
I
LU
o
c_ w
LJ (O
to 4 ". .— ,
C
cz.
cz CU o
cu e 4—
E c >
c_
o
-f—
"o.
D
to
to 3î
3: cu
cu C-
f
o “o
i
l
l
U- ID O X
c_
vO
£_
o
cn
Li_
Chapter 5
113
pressure
range,
P a rtic u la rly
d isch arg e,
pressure
th e
perhaps
n o tic e a b le
30^
was
of
th e
th e
to ta l
in cre asin g
pressure
lo c a lisa tio n
range.
of
a t t h e m icrowave i n p u t end o f t h e d i s c h a r g e t u b e ,
was i n c r e a s e d .
need
fo r
fu rth e r
I t was t h i s o b s e r v a t i o n
co u p le r
d e v e lo p m e n t
th a t
w hich
th e
as th e
d em o n strated
r e s u lte d i n th e
S c h w in g e r c o u p l e r b e i n g d e s i g n e d and c o n s t r u c t e d .
D u rin g
th e
p re io n isa tio n
use
m ethod
of
th e
lo n g itu d in a J.
u sin g
an
tu b e
a u x ilia ry
d ischarge
d ev elo p ed .
I t c o n s i s t e d o f a q u a r t z tu b e 1mm i n
and
in
10cm
sh o rt-circu it
connect
th e
len g th
w hich
te rm in a tio n .
d isc h a rg e
e n te re d
F le x ib le
tube
to
a
th e
in te rn a l
w a v eguide
p la stic
sm all
co u p le r
tu b in g
used
th e
to
g a s h a n d l i n g s y s te m t h a t
The p o s i t i o n
t h e t u b e and t h e x e non p r e s s u r e w e re v a r i e d t o f i n d c o n d i t i o n s o f
re lia b le
o p e r a t i o n b u t w i t h s m a l l power a b s o r p t i o n .
Xenon p r e s s u r e s
i n t h e r a n g e 1 t o 5 T o r r w ere fo u n d t o be s a t i s f a c t o r y .
th a t
was
d ia m e te r
th ro u g h
was
a ll o w e d t h e tu b e t o be e v a c u a t e d and f i l l e d w i t h x e n o n .
of
tu b e
th e
I t was fo u n d
a t low p r e s s u r e s ( < 1 0 0 T o rr ) d i s c h a r g e s w e re i n i t i a t e d w i t h l e s s
tendency
fo r
a
d e la y
w h ile
f o r m a t i o n was e x te n d e d s l i g h t l y .
t h e h ig h p r e s s u r e l i m i t f o r d i s c h a r g e
Chapter 5
5 .3.3
119
g c h w ln g e r C o u p le r
A
d i s c h a r g e c o u p l e r b a s e d on t h e S c h w in g e r r e v e r s e
c o u p le r
was
4 .2 .2 ,
th e
c o n stru c te d
of
o th er h a lf
a lso
does
m o u n tin g
b ein g i d e n t i c a l e x c e p t f o r th e c o u p lin g s l o t s ,
n o t show
fix in g screw s,
b rac k e ts.
w aveguide j o i n t s
The m ain w a v e g u id e and
s t a n d a r d w a v eguide
brass.
For
s i m p l i c i t y t h e d ia g r a m shows o n l y h a l f o f t h e c o u p l e r ,
th e
m ain
t h e d e s ig n d e t a i l s g i v e n i n S e c t i o n
A s i m p l i f i e d d ia g r a m o f t h e c o u p l e r i s shown i n F i g 5 . 7 .
sake
from
u sin g
d ire c tio n a l
and
bends
and
or th e m irro r
w e re
c o n stru c te d
t h e a u x i l i a r y g u i d e was m ach in ed fro m
The l o w e r h a l f o f t h e a u x i l i a r y g u i d e was s o l d e r e d o n t o
g u id e
re m o v a b le
w h ile
screw s.
th e
upper
h a lf
was
th e
f i x e d t o t h e l o w e r h a l f by
The c o u p l i n g s l o t s w ere m i l l e d i n t h e common w a l l
b e tw e e n t h e two g u i d e s u s i n g d i m e n s io n s d e r i v e d fro m F i g 4 .5 w i t h t h e
g u id e
d im e n s io n s 10.16mm by
44.6mm,
Each
sta g g e red
b e tw e e n
c o u p lin g
e lem en ts
and
th e
c o u p lin g
fac to r
was
w avelength
a lo n g
th e
g u id e.
The
a t 20,
0 .2299,
The c o u p l i n g f a c t o r s ,
0 .1 8 6 9 ,
th e
0 .7 4 0 7 ,
The s l o t l e n g t h s
o b t a i n e d by u s i n g t h e s e v a l u e s i n F i g 4 .5 w ere ( i n mm) 2 3 . 4 3 ,
1 6 .5 8 , 1 5 .5 3 , 1 4 .8 0 , 1 4 . 2 5 , and I 3 . 8 O .
to ta l
c a lc u la te d
w e re 2 . 8 5 7 ,
and 0 .1 5 7 5 .
spacin g
Seven c o u p lin g
i n o r d e r t o g i v e 95^ c o u p l i n g ,
set
as
i s a p a ir of s l o t s of equal len g th
e q u a t i o n s ( 1 ) and (2 ) i n S e c t i o n 4 . 2 , 2 ,
0 .2985,
g u id e
i s t h r e e - q u a r t e r s o f a w av elen g th .
w e re u s e d a n d ,
0 .4 2 5 5 ,
elem en t
by a q u a r t e r w a v e l e n g t h
e lem en ts
u sin g
22.8mm
1 8 .3 5 ,
I------ 1
I
I
—
I
" iO t~
X'
x'
%
A and B-auxiliary guide,
A removable.
•
r
V■S,
C-mÜTGd bends (details
from Harvey 1963).
D-main guide.
©
E-coupling slots.
F -preioniser,front and side view.
G-section at A-A with discharge tube
and preioniser present.
full size
Figure 5.7 Schwinger coupler (half view).
Chapter 5
120
The
a s s e m b le d
c o u p le r
disch arg e
tu b e o r t h e
con n ected
to
th e
c o u ld
m irro r
be u sed w i t h t h e B r e w s t e r window
m o u n ts ,
d escrib ed
above.
It
was
w aveguide a s s e m b ly o f F i g 5 .4 and u se d dui-'ing t h e
f i n a l p h a s e s o f t h e e x p e r i m e n t a l w ork.
W ith o u t
th e use
of
a
p reio n ise r,
th e
perform ance
of
th e
S c h w in g e r c o u p l e r was s i m i l a r t o t h e l o n g i t u d i n a l c o u p l e r i n te rra s o f
th e
p r e s s u r e r a n g e o v e r which a d i s c h a r g e c o u ld be
th e
sp ik e
ty p e
p reio n ise r
shown
in
F ig
5 .7
o b tain e d .
was i n t r o d u c e d t h e
p r e s s u r e r a n g e was e x te n d e d s l i g h t l y f o r t h e e x tr e m e c a s e s .
fo r
h ig h
h a l o g e n d onor - low b u f f e r g a s g a s m i x t u r e s ,
low u p p e r p r e s s u r e l i m i t f o r d i s c h a r g e f o r m a t i o n ,
lim it
was
pressure
th an
in cre ase d
c o n sid e rab ly
w ith
th e
lo n g itu d in a l
little
lo n g itu d in a l
c o u p le r,
retu n in g ,
ab so rp tio n .
v isu a lly ,
h o w e v e r,
a fte r
co u p le r.
th e upper p re s s u re
was
In
However,
which h ave a
by t h e p r e i o n i s e r .
o v e r w hich h i g h a b s o r p t i o n o c c u r r e d
When
The r a n g e o f
m a rg in ally
c o n tra st
w id er
w ith
t h e S c h w in g e r c o u p l e r r e q u i r e d v e r y
pressure
changes,
I n co m p a rin g t h e two c o u p l e r s f o r
i n a p u r e h e liu m d i s c h a r g e ,
to
m ain ta in
u n ifo rm ity ,
h ig h
ju d g e d
t h e S c h w in g e r c o u p l e r g a v e a
b e t t e r p e rf o r m a n c e t h a n t h e l o n g i t u d i n a l c o u p l e r ,
th e upper p re s s u re
l i m i t s f o r u n i f o r m i t y b e i n g a b o u t 1 .5 atm and 1 atm r e s p e c t i v e l y .
h ig h er
d iv id e d
pressures,
in to
t h e S c h w in g e r c o u p l e r g a v e a d i s c h a r g e w hich
seven
c o u p lin g
e le m e n t.
occurred
b efore
sectio n s
th e
each
lo ca ted
For in c re a s in g p re ssu re th e
in
th e
lo ss
At
was
v ic in ity of a
of
u n ifo rm ity
t h e h i g h p r e s s u r e f a l l i n power c o u p l i n g b u t n e a r e r
t o i t th an w ith th e l o n g it u d in a l c o u p le r .
Chapter 5
121
T his
f i n a l o b s e r v a t i o n i n d i c a t e s t h a t a f u r t h e r im provem ent may
be
p o ssib le
spaced.
a
if
th e
e lem en ts
o f t h e c o u p l e r c o u ld be more c l o s e l y
I t i s r e c a l l e d t h a t t o o b t a i n d i r e c t i o n a l i t y and m a t c h in g i n
m u l t i - e l e m e n t c o u p l e r t h e e le m e n t s p a c i n g m u st be a n odd number o f
w av elen g th s.
sp acin g
from
Thus t h e o n l y p o s s i b i l i t y i n t h i s c a s e i s t o r e d u c e t h e
th re e -q u a rte r
w av elen g th
to
o n e - q u a r te r w av elen g th .
T h is would r e q u i r e a b o u t 300 e l e m e n t s and a d i s c h a r g e c o u p l i n g r e g i o n
of
over
3m
o v e rla p p in g .
in
len g th
f o r t h e s l o t s t o be s h o r t enough t o p r e v e n t
T h erefo re to o b ta in th e b e n e fit of q u a r te r
w avelength
e le m e n t
sp acin g ,
a d i f f e r e n t d e s i g n f o r c o u p l i n g e l e m e n t s s h o u ld be
so u g h t.
D a ta f o r ro u n d h o l e e l e m e n t s and *T’ s l o t s a r e g i v e n i n ’ The
M icrowave E n g i n e e r s ’ Handbook 1 9 6 2 ’ .
Chapter 6
6
6,1
P p t l G al_Sp_eG.tr]am.Analyser
The
p ro d u ctio n
of a la r g e q u a n tity of ex p e rim e n tal d a ta d u rin g
th e
i n v e s t i g a t i o n o f e x c im e r m o le c u le f o r m a t i o n was made p o s s i b l e by
th e
use
WP1).
of
an
o p tic a l
spectrum
a n a l y s e r (OSA) (B & M S p e c t r o n i c
The c o m p le te i n s t r u m e n t c o n s i s t e d o f a m o nochrom ator,
tu b e
ca m e ra ,
and
a
p ro ce ssin g
u n it
w ith
a
c o n tro l
v id ic o n
p a n e l and
c a th o d e -ra y
tu b e d i s p l a y .
tim e
o p t i o n was a l l t h a t was r e q u i r e d f o r a f u l l y o p e r a t i o n a l
sweep
re c o rd in g
The p r o v i s i o n o f an X - Y r e c o r d e r w i t h a
s y s te m . ‘ A B ry a n s 26000 A4
recorder
was
used
c o n n ected
d i r e c t l y t o t e r m i n a l s on t h e OSA p r o c e s s i n g u n i t .
The
p lan e
m onochrom ator
re fle c tio n
was com pact and u t i l i s e d a n a r r a n g e m e n t o f a
d iffra c tio n
a
p a ra b o lic
scan n in g
sin e -d riv e
w ith a r e v o l u t i o n c o u n te r to g iv e an a p p ro x im ate
lo ca ted
to
by
and
W avelength
p ro p o rtio n a l
was
g ratin g
w avelen g th .
r o t a t i o n o f t h e g r a t i n g u s i n g a m anual
F u rth e rm o re ,
th ree
2400
l i n e s p e r mm and was b l a z e d i n
band
p lan e.
th e
g ratin g
on t h e r o t a t i o n t a b l e i n one o f t h r e e a n g u l a r
th at
o p e ra tio n
m irro r.
s c a n n i n g r a n g e s w e re a v a i l a b l e .
th e
read in g
c o u ld be
p o sitio n s
so
The ÜV g r a t i n g u s e d had
range
3000 - 6500 S.
In
t h e o u t p u t s l i t o f t h e m onochrom ator was removed s o t h a t a
o f t h e s p e c tr u m u n d e r s t u d y was r e s o l v e d a t
th e
o u tp u t
focal
Chapter 6
The
preceded
123
v id ic o n
ca m e ra o p t i c a l d e t e c t i o n was by a p h o t o d io d e a r r a y
by a n image i n t e n s i f i e r t u b e .
The c a m era was
a tta c h e d
to
th e
m onochrom ator so t h a t t h e f r o n t s u r f a c e o f t h e image i n t e n s i f i e r
was
a t t h e m onochrom ator f o c a l p l a n e .
se n sitiv ity ,
th e
image
As
w ell
as
g iv in g
a
h ig h
i n t e n s i f i e r c o u ld be u s e d a s a n e l e c t r o n i c
sh u tte r.
The d io d e a r r a y was 2cm wide w h ic h ,
c o lle cte d
a
spectrum about
1?oE
w ide.
w i t h t h e UV
g ratin g ,
I t c o n t a i n e d 20000 d i o d e s
a r r a n g e d i n 500 c o lu m n s, w i t h 400 d i o d e s i n e a c h colum n.
An e l e c t r o n
s c a n n i n g s y s te m was u s e d t o i n t e r r o g a t e t h e d io d e colum ns and p ro d u c e
a s ig n a l p ro p o rtio n a l to th e o p tic a l in te n s ity .
The
i n t e n s i t y i n f o r m a t i o n from t h e cam era
p ro ce ssin g
u n it
c o rre sp o n d in g
second.
and
sto re d
in
t o a d io d e colum n,
T h is
set
500,
and
was
1 6 -b it
u p d a te d
passed
re g iste rs,
about
30
th e
each
tim es
a
o f r e g i s t e r s w i l l now be r e f e r r e d t o a s t h e r e a l
tim e r e g i s t e r w i t h d a t a s t o r e d i n t h e 500 ’ c h a n n e l s ’ .
m em ories,
to
memory A and memory
o f t h e r e a l tim e d a t a .
Two a d d i t i o n a l
B, w e r e p r o v id e d t o a ll o w a c c u m u l a t i o n
The number o f a c c u m u l a t i o n s c a n s
c o u ld be s e t
on t h e c o n t r o l p a n e l .
The
re g iste r
o u tp u t
and
d isp lay
sig n a ls
w ere
v i a a d i g i t a l to an alo g u e c o n v e r te r .
o b t a i n e d fro m a s i n g l e
F o r any
channel
th e
o u t p u t c o u ld be s e t t o g i v e t h e r e a l tim e v a l u e , e i t h e r o f t h e memory
v a lu e s,
o r t h e d i f f e r e n c e b e tw e e n t h e memory
v a lu e s.
The
screen
d i s p l a y c o n s i s t e d o f 500 p o i n t s , r e p r e s e n t i n g t h e 500 c h a n n e l s , w hich
g ave
th e appearance of a
c o n tin u o u s
i n t e n s i t y - w av elen g th
curve.
T h is was g e n e r a t e d by a c y c l i c a l t r a n s f e r o f t h e c h a n n e l d a t a , i n t h e
Chapter 6
124
r e a l tim e r e g i s t e r o r t h e m em o rie s, t o t h e d i s p l a y r e g i s t e r .
The
u sin g
Y - te rm in a l of th e X - Y re c o rd e r o u tp u t
th e
channel
c o n tro l p a n e l,
reco rd s
mode
w ith
th e
r e c o r d e r tim e sweep,
th e
X “ Y
recorder
c o u ld
p rese n ted i n th e d is p la y .
which
gave
a
be
used
be
se t,
In p r a c tic e a
e m issio n
w h ic h ,
in
g a v e te m p o r a l i n t e n s i t y
when t h e s y s te m was s e t t o r e a l tim e f u n c t i o n i n g .
s p e c tr u m
used
f o r any d e s i r e d c h a n n e l .
was c h o s e n on t h e p eak o f t h e e x c im e r
c o n ju n c tio n
c o u ld
to
I n memory
o b t a i n a copy o f t h e
To do t h i s
th e
X - sig n a l
v o l t a g e p r o p o r t i o n a l t o t h e c h a n n e l num ber.
was
An
o u t p u t sweep from c h a n n e l 1 t o c h a n n e l 500 to o k a b o u t 80 s e c o n d s .
The
th e
f a c i l i t y f o r r e c o r d i n g two s p e c t r a and s u b t r a c t i n g them
d isp lay
(and
su b tra c tio n
from
weak
th e
had
several
th e
rec o rd in g
uses
o f sp ectru m
OSA u s e d d u r i n g t h e e x p e r i m e n t a l
cu rren t
whenever
record)
in c lu d in g th e
o f a b a c k g ro u n d s p e c t r u m and t h e p h o t o d i o d e d a r k c u r r e n t
s p e c t r a and
p a rtic u la r
dark
ch art
sig n a l
work
had
changes.
cu rren t
a c c u m u la te d
The
an
ex cessiv e
o v e r th e c e n tr e of th e d io d e a r r a y .
T herefore
a s p e c t r u m was a c c u m u la te d f o r a c e r t a i n number
d ark
in
s ig n a l,
w ith th e source sw itc h e d o f f ,
f o r t h e same number o f s c a n s
and
su b tra c te d
of
scans,
had t o be
from
th e
sp ectru m .
I n i t i a l , ro u g h , w av elen g th c a l i b r a t i o n o f th e r e v o l u t i o n c o u n te r
on t h e m onochrom ator was c a r r i e d o u t u s i n g s m a l l ,
and m e rc u ry la m p s .
m ix tu res
pressu res
q u a rtz tu b e,
neon
However, i t was found t h a t t h e s p e c t r a o f e x c im e r
which had b e e n s u b j e c t t o s e v e r a l m i n u t e s o f
below 0 ,1 atm w ere r i c h i n s i l i c o n l i n e s .
d isc h a rg e
at
T hese l i n e s a r e
Chapter 6
1 25
p le n tifu l
t h r o u g h o u t t h e Ü - V s p e c t r a l r e g i o n o f i n t e r e s t and
w e re
f r e q u e n t l y u t i l i s e d f o r a c c u r a t e w a v e le n g th d e t e r m i n a t i o n .
The r e s p o n s e
rap id ly
in te rru p tin g
record.
rise
tim e o f t h e OSA
an
- r e c o r d e r s y s te m was a s s e s s e d by
e m issio n
g iv in g
a real
tim e
in te n sity
E x a m in a ti o n o f t h e r e c o r d i n g showed t h a t t h e c h a r a c t e r i s t i c
and f a l l t i m e s w e re i n t h e r e g i o n o f 0.-3s.
T h i s was due m a i n ly
t o t h e X - Y r e c o r d e r r e s p o n s e s i n c e t h e OSA o u t p u t was fo u n d t o have
a s l i g h t l y f a s t e r resp o n se th an t h i s , of about 0 ,1 s ,
The o b s e r v a t i o n
t h a t t h e p u l s e d n a t u r e o f t h e s o u r c e was n o t a p p a r e n t i n t h i s o u t p u t ,
and
t h e f a c t t h a t t h e p h o t o d io d e s c a n n i n g f r e q u e n c y was 30 s c a n s p e r
second,
in d ic a te d
t h a t a c c u ra te
a v e r a g i n g and i n t e g r a t i o n o f t h e
p u l s e s was t a k i n g p l a c e .
6 .2
Gas H a n d lin g System
The
g a s h a n d l i n g s y s te m ,
f le x ib le in use,
h a lo g e n
gases.
o p e ra tio n
at
shown i n F i g 6 . 1 ,
m a i n t a i n h i g h g a s p u r i t y , and t o be c o m p a t i b l e w i t h
In a d d itio n to t h i s th e
several
a tm o s p h e r e s
c o n tro lle d
g a s s u p p l y and m ix in g
p o ssib le .
To
v a lv e s
s y s te m
pressure
w ith
as
had
and
little
to
g iv e
used
gas
g i v e h a l o g e n c o m p a t i b i l i t y monel p i p e s ,
at
sealin g
jo in ts.
safe
had t o f a c i l i t a t e
w astage
jo in ts,
w ere u s e d w i t h v i t o n t u b e f o r f l e x i b l e c o n n e c t i o n s and
»o’ - r i n g s
w ith
was d e s ig n e d t o be
as
and
v ito n
The o t h e r m a t e r i a l s i n c o n t a c t
t h e g a s w e re s t a i n l e s s s t e e l i n t h e p r e s s u i ’ e g a u g e s ,
alu m in iu m
i n t h e s t o r a g e t a n k and t h e q u a r t z o f t h e d i s c i i a r g e t u b e ,
.The m e t e r s
and
w ith
sto ra g e
tan k
c o u ld
be
rep laced
by
c om ponents
monel
r :
vacuum
pump
discharge
tube
pressure
gauge (low)
f l e x i b l e connection
(v ito n )
pressure
gauge (high)
b u ffe r
halogen
donor
s to ra g e /
mixing tank
Figure 6.1 Gas handling a p p a ra tu s
Chapter 6
126
gas “ c o n ta c t
su rfaces
if
necessary
(if
it
was
r e q u ir e d to use
f l u o r i n e a s a d onor g a s , f o r e x a m p l e ) .
G ases
w e re s u p p l i e d
s u p p lie rs
v ia
fo llo w in g
a p e rio d of d e g assin g ,
of
th e
sta n d a rd
d ire c t
m in o rity
in d ic a tio n s.
from
c o n tro l
th e
v a lv e s.
b o ttle s
M ixing
fro m
was c a r r i e d o u t ,
by p a s s i n g t h e r e q u i r e d q u a n t i t i e s
g a s e s i n t o th e s to r a g e tan k u s in g p a r t i a l p r e s s u r e
The m a j o r i t y g a s was t h e n l e t i n ,
to ta l pressure,
o b tain ed
as r a p id ly as p o s s ib le .
up t o t h e
req u ired
I n t h i s way m ix in g c o u ld be
e n s u r e d by t h e a c t i o n o f t u r b u l e n c e w i t h i n t h e m ix in g t a n k .
It
was fo u n d d u r i n g e x p e r i m e n t a l work t h a t t h e s e c t i o n o f
pip e
b e tw e en t h e d i s c h a r g e tu b e and t h e s t o r a g e t a n k was s u f f i c i e n t l y lo n g
to
e n a b le i t
t o be u s e d a s a s e c o n d a r y g a s s t o r e .
T h is
e x p e r i m e n t a l r o u t i n e t o be u s e d t h a t had v e r y l i t t l e
a llo w e d
an
gas w astag e.
As
d e s c r i b e d i n C h a p t e r 7 , f o r a g i v e n s e t o f t h r e e g a s e s f o r an e x c im e r
m ix tu re
(rare-g as,
h a lo g e n
donor,
b u ffer)
it
was
d e sire d
to
i n v e s t i g a t e t h e e x c im e r e m i s s i o n i n t e n s i t y i n t e r m s o f t h e f u l l r a n g e
of
m ix tu re
ra tio s
o ccu rred .
For a
tem poral
rec o rd in g
and
g iv en
w e re
to ta l
p ressures
m ix tu re
ra tio
o b tain ed
at
o p e ra tio n a l
range u s in g th e sequence;
p ressure
~
spectrum
pressure
- tem poral r e c o r d in g .
s to re d
g iv en
th e
rec o rd in g
-
a
fo r
w hich
spectrum
a
d ischarge
rec o rd in g
and
about e ig h t p re ssu re s in th e
tu b e e v a c u a t i o n - f i l l t o new
tu b e
e v a c u a tio n
I t was u s u a l l y fo u n d
- f i l l t o same
th a t
th e
gas
i n t h e p ip e w o rk was s u f f i c i e n t f o r a ].l t h e m e a su re m e n ts f o r a
m i x t u r e i f t h i s s e q u e n c e was u s e d w i t h m e a s u re m e n ts
o rder
rare-g as
of
d e c re a sin g
p ressure.
tak en
in
For a g iv e n r a t i o of donor to
t h e f i r s t m i x t u r e t e s t e d was alvrays t h a t w i t h l e a s t
bu ffer
Chapter 6
127
g a s.S in c e
i t was g e n e r a l l y found t h a t t h e maximum d i s c h a r g e p r e s s u r e
in c re a s e d w ith th e b u f f e r f r a c t i o n ,
to
th e
and
tan k
b u f f e r g a s c o u ld s im p ly be added
b e tw e en each r u n t o change i t s f r a c t i o n i n t h e m i x t u r e
no more r a r e - g a s and d onor
gas
w ere
req u ired
fo r
th e
whole
e x p e r i m e n t a l r u n a t t h a t p a r t i c u l a r donor t o r a r e - g a s m i x t u r e r a t i o .
It
was
disch arg es
th e
in
1
6.1
so
in crease
to o b tain
a d ju stm e n t
of
t h a t g a s f lo w e d from t h e s t o r a g e t a n k ,
vacuum
pump.
To
ach ie v e
th is
and 6 i n F ig 6.1 w ere c a r e f u l l y a d j u s t e d w i t h v a l v e s 2 - 5
and t h e
sh o rt
F ig
g a s h a n d l i n g s y s te m ,
T h i s was done by c a r e f u l
th e d isc h a rg e tube to th e
v a lv e s
open
u sin g th e
i n flo w in g g a s .
v a lv e s
th r o u g h
and
p o ssib le ,
th e
r e m a i n d e r c l o s e d . T h i s t e c h n i q u e was
used
s im p l y
to
r e c o r d e d i n t e n s i t y o f a s p e c tru m t h a t was weak due t o a
gas l i f e .
I t was n o t u s e d i n any o f t h e
ro u tin e
ex p erim en ts
s o no a t t e m p t s w e re made t o m e a s u re t h e f lo w r a t e o r p r e s s u r e i n
th e d isch arg e tube.
6 .3
P u l s e R e c o r d in g System
The
te m p o r a l r e c o r d i n g s y s te m b a s e d on t h e OSA
lim ita tio n s
d e riv in g
had
two
m a jo r
from t h e lo n g r e s p o n s e tim e i n t h a t v a r i a t i o n s
d u r i n g a s i n g l e o p t i c a l p u l s e and v a r i a t i o n s b e tw e e n p u l s e s c o u ld n o t
be
observed
(0 .1 s).
d e v e lo p e d
on
a
tim e sc a le
of
le ss
th an
t h e OSA r e s p o n s e tim e
To make t h e s e o b s e r v a t i o n s p o s s i b l e a s e p a r a t e
u sin g
th e
same
m onochrom ator
as
b efo re
w ith
a
fast
and a s t o r a g e o s c i l l o s c o p e .
used
o u t p u t s l i t i n p l a c e and s e t t o p a s s t h e peak o f t h e
its
m onochrom ator
was
p h o to m u ltip lie r
w ith
The
s y s te m
was
Chapter 6
e x c im e r
128
e m issio n .
The d i s c h a r g e a p p a r a t u s r e m a in e d u n d i s t u r b e d
for
th e p u lse rec o rd in g ex p erim en ts.
To r e c o r d s i n g l e o p t i c a l p u l s e s ,
was
th e f a s t p h o to m u ltip lie r o u tp u t
d i s p l a y e d u s i n g a T e t r o n i x 7834 s t o r a g e o s c i l l o s c o p e .
o sc illo sc o p e
th e
p o in t
th e
at
In
th is
s i g n a l i s t r a n s m i t t e d t h r o u g h a d e l a y l i n e b e tw e e n
which
th e
trig g e r
sig n a l
is
o b tain ed
and
th e
Y “ a m p lifie r.
T h is e n a b l e s t h e l e a d i n g edge o f n a n o sec o n d r i s e t i m e
p u lses
view ed
to
be
and
th erefo re
in te rn a l
s a tisfa c to ry
f o r rec o rd in g th e o p tic a l p u ls e s .
d e la y
c o u ld
be a p p l i e d t o t h e t r i g g e r s i g n a l s o t h a t
p u lse
c o u ld
a d d itio n
to
d e riv ed
However,
was
a v a ria b le
th e d isp la y e d
be a c h o s e n number o f p u l s e s a f t e r t h e f i r s t p u l s e .
t h i s a second
trig g e r
p u lse
w ith v a r i a b le d e la y
In
is
from t h e i n i t i a l t r i g g e r s i g n a l and c a n be u s e d t o t r i g g e r a
se c o n d
in p u t to th e o s c illo s c o p e .
o b tain
a
two
trig g e rin g
p a ir
o p tic a l
It
was
th ere fo re
p o ssib le
to
o f t r a c e s o n t h e o s c i l l o s c o p e s t o r a g e s c r e e n show ing
p u lse s,
e a c h p u l s e o c c u r r i n g a f t e r a c h o s e n number
of
p u l s e s had e l a p s e d f o l l o w i n g t h e f i r s t p u l s e o f t h e s e q u e n c e .
In th e
ex p erim en tal
tak in g
w o rk ,
rec o rd s o f th ese
p u lses
w e re
made
by
t r a c i n g s from t h e o s c i l l o s c o p e s c r e e n .
It
was
m icrow ave
th e
re a lise d
th a t
a
t y p i c a l one s e c o n d b u r s t
p u l s e s t h e o p t i c a l p u l s e i n t e n s i t y m ig h t b u i l d
up
of
d u rin g
f i r s t few p u l s e s and be s u b j e c t t o o t h e r v a r i a t i o n s t o o r a p i d t o
be r e v e a l e d by t h e OSA s y s t e m .
a
d u rin g
su c ce ssio n
p o ssib le
p u lse
of
p u lse s
I t was t h e r e f o r e d e s i r a b l e t o d i s p l a y
to g eth er
on t h e o s c i l l o s c o p e .
I t was n o t
t o do t h i s s im p l y by u s i n g a slow sweep r a t e b e c a u s e w i t h a
w id th
to
p u lse
i n t e r v a l r a t i o o f 1 : 3000 t h e p u l s e s became
C hapter 6
129
e x t r e m e l y n a rr o w .
recorded
A lth o u g h t h e v e r t i c a l l i n e s o f t h e p u l s e s c o u ld be
q u i t e e a s i l y by t h e o s c i l l o s c o p e s t o r a g e s c r e e n ,
swamped
by t h e b a s e l i n e b e tw e e n p u l s e s .
sh ifte d
to
a
p o s i t i o n below t h e s c r e e n ,
sa tu ra te d
th e
sto ra g e
re c o rd in g
th e
p u lses
was
Even w i t h
screen
when
w e re u s e d .
t h e y w ere
th e
base
lin e
in te rn a l sc a tte rin g s t i l l
se n sitiv itie s
su ffic ie n t
fo r
As a c o n s e q u e n c e o f t h i s a s y s te m
d e v e lo p e d t o c a u s e b l a n k i n g o f t h e
o sc illo sc o p e
trace
b e tw e e n
p u lses.
The
co n tro l
stra ig h tfo rw a rd
of
th e
T etro n ix
o sc illo sc o p e
b lan k in g
and r e q u i r e d t h e i n t e n s i t y c o n t r o l t o be f u l l y
was
down
and a -2V r e c t a n g u l a r s i g n a l t o be f e d t o t h e Z - m o d u l a t i o n i n p u t i n
co in c id e n c e
g e n e ra to r
c o u ld
in
w i t h t h e p u l s e t o be o b s e r v e d .
was
A
Venner
used t o g e n e r a te t h i s u n b lan k in g s i g n a l .
TSA628
p u lse
T his d e v ic e
be t r i g g e r e d e x t e r n a l l y and a d j u s t e d t o g i v e a -2V p u l s e e q u a l
d u ratio n
sig n a l
to
th e
o p tic a l
p u lse.
I t was fo u n d t h a t t h e o p t i c a l
c o u ld n o t be u s e d t o t r i g g e r t h e p u l s e g e n e r a t o r b e c a u s e
in h eren t
d elay
100ns
to o l a t e .
p u lse
in
th e
th e
i n t h e g e n e r a t o r c a u s e d t h e u n b l a n k i n g t o o c c u r some
T h e re fo re th e r a d a r s e t sync p u ls e ,
s y s te m ,
was
used
th e
e a rlie st
to g e th e r w ith a d e la y in tro d u c e d
b e tw e e n t h e p h o t o m u l t i p l i e r and o s c i l l o s c o p e by means o f 20m o f 50ohm
co a x ia l
c a b le .
shown i n F i g 6 . 2
The c o m p le te s y s te m f o r m u l t i p l e p u l s e r e c o r d i n g i s
C
microwave
apparatus
3 —
- discharge tube
'
------:V ]]:
microwave
r e f l e c t io n
d e te c to r
CZH-
-H-
a t te n u a t o r
photomultiplier
g en erato r
Delay cable
2 0 m ,5 0 q
coaxial
e x t.trig
z~mod.
y -in p u ts
oscilloscope
Figure 6.2 Pulse recording system
C hapter 7
7
130
m E RIMEILTS.
T h is
re su lts
g iv in g
from
c h a p te r
is
concerned
w ith
th e
t o be o b t a i n e d u s i n g t h e a p p a r a t u s d e s c r i b e d above and
th e d e t a i l s o f th e ran g e o f th e i n v e s t i g a t i o n s .
t h e e x p e r i m e n t s w e re i n t h r e e f o rm s .
e m issio n
w ide
p r o c e d u r e s t h a t e n a b le d
bands
tim e
of
w e re o b t a i n e d on s p e c tr u m r e c o r d s a p p r o x i m a t e l y 170%
th e
sc ale s.
inherent
in
The raw d a t a
F i r s t l y t h e B - X e x c im e r
w i t h l i n e a r i n t e n s i t y and w a v e l e n g t h s c a l e s .
records
w ith
S e c o n d ly ,
tim e
e m i s s i o n pealc w e re o b t a i n e d on l i n e a r i n t e n s i t y and
S ince a v e ra g in g o f th e
th ese
reco rd s,
a
IIOOpps
s y s te m
p u lse
w ith
(d e sc rib e d
ab o v e) was d e v e lo p e d s o t h a t s i n g l e
u n a v e ra g e d
p u l s e b e h a v io u r c o u ld be o b s e r v e d .
frequency
was
a f a s t r e s p o n s e tim e
p u lse
and
m u ltip le
The raw d a t a o b t a i n e d
u s i n g t h i s t e c h n i q u e w ere i n t h e form o f p h o t o g r a p h s o r t r a c i n g s o f a
sto ra g e o s c illo s c o p e d is p la y .
ty p es,
w ere o b t a i n e d f o r a v e r y w ide r a n g e o f g a s m i x t u r e s and t o t a l
p ressures
The
D a ta r e c o r d s , e s p e c i a l l y t h e f i r s t two
d u rin g
t h e e x e c u t i o n o f a l e n g t h y e x p e r i m e n t a l programme.
p r o c e d u r e s t h a t w e re d e v e lo p e d
c a rrie d
out
co n sisten c y
in
a
re a listic
a ll o w e d
p erio d
of
th is
tim e
programme
w h ile
to
be
m ain ta in in g
o f e x p e r i m e n t a l c o n d i t i o n s and m i n i m i s i n g t h e u s e o f t h e
e x p en siv e g a s e s .
Chapter 7
7 •1
13'
E x p e r i m e n t a l M ethods
7 .1 ,1
In te n sity
By
vs Time R e c o r d in g
s e ttin g
maximum
t h e OSA r e c o r d e r o u t p u t t o g i v e t h e i n t e n s i t y a t
p o i n t o f an
re c o rd in g s
of
e x c im e r
in te n sity
B ~ X
s p e c tr u m
in
real
tim e
th e
mode,
vs tim e w ere o b t a i n e d w hich g a v e t h e b a s i s
f o r a s s e s s m e n t s o f r e l a t i v e p eak f l u o r e s c e n t o u t p u t and e f f e c t i v e g a s
life
in
records
te rra s
of
th e X -
m ix tu re
Y p l o t t e r was
trig g e re d
by
m icrow ave
so u rce.
a lte re d ,
a c c o rd in g
p lo tte r
w here
w ere
sa tu ra tio n
of
a
fo r
tim e
a lin e a r
of
lo ss
sweep
and
push b u t t o n j u s t b e f o r e s w i t c h i n g o n t h e
S c a lin g o f
to
To p ro d u c e t h e s e
th e
th e
in te n sity
c o o rd in a te
c o u ld
s t r e n g t h o f e m issio n e x p e cte d ,
th e
OSA,
t h e v i d i c o n cam era m ig h t o c c u r ,
p l a c e d be tw e en t h e d i s c h a r g e tu b e and t h e
be
by t h e
For
cases
g lass f i l t e r s
m ono ch ro m ato r.
The
i n t r o d u c e d by a f i l t e r was s im p l y o b t a i n e d by u s i n g
same e x p e r i m e n t a l a r r a n g e m e n t b u t w i t h a slo w g a s
d isch arg e
by
means
set
and p r e s s u r e .
g a i n c o n t r o l and a r a n g e f a c i l i t y o n
fra c tio n a l
th e
ratio
tube g iv in g a c o n s ta n t o p t i c a l o u tp u t.
f lo w
in
th e
The l o s s was fo u n d
i n s e r t i n g t h e f i l t e r d u r i n g t h e X-Y r e c o r d e r sweep
in
order
produce
a s te p in th e rec o rd .
a llo w e d
t h e f r a c t i o n a l f a l l i n i n t e n s i t y shown i n t h e r e c o r d
to
The l i n e a r i t y o f t h e v i d i c o n r e s p o n s e
t a k e n a s t h e f r a c t i o n a l l o s s i n t r o d u c e d by t h e f i l t e r .
to
be
C hapter 7
Two
132
ro u tin e s
w e re
used f o r g as rep lacem en t d u rin g ex p e rim e n ts
y i e l d i n g i n t e n s i t y vs tim e r e c o r d s :
Method
1 F o l lo w in g
p re p a ra tio n
of
th e
cu rren t
gas
m ix tu re
and
e v a c u a t i o n o f t h e d i s c h a r g e t u b e and p i p e n e tw o rk , a f i r s t sam ple was
le t
on
i n t o th e d isc h a rg e tu b e .
and
optimum
d isch arg e
tu n in g
The m icrowave s o u r c e was t h e n s w i tc h e d
set
c o u ld be s t r u c k .
fo r
th e
h ig h est
The d i s c h a r g e tu b e was
r e f i l l e d w i t h f r e s h g a s t o t h e same p r e s s u r e ,
re c o rd in g
in itia te d .
in te n sity
had
f a l l e n by a b o u t 70 %,
a t which p o i n t t h e p r e s s u i ’e was
b e tw e e n
th e
tu n er
tu b e
and t h e vacuum pump.
in
As h a s been m e n tio n e d e a r l i e r ,
t h i s was
th e
b efo re
gas
tap
T h i s p r o c e s s was
I f a t any tim e
t h e r e f l e c t e d m icrow ave s i g n a l o c c u r r e d ,
was r e a d j u s t e d f o r optimum t u n i n g
ste p .
as
d isch arg e
u sin g
u n t i l e x tin c tio n of th e d isch arg e o cc u rre d .
in crease
ev acu ated ,
The s y s te m was t h e n l e f t u n d i s t u r b e d u n t i l t h e
by a n i n c r e m e n t a s r a p i d l y a s p o s s i b l e
an
th en
and te m p o r a l i n t e n s i t y
reduced
re p e a te d
p r e s s u r e a t w hich a
th e
next
th e E - H
p r essu re
s u f f i c i e n t gas f o r a ru n such
u s u a l l y p r e s e n t i n t h e pip ew o rk
b e tw e e n
th ed isch arg e
tu b e and t h e s t o r a g e t a n k .
Exam ples
F ig 7 ,1 ,
edge
g e n e ra lly
app ro ach ed .
pressures
life .
records
o b tain ed
Each tim e t h e t o t a l
sim u lta n e o u s
risin g
of
gas
rep la ce m e n t,
by
p r e s s u i ’e
t h i s t e c h n i q u e a r e shown i n
is
reduced,
which
g iv es
a new i n t e n s i t y pealc r e s u l t s .
The
o f t h e p e a k s o c c u r d u r i n g t h e p r e s s u r e change w hich
rap id
at
first
but
slo w e r
as
th e
The f a l l i n g e d g e s o f t h e p e a k s o c c u r
in d ic a te d
new
at
p ressure
th e
was
was
c o n sta n t
o n t h e h o r i z o n t a l ( t i m e ) a x i s and r e v e a l t h e g a s
I t c a n be s e e n t h a t f o r a g i v e n m i x t u r e r a t i o p eak
in te n sity
1000 " 900 "
8ÔÔ
^
70Ô'
"
600
"
500
" 4Q(T'''
300
"
300
200
"
2 0 0 '^ ’' 100
S F ô : X e :Hi
800
900
700
600 " 500 " 400
S f g : X e :He
1000
' ' 900 " 800
" 700
‘ ‘ 600^^00
" 4 0 0 “ ' 300
200
pressure
c o n sta n t pressure intervals, in mB
reduction
Figure7.1 Temporal records by method 1
100
'
,5Sec
100
C hapter 7
vs
133
to ta l
seen
pressure
I t c a n a l s o be
t h a t gas l i f e in c re a s e s w ith t o ta l p re s s u re but in th ese
q u a n tific a tio n
in
th e
is
of
fa llin g
in te n sity .
T hese
be
p r e s e n t a t th e low er p r e s s u r e s .
e f f e c t i v e l y u s e d up d u r i n g i t s
e ffe c tiv e ly
was
used
re su lts
c le a rly
a m a jo r d i f f i c u l t y w i t h method 1 i n t h a t g a s l i v e s e q u a l
o r l e s s t h a n t h e tim e r e q u i r e d f o r p r e s s u r e
are
cases
d i f f i c u l t due t o c o m p l e x i t i e s i n t h e c u r v e s h a p e s
reg io n s
d em onstrate
to
c u r v e s c a n be drawn i m m e d i a t e l y .
red u cin g
for
a ll
th e
th e
changes
Under t h e s e c o n d i t i o n s g a s w i l l
passage i n t o th e
peak v a lu e o b t a i n a b le .
XeF
(1 - 1 ,5 s )
e x p erim en ts,
a
d isch arg e
tube,
W hile t h i s m ethod
d iffe re n t
tech n iq u e
(m ethod 2) was e v o lv e d and u s e d f o r a l l r e m a in i n g e x p e r i m e n t s .
Method 2 I n t h i s m ethod an e n t i r e l y f r e s h g a s sam ple was u s e d a t each
pressure
and t h e m icrow ave s o u r c e was s w i tc h e d o f f
changes.
An
i n t e n s i t y « tim e
p lo t
was
d iffe re n t
p r e s s u r e s f o r a g iv e n m ix tu re r a t i o
d u rin g
o b tain ed
at
u sin g
pressure
about e ig h t
th e
fo llo w in g
ro u tin e .
1.
Gas
p laced
in
tu b e
to
maximum
d isch arg e
pressure,
tu n in g
o p tim ise d .
2 . Tube e v a c u a t e d and a ll o w e d t o c o o l , r e f i l l e d
t o maximum p r e s s u r e .
3 . C h a r t r e c o r d e r sweep on, m icrow ave s o u r c e on, m icrow ave s o u r c e o f f
a f t e r a b o u t 70% f a l l i n o p t i c a l o u t p u t .
4.
Tube e v a c u a t e d ,
f r e s h g a s i n t r o d u c e d t o new p r e s s u r e ,
co u p lin g
r e t u n e d , t u b e e v a c u a t e d and a ll o w e d t o c o o l .
5 . Gas r e p l a c e d t o new p r e s s u r e ,
[ R o u t i n e c o n t i n u e d fro m s t e p 3 . ]
T his
m ethod p r o v i d e d g r e a t e r c o n s i s t e n c y o f c o n d i t i o n s t h a n m ethod 1
but
was
much more tim e consum ing and u s e d a g r e a t e r q u a n t i t y o f g a s
fo r
each r e s u l t .
E xam ples o f r e c o r d s u s i n g m ethod 2 a p p e a r
in
F ig
C hapter 7
13*'
7 .2 .
In
th is
case
i n t e n s i t y / t i m e r e c o r d s w e re o b t a i n e d a t e l e v e n
to ta l
p r e s s u re s f o r th e m ix tu re in d ic a te d .
Each
record
shows
th e
c h a r a c t e r i s t i c r a p i d r i s e t o a maximum i n t e n s i t y a t t h e i n i t i a t i o n o f
the
d i s c h a r g e and t h e s u b s e q u e n t de c ay ( p e r h a p s t o a c o n s t a n t l e v e l )
from which g a s l i f e m e a s u re m e n ts w e re o b t a i n e d .
7 .1 .2
S p e c tru m R e c o r d in g
S p e c tru m
records
w e re
o b tain ed
u sin g
th e
OSA
fo r
s e v e r a l,
p u r p o s e s . P r i m a r i l y a s p e c t r u m was o b t a i n e d f o r e v e ry g a s m i x t u r e and
pressure
th a t
was
used
i n t h e te m p o r a l r e c o r d i n g e x p e r i m e n t s .
In
e v e r y c a s e c a r e was t a k e n t o e n s u r e t h a t f r e s h g a s was u s e d , t h a t t h e
d i s c h a r g e t u b e h ad c o o l e d ,
used
a nd t h a t t u n i n g was optimum.
i n memory mode so t h a t t h e
number
of
in te rn a l
d a ta
s p e c tr u m
tra n sfe r
was
c y c le s.
The OSA was
a c c u m u la te d
The
c h o s e n was such t h a t t h e m icrow ave s o u r c e c o u ld be
on
o ff
p lac e .
a
w ork,
These
sp e ctra
cases
w e re
T herefore,
th e
r e p r e s e n t e d t h e i n t e g r a t e d s p e c t r a o f 1100 p u l s e s .
r e c o r d i n g s c o u ld t h e n be u s e d a s
re la tin g
sp e ctra
one s e c o n d b u r s t from t h e m icrow ave s o u r c e u s i n g
m o n o s t a b le s w i t c h d e s c r i b e d i n S e c t i o n 5 . 2 . 1 .
recorded
one
d u rin g
sw itc h e d
t h e p e r i o d d u r i n g w hich a c c u m u l a t i o n was t a k i n g
F o r t h e m ain b u l k o f t h e e x p e r i m e n t a l
o b tain ed
th e
w ith in
a
number o f c y c l e s
(scans)
and
over
in te n sity
to
m ix tu re
an
a lte rn a tiv e
m ethod
fo r
r a t i o and p r e s s u i ’e b u t o n l y f o r t h e
w here g a s l i f e t i m e s w e re known t o be c o n s i d e r a b l y g r e a t e r t h a n
second.
records
was
d istrib u tio n
However,
to
of
fin d
th e
th e
if
m ain p u r p o s e i n o b t a i n i n g t h e spectrvmi
v a ria tio n s
sp e ctra
o ccurred
in
th e
in te n sity
and t o d e m o n s t r a t e how t h e v a r i a t i o n s
î
-te
>un
g
I—
2:
e
u
u
eu
00
un
LU
s:
CO
•a
o
jc.
A—
eu
e
> •.
JO
LO
X3
o
m
rn
eu
2:
ULT
t_
O
w
eu
<a
CL
ev
00
ü_
o
Chapter* 7
1 35
d e p e n d ed on b u f f e r g a s ty p e and t o t a l p r e s s u r e .
I n a d d i t i o n t o t h e r e c o r d s o b t a i n e d d u r i n g t h e m ain e x p e r i m e n t a l
programme,
s p e c t r a w ere o b t a i n e d a t t h e o u t s e t o f t h e i n v e s t i g a t i o n
o f any p a r t i c u l a r e x c im e r m o le c u le f o r t h e p u r p o s e s o f i d e n t i f i c a t i o n
and
to
id e n tify
pealc.
t h e OSA d a t a c h a n n e l l y i n g n e a r e s t t o t h e s p e c tr u m
The o t h e r o u t s t a n d i n g r e a s o n f o r o b t a i n i n g
occurred
b o th
d u rin g
th e
records
a t t e m p t s t o o b t a i n l a s i n g d e s c r i b e d b e lo w .
o f t h e s e c a s e s t h e number o f
encom pass
s p e c tr u m
a c c u m u la tio n
scans
was
set
In
to
t h e o p e r a t i o n a l p e r i o d o f t h e d i s c h a r g e w hich was s e t t o a
v a r i e t y o f v a l u e s d e p e n d in g o n t h e r e q u i r e m e n t s .
7 * 1 .3
P u l s e R e c o r d in g
The
w ith in
p u l s e r e c o r d i n g a p p a r a t u s was d e v i s e d
sin g le
o p tic a l
p u lse -to -p u lse
OSA
s y s te m .
m icrow ave
s a m p le s
p u lse
p u lses
so
was
v a ria tio n s
c o u ld be d i s p l a y e d and t o r e c o r d any
v a r i a t i o n s t h a t w ere t o o r a p i d t o be d e t e c t e d by
th e
same m i x t u r e and p r e s s u r e .
recorded
th e
so
th a t
o p tic a l
c o rre la tio n s
b e tw e e n
m icrow ave
th e
These r e c o r d i n g s a l s o a llo w e d a c h e c k t o be k e p t
c o u ld
on
efficien cy
R e su lts
w e re o b t a i n e d u s i n g t h e p u l s e r e c o r d i n g s y s te m f o r t h e
e x p erim en ts
pressures
used
in
for
p u lse
tem poral
o v e ra ll
and
tu n in g
a
a s i n d i c a t e d i n S e c t i o n 7*2
gas
The r e f l e c t e d m icrow ave
re v e a le d .
th e
and
co n sec u tiv e
of
of
p u lse
for
b eh a v io u r
m ix tu res
th e
I n a d d i t i o n i t was fo u n d t h a t c o r r e s p o n d i n g o p t i c a l and
r e f l e c t i o n p u l s e s c o u ld be o b t a i n e d
of
th a t
be
th e
each o p t i c a l p u ls e r e c o r d .
sm all
fra c tio n
b e lo w .
The
of
gas
th e
same
KrF
h a n d lin g
C hapter 7
136
p r o c e d u r e s w e re a s d e s c r i b e d f o r method 2 a b o v e .
Some
e x a m p le s
from
t h e p u l s e r e c o r d i n g t e c h n i q u e a r e shown i n
F ig 7 . 3 . T h i s f i g u r e was p ro d u c e d by ta lc in g t h e o r i g i n a l o s c i l l o s c o p e
s c r e e n t r a c i n g s , which w e re on a c e t a t e , and r e t r a c i n g them and a d d in g
th e s c a le s i n d e t a i l .
re fle c tio n
p u lses
same tim e s c a l e .
gas
w e re
D u rin g t h e r e t r a c i n g t h e o p t i c a l and m icrow ave
w e re s u p e rim p o s e d s i n c e t h e y w e re o b t a i n e d o n t h e
To o b t a i n t h i s s e t o f r e c o r d s f o u r s a m p le s o f f r e s h
req u ired .
The
f i r s t two s a m p le s w e re u s e d t o o b t a i n t h e
o p t i c a l p u l s e a m p l i t u d e e n v e l o p e s , shown i n ( a ) , which d i f f e r o n l y i n
th e
tim e
base
v e rtic a l
and
screen
but
t h e 2 0 m s /d iv t r a c e t h e c l o s e l y s p a c e d
th e
area
under
p u lses
i n d i v i d u a l p u l s e s w e re n o t
t h e cui^ve was u n i f o r m l y b r i g h t .
dual
beam
fa c ility .
f i r s t o p t i c a l p u l s e was
recorded
d isch arg e
d e la y
from t h e f i r s t d i s c h a r g e p u l s e .
second,
are
m ethod
th e
two
on
c o n n e ctin g
th at
a fte r a
d isc e rn ab le
The t h i r d g a s
th e s ig n a l
p h o to m u ltip lie r c a b le .
u sin g
30ms d e l a y from
S ince th e p u ls e r a t e i s
th e
th e
1100
The p o s i t i o n s o f t h e s e l e c t e d p u l s e s
t h e p u l s e e n v e lo p e r e c o r d s .
used
W ith t h e
r e c o r d e d p u l s e s r e p r e s e n t t h e 3 3 r d and 1 9 8 th
w e re o b t a i n e d w i t h t h e f o u r t h
as
th e
The s e c o n d p u l s e was r e c o r d e d a f t e r a 180ms
of th e t r a i n o f p u lse s .
shown
records
p u lse.
on
The o s c i l l o s c o p e was s e t s o t h a t
first
p u lses
d isc e rn ab le
was u s e d t o p r o d u c e t h e two o p t i c a l p u l s e r e c o r d s
o sc illo sc o p e
per
w e re
w e re n o t c o p ie d o n t o t h e r e c o r d .
b a s e s e t a t lO O m s/div,
sam ple
th e
In
lin e s of th e in d iv id u a l
o sc illo sc o p e
tim e
s e ttin g .
fo r th e
two
c a b l e from t h e
gas
The m icrow ave r e f l e c t i o n
s a m p le
u sin g
th e
same
o p t i c a l p u l s e r e c o r d s s im p ly by
d e t e c t i o n d io d e i n p la c e o f th e
o
oo
o
nn
0
1Ô0 ms
500 ms
' (a) Puise amplitude envelopes
lOOms/div
2 0 ms/div
0
500ns
(b) Single p u is e s .
o p tic a l,
Delay 30ms(ie. 33rdpulse )
All records
Î
Intensity
NF^ :Kr
0
5Ô0ns
microwave reflection
Delay 180ms (ie.198th pulse)
1:3 , t o t a l pressure
— ^ Time
Figure 7.3 Examples of pulse records.
30Tprr
C hapter 7
7 .2
137
E x p e r i m e n t a l Programme
The
e x p e rim e n tal
work
c o n siste d
of
p relim in ary
d e v e lo p m e n t
f o ll o w e d by t h e e x e c u t i o n o f an e x t e n s i v e progran\me i n w hich t h e m ain
body
of
d a t a w ere c o l l e c t e d .
A lth o u g h t h i s programme to o k t h e form
o f a s e q u e n t i a l r o u t i n e i n w hich e a c h e x c im e r was s t u d i e d i n t u r n , i t
w ill
be
more
a p p ro p riate
c h ro n o lo g y
th ree
to
c la ssify
th e
e x p erim en tatio n
to th e p r e s e n t a t io n o f d a ta r a t h e r th an
of
t h e w ork.
broad s e c t i o n s ;
m ix tu re r a t i o s
T h is
u sefu l
in
adhere
te r m s
to
th e
T h e re fo re th e ex p erim en ts a re d iv id e d i n t o
spectrum
and p r e s s u r e s ,
id e n tific a tio n ,
in v e stig a tio n
of
and v a r i o u s m i s c e l l a n e o u s e x p e r i m e n t s .
breakdow n i s shown i n T a b le 7,1 which a l s o i n d i c a t e s t h e m eth o d s
used
and
t h e m ain
ex p erim en tal v a r ia b le s .
fu ll
r a n g e o f m i x t u r e r a t i o s t h a t w ere t e s t e d
T a b le 7*2 p r e s e n t s t h e
a nd
th e
app ro x im ate
p r e s s u r e r a n g e f o r w hich a d i s c h a r g e was o b t a i n e d f o r each m i x t u r e .
EXPERIMENT
Spectrum
METHOD
identification
iKeF
Kr F
A rF
XeCl
KpCI
ArCllnot
found]
As in Section 7.1.2
or similar.
XeO
Experimental programme
fo r mixture ratios and
to ta l
pressurelsee Table 7.2)
Spectra - 7.1.2 , intensity vs
XeF
tim e -m e th o d 1 in 7.1.1,pulse
records 7.1.3. ( 5 mixtures).
KrF
7.1.2 , method 2 in 7.1.1,
7.1.3 (3 mixtures).
7.1.2,method.1 -7.1.1.
XeCl
ArF (weak spectra only)
KrCl
2 mixtures
7.1.2
Variables B uffer and
donor ty p e ,m ix tu re
ratio,
t o t a l pressure.
Miscellaneous
1.Lasing attem pts in X e F ,
KrF, and XeCl.
2.
High and low pressure
spectra in KrF.
3 . Comparison of two tube
7.1.2 , method 1-7.1.1.
diam eters, K rF .
4.
Effect of tube coo7.11
ling ,KrF.
Table7.1 Principal classification of experiments.
1
BUFFER
DONOR IRARE
SF6 NF3 IGAS He 1 Ne Ar
KrF
1
1
1
1
1
2
3
4
5
1
1
1
6
1
1
1
1
3
3
3
3
1
1
7
8
1
10 P)1
9
1
11
1
13
17
18
1
20
21
30
30
1
1
1
1
28
29
30 P)
31
1
1
1
1
1
1
32
33
34
35 P)
36 p)1
37 1
1
1
1
1
46
1
1
1
1
1
49
1
1
1
1
1
5
33
100
500
7
4
16
100
1000
10
30
100
300
30
26 66
40 110
40 180
10
13 250
26 300
26 4 0 0
100
300
3 100
3
3
3
3
3
3
1200
210
DONOR RAREI BUFFER
SFs INF3 ' GAS He Ne Ar
XeF
P)1
6 460
1
6 1400
1
6 3000
1
76
3
1
1
P)1
1
P)1
1
800
P)1
1000
1400 P)1
240 P)
66 500
66 700
3 0 0 1200
6 0 0 1000 HQ
13 2 6 0 1
26 4 0 0 1
80 50 0 1
130 600 1
4 0 0 1400 1
500 1300 1
26 400 1
53 500 1
110 5 0 0 1
200 1300 1
13 79
1
30
3
700
200
500
400
13
500
0.5
1
3
3
22 0
220
400
300
26 500
13
100 100
100 300
100 1000
3
3
3
3
3
3
26 200
13
13
40
50
50 0
100
30 300
30 1000
30 2000
100
1
1
22
23
24
25
26
27
44
30
1
1
1
19
41
10
10
10
10
10
1
1
1
1
14
15
16
39
40
3
1
12
38
3
1
Pl
100 800
100 1000
100
3
10
30
3
10
30
100
300
1000
1
1
1
1
1
1
1
SF6
3
230
3 680
0.75 57
0.75 170
3
76
3
230
76
3
1
1
1
1
3
3
3
3
3
0.5
1
3
10
230
76
680
76
230
XeCl
30
100
300
3
3
3
100
300
1000
20 200
20 1000
20 2000
100
100 100
100 300
100 1000
20
80
NFi
ArF
1 30
30
1 30
60
3 250
100
100 100
100 200
13 170
13 210
13 250 1
4 0 300 1
13 170 1
13 250 1
26 500 1
4 0 900 1
110 1300
1
300 1500 HCl
400 1700 1
7 180 1
200 1000
P}-Also
30
30
30
%
50
50
50
50
50
50
50
50
50
50
50
9 0 0 's
1000s
900]s
500 5
800 5
1100 5
800 5
1000 s
900 5
T200 5
900 6
50 800 6
50 1000 6
50 500 5
50 600 c
50 1000 6
13
13
7
7
7
7
7
110 6
200 6
/MO 6
120 6
120 1
79 1
79 "
100 350 1
200 800 '
100 800 '
100 900 '
100 1000 1
300 1100 1
40
66
100
100
100
120
170
300 f
900 6
900 E
KrCl
5 0 hooo
5 0 13000
u se d in pulse e x p e r im e n ts
100
■ P u - Lowest,highest pressures of discharge in mB.
Table?.2 Experimental programme-mixture ratios and pressure ranges.
E
E
£
£
£
£
S
C hapter 8
8
138
RESULTS
The
traced
r e s u l t s ap p e arin g i n th e f ig u r e s of t h i s c h a p te r a r e e i t h e r
c o p i e s o f t h e raw d a t a o r g r a p h s p ro d u c e d
taken
from
th e
raw d a t a .
b a sis
g i v i n g a s much o f t h e d a t a
from
m e a s u re m e n ts
They a r e p r e s e n t e d f i r s t on an e m p i r i c a l
as p o ssib le in
a
c o n d e n se d f o rm .
F o llo w in g t h i s i s a s e r i e s o f s e c t i o n s i n w hich t h e d a t a a r e s e l e c t e d
from
t h e raw r e s u l t s
se ctio n
c o n ta in s
a c c o rd in g to v a rio u s a n a l y t i c a l
a
d isc u ssio n of
th e o u tsta n d in g
to p ic s.
Each
f e a tu r e s of th e
graphs p rese n ted .
8.1
E m p iric a l P r e s e n t a t i o n o f R e s u lts
The
vs
tim e
7 ,2 ),
d a t a shown i n F i g s 8 .1
reco rd s
In a l l of
fo r
t o 8 ,6 a r e t r a c i n g s o f t h e i n t e n s i t y
n e a r l y a l l o f t h e KrF m i x t u r e s (1 -4 ? i n T a b le
th ese
fig u re s
th e
rec o rd in g s
are
arranged
in
v e r t i c a l colum ns o f i n c r e a s i n g t o t a l p r e s s u r e w i t h a c o n s t a n t m i x t u r e
ra tio
F ig
w i t h i n e a c h colum n.
8,1
m ix tu res
but
on
a
la rg e r
number 1 t o 2 7 .
sc ale .
These r e s u l t s a r e f o r SF^:K r;H e
The 27 m i x t u r e s (co lu m n s)
are
p laced
groups,
each
g r o u p t h e colum ns a r e i n o r d e r o f i n c r e a s i n g d i l u t i o n d e s c r i b e d
th e
p a rtia l
SFg c o n t e n t .
g r o u p h a v in g a p a r t i c u l a r S F^iK r r a t i o .
in
fiv e
by
ea ch
F i g u r e s 8 . 2 ( a ) and 8 . 2 ( b ) a r e t h e same a s
W it h in
p r e s s u r e r a t i o o f th e t o t a l r a r e - g a s c o n te n t to th e
.c
Figure8.1 KrF intensity vs time records, SF^iKrHe mixtures (1 -2 7 in Table7.2)
reduced by 0.09. Time scale 10 sec per division.
o
o
un
o
m
co
m
o
o
un
o
o
m
m so
o
m
CM
o
o
m
o
oo
m
o
sO
CD
m
un
CD
o
s
CD
-d" û i
CD U J
OQ
Z
LU
cr
Figure 8.2 (a) As Fig.8.1, 0.18 reduction
(continued in Fig.8.2(b)).
CSI
so oo
CM
O
O
•*4- o
cs» o
o
o
o
o
m. o
m m
o
CM
o
m
o
vO
oo
o
m
o
o
m
CM
o
o
m
o
oo
m
o
o
LA
sO
m
o
ÇO
VO
o
oo
cr
LL.
ÜJ L/0
CQ
cr
Figure 8 . 2 ( b )
o
l/)
Œ
CC
a
LU
ex.
tn
(/)
LU
ex 110
Ü_
o130
150
170
230
300
1:10
1:30
1:100
mixture
Figure8.3 KrF Intensity vs time records, Nf^:Kr mixtures ( 2 8 - 3 4
reduced by 0 . 2 . 1 0 sec per division.
1:300
200
400
500
CÛ
600 S .
un
t/)
LU
Ce:
CL
700 <
o
800
1000
NF3iKr:He
1:3:100
SF^iKriHe 1:3:100
Figure 8.4 KrF Intensify vs i~ime records, donor comparison (35,36).
1 0 sec per division.
100
130
160
190
1 :3 :3 0
L-TOTAL PRESSURE-TORR'
Figure8.5 KrF Intensify vs time, Ar buffer (37-40)J0sec per div.
100
110
130
ce
ce 150
o
160
LU
190
ce 230
Z)
t/i
m 300
LU
ce
ÛL
<c
o
380
460
530
610
760
910
1140
1290
mixture
100
43
300
44
Figure 8.6 KrF In te n s ity vs Mme records, Ne b u f f e r . (41-47).
1 0 sec per division.
1000
Chapter 8
I 39
F ig u re
( 28 - 3 4 )
F ig u re
is
8 . 3 c o n t a i n s t h e r e c o r d s f o r t h e b i n a r y NF^iKr
w ith
colum ns
miLxtures
arranged i n th e o rd e r of in c r e a s in g d i l u t i o n .
8 .4 shows t h e r e c o r d s f o r t h e two m i x t u r e s ( 3 5 -3 6 ) w here
compared w i t h NF^.
R e c o rd s f o r t h e m i x t u r e s o f SFg.*Kr:Ar ( 3 7 - 4 0 )
are
shown i n F i g 8 .5 w here t h e SF^rKr r a t i o was c o n s t a n t a t 1 ;3
th e
colum ns
in
SF^
are in o rd er of in cre asin g d ilu tio n .
and
The r e c o r d s shown
F i g 8 .6 a r e s i m i l a r t o t h o s e o f F i g 8 .5 o n l y h e r e t h e b u f f e r
gas
i s Ne.
The
d a ta
shown
in
F ig s
8 . 7 t o 8 .1 3
vjere o b t a i n e d fro m peak-
in te n sity
and i n t e n s i t y h a l f l i f e m ea su rem e n ts o f t h e
d escrib ed
in
can
o b tain ed
raw d a t a .
records.
d a ta
as
The a p p r o p r i a t e m ethods and m i x t u r e r a t i o s
be found i n T a b l e s 7 .I and 7 . 2 .
re su lts
th e
T a b le 8 . 1 .
raw
F i g u r e s 8 .1 4 t o 8 .1 7
show
th e
u s i n g t h e p u l s e r e c o r d i n g s y s te m and a r e c o p i e s o f
T ab les 8 . 1 ,
7*1»
and 7 . 2 g i v e t h e d e t a i l s o f
th ese
.
50
r-
X
63
VI
1
1
I
X
^
X
1
51
'
1
X
.
1
1
52
,
X
^
I
- V — Æ—
j
•
...... L
1-----1___ I___j_
6 3 , 6 4 , 6 5 all l i f e t i m e s
belov/ 0 . 2 s
64
53
J
I
1
I
I
I
I
1
I
I____
»
I
1-
L
65
54
J
»
I
1
I
I
I
I
L
_X
I
I
I
I
I
I
I
L
55
J
!--------- 1___ _ l ______ 1 --
I______ L
58
-
56
*
ft
X
•
X
J
1--------- 1---------1______ I______ I
I
'
«
I _______ L
*
57
•
A
'
'
*
.
.
•
•
K
,
0
,
,
,
,
,
,
1
-
q
'
y,
X
X
’
X
X
59
"
-
X X
•
.
»
X
X
•
?
X
-
" 62
•»
X
•
X
1
1
— '
K
X
ic~
* 60
•
X
-
—
X
1
1
1
X
X
,
X
,
I
I
•
X
X
1
X
.. 1 -
,
X
X
X
'
X
?
r
X
1
K
fX
,
_ .L .
Figure 8.7Empiricai presentation,XeF. Explanation-Table 8.1 and7.2.
J --------- 1____
I
V I V
I
I
I
12
XX
-
X
_L
-
. 2
Xx
13
8
.y
<
9
X
'
14
X
ac
K«..
1----- 1-----u
J
1-----1----- 1
- 15
X
- 4
?
X
X ■
J
f
L
Points belonging
to graph below
- ^ 1 . *
t______L
Fi gur e 8.8 KrF
X •
28
23
16
■1
I
I
I
L
.J
1
L.
29
24
I
1
I
I
I
1-----1
X
K
X '
17
30
25
1.
JL
I
I
1
_J
1
31
!l
J
I
L
-V—
19
J
I—
32
_ 26
L
20
XX
J
1
L.
.• *
* '
•
,
— I--------1--------- 1---------1-------:
21
X
33
X
27
22
34
J
I
I
I
F i g u r e 8 .9 KrF
I
I
I
L
■I
..I —
I.
48
35
37
o X
X X ®
49
a
36
—
i-
0
■_
38
.1-----1-----1___ I
/A
J — -—
I----------- 1------------1
t
I
I
I
___ I....
© in s t a b i li ti e s
39
XyX
lî-
1______ L
40
% '" ,
F i g u r e 8.10KrF
I
I
41
45
42
-I
U
1
I
I
I
L
J S — !X___ 2 i
I
I
I
• X
"Xt
J
46
J.
43
- »*x
I
I
I
J
X
K
44
• %
J
L
- 47
,
J
1
I
I
F i g u r e 8.11 KrF
I
L
1
I
iO
x ..t
% _____1______ I______ 1___ _ _ i--------- 1-------— ,— u
66
67
tV.v.
73
78
68
•
-I—--- 1----- u
% 69
- 74
J ---------1-------- 1-------- 1---------1-------- l _ _ _ l _____ L
70
83
75
71
J
I
79
76
72
60
F ig u r e 8.12XeCl
!---------1-------- 1-------- L
93
J
1_______ 1_______ t______ J ............. 1________ L
94
J
F i g u r e 8.13KrCl
J
{
I
I
!
I
I
I
L
Peak in te n s ity and in te n s ity h a l f - l i f e vs pressure. (Derived from
spectrum,and intensity vs tim e,records).
Vertical
Horizontal
Axis
Axis
Mixtures Pressure Relative
Half
Figure Excimer (Table 7.2) Scale
Intensity Life X
8.7
XeF
5 0 -6 5
lOOmB/div
8 .8
KrF
1 -1 5
lOOTorr/div
8.9
KrF
1 6 -3 4
11
1
8.10
KrF
35—40
11
!1
4 8 -4 9
!1
1i
11
r1
KrF
4 1 -4 7
1t
&12
XeCl
6 6 -7 5
!1
0
7 6 —78
I 1
0
7 9 -8 3
11
9 3 —94
]1
KrCl
0 linear f i t
1se c/di v
8.11
&13
X exponential f i t
!
*
Relative in t e n s it y only comparable within each set of mixtures
except KrF where the four sets are intercom parable.
Multiple pulse and single pulse in te n s ity vs time.(Assembled from
oscilloscope tracings).See also Figure7.3.
Figure Excimer
Column (a)
Column(b) and(c)
Multiple pulse amplitude envelopes, Single delayed pulse
KrF
8.14
815
KrF
—
f a s t ,—
- - s lo w time base ~
ms/div indicated.
microwave refle c tio n
- - — optical.Delay shown
in ms.100ns/div.
8.16
KrF
8.17
KrF
Multiple pulse amplitude envelopes.
Table 8.1 Key for Figures 8.7 to 8.T7.(Data p re s e n ta tio n on an empirical basis J
microvyave pulse with
no absorption
20
180
‘100
70T
■100
180
60T
100
180
50T
100
180
40T
— p.
r\
180
100
30T
20T
"T
Figure 8.14KrF
N Fq:K r1:3
(30). Explanation - Table 8.1
10 T
-200
“'-200
200
' r —r
150T
---- 1--- ^I---^----Î""
185
■»— r —1-{—
200
r
HOT
801
60T
50
40 T
30T
F i g u r e 8.15KrF NF-,:Kr:He 1 :3 :10
4 0 0 mB
4 0 0 mB
100
100
300 mB
3 0 0 mB
100
100
200 rnB
2 0 0 mB
20
100
100 mB
100 mB
0
50
rnS
N F3:K r:H g 1:3:100
100
ms
S F s:K r:H e
1 :3 :1 0 0
Figure 8.16 KrF Amplitude envelopes (cont. Fig8.17) (35,36).
20
1000 mB
8 0 0 mB
L
100
800 mB
T T
100
700mB
100
6 0 0 mB
100
6 0 0 mB
100
500 mB
500 mB
0
mS
NF3 : Kr : He
Figure 8.17KrF
1:3:100
100
100
mS
SF6-.K r:H e
1 :3 :1 0 0
100
Chapter 8
8 .2
140
E xcim er S p e c t r a
The
B “ X e m is s io n s p e c t r a o f a l l th e r a r e - g a s h a lid e m o le c u le s
o b s e r v e d (XeF,
to
XeCl,
KrF, K rC l, and ArF) a r e p r e s e n t e d i n F i g s 8 .1 8
8 .2 2 w ith th e v i b r a t i o n a l assig n m en ts g iv e n in th e l i t e r a t u r e f o r
XeF
and XeCl,
In o rd e r to d e m o n stra te th e e f f e c t o f th e
to ta l
gas
p r e s s u r e on t h e e m i s s i o n p r o f i l e , a low p r e s s u r e s p e c tr u m i s i n c l u d e d
f o r XeF,
XeCl, and KrF.
th ere fo re
low
q u ite
d iffic u lt
b a c k g ro u n d s p e c t r u m ,
rate s
w e re
The s p e c tr u m o f ArF ( F i g 8 .2 2 ) was we ale and
req u ired
to o b tain .
To p r o d u c e a s p e c tr u m w i t h a
lo n g i n t e g r a t i o n t im e s and f a s t
gas
flo w
t o c o m p e n s a te f o r t h e s h o r t e m i s s i o n l i f e t i m e .
B e cause o f t h e s e d i f f i c u l t i e s ,
ArF was n o t s t u d i e d i n d e t a i l i n t h i s
w ork.
A t t e m p ts
However,
id e n tify
w ere
made
to
s t u d y t h e s p e c tr u m o f t h e XeO e x c im e r .
t h i s e m i s s i o n p ro v e d t o be v e r y d i f f i c u l t
in
th e p re s e n t a p p a ra tu s.
to
o b tain
and
The c l e a r e s t r e s u l t r e c o r d e d i s
shown i n F i g 8 .2 3 and was o b ta i,n e d u s i n g a lo n g i n t e g r a t i o n tim e w i t h
f a s t g as flo w .
A
D e sp ite t h i s ,
num erous b a c k g ro u n d l i n e s a r e p r e s e n t .
m erc u ry s p e c t r u m was s u p e rim p o s e d on t h i s r e c o r d by s w i t c h i n g
the
a lo n g
d isch arg e
and
a llo w in g
th e d is c h a r g e tube a x i s .
o ff
t h e e m i s s i o n o f a m e r c w y lamp t o p a s s
The s m a l l s p e c t r u m i n
F ig
8 .2 3
is
r e p r o d u c e d from K enty e t . a l . (1 9 4 6 ) and d e m o n s t r a t e s c l e a r l y t h a t t h e
XeO s p e c tr u m i s p r e s e n t i n t h e r e c o r d .
in
O
eu
c^<C
o
o
“ Ln
m
CD
CD
_Û
O
m
o>
o
vO
W
m
o<
o
Ln
m
CL
X
CD
LU
co
co
IL .
vO
eu
m
ui
NO
rC7S
m
eu
c
eu
in
!g
en
C
m
eu
t/î
.4 -.
c
eu
E
c
o<
o
o
gi
t/}
t /)
m
m
fO
c
o
o
4—
m
CM
c_
-O
O
U
eu
CM
t/)
OC
o>
o
o
(U .
CD
CO
O
o
LJ
o
o
ON
m
X
J
CO
LJ
X
CTn
co
eu
c_
o
en
oC
o
o
m
_ o
ca
E
o
o
-j-
g
’ un
(S)
8
m
rc
iê
lûF
un
E-
Z)
c..
u
eu
CL
(/)
¥
m
LL_
<z>
(NI
cd
2
®<C
o
oi
CÛ
E
o
o
un
o
o
o
o
un
<u
rc
LJ
3=
E
3
L_
4-w
W
eu
m
CL
CÛ
LJ
CM
cxC
o
o
cd
OJ
i_
3
en
o<C
o
o
o
CM
ÛQ
E
o
CM
O
m
o<C
o
, o
On
00
Ê
3
t_
J—
U
ÜJ
□u
10
X
t
en
<
CM
CM
CQ
QJ
C_
3
en
û-
5556
5512
m
5452
5383
5315
5274
5238
5200
oo
w
CL
o
O
CM
C-
o<
o
m
O
VO
O
m
CN
cd
oo
o
o
cm
C hapter 8
8 .3
141
M ix t u r e R a t i o s and T o t a l F r e s s u r e
One
o f t h e aim s o f
e m p iric a lly ,
th e
flu o re sc e n t
These
th e
m ix tu re
e m issio n ,
present
ra tio s
i n v e s t i g a t i o n was t o
fin d ,
and t o t a l p r e s s u r e f o r which t h e
f o r any g i v e n e x c im e r s y s te m ,
was
a maximum.
r a t i o s and p r e s s u r e s c o u ld t h e n be u s e d a s a s t a r t i n g
p o in t in
a tte m p ts to o b ta in la s in g .
8 .3 .1
XeF M ix t u r e s
For
in
XeF t h e r e s u l t s i n F i g 8 .7 g i v e an i n d i c a t i o n o f t h e t r e n d s
o u t p u t a c com panying v a r i a t i o n s i n m i x t u r e s .
n o tab ly
t h e m i x t u r e s w i t h NF^ d o n o r ,
th e
I n some c a s e s ,
e m issio n
m ost
life tim e s
are
s h o r t , b e in g w e l l below t h e 0 , 3 s e c o n d r e s p o n s e tim e o f t h e r e c o r d i n g
s y s te m
o v e r t h e w hole p r e s s u r e r a n g e .
re la tiv e
over
For
th ese
a
h ig h er
i n t e n s i t y t h a n t h a t r e c o r d e d would be o b t a i n e d i f o p e r a t i o n
a s m a l l number o f p u l s e s had b e e n f e a s i b l e .
th ree
cases
groups
T a b le 7 . 2
W it h in e a c h o f t h e
o f t h e m i x t u r e s o f SF^:Xe;He ( 5 0 - 5 2 ,
and F ig 8 .7 ) »
53-55,
th e peak i n t e n s i t y o c c u rs a t
5 6 -5 7 i n
h ig h er
to ta l
p r e s s u r e a s t h e m i x t u r e becomes more d i l u t e and a l s o t h e g a s l i f e t i m e
r i s e s r a p i d l y w ith t o t a l p r e s s u r e .
g en eral
pealc
e ffe c ts
e m issio n
life tim e s.
a p p a ra tu s,
fra c tio n
of
to
W it h in
in cre asin g
lo w e r
th e
i t seems t h a t ,
to ta l
Comparing t h e s e t h r e e g r o u p s ,
th e
t h e donor f r a c t i o n a r e t o s h i f t t h e
p ressure
and
g iv e
in c re a se d
gas
l i m i t a t i o n s s e t by t h e r e s p o n s e tim e o f t h e
f o r SF^:Xe:He m i x t u r e s , t h e s m a l l e r d o n o r
may be more s u i t a b l e .
M ix tu res a p p ro x im atin g 1 :6 :5 0 0 ,
fo r
ex a m p le, may be optimum f o r peak o u t p u t f o r s m a l l numbers o f p u l s e s .
Chapter 8
The
142
r e s u l t s f o r m i x t u r e s 62~67 i n
is
h ig h er
o u tp u t
sig n a l
o c c u rrin g th rough v ery s h o r t l i f e t i m e s .
bu ffer
show
a
o b tain ed
F i g 8 .7
sm all
show
w i t h NF^ a s d o n o r ,
o u tp u t
o n ly .
Thus
th at
a
much
d e s p i t e th e reduced
R e s u lts u sin g
it
argon
seems t h a t f o r h i g h
i n t e n s i t y f o r s m a l l numbers o f p u l s e s i n XeF e m i s s i o n ,
NF^ s h o u l d be
u se d a s d onor and, s i n c e g r e a t e r i n t e n s i t i e s a r e s e e n f o r m i x t u r e s 58
and
59 t h a n f o r 53 and 5 4 ,
optimum
may
ra tio s
neon s h o u ld be u s e d a s t h e b u f f e r .
f o r f lu o r e s c e n t em issio n a re d i f f i c u l t to a s s e s s b u t
n o t be p a r t i c u l a r l y c r i t i c a l .
ap p ro x im ate
The
range
h ig h er d ilu tio n ,
1 : 3 :1 0 0 - 1 0 0 0
Thus NFg:Xe;Ne
may
su ffice .
m ix tu re s
It
th e
may be t h a t t h e
w h ile g iv in g l e s s f l u o r e s c e n t e m issio n ,
c o u ld g iv e
b e tte r
lase r
life ,
SFg i s s u p e r i o r t o NF^ b u t l a s e r o p e r a t i o n may be much h a r d e r
to
a c h ie v e
o p e ra tio n
in
w i t h SF^.
due t o r e l a x a t i o n o f t h e B s t a t e .
F o r lo n g
T h e r e f o r e i n a p p l i c a t i o n s w here lo n g g a s l i f e
i s o f p r im a r y i m p o r ta n c e i t may be p o s s i b l e t o u s e SF^ i n s t e a d o f NF^
i f reduced l a s e r o u tp u t i s a c c e p ta b le .
8 .3 .2
KrF M ix t u r e s
The
th e
These
KrF
re su lts
( 1 - 4 9 i n T a b le 7 . 2 ) w ere t h e m ost d e t a i l e d o f
ex p erim en tal sequence,
may
be
exam ined
e s p e c i a l l y 1-27 f o r S F ^ :K r:H e
m ix tu re s.
i n F ig s 8 .1 ,
8 . 2 ( a ) and 8 . 2 ( b ) and a l s o i n
F i g s 8 ,8 and 8 . 9 w here t h e g r o u p s 1 - 6 ,
7 - 1 2 , 13-17» 18-23» a n d 2 4 -2 7
c o r r e s p o n d t o a p r o g r e s s i v e d e c r e a s e i n do n o r f r a c t i o n ,
ea c h
g r o u p a r a n g e o f d i l u t i o n by t h e
m ajo rity
of
cases
th e
b u ffer
is
w h ile w ith in
teste d .
gas l i f e t i m e i s lo n g e r th an 0 .3 s e c .
In
th e
I t is
C hapter 8
m ost
143
n o t i c e a b l e t h a t c h a n g e s i n t h e pealc i n t e n s i t y w i t h
m ix tu re
ratio s
c le a rly
i n F i g 8 .2 4
pressure
at
are
w here
p a rticu la rly
th e
pealc
sharp.
in
T h i s i s shown more
in te n sity
and
th e
a b so lu te
which i t o c c u r s a r e p l o t t e d a g a i n s t d on or f r a c t i o n on a
n e g a tiv e log s c a le .
graph.
not
changes
The d o n o r : r a r e - g a s r a t i o i s c o n s t a n t w i t h i n e a c h
The b ro a d t r e n d i s t o a maximum w i t h d o n o r ; r a r e - g a s r a t i o s i n
t h e r a n g e 1:1 t o 1 :3 w i t h d o n o r : t o t a l g a s c o n t e n t r a t i o s i n t h e r a n g e
1 :5
to
1:1
t h e maximum o c c u r s a t a b o u t 5 T o r r w here t h e B - X e m i s s i o n band
is
1 :3 0 0 .
s till
are
rath e r
p referred
However,
broad.
and
for
i n t h e e x tre m e c a s e o f SF^:K r i n t h e r a t i o
0
For h ig h r e l a x a t i o n h ig h e r t o t a l p r e s s u r e s
peak
e m i s s i o n above
say
500 T o r r
to ta l
p r e s s u r e , r a t i o s i n t h e r e g i o n o f 1 : 3 : 1 0 0 may g i v e t h e optimum l a s i n g
m ix tu re .
8 .3 * 3
XeCl M ix t u r e s
The
c h o o s in g
r e s u l t s f o r XeCl ( F i g 8 .1 2 ) g i v e o n l y
an
optimum
m ix tu re
sin c e
th e
a
rough
b e h a v io u r
a t,
F ig u re 8 .2 5
and t h e p r e s s u r e i t o c c u r s
a g a i n s t d o n o r f r a c t i o n i n t h e same f a s h i o n a s F i g 8 . 2 4 .
re su lts
suggest
r a t i o 1 :2 0 :2 0 0 .
an
fo r
shows no s h a r p
f e a t u r e s and t h e r a t i o s w e re n o t t e s t e d i n g r e a t d e t a i l .
p r e s e n t s t h e v a r i a t i o n o f p eak i n t e n s i t y ,
b a sis
T hese
optimum m i x t u r e o f HCl:Xe:He i n t h e a p p r o x i m a t e
S B ;K
ce:
g
UJ
q:
00
1:10
00
UJ
00
LU
1:30
<
UJ
CL
UJ
LU
a:
- m Torr ijQo
-300
-100
DONOR FRACTION
Figure 8.24 Peak intensify and corresponding fofa I pressure vs donor fraction.
KrF with helium buffer.
HCl:X
CK
g
UJ
a;
1:20
uo
UJ
g
§
LU
<
LU
CL
r 4 0 0 Torr
1:100
LU
>
œ
3
10
100
1000
DONOR FRACTION
Figure8.25Peak intensity and corresponding pressure vs donor
fra c tio n .> Z l with helium buffer.
C hapter 8
8 .3 .4
144
L a s in g A t t e m p ts
A t t e m p ts
XeCl
u sin g
above.
ranges
of
m ix tu re s
KrF,
and
i n t h e v i c i n i t y o f t h o s e m e n tio n e d
The low o p t i c a l l o s s a r r a n g e m e n ts d e s c r i b e d i n S e c t i o n 5 . 3 . 2
w ere
used
a v a ila b le
o p tic a l
w ith
th e
m ost
( a b o u t 98% ).
a b so rp tio n
a v a ila b le ,
h ig h ly
S in ce
and
g a in
re fle c tiv e
a p p a ra tu s
at
th e
t h e e m i s s i o n s p e c tr u m was
in creased
w ere
w ere made t o o b t a i n l a s e r o p e r a t i o n i n XeF,
in te n sity
at
w e re
made
w ith
fa ste st
th a t
c o u ld
be
lasin g
exam ined
th e
f lo w in g
p ro d u c e d
gas
for
in
pressures.
u sin g
th e
m irro rs
m ea su rem e n t
w av elen g th
t h e e m i s s i o n band c e n t r e s .
t e s t e d o v e r a w ide r a n g e o f t o t a l
a tte m p ts
fo r
d ie le c tric
was
in d ic a tio n
of
not
of
S t a t i c m ix tu re s
F o l lo w in g
th is
f lo w r a t e s up t o t h e
a p p a ra tu s.
T h is
was
p a r t i c u l a r l y e f f e c t i v e i n i n c r e a s i n g t h e i n t e g r a t e d (1 s e c ) i n t e n s i t y
o f m i x t u r e s c o n t a i n i n g NF^.
th e
of
t e s t s o f n e t g a i n a t t h e e m i s s i o n band c e n t r e s .
seems
lik e ly
e x c im e r
m icrow ave
was
is
to
50kW.
present
be i n s u f f i c i e n t f o r l a s e r o p e r a t i o n .
e v e n more l i k e l y when i t
pumped
in
The d i s c u s s i o n s
S e c t i o n 2 . 3 i n d i c a t e d t h a t t h e pump power d e n s i t y i n t h e
a p p a ra tu s
o n ly
However, no e v i d e n c e was fo und i n any o f
is
c o n sid e re d
l a s e r r e p o r t e d by M endelsohn e t .
p u l s e power o f 600kW,
th at
a l,
th e
T h is
m icrow ave
(19 8 1 ) u s e d a
w h i l e t h e p u l s e power u s e d h e r e was
I n a d d i t i o n t h e y r e p o r t e d a n e f f i c i e n c y o f 0,01% w h e r e a s
th e c a l c u l a t i o n s o f S e c tio n 2 .3 an o v e r a l l e f f i c i e n c y
of
0.084%
u s e d t o g i v e t h e m ost o p t i m i s t i c t h r e s h o l d pump power d e n s i t y o f
lOkW cm~^.
Chapter 8
8 .3 .5
145
M ix t u r e s . With, No B u f f e r Gas
It
c a n be s e e n i n T a b le 7 . 2 t h a t some m i x t u r e s w e re
w hich no b u f f e r g a s was p r e s e n t ,
Peak
nam ely 8 F ^ ; E r ,
i n t e n s i t i e s and t h e p r e s s u r e s t h a t
a g a in st
th e
th ey
tested
in
NF^:K r, and HCl;Xe.
occur
donor f r a c t i o n ( i n v e r s e ) i n F i g 8 . 2 6 .
at
are
shown
I t i s no ted t h a t
h i g h r e l a t i v e i n t e n s i t i e s a r e p o s s i b l e w i t h no b u f f e r g a s .
The g r a p h
for
XeCl
The
g r a p h f o r KrF w i t h SF^ a s donor i s r a t h e r i r r e g u l a r and a c h o i c e
of
th e
an
i s smooth w i t h an optimum r a t i o o f a b o u t 1 :1 0 0 f o r HCl:Xe.
optimum
donor,
m i x t u r e would be m e a n i n g l e s s .
Where NF^ i s u s e d f o r
th e r e s u l t s a re h ig h ly i r r e g u l a r .
I n a l l c a s e s t h e peak
i n t e n s i t y o c c u r s a t a p r e s s u r e o f b e tw e e n 30 a nd 100 T o r r .
XeCl
HChXe
KrF
S F ^ r Kr
cx
ex
o
LU
cx
ZD
00
00
LU
cx
CL
Q
z
<
I—
►
—«
I—
z
»— I
LU
>
LU
CX
800
600
400
200
X
0.5
3
10
30
100
300
DONOR FRACTION
Figure 8 .2 6 Mixtures with no b u ffe r Peak intensify and corresponding
pressure vs donor fr a c tio n /
'
Chapter 8
8 .4
146
Temperal_ B e h a y io u r
In
e x c im e r
G e n e ra lly
la se rs,
gas
m i x t u r e s h ave a l i m i t e d u s e f u l l i f e .
t h e l a s e r o u t p u t f o r a s i n g l e g a s f i l l d e c r e a s e s w i t h tim e
u n t i l l a s i n g no l o n g e r o c c u r s .
the
T h i s means t h a t e x c im e r l a s e r s s u f f e r
i n c o n v e n i e n c e and e x p e n se o f f r e q u e n t g a s r e p l a c e m e n t .
For th is
r e a s o n a m a jo r p a r t o f t h e p r e s e n t s t u d y i n v o l v e d t e m p o r a l r e c o r d i n g s
of
t h e e x c im e r e m i s s i o n s from which g a s l i f e t i m e s c o u ld be m e a s u r e d .
However,
very
t h e i n t e n s i t y f o l l o w s a s im p l e e x p o n e n t i a l d e c a y t o z e r o i n
few
cases
b eh av io u r
in
and
g e n e ra lly
i s d isp la y e d .
an
in te re stin g
re su lts
Method 2
th a t
are
a ll
and t h e p u l s e r e c o r d i n g
is,
alre ad y
r e v ie w e d
complex
tim e
The d e t a i l s o f t h i s b e h a v i o u r a r e d e s c r i b e d
t h i s s e c t i o n i n term s o f th e v a rio u s
The
and
a l l t h e KrF r e s u l t s .
b e e n p r e s e n t e d i n F i g s 8.1
p aram eters t h a t
th o se
w h e re
affect
it.
te m p o r a l r e c o r d i n g by
m ethod ( s e e C h a p t e r 7)
w ere
used,
The raw d a t a f o r t h e s e r e s u l t s h a v e
to
8 .6
fo r
th e
in te n sity -tim e
r e c o r d s and i n F i g s 8 . 1 4 t o 8 .1 7 f o r t h e p u l s e r e c o r d i n g m eth o d .
It
i s p o i n t e d o u t h e r e t h a t t h e s m a l l d i s c h a r g e volume and h i g h
r e p e t i t i o n r a t e a f f o r d e d by t h e m icrow ave a p p a r a t u s p r o v i d e s a u n iq u e
o p p o rtu n ity
for
a c ce lera te d
gas
life tim e stu d ie s.
The a c t i v e g a s
volume i n DC d i s c h a r g e pumped e x c im e r l a s e r s i s u s u a l l y a b o u t 1 l i t r e
w h ile
re p e titio n
ra te s
are
u su a lly
a p p a ra tu s
t h e volume was a b o u t 0.5cm
IIO O pps.
Thus
b e tw e e n
(The
th e
ex p erim en ts
th a t
about I p p s ,
and t h e
w e re
I n t h e m icrow ave
re p e titio n
ra te
was
c a r r i e d o u t w ould t a k e
10^ and 10^ t i m e s l o n g e r u s i n g a c o n v e n t i o n a l e x c im e r l a s e r .
u n c e r t a i n t y i n t h i s s c a l e f a c t o r a r i s e s fro m u n c e r t a i n t y i n t h e
r o l e o f t h e d i f f e r e n t g a s vo lu m e s; t h e power d e n s i t y i s c o m p a ra b le i n
C hapter 8
147
both c a s e s ) .
Where
life tim e s
m u ltip lic a tio n
For
donor
th a t
quoted
,a n d
expressed
in
by 1100 w i l l g i v e t h e l i f e t i m e i n numbers o f
c o m p a r is o n
m e a s u re d
are
w ith
gas
liv e s
in
o th er
sy stem s,
i n t h i s work s h o u l d be n o r m a l is e d f o r g a s
p a rtia l
seconds,
p u lse s.
th e gas l i v e s
volume
and
•“'S
The d i s c h a r g e volume was a b o u t 0.63cm ' so
pressure.
m u l t i p l i c a t i o n o f a l i f e t i m e by 1 .6 x 1 0 ^ g i v e s t h e l i f e t i m e
litre
of
d iv id in g
gas.
re la tio n
N o rm a lisa tio n
a l i f e t i m e by t h e
However,
sin c e
th ere
th e
fo r
do n o r p a r t i a l p r e s s u r e r e q u i r e s
c o rre sp o n d in g
appears
per
donor
p a rtial
pressure.
t o be a n o n - l i n e a r and i n c o n s i s t e n t
b e tw e en donor p a r t i a l p r e s s u r e and g a s l i f e t i m e t h r o u g h t h e
r e s u l t s n o r m a l i s a t i o n f o r do n o r f r a c t i o n i s n o t p o s s i b l e .
8 .4 .1
M n g l e P u l s e B e h a v io u r
S in g le
o p tic a l
p u lses
w e re r e c o r d e d a s d e s c r i b e d i n C h a p t e r 7
and
a p p e a r i n t h e d a s h e d c u r v e s o f colum ns ( b ) and ( o ) i n
and
8 .1 5
on
a
tim e
s c a l e o f 1 0 O n s / d iv .
F i g s 8 ,1 4
The c o n t i n u o u s cur*ves i n
t h e s e r e c o r d s a r e o f t h e s i m u l t a n e o u s o u t p u t from t h e d e t e c t i o n d io d e
in
th e
m icrow ave
m icrow ave
ap p a ra tu s
a b so rp tio n .
a
ro u g h
in d ic a tio n of th e
The numbers appended t o each r e c o r d g i v e
d e l a y i n ms b e tw e e n t h e f i r s t m icrowave p u l s e and
o p tic a l
are
g iv e
The m icrow ave p u l s e w i t h no a b s o r p t i o n t a k i n g
p l a c e i s shown i n F i g 8 . 1 4 .
th e
and
p u l s e ( a n d m icrow ave p u l s e ) .
th e
recorded
The i n s t a n t s o f t h e r e c o r d i n g s
i n d i c a t e d on t h e p u l s e a m p l i t u d e e n v e lo p e r e c o r d s i n column
(a)
where t h e numbers r e p r e s e n t t h e m s / d i v f o r t h e two t i m e - b a s e s used*
C hapter 8
148
B efo re
a tte m p t
in te rp re tin g
th ese
reco rd s
i t s h o u ld be n o t e d t h a t no
was made t o o b t a i n a c a l i b r a t i o n o f
th e
o p tic a l
in te n sity
sc a le or of
t h e m icrow ave s i g n a l s t r e n g t h ;
t h e m icrow ave s i g n a l
e sp ecially
may be n o n - l i n e a r ( i n
due
in v o lv e d .
In a d d itio n
m icrow ave
w ith
to
th e
h ig h
pow ers
t h e te m p o r a l s u p e r p o s i t i o n
some
The m icrow ave s i g n a l s show,
u n c e rtain ty ,
of th e
p ro b ab ly of
t y p i c a l l y , an e a r l y sp ik e
by a ro u g h p l a t e a u w hich i s due t o low a b s o r p t i o n a t f i r s t ,
re fle c tio n
ab so rp tio n
th e
th is
and o p t i c a l s i g n a l s h a s
a ro u n d lO n s,
fo llo w e d
to
power)
sc ale
from
th e
sh o rt
c i r c u i t term in a tio n ,
d u rin g th e re m a in d e r o f th e p u ls e .
re fle c te d
w aveguide
(unabsorbed) s i g n a l ,
te rm in a tio n ( i e .
f o l l o w e d by
The d e g r e e
a f t e r breakdow n,
tra n sm issio n
r a t h e r t h a n r e f l e c t i o n from t h e d i s c h a r g e ,
th ro u g h
to
w hich
i s due t o t h e
th e
d isc h a rg e),
c a n n o t be d e t e r m i n e d from
th e s e re c o rd s .
The
pealc i n t h e o p t i c a l s i g n a l o c c u r s i n m ost c a s e s a b o u t
a fte r
th e
peaks
a r e b e tw e en 100ns and 200ns w ide and t h e w i d t h b e a r s l i t t l e
no
p rin c ip a l
re la tio n
to
th e
i n c r e a s e i n m icrow ave a b s o r p t i o n .
50ns
m icrow ave
a b so rp tio n .
The o p t i c a l
A ls o t h e r e i s no c l e a r
re la tio n
be tw e en t h e o p t i c a l p u l s e w id th and t h e t o t a l p r e s s u r e .
s h iftin g
fro m
th e
th e e a rly p u lse s to l a t e r p u lse s,
l o s s of th e in te n s e peak.
bu ffer
w ith o u t.
gas
in
th e
m ix tu re
G e n e rally
have
a ll
or
th e
th e
In
m ain change i s
re su lts
w ith
a
a w id er o p t i c a l p u ls e th a n th o se
C hapter 8
149
W ith
in
th e e x c e p tio n o f th e (p erh a p s s p u rio u s ) r e s u l t a t
F ig 8 .1 5 ,
breakdow n
is
more
p u lses
in th e t r a i n of p u lse s.
b efore
th e
o p p o site
230T orr
r a p i d a t low p r e s s u r e s f o r e a r l y
Below a b o u t BOTorr breakdow n
m icrowave p u l s e h a s r i s e n t o i t s maximum.
occu rs
However,
th e
a p p e a r s t o be t h e c a s e f o r l a t e r p u l s e s (colum n ( c ) ) i n t h e
u n b u ffered m ix tu re (F ig 8 .1 4 ) .
The m ost o u t s t a n d i n g f e a t u r e o f t h e s e r e c o r d s i s t h e l a c k o f any
stro n g
on
dependency o f t h e s i n g l e o p t i c a l and m icrow ave p u l s e f e a t u r e s
to ta l
seems
pressure
or th e p resence of a b u f f e r g a s.
m e r e ly t o p e r m i t o p e r a t i o n a t h i g h e r
c o n c lu d e d
th en
th a t
th e
o p tic a l
pressure.
It
m ust
be
p u l s e i n t e n s i t y and w i d t h i s n o t
l i m i t e d by t h e number d e n s i t y o f t h e d onor g a s .
th e
The b u f f e r g a s
The o b s e r v a t i o n t h a t
f l u o r e s c e n t o u tp u t d e c re a s e s d u rin g th e second h a l f of th e p u ls e
e v e n th o u g h , i n many c a s e s , t h e m icrow ave a b s o r p t i o n r e m a in s h i g h , i s
o f c o n s id e r a b le im p o rta n c e .
th e
so urce o f t h i s d e c re a s e .
from
(le ss
w hich
cause
T h e re a r e p e r h a p s
may be s o u g h t ;
two
gen eral
areas
gro w in g d i s c h a r g e i n e f f i c i e n c y
m e t a s t a b l e e x c i t a t i o n ) an d q u e n c h in g by a s p e c i e s g e n e r a t e d i n
th e r e a c tio n .
passed
a
However, t h e r e i s no c l e a r i n d i c a t i o n o f
F o r e xam ple, t h e e l e c t r o n e n e rg y d i s t r i b u t i o n may h a v e
th r o u g h t h e optimum f o r m e t a s t a b l e p r o d u c t i o n by
h a l f o f th e p u lse .
th e
second
C hapter 8
8 .4 .2
150
P u l s e E n v e lo p e R e c o rd s
R e c o rd s
F i g s 8 .1 4
p u lses
th e
a
record
ranges
are p a r tic u la r ly
v a ria tio n s
a p p a ra tu s.
stro n g
e n v elo p es
of
o p tic a l
p u lses
and 8 . 1 5 colum n ( a ) and F i g s 8 .1 6 and 8 . 1 7 •
in
re su lts
show ing
on
a
ap p ro x im ate ly
im p o rta n t
tim e sc a le
below
The number o f
from 20 t o 2 0 0 0 .
fo r
in d ic a tin g
th e
0 .3 s e c
lim it of
th ere is
s till a
I t i s im m ed iately se en t h a t
v a ria tio n
appear in
These
p u lse -to -p u lse
i n p eak i n t e n s i t y w i t h t o t a l p r e s s u r e .
t h e OSA
lac k
of
The c u r v e s
at
t h e l o w e r p r e s s u r e s i n F i g s 8 .1 4
and 8 .1 5 and f o r t h e NF_ m i x t u r e
in
F i g 8 ,1 6 c a n be d e s c r i b e d q u i t e w e l l by a r a p i d r i s e t o a maximum
f o ll o w e d
by an e x p o n e n t i a l d e c a y .
to
t o h a l f o f i t s peak v a l u e i s p l o t t e d a g a i n s t t o t a l p r e s s u r e
fa ll
(on
su ch
The tim e t a l œ n f o r t h e
lo g -lo g s c a le s ) f o r th ese cases i n
F ig 8 .2 7 .
O th e r
in te n sity
fea tu re s,
a s t h e g r a d u a l r i s e t o maximum t h a t o c c u r s a t h i g h e r p r e s s u r e s ,
t h e l o n g te r m p l a t e a u , and i n s t a b i l i t i e s , a r e a l s o p r e s e n t i n t h e OSA
tim e
records.
featu res
It
w ill
th erefo re
be a p p r o p r i a t e t o d i s c u s s t h e s e
in c o n ju n c tio n w ith th e c o n s id e ra tio n of th e
OSA
tem poral
r e c o r d s t h a t now f o l l o w s .
8 .4 .3
Temporal R e c o rd s
The
F i g s 8.1
OSA
te m p o r a l
and 8 , 2 .
records
for
appear in
8 ,1 6 and
8 ,1 7
F i g 8 ,3 f o r u n b u f f e r e d m i x t u r e s u s i n g NF^, and
F i g s 8 .5 and 8 ,6 f o r Ar and Ne b u f f e r s ,
d isp la y
m ix tu re s
O ther r e s u l t s a p p ear i n F ig s 8 . 4 ,
f o r d o n o r c o m p a r is o n ,
reco rd s
SF^;K r:H e
re sp e c tiv e ly .
Some o f t h e s e
an app ro x im ate r a p id r i s e - e x p o n e n tia l decay curve
I ( iT ~ n — r —T------ r
o
"m _i
1
I
I
t"
—I
r
r r - i — (— I------1
r
5
UJ
u_
t/) t LJ
<c u_ LU
ID D LO
<C
3:1
u.
in
m
\
in
\
X
\
\
S
X
|0
ex.
cx
o
hLU
cx
CD
cn
ZD
L/1
N ii_
I/)
LU
CX
CL
X
X
X
CD
h-1
X
\
X
m
\
m'
cc
\
CLN
G> \
X
\
\
\
C3
Figure 8.27
C hapter 8
so
1 51
t h a t t h e i n t e n s i t y h a l f - l i f e may be m ea su red and p l o t t e d
to ta l pressure.
T h i s i s shown ( o n l o g - l o g s c a l e s )
a g a in st
i n F i g s 8 .2 7 and
8 .2 8 w here t h e numbers app e n d ed t o t h e d ia g ra m s r e f e r t o t h e m i x t u r e s
in
T a b le 7 * 1 .
sty le
i f th ey s h a re th e
lin k e d
Both
P o i n t s a r e marked and j o i n e d by l i n e s u s i n g t h e same
by
same
d o n o r:ra re -g a s
f i g u r e s i n c l u d e an i n d i c a t i o n o f t h e
to
v a ria tio n
of
th e
in d ic a te
d e p a rtu re s
from
th e
stra ig h t
fo rm a tio n
g ra d ie n ts
d i r e c t d e p e ndency o f l i f e t i m e on
re se rv o ir
of
donor
A p o s s i b l e mechanism f o r s u c h d e p a r t u r e s i s
th e e x is te n c e of secondary donors o f s h o r t l i f e t i m e .
e x c im e r
lin e
These a r e p r o v id e d i n o r d e r
p r e s s u r e t h a t a s im p le model o f a f i n i t e
m o l e c u l e s would p r e d i c t .
of
cro sses
h a l f - l i f e w ith p r e s s u r e cubed,
p r e s s u r e s q u a r e d , and p r e s s u r e d i r e c t l y .
to ta l
(eg.
d a s h e d l i n e s i n F i g 8 .2 7 a r e f o r SF^rKr a t 1 : 3 m i x t u r e s ) .
c o rre sp o n d in g
to
ra tio
from
The p r o b a b i l i t y
su c h m o l e c u l e s would t h e n i n c r e a s e w i t h
c o l l i s i o n f r e q u e n c y and t h e r e f o r e t o t a l p r e s s u r e .
Many
o f t h e OSA te m p o r a l r e c o r d s and p u l s e e n v e lo p e r e c o r d s
do
n o t conform t o a r a p i d r i s e - e x p o n e n t i a l d e c ay model and t h e v a r i o u s
f e a t u r e s o f t h i s d e p a r t u r e a r e c a t e g o r i s e d and d e s c r i b e d below .
8 .4 .4
C o n stan t I n t e n s i t y
In
a l l o f t h e i n t e n s i t y - tim e r e c o r d s
a p p ro x im ate ly
of
c o n sta n t
th e
in te n sity
dui-’i n g t h e m easurem ent p e r i o d .
t h e r e c o r d s ( 3 0 s e c ) was i n c r e a s e d i n some c a s e s ( s e e
becomes
The d u r a t i o n
th e
dashed
l i n e s i n F i g s 8.1 and 8 .2 m i x t u r e s 18-24) t o i n v e s t i g a t e t h e d e c a y o f
th e
c o n sta n t le v e l.
I t was fo u n d t h a t t h e
in te n sity
c o u ld
r e m a in
VO
-4-
m
m
CC
CC
o
UJ
cc
ZD
00
00
LU
cc
CL
K—
o
a.'
LU
CO
Cn !
LU
OO
CU
t_
3
oi
IL.
LJ
LU
(/)
o
Chapter 8
152
c o n sta n t
over
o r p e r h a p s i n c r e a s e s l i g h t l y o v e r s e v e r a l m in u t e s ( i e .
1 0 0 ,0 0 0 p u l s e s ) .
e x p la n a tio n
p o p u latio n
lasers,
is
T h is i s a n i m p o r t a n t o b s e r v a t i o n f o r w hich no
o ffered ,
a lth o u g h
i s in v o lv e d .
very
p o ssib le .
for
much
I t su g g e sts t h a t gas l i f e t i m e s ,
g rea ter
T h is w ould,
i t i s c l e a r t h a t a s t a b l e donor
th an
i n e x c im e r
t h o s e a c h i e v e d a t p r e s e n t may be
o f co u rse,
be d e p e n d e n t on a c h i e v i n g
lase r
a c t i o n u n d e r non-optimum c o n d i t i o n s w h e re t h e f l u o r e s c e n t e m i s s i o n i s
r e l a t i v e l y low.
8 .4 .5
T h re e P r o c e s s b e h a v i o u r
The
r e c o r d i n F i g 8 . 2 ( b ) f o r m i x t u r e 19 a t
IIO T o rr
has
th ree
maxima; one s h o r t d u r a t i o n s p i k e ( < 1 s e o ) , one o f a b o u t 2 0 s e c , and one
for
th e e v e n tu a l c o n s ta n t l e v e l
su g g ests
th a t
for
m ix tu re s
of
w ith
many
m in u tes
d u ratio n .
SF^ d o n o r a model b a s e d o n t h r e e
processes
f o r t h e d e t e r m i n a t i o n o f t h e e x c im e r f l u o r e s c e n t
in te n sity
may
sh o rt
a p p ro p riate.
d u ra tio n sp ik e ,
e m issio n
may
be
but
The
th e
e m issio n
p ro cesses re s p o n s ib le f o r th e
w hich i n many c a s e s may
be
p resen t
in
th e
t o o s h o r t i n d u r a t i o n f o r r e c o r d i n g by t h e OSA s y s te m ,
r e p r e s e n t t h e m ost e f f i c i e n t
in v o lv e
T h is
use
of
th e
donor.
h a rp o o n r e a c t i o n o r t h e i o n i c r e a c t i o n .
T h is
w ould
T e rm in atio n of
t h i s p r o c e s s would o c c u r a s t h e o r i g i n a l d o nor m o l e c u l e s w e re u s e d up
or
as
a
stro n g ly
in te rm e d ia te
h a lo g e n donor,
p roduct
q u e n c h in g
p r o c e s s may
sp ecies
in v o lv e
some
( e g , F^) was g e n e r a t e d .
tem porary
product
of
The
th e
w h i l e t h e l o n g te r m p r o c e s s m u st u t i l i s e a s t a b l e end
f o r h a lo g e n d o n a tio n .
t h e o r i g i n a l d o n o r m o le c u le o r ,
T h i s may be a m o le c u le d e r i v i n g
more l i k e l y ,
from
a m o le c u le form ed fro m
C hapter 8
th e
153
h a l o g e n and i m p u r i t i e s ,
e s p e c i a l l y from t h e w a l l m a t e r i a l
(S iF
f o r ex am p le).
The
presen t
d e g r e e t o which any one o f t h e s e h y p o t h e t i c a l p r o c e s s e s a r e
i n t h e te m p o r a l r e c o r d s d e p e n d s on t h e m i x t u r e
to ta l
pressure
and
th e
gas
ty p e s.
G e n e rally ,
ra tio ,
th e
th e i n i t i a l sp ik e
becomes w i d e r w i t h i n c r e a s e d t o t a l p r e s s u r e a s i s shown a b o v e .
A lso,
in c r e a s i n g th e d i l u t i o n d e c re a s e s th e sp ik e w id th a t a c o n s ta n t t o t a l
pressure
lo n g
e x cep t a t th e lo w e st d i l u t i o n l e v e l s .
te rm
processes
b o th
become
The i n t e r m e d i a t e and
stro n g e r
a s t h e don or
d e c r e a s e s , w h i l e t h e i n t e r m e d i a t e p r o c e s s seems t o
fra c tio n
decrease, r e l a ti v e
t o t h e lo n g te r m p r o c e s s , a t h i g h t o t a l p r e s s u r e .
8 .4 .6
I n t e n s i t y . D uring. E a r l y P u l s e s
C e r t a i n OSA t e m p o r a l r e c o r d s and p u l s e e n v e lo p e r e c o r d s i n d i c a t e
th a t
th e i n i t i a l r i s e in p u lse i n t e n s i t y to th e f i r s t
c o u ld t a k e p l a c e o v e r many p u l s e s .
m i x t u r e 24
F ig 8 .3 .
(SF^ d o n o r) i n F i g 8 . 2 ( b ) and m i x t u r e 32
(NF^ d o n o r )
b e i n g 1 :1 0 0 and 1 : 3 0 .
a s p i k e i s j u s t d i s c e r n a b l e i n F i g 8 .3 a t 110 and 1 3 0 T o r r,
may w e l l be p r e s e n t
F ig 8 . 2 ( b ) ,
but
at
o th er
pressu res
and
th e
m ix tu re
h y p o th etic a l
in
i s o f t o o s h o r t a d u r a t i o n t o be r e c o r d e d c l e a r l y .
p e a k i n t h e s e c a s e s i s t h e r e f o r e l i k e l y t o be due t o t h e
process
in
T hese m i x t u r e s a r e s i m i l a r i n t h a t n e i t h e r h a s a b u f f e r g a s
However,
The
(sp ik e)
The most s t r i k i n g c a s e s o c c u r f o r
and t h e d o n o r ; r a r e - g a s r a t i o s a r e q u i t e c l o s e ,
and
p eak
process
m e n tio n e d
above.
i s a p p a r e n t i n many r e c o r d s .
second
The slo w r i s e - t i m e f o r t h i s
Thus t h e o n l y
cases
w here
a
C hapter 8
154
d isc e rn ab le
rise -tim e
i s p r e s e n t f o r th e e a r l y peak ( f i r s t p ro c e s s )
a r e t h o s e o f t h e p u l s e e n v e lo p e r e c o r d s o f F i g s 8 .1 4 t o 8 . 1 7 ,
low est
pressu res
reached
the
r e c o r d s show t h a t t h e pealc i n t e n s i t y may be
by t h e f i r s t p u l s e .
in te n sity
taken
th ese
At t h e
In g e n e ra l as th e p re s s u re i s in c re a s e d
o f t h e f i r s t p u l s e d e c r e a s e s and t h e number o f p u l s e s
t o r e a c h maximum
in creases.
When
F i g s 8 .1 4
and
8 .1 5
are
compared t h e p a t t e r n o f b e h a v i o u r i s s e e n t o s h i f t t o h i g h e r p r e s s u r e
when
b u ffe r gas i s p re s e n t.
C o n v ersely ,
th e r is e - tim e a t
t o t a l p r e s s u r e i s l e s s i n t h e more d i l u t e m i x t u r e .
a
g iv en
C le a n ly th e n , th e
more d o n o r g a s t h e r e i s p r e s e n t i n t h e d i s c h a r g e , t h e l o n g e r t h e tim e
tak en
to
m o le c u le
reach
is
th e
maximum.
b e in g
T his s u g g e s ts t h a t a seco n d ary donor
g e n e ra te d
which
p e rm its
g rea ter
flu o rescen t
e f f i c i e n c y t h a n t h e p r im a r y d o n o r .
P o s s i b l e c a n d i d a t e s f o r s e c o n d a r y d o n o r m o l e c u l e s w e re s u g g e s t e d
in
S e c tio n 2 .2 .3 »
I t was p o i n t e d o u t t h a t w here SF^ o r NF^ a r e u s e d
as donors,
F^ w i l l be p ro d u c e d and may l e a d t o g r e a t e r e f f i c i e n c y i f
q u a n titie s
are s u f f ic ie n t.
re a c tio n
w ith
F^
is
rap id
T h is i s because
(see
th e
T a b le 2 . 3 ) .
e x c im e r
For
fo rm a tio n
NF^ d o n o r t h e
p r o d u c t i o n o f NF^ may g i v e i n c r e a s e d e f f i c i e n c y due t o a f a s t e x c im e r
fo rm a tio n
p ro d u cts
re a c tio n
(Chow 1 9 7 7 ) .
I t i s n o t known w h e t h e r any o f t h e
from SF^,
su c h a s SF^,
SF^,
fo rm a tio n r a t e s .
e tc .,
have
fast
e x c im e r
C hapter 8
8 .4 .7
155
U n b u f f e r e d M i x t u r e s o f N i t r o g e n - T r i f l u o r i d e and K ry p to n
The r e s u l t s o f F i g 8 .3 f o r KrF i n t h e u n b u f f e r e d N F i:K r m i x t u r e s
are
p e r h a p s t h e m ost I n t e r e s t i n g
P a rtic u la rly
in
o u tsta n d in g
re su lts
in
th is
w ork.
a re th e r e s u l t s fo r in te rm e d ia te p re ssu re s
t h e more d i l u t e m i x t u r e s w h e re
in te n sity
o b tain ed
th e
and v e r y lo n g d u r a t i o n .
e m issio n
is
b o th
In a d d itio n to t h is ,
of
h ig h
th e o v e ra ll
r e s u l t s may be d e s c r i b e d i n t e r m s o f t h e t h r e e p r o c e s s e s , a s o u t l i n e d
in
S e c tio n
8 .4 .5 ,
rep resen ted
processes
These
a t h i g h d o n o r f r a c t i o n s w h e re a s
are
stro n g
or
even
d o m in a n t
th e
second
and
w ith
1 : 3 ) and low i n t e n s i t y ( 1 : 1 0 ) .
in sta b ility
I f t h e e n t i r e r e s u l t s f o r KrF
SFg a s donor a r e exam ined ( F i g s 8.1 and 8 . 2 ( a ) and
slig h t
a d d itio n a l
in d ic a tio n s
th ird
i n t h e more d i l u t e c a s e s .
two r e g i o n s a p p e a r t o be s e p a r a t e d by a r e g i o n o f
(ra tio
are
by o b s e r v i n g t h a t t h e f i r s t p r o c e s s i s s t r o n g l y
(b ))
th ere
t h a t t h e same b e h a v io u i’ i s p r e s e n t w i t h t h e
p o ssib ility th a t
th e
buffer
gas
ten d s
to
sh ift
th e
b eh av io u r to h ig h e r t o t a l p r e s s u r e .
C l e a r l y t h e l i f e - t i m e s shown i n t h e r e s u l t s o f F i g 8 .3 c a n n o t be
e x p l a i n e d i n te r m s o f t h e d o n o r m o l e c u l e s b e in g u s e d up,
sin g le
do n o r
to ta l
pressure,
t h e l i f e t i m e i s g e n e r a l l y g r e a t e r when t h e
fra c tio n is le s s .
I t i s d i f f i c u l t t o s p e c u l a t e on t h e p r o c e s s
re sp o n sib le
range
and
for
th e
b eh a v io u r observed because o f th e r a t h e r broad
of p o s s i b i l i t i e s .
assess
to
sin c e fo r a
th e
F u r t h e r measui’ em ents w ould be
req u ired
to
r e l a t i v e i m p o r ta n c e o f t h e i o n i c a nd m e t a s t a b l e c h a n n e l s
record
th e
e v o lu tio n
of
v a rio u s
re a c tio n
sp ecies.
In
a d d i t i o n , i t would be h e l p f u l t o o b t a i n p u l s e e n v e lo p e r e s u l t s ( s h o r t
tim e sc a le )
and e x te n d t h e l o n g te rm r e c o r d i n g f o r a l l t h e
m ix tu re s.
C hapter 8
A
1 56
fa irly
and
p r e c i s e i n d i c a t i o n o f t h e t o t a l m icrow ave power a b s o r p t i o n
o p t i c a l power e m i s s i o n w ould be a l s o be m ost u s e f u l
if
reasons
f o r t h e b e h a v io u r o b s e r v e d w e r e t o be s o u g h t .
8 .5
Donor Com parison
The
re la tiv e
s e le c tin g
p e rf o r m a n c e o f NF^ and SF^ c a n be d e m o n s t r a t e d by
c o m p a ra b le p a i r s o f r e s u l t s from t h e m ain
body
of
d a ta .
R e s u l t s s e l e c t e d from t h e XeF e x p e r i m e n t s a r e c h o s e n from F i g 8 .7 and
p r e s e n t e d i n F ig 8 . 2 9 .
(m ethod
th e
be
1)
used
As m e n tio n e d b e f o r e ,
t h e e x p e r i m e n t a l m ethod
f o r XeF i s l i k e l y t o g i v e d e p r e s s e d i n t e n s i t i e s a t
s h o r t e r g a s l i f e t i m e s and t h e r e f o r e t h e r e s u l t s o f F i g 8 .2 9
d isto rte d .
may
T h i s means t h a t c o r r e c t e d r e s u l t s would p r o b a b l y g i v e
some
c o n sid e rab le in c re a s e in i n t e n s i t i e s a t
Such
a c o r r e c t i o n would be g r e a t e r f o r t h e NF^ r e s u l t s s i n c e t h e g a s
life tim e s
a re so s h o r t .
th e
lo w e r
T h e r e f o r e i t c a n s a f e l y be
pressures.
c o n c lu d e d
th a t
f a r g r e a t e r i n t e n s i t i e s a r e o b t a i n e d when NF^ i s u s e d a s t h e d o n o r i n
XeF m i x t u r e s b u t t h a t t h e g a s l i f e t i m e i s much l e s s t h a n f o r m i x t u r e s
w ith
th e
SFg
donor.
T h i s i s c o r r o b o r a t e d by F i g 8 .3 0 which shows
some XeF r e s u l t s u s i n g t h e OSA r e c o r d i n g m ethod 2 .
Donor
p e rf o r m a n c e i n
( c o m p i le d
from
b u ffer gas.
compared
F ig s 8 .2
KrF
and
ex p erim en ts
is
shown
in
F i g 8 .31
8 . 3 ) which c o n t r a s t s m i x t u r e s w i t h no
M i x t u r e s 35 a nd 36 w h e re He was u s e d a s t h e b u f f e r ,
are
i n F i g s 8 .1 6 and 8 .1 7 f o r p u l s e e n v e lo p e r e c o r d s and i n F i g
8 .4
f o r OSA t e m p o r a l r e c o r d s .
XeF
re su lts,
The l a t t e r r e s u l t s a r e s i m i l a r t o t h e
show ing g r e a t e r p e a k i n t e n s i t i e s and s h o r t e r l i f e t i m e s
53
62
S p 6 :X e:H e
N % :X e :H e
1:3:76
Ü J lÉ
1--------- 1--------- 1--------- 1______ I______I
I
1:3:76
I
J
1
L
—IK— ÎΗ IL
J
I
L
63
NF3 :Xg:Hg
1:3 :680
tn
LU
LL.
LL.
-1----- 1---- 1-----Î-----!----- 1___ L
64
NFg:Xe:Ne
>“
I—
C/)
1 :3 :7 6
LU
I—
LU
>
K—I
H"
<C
J
1---------1--------- 1--------- 1______ I______I
I
I
65
N F 3 :X e :N e
1:3 : 230
J
TOTAL
-> •
1--------- 1--------- 1______ I______ I______ l_
PRESSURE 100mB/div
SF^ Donor
Figure 8.29 XeF Donor comparison
NF3 Donor
(gas life - M m e s < 0 .3 s )
X
m
o
C
O
Q
eu
c,
Z)
c/î
.00 ^
m
(/)
eu
£_
CL
no
-4—
o
c
o
o
-4—
CQ
a
E
<o
o
iT
m
>
*"0
eu
o
OO
x:
'O OJ rn
00 X
o
c
o
Q
u
eu
10
m
i/T
'ü
£_
O
U
eu
c_
eu
E
to
>
>%
to
c
eu
•-f—
*
c
, .'O
U_
OO
QJ
3:
o
o
c
mC]
%:
LL.
eu
X
o
m
cd
eu
e_
3
gi
u..
VJOOT
L
120T
230
SF6
mixture
orSB:Kr
mixtures
1:1
Figure 831Donor comparison.Intensity vs time records
C hapter 8
for
NFg,
at
h ig h er
157
e x c e p t t h a t t h e d i s c h a r g e shows a n o s c i l l a t o r y i n s t a b i l i t y
p r e s s u r e s w i t h NF^ a s d o n o r .
The r e s u l t s o f P i g 8.31 (no
b u ffer
gas) a re q u i t e c o m p lic a ted .
I n th e r i c h e r m ix tu re s
1 :3 ),
th e
low er
life tim e s
NF^
lo w e r
more
SFg
m ix tu re s
h ave
a
A ls o
th e
show g r e a t e r d i s c h a r g e i n s t a b i l i t y and a r e c o n f i n e d t o
o p e r a t i n g p r e s s u r e s t h a n t h e SFg m i x t u r e s .
d i l u t e m ix tu re s,
rem a in in g
T h is b e h a v i o u r a p p e a r s a l s o
f o r t h e SFg m i x t u r e s b u t i s r a t h e r l e s s m arked.
are s lig h tly le ss
For th e
t h e NF^ r e s u l t s a b r u p t l y t a k e o n t h e i n t e n s e ,
lo n g d u r a t i o n b e h a v i o u r d e s c r i b e d a b o v e .
SFg
to
peak i n t e n s i t y b u t l o n g e r
and a g r e a t e r c o n s t a n t l e v e l i n t h e l o n g t e r m .
m ix tu re s
( 1 :1
th an
w ith
NF^
but
th e
The i n t e n s i t i e s w i t h
tim esc a le
m e a s u re m e n ts i s t o o s h o r t t o j u s t i f y l i f e t i m e c o m p a r is o n s .
of
th e
C hapter 8
8 .6
158
B u f f e r Gas Type
8 .6 .1
B u f f e r s i n XeF M i x t u r e s
The
re su lts
m ix tu re s
poorer
not
of
F i g 8 .7
a r e re d ra w n i n F i g 8 . 3 2 .
re su lts
th an
He o r Ne.
s i g n i f i c a n t i n th e lo w er
d ilu tio n ,
g iv es
a l l o w i n g c o m p a r is o n o f b u f f e r s i n XeF
I t i s c le a r th a t
d ilu tio n
case
b u t,
at
th e
fo r
th ese
m ix tu re s
as
re v e a le d
fo r
th e
m ethod 2
which a p p e a r s i n F i g 8 , 3 3 .
However,
th ey
appear
a
d ifferen ce
The
gas
i n F i g 8 .7 a r e n o t
in
life tim e
is
r e s u l t s o b t a i n e d by t h e OSA te m p o r a l r e c o r d i n g by
H e re ,
w here t h e t o t a l p r e s s u r e
t h e p eak i n t e n s i t y w i t h He b u f f e r i s o n l y m a r g i n a l l y l e s s
t h a t w ith
d iffe re n t.
h ig h er
t h e i n t e n s i t y o b t a i n e d w i t h Ne i n c r e a s e s c o n s i d e r a b l y and
d iffe re n t.
300mB,
much
The d i f f e r e n c e b e tw e e n He and Ne i s
s ig n ific a n tly
th an
g iv es
a peak a t h i g h e r t o t a l p r e s s u r e t h a n t h e He b u f f e r .
life tim e s
is
Ar
Ne
bu ffer
w h e re a s
th e
gas
life tim e s
are
q u ite
The h a l f - l i v e s a r e 2 . 5 s and 9s a t t h e lo w e r d i l u t i o n and
I s and 8s a t t h e h i g h e r d i l u t i o n f o r He and Ne r e s p e c t i v e l y .
:3 :7 6 (53)
. S F 6:X e:N e
1 :3 :7 6 (58)
6 :X e:A r 1 :3 :7 6 (6 0 )
T
T
SF6:Xe:Ne
1:3:230(59)
SF6:Xe:He 1:3:230(54)
SF6:Xe:Ar 1:3:230(61)
1000
Pressure (mB)
Relative intensities from intensity time record peaks as in Fig.8.7.
Figure 8.32 Buffer comparison -XeF mixtures.
SF6:Xe:He
1:3:76
SF6:Xe:Ne 1 :3 :7 6
SF6:Xe:Ar
1:3 :7 6
GJ
SF6:Xe:He
1:3:230
SF6 :X@:Ne
SF6:Xe:Ar
1:3:230
1:3:230
Time (Sec)
Figure8.33
Buffer comparison in XeF mixtures. I vs t records by method 2.
Chapter 8
8 .6 .2
159
B u f f e r s i n KrF M ix t u r e s
The t h r e e b u f f e r s ,
on
in te n sity
8 .1 0 ,
in
He, Ne, and Ar a r e compared i n t h e i r e f f e c t s
F ig 8 .3 4 .
T h i s f i g u r e i s c o m p ile d from F i g s 8 . 8 ,
and 8.1 1 and s o g i v e s c u r v e s o f
p eak
in te n sitie s
from
OSA
tem p o ral r e c o rd s a g a in s t t o t a l p r e s s u r e .
E m is s i o n
from
th e
Ar b u f f e r e d m i x t u r e s i s c o n s i d e r a b l y w eak er
th an
from t h e He and Ne b u f f e r e d m i x t u r e s .
w ith
Ar b u f f e r i s c o n f i n e d t o low p r e s s u r e (b elo w a b o u t lOOTorr) and
disch arg es
In a d d itio n ,
c o u ld n o t be form ed i n m i x t u r e s more
d ilu te
o p e ra tio n
th an
th o se
te ste d .
In
com paring He w i t h Ne,
no p a r t i c u l a r d i s t i n c t i o n i s a p p a r e n t
i n m i x t u r e s a t t h e r a t i o 1 : 3 : 1 0 0 o r any o f t h e l e s s d i l u t e c a s e s .
g rea ter
d ilu tio n ,
in te n sitie s
th e
He
b uffered
w h i l e t h o s e w i t h Ne c o n t i n u e t o
even i n th e r a t i o 1 :3 :1 0 0 0 .
bu ffer
m ix tu re s
g iv e
g iv e
high
much
At
reduced,
in te n sitie s
I t i s a l s o n o t i c e a b l e t h a t t h e u s e o f Ne
e x t e n d s t h e h i g h p r e s s u r e o p e r a t i o n beyond t h a t f o r He b u f f e r
i n t h e more d i l u t e m i x t u r e s .
Gas
which
life tim e s
are
compared
f o r t h e t h r e e b u f f e r s i n F i g 8 .3 5
g iv e s th e g as h a l f - l i v e s a g a in s t
sc ale s.
The
re su lts
used
for
to ta l
reliab ly
m ea su red
in
th e
OSA
re su lts
and
These r e s u l t s i n d i c a t e t h a t t h e b u f f e r
effect
life tim e
in
th e
lo g -lo g
1 2 , and 40 c o u ld n o t
in clu d e d .
on
on
t h i s f ig u r e correspond t o th o se of
F i g 8 ,3 4 e x c e p t t h a t l i f e t i m e s f o r m i x t u r e s 11,
be
pressure
less
d ilu te
are th e re fo re not
ty p e
m ix tu re s.
has
The
little
lack of
t-
^
J
J
>I—
#i
(/)
z:
J
o
j
1----- 1___ 1___ .1___ i__ «J
J
!
J
1------- 1_____ I_____ I_____I_____ I
J
1--------1------- 1--------1------- 1_____I
-1
i
1:3:3 (42)
J
0 0
L
1:3:3 (38)
1-------- 1-------- 1-------- 1-------\ --------X
1:3:4 (8)
1
I
»____ 1.,...
1:3:16 (9)
I
1
1:3:10 (43)
JL
J
®o©
L
1:3:10 (39)
I____ I
1-------1------- 1------- 1____ 1____ I
1: 3:100
I
( 10)
o 1:3:30 (44)
1:3:30(40)
1:3:100 (45)
LU
I—
z
0
J
«
J
1------- 1____ I____ I_____I____ L
1:3:300 (46)
1------- 1--------1--------1_____I_____ L
1:3:500 (11)
a
J
E
I
I
1:3:1000 (12)
SF^:Kr:He
t- - I
J
1-------- 1-------- 1---------1-------- 1-------- 1-------- !-------- 1_____ I-------- 1
1:3:1000 (47 -mixt*urG)
SF6:Kr:Ne
o
1
SF^:Kr:Ar
Figure8.34 Buffer comparison.Intensity vs pressure(100Torr/div). KrF.
.1
N,
o
CD
X
X
X
'>a
X
X
X
X
O '
N
X
X
X
X
X
■
X
%
(X.
c%
o
CN
LU
J3
ra
?—
j.
cx
ZD
m
o
^
CU
t—
Oi
in
<3J
3
J3
t_
<C
LU
Œ
CL
“H
g
g
(U
GÜ
I/)
I
I/)
QJ
t_
3
*4—
k:
d
o
(_
fU
cl!
e
o
w
c_
cu
it
ZD
CQ
LL
CX:
ÜJ
Ut=—f
__J
1
LL. __
__J UJ
< LU
3=
to
<
13
to
m
m
cd
Of
L_
z;
cn
LU
C hapter 8
160
measui-’ement
makes i t d i f f i c u l t
d iffe re n c e
b e tw e e n
He
and
to
Ne
a sc e rta in
m ix tu re s
in
w h eth er
th ere
is
a
t h e m ore d i l u t e c a s e s
s i m i l a r t o t h a t o b s e r v e d i n t h e XeF m i x t u r e s ,
, In
Ar
is
l o o k i n g f o r an e x p l a n a t i o n f o r t h e low e x c im e r e m i s s i o n when
th e
b u ffer,
a c c o m p a n ie s
h ig h
it
m ig h t
be
s u p p o s e d t h a t t h e e f f e c t s im p l y
th e use of a h e a v ie r b u f fe r g as.
in te n sitie s
w e re
o b tain ed
in
However,
re la tiv e ly
th e u n b u ffe re d m ix tu re s w here,
p r e s u m a b ly ,
th e r a r e - g a s a c t s as th e b u f f e r g a s .
th at
n o t a good b u f f e r g a s s im p ly b e c a u s e t h e low m e t a s t a b l e
Ar
is
It
energy
l e v e l r e s u l t s i n a s i g n i f i c a n t p o p u l a t i o n o f Ar
S in ce,
i f Ar i s t h e b u f f e r g a s ,
seems
lik e ly
m e ta sta b le s.
Ar w i l l have a number d e n s i t y o f 10
t o 100 t i m e s t h e r a r a - g a s (Kr o r Xe) d e n s i t y , a l a r g e f r a c t i o n o f t h e
a v a ila b le
e n e rg y
may
fo rm a tio n
c h an n el.
One
be
d iv erted
p o ssib le
away
from
mechanism
fo r
t h e d e s i r e d e x c im e r
th e
lo ss
of
Ar
m e t a s t a b l e s i s t h e f o r m a t i o n o f ArF e x c i m e r s .
The
b e tte r
h ig h
d i l u t i o n p e rf o r m a n c e w i t h Ne b u f f e r (com pared
w i t h He) may be h a r d e r t o e x p l a i n .
to
from
Some o f t h e d i f f e r e n c e may be due
t h e r e d u c e d d i s c h a r g e e f f i c i e n c y r e s u l t i n g fro m momentum t r a n s f e r
e l e c t r o n s t o He when He i s p r e s e n t i n l a r g e q u a n t i t i e s
d isch arg e.
in
th e
C hapter 8
8.7
151
Ik )lli8 lo n a l_ i{ela x a tjl.o h
The
records
e x c im e r
of
th e
e x c im e r
s p e c t r a o b t a i n e d f o r m ost o f t h e
m i x t u r e s a r e m ost u s e f u l i n a l l o w i n g i n v e s t i g a t i o n s
band p r o f i l e t o be c a r r i e d o u t .
of
The s i g n i f i c a n c e o f t h e d i s t r i b u t i o n
of
e n e rg y i n t h e e m i s s i o n band was d i s c u s s e d i n S e c t i o n 2 . 1 , 3
it
was
e m p h a s ise d
th a t
th e
rap id
c o llisio n a l
w here
re d istrib u tio n
of th e
v i b r a t i o n a l - r o t a t i o n a l m a n i f o l d was a d e t e r m i n a n t o f l a s e r e f f i c i e n c y
and
th e
th re sh o ld
re d istrib u tio n
th e
e x c im e r
sta te s.
pump
power
d e n sity .
When
c o llisio n a l
i s slow t h e e m i s s i o n s p e c tr u m w i l l be b r o a d e r b e c a u s e
is
fo rm e d
in
a
ran g e
o f r o t a t i o n a l and v i b r a t i o n a l
O b serv atio n s of th e v a r i a t i o n s in s p e c t r a l c o n te n t
of
th e
KrF e x c im e r e m i s s i o n s a r e now d e s c r i b e d i n d e t a i l ,
A
ty p ic a l
tra n sitio n
spectrum
th e
exam ple
o f t h e e m i s s i o n b a n d - s p e c tr u m f o r t h e B - X
i n KrF was shown i n F i g 8 . 2 0 ,
The
m ain
peak
of
i s due t o a t r a n s i t i o n from t h e g ro u n d v i b r a t i o n a l l e v e l o f
bound (B) e l e c t r o n i c s t a t e t o t h e unbound (X) e l e c t r o n i c
T r a n s i t i o n s o r i g i n a t i n g fro m t h e f i r s t ,
sta te s
pealcs
th is
s e c o n d and t h i r d v i b r a t i o n a l
(a b o v e t h e g ro u n d s t a t e ) g i v e r i s e t o
in d ic a te d
on
s ta te .
th e
th re e
su b sid ia ry
t h e s h o r t w a v e le n g th s i d e o f t h e m ain p e a k .
o r d e r t o g i v e a m e a s u re o f t h e d e g r e e o f c o l l i s i o n a l r e l a x a t i o n ,
ra tio
In
th e
( r ) o f th e c e n tr a l peak i n t e n s i t y (I^ ) to th e f i r s t s u b s id ia ry
p e a k i n t e n s i t y ( I ^ ) i s u s e d and p r o v i d e s a m e a s u re i n d e p e n d e n t o f t h e
a b so lu te
S p e c tra
in te n sity
o f t h e s p e c tr u m (T he r a t i o i s g i v e n by r s l ^ / l ^ ) .
w e re o b t a i n e d f o r a r a n g e o f t o t a l p r e s s u r e s f o r each o f t h e
m i x t u r e s i n T a b le 7 , 2 and t h e i n t e n s i t y r a t i o was m e a s u re d f o r a l l o f
th ese r e s u l t s .
C hapter 8
162
In
o rd er to i l l u s t r a t e th e g e n e ra l f e a tu re s of
process
g iv en
a
to
(d ilu tio n s).
effect
of
d e c re a sin g
is
th a t
lin e ,
re su lts
are
d iv id e d
d o n o r:ra re -g a s r a t i o ,
in c re a sin g
th e
d ilu tio n
in to
th re e
groups,
each w ith s e v e r a l m ix tu re s
ratio
is
1 :1 ,
th e
( u s i n g He) i s t o g i v e m a rk e d ly
r e l a x a t i o n a t any g i v e n t o t a l p r e s s u r e .
A n o th e r
fea tu re
r e s u l t s f o r a g iv e n m ix tu re f a l l ro u g h ly on a s t r a i g h t
t h e g r a d i e n t o f which i n c r e a s e s a s t h e m i x t u r e
th e se
of
th e
The
I n t h e r e s u l t s w h e re ,the SF^rKr
th e
d ilu te .
rela x atio n
s e l e c t i o n o f r e s u l t s c o v e r i n g a w ide r a n g e o f m i x t u r e s i s
i n F ig 8 .3 6 .
a c c o rd in g
th e
becomes
more
I n t h e s e t s o f r e s u l t s f o r S F^:K r r a t i o s o f 1 : 1 0 and 1 : 1 0 0 ,
t r e n d s become p r o g r e s s i v e l y l e s s d i s t i n c t .
d istin c tio n
a c c o m p a n ie s
lac k
a d e c r e a s e i n t h e f r a c t i o n o f Kr i n t h e
m ix tu re s.
These t r e n d s a r e c o n s i s t e n t
itse lf
much more
is
C learly th is
e ffe c tiv e
w ith th e p o s s i b i l i t y t h a t
th an
He
in
cau sin g
Kr
v ib ra tio n a l
r e l a x a t i o n i n KrF.
I n o r d e r t o com pare t h e d i f f e r e n c e s i n v i b r a t i o n a l r e l a x a t i o n i n
KrF
th a t
o c c u r when
th e
in te n sity
ratio
m ea su red
m ix tu re s.
F ig u re 8 .3 7
to ta l
was
d iffe re n t
g iv es
Ne
th e
an
gases
a p p ro p riate
in te n sity
low p r e s s u r e s .
below
a re used,
se le c tio n
th e
of
r a tio p lo tte d a g a in st
p r e s s u r e i n t h e same way a s i n F i g 8 , 3 6 ,
when Ar was u s e d a s t h e b u f f e r ,
fa irly
fo r
bu ffer
I t is re c a lle d
th a t
d i s c h a r g e s c o u ld o n l y be o b t a i n e d a t
T h e r e f o r e Ar c a n o n l y be com pared w i t h He and
about 200T orr,
F ig u re 8 .3 7 i n d i c a t e s t h a t r e l a x a t i o n i s
c o n s i d e r a b l y g r e a t e r w i t h Ar b u f f e r t h a n w i t h Ne f o r a n e q u a l m i x t u r e
ra tio .
occu rs
When
Ne
is
com pared w i t h He,
s lig h tly g rea ter rela x atio n
f o r t h e He b u f f e r i n b o t h o f t h e m i x t u r e s
te ste d .
A lth o u g h
un
rrî
o
-m
O:J
I—
n
üQ
m
~«N
QJ
(/)
C
ÜJ
m
o
o
ro
QJ
t/)
QJ
CL
7o X
a E
o QJ
ro ÜC
-m
[_
’>
c_
L lf
c l/l
o C
'O
u
QJ
to
œ QJ
TD ♦4—
c fO
fO - 4—
o
LTl
m
-■4—
(/)
£_
(/)
c
o
•4—
o
m
m
X
fO
r9
■>
«4—
o
c
o
-L -
fO
X
ro
03
"ÔJ
X
UL
C-
hd:
ÜJ
m
tx
3
oo
( / ) ÛC
<c t/) CC
ÜJ O
o ex
I— CL
QJ
t_
Z)
en
CD
o
o
Lu
o
□%
O
m
£_
<
O
o
QJ
z :
o
S
QJ
X
o
rn
o
o> §
%— s —
p
mm m m m m m
L.
NO
LL
^—
00
m
U_
Z
NT—
0 G o 0
%
m
n
;—
c—
0 •
Q
o
G
c
o
00
*£_
fD
CL
Q
G
0
B
E
O
u
CD
m
G
CQJ
M—
a
Q
O
JD
C
0
fü
fi
-X
G
-css
□
m
’üJ
CL
u_
isL
m
cd
QJ
t-
ZD
01
Ü_
0
CL
~T“
O
O
Ln
B
o
o
o
T
I
I
I
O
o
in
l
I
I
J
O
Chapter 8
163
th e r e s u l t s
f o r t h e b u f f e r c o m p a r is o n show o n l y m a r g i n a l d i f f e r e n c e s ,
a stro n g e f f e c t
h ig h er
d ilu tio n s
F ig 8 ,3 6 a t
d i s p l a y much lo w e r r e l a x a t i o n ,
a re th re e so u rces of e rr o r
in te n sitie s
a s was t h e e a s e i n
rec o rd in g s
F irstly ,
(to
i n m e a s u r in g
th e
v ib ra tio n a l
w hich may a c c o u n t f o r t h e s c a t t e r i n t h e p o i n t s o f
F i g s 36 and 3 7 .
sp e ctra)
th a t, a t a g iv en p re s s u re , th e
low Kr f r a c t i o n s .
T h e re
peak
i s s e e n i n F ig 8 ,3 7 i n
which
th e
may
be
general
added
n o ise
th e
made i t d i f f i c u l t t o m e a s u re t h e
th e
s p e c tr u m
o ccu rrence of
b a c k g ro u n d
p eak
in
h e ig h t
a c c u ra te ly .
S e c o n d ly , t h e s p e c tr u m b a s e l i n e p o s i t i o n , a s r e c o r d e d by t h e OSA and
ch art
r e c o r d e r s y s te m ,
th ese
erro rs
w ere
sm a ll;
source
on
was
th e
Both o f
would be p a r t i c u l a r l y d i s t u r b i n g w h e re t h e i n t e n s i t i e s
ie ,
a t t h e l o w e s t and h i g h e s t
e r r o r a r i s e s from t h e
t h e w a v e le n g th s c a l e ,
used
At
of
was s u b j e c t e d t o s l i g h t v a r i a t i o n s .
p ressures.
The
d i f f i c u l t y of lo c a tin g th e p o s itio n ,
of th e v ib r a tio n a l peaks.
The
tech n iq u e
t o l o c a t e t h e c e n t r e o f t h e m ain pealc v i s u a l l y and m e a s u r e
h e i g h t o f t h e s e c o n d p eak a t a f i x e d d i s t a n c e from t h i s
sm all
in te n sitie s ,
a c c u ra te ly
th e re c o rd in g .
be
a c h ie v e d ,
fills
The
peak
c e n tre
in
e x p erim en t
F i g 8 ,3 8 )
c o u ld
not
be l o c a t e d
n o ise
I n o r d e r t o t e s t w h e th e r g r e a t e r r e g u l a r i t y c o u ld
t h e m i x t u r e S F^:K r:H e a t 1 : 3 : 1 0 0 was t e s t e d w i t h
sp ectra
th e
p o in ts
as
was r e p e a t e d
w ere
though
fo u n d
th e
more
w ere c o l l e c t e d by a c c u m u l a t i o n o v e r s e v e r a l g a s
a t each e x p e r i m e n t a l p r e s s u r e .
sc a tte r
re su lts
th e
c e n tre .
due t o i t s f l a t s h a p e and t h e h i g h e r p r o p o r t i o n o f
in
care.
th ird
and
to
T h is c o n s i d e r a b l y r e d u c e d
th e
t h e p l o t i n F i g 8 ,3 8 d e m o n s t r a t e s .
The
th e
se co n d
re su lts
(also
shown
in
be s i g n i f i c a n t l y d i s p l a c e d from t h e f i r s t
sc a tte r
was
still
sm a ll.
F ig u re 8 .3 8
a lso
200
Pi i )
100 -
SF%:Kr:He
1 : 3 :100
E
s
•
•
—r -
1.5
”T—
2.5
Figure8.38 KrF Relaxafion : large signal results
C hapter 8
164
in d ic a te s
t h a t t h e i n t e n s i t y r a t i o may a p p ro a c h a c o n s t a n t v a l u e ( o f
a b o u t 1 .4 ) a s t h e p r e s s u r e a p p r o a c h e s z e r o .
F i g u r e 8 .3 7
may
be
c o n t a i n s a p l o t f o r a m i x t u r e c o n t a i n i n g NF^
c o n t r a s t e d w i t h t h e m i x t u r e u s i n g SF^ a s d o n o r .
w hich
F o r t h e SF^
m ix tu re th e P - r r e l a t i o n s h i p rem a in s a p p ro x im ate ly l i n e a r w h ile th e
NF^
m ix tu re
a ro u n d
shows
3*2.
an
However,
a p p ro a c h
to
s a t u r a t i o n f o r a v alu e of r of
t h i s r e s u l t a r i s e s from v e r y few d a t a
p o in ts
and may n o t be r e l i a b l e .
For
v a lu e
a ll
of
t h e above r e s u l t s t h e i n t e n s i t y r a t i o a p p r o a c h e s a
which i s b e tw e e n 1 and 2 a s t h e t o t a l p r e s s u r e ,
c o llisio n a l
relax atio n ,
app ro ach es
zero .
S ince
and h e n c e t h e
t h e s p o n ta n e o u s
l i f e t i m e o f t h e m o le c u le i s n o t d e p e n d e n t on t h e p a r t i c u l a r v i b r a t i o n
sta te ,
th is
ratio
a l s o r e p r e s e n t s th e r a t i o o f b o th th e fo rm a tio n
r a t e s and t h e p o p u l a t i o n s o f t h e two v i b r a t i o n s t a t e s .
The
ratio ,
r,
o f t h e p o p u l a t i o n s o f t h e two s t a t e s i n t h e r m a l
e q u i l i b r i u m , w i t h n^ and n^ a s t h e p a r t i c l e d e n s i t i e s , i s g i v e n by
r = n ^ /n g =
T h is
v a lu e
e m issio n
rate .
g iv es
a p p ro p riate
at
h i g h p r e s s u r e w here t h e s p o n ta n e o u s
r a t e i s n e g l i b l e compared w i t h t h e
In
v ib ra tio n a l
1 ,4 2 x 1 0
is
13
Hz,
KrF
th e
c o llisio n a l
rela x atio n
w a v e le n g th s p a c i n g b e tw e e n t h e f i r s t and se co n d
f e a t u r e i s a b o u t 29^ w hich g i v e s a f r e q u e n c y s p a c i n g
U sing
th is
and
a p o p u l a t i o n r a t i o o f 9»7*
300K
of
f o r T i n th e p rev io u s e q u a tio n
The maximum r a t i o o b s e r v e d i n
th e
C hapter 8
re su lts
165
was
a b o u t 5 w hich s u g g e s t s t h a t t h e r m a l e q u i l i b r i u m was n o t
e sta b lish e d .
S i n c e t h e downward
g rea ter
th an
th e
ig nored
and t h e r e f o r e t h e r e l a t i o n be tw e en t h e p o p u l a t i o n r a t i o (a n d
upward
ra te
in
ra te
in te n sity
lin e a r.
T h is r a t e w i l l be d i r e c t l y p r o p o r t i o n a l
and
ob served.
is
t h i s reg im e,
o bserved
freq u en cy ,
ratio )
tra n sitio n
co n sid e rab ly
t h e l a t t e r c a n be
and t h e downward t r a n s i t i o n r a t e w i l l be
th e r e f o r e th e t o t a l p re s s u re ,
I t is c le a r th a t g rea ter re la x a tio n
to
th e
c o llisio n
g iv in g th e l i n e a r i t y
th an
th a t
o b served
c o u ld be a c h i e v e d by o p e r a t i o n a t h i g h e r p r e s s u r e s t h a n t h o s e r e a c h e d
in th e experim ents.
It
is
rela x atio n
in te re stin g
w ith
v a ria tio n .
to
c o llisio n
a p p ly
th is
freq u en cy
to
a rg u m e n t
th e
fo r
e ffe c ts
I t m ig h t be e x p e c t e d t h a t i n c r e a s e s i n t h e
in creased
of
m ix tu re
fra c tio n
of
th e l i g h t e s t gas i n th e m ix tu re ( th e b u f fe r g a s ) , o r rep lacem en t of a
h e a v i e r b u f f e r g a s by a l i g h t e r one,
due
in
to
would g i v e i n c r e a c e d r e l a x a t i o n
th e h ig h e r c o l l i s i o n frequency i n th e l i g h t e r g a s.
However,
a l l of th e c a se s p r e s e n te d g r e a t e r d i l u t i o n g iv e s g r e a t l y reduced
rela x atio n
(steep er
g ra d ie n ts)
at
any
g iv en
to ta l pressure.
In
a d d i t i o n , a s m e n tio n e d a b o v e , Ar g i v e s g r e a t e r r e l a x a t i o n t h a n Ne b u t
in
th e
He,
Ne
rela x atio n .
c o m p a r is o n t h e l i g h t e r g a s ,
He,
does g iv e b e t t e r
From t h e s e r e s u l t s , r a r e - g a s e s can be p l a c e d i n o r d e r o f
e f f e c t i v e n e s s i n r e l a x i n g t h e KrF v i b r a t i o n a l m a n i f o ld a s Kr, A r, He,
Ne.
in
I t i s l i k e l y t h a t th e c o l l i s i o n freq u en cy e f f e c t i s
favour
of a d iffe re n c e in c o llis io n c ro s s -se c tio n fo r re la x a tio n
b e tw e e n
t h e s e a to m s.
in
more
th e
e le c tro n s
supp ressed
F o r e x a m p le,
re a c tiv e
is le ss.
t h e c r o s s - s e c t i o n may be g r e a t e r
h e a v i e r atom s w h e re t h e b i n d i n g o f t h e o u t e r
The r e l a x a t i o n may t h e n i n v o l v e a n
in te rm e d ia te
C hapter 8
- 166
tria to m ic sp ecies.
It
o th er
is
se ctio n s,
gas ty p es,
and
n o ted i n c o n c lu s io n t h a t ,
t h e t r e n d s i n t h e r e s u l t s t h a t accompany c h a n g e s i n
m ix tu re r a t i o ,
co m p le x .
i n comiGon w i t h t h e r e s u l t s o f
o r t o t a l p r e s s u r e a r e somewhat s u r p r i s i n g
The r e l a x a t i o n p r o c e s s c a n be i n c l u d e d i n t h e
a r e a s i n v e s t i g a t e d w h e re know ledge i s l a c k i n g .
several
REFERENCES
16?
REFE.EENGES.
S . A,Ahmed and R .K o c h e r, P r o c , IEEE, 1 7 3 7 ( 1 9 6 4 ).
L ,B ertra n d ,
J.M .G agne, R . G . B o s i s i o ,
E l e c t r o n . , 1 4 ( 1 ), 8 ( 1978) ,
and
M.M oisan, IEEE J . Quantum
R . G .B o s i s i o ,
C .F .W e i s s f l o c h , and M.R,W e rth e im e r, J . Microwave Power,
7 ( 4 ) , 3 2 5 ( 1972) .
J.E .B ra n d e lik
7 (1980).
and
G .A ,S m ith ,
IEEE
J.
Quantum
E le c tro n .,
1 6 (1 ),
C .A .B ra u and J . J . E w i n g , A p p l, P h y s. L e t t . , 2 7 , 4 3 5 ( 1 9 7 5 a ) ,
C .A .B rau and J . J . E w i n g , J . Chem. P h y s . , 6 3 ( 1 1 ) , 4 6 4 0 ( 1 9 7 5 5 ).
R.Burnam and N .D je u , A p p l. P h y s. L e t t , , 2 9 ( 1 1 ) , 7 0 7 ( 1 9 7 6 ) .
H .S .C a rs la w
1959).
and
J .C .Jaeger,
C o n d u c tio n o f H e a t i n S o l i d s .
( O x fo rd
W.Chow, M .S tu k e, and F . P . S c h a f e r , A p p l. P h y s . , 1 3 , 1 ( 1 9 7 7 ) .
C . P . C h r i s t e n s e n and R.W.Waynant, C o n fe re n c e on L a s e r s and E l e c t r o E le c tro -o p tic s.
T e c h n i c a l D i s e s t , _ A p r i l 1 4 - 1 6 . 1 9 8 2 . Page 16,
( O p t i c a l S o c i e t y o f A m e r ic a ) .
J.C ran k , I h s
M a ih e m atlo s , o f
D iffu sio n ,
( C l a r e n d o n , O xford
1955).
T .H .D unning and P . J . H a y , J , Chem, P h y s . , 6 9 ( 1 ) , 1 3 4 ( 1 9 7 8 ) .
J . J . E w i n g and C .A .B ra u , A p p l, P h y s. L e t t . , 2 7 , 3 5 0 ( 1 9 7 5 ) .
F . C . F e h s e n f e l d , J . Chem. P h y s , , 5 3 ( 5 ) , 2 0 0 0 ( 1 9 7 0 ).
C . H . F i s h e r and R . E , C e n t r e , J . Chem. P h y s . , 6 9 ( 5 ) , 2 0 1 1 ( 1 9 7 8 ) .
M .R ,F la n n e ry
and
T ,P .Y a n g ,
S .F .F u lg h u m , M .S .F e ld ,
1 6 (8 ), 8 15(1980).
and
A p p l.
A li
P h y s.
Javan,
L e tt,,
3 2 (5 ), 327 (1 9 7 8 ).
IEEE J , Quantum E l e c t r o n , ,
M .F.G olde and B .A .T h r u s h , Chem. P h y s . L e t t , , 2 9 , 4 8 6 ( 1 9 7 4 ) .
J .P .G o l d s b o r o u g h , A p p l. P h y s. L e t t , , 8 ( 9 ) , 2 1 8 ( 1 9 6 6 ) .
M.C.Gower, R .E x b e r g e r ,
P .D .R ow ley,
L e t t . , 3 3 (1 ), 65(1978).
and
K .W .B illm an,
A ppl.
P h y s,
REFERENCES
K ,G ,Handy
168
and
J .E .B ra n d e lik ,
A ,F .H arvey, Miorowave
York 1 9 6 3 ) .
P .J . H a y , W.R.Wadt,
(1 9 7 9 ).
and
J.
A p p l.
E n g in e erin g ,
P h y s.,
4 9 ( 7 ), 3753(1978).
(Academ ic P r e s s , London and New
T .H ,D unning, Ann. Rev. P h y s. Chem., 311-346
S.C .H aydon, Ms_ch.arge and P lasm a P h v s i c s , ( D e p a rtm e n t o f U n i v e r s i t y
E xtension,
The U n i v e r s i t y o f New E n g la n d , A r m id a le , A u s t r a l i a
1964).
M .A.Heald and C .B .W h arto n , P la sm a D i a g n o s t i c s w i t h M ic r o w a v e s .(W ile v .
New York, London, Sydney 1 9 6 5 ) .
G .H e rz b e rg , M o le c u la r , S p e c t r a and M o le c u l a r S t r u c t u r e . Volumes 1 and
2 , (Van N o s t r a n d , New York 1 9 5 0 ) .
F .G .H o u te rm a n s , H e lv . P h y s, A c t a . , 3 3 , 9 3 3 ( 1 9 6 0 ) .
J.C .H sia ,
J.A .M angano,
3 4 (3 ), 2 0 8(1979),
J.H .Ja c o b ,
and
M .Rokni, A p p l. Phys. L e t t . ,
J . H . J a c o b and S .A .M a n i, A p p l. P h y s. L e t t . , 2 6 , 5 3 ( 1 9 7 5 ) .
T .H ,J o h n s o n and A .M .H u n te r, J . A p p l. P h y s . , 5 1 ( 5 ) , 2 4 0 6 ( 1 9 8 0 ) .
W .J o s t , D i f f u s i o n
York 1 9 5 2 ).
in .
S o lid s.
L i q u i d s . G a se s. (A cadem ic P r e s s , New
C .K e n ty ,
J . O . A i c h e r , E .B .N o e l,
R e v ., 6 9 , 3 6 ( 1 9 4 6 ) .
A .P o ritsk y ,
and
V .P ao lin o ,
Phys,
M .K rauss and B .L i u , Chem, P h y s . L e t t , , 4 4 ( 2 ) , 2 5 7 ( 1 9 7 6 ) .
J . I . L e v a t t e r and S . C . L i n , J . A p p l. P h y s . , 5 1 ( 1 ) , 2 1 0 ( 1 9 8 0 ) .
E.W,McDaniel and E.A.M ason,
The M o b i l i t y a n d _ D i f f u s i o n o f I o n s i n
G a s e s , ( W ile y , New Y ork, London, Sydney, T o r o n to 1 9 7 3 ) .
A.D.MacDonald, M icrowave Breakdown i n G a s e s . ( W ile y , New York, London
Sydney 1 9 6 6 ) .
J.P .M cG eehan, B .C .O ^ N e i l l , A .N .P r a s a d ,
D :A ppl. P h y s . , 8 , 1 5 3 ( 1 9 7 5 ) .
A ,J .M e n d e ls o h n , R.N orm andin,
L e t t . , 3 8 ( 8 ), 603(1981).
and
J.D .C ra g g s,
J,
P h y s.
S . E . H a r r i s , and J .F .Y o u n g , A ppl, P hys.
REFERENCES
169
The_. Microwave E n g i n e e r s ' Handbook
H o riz o n House - M icrowave I n c . ,
46, M a s s a c h u s e t t s ( 1 9 6 2 ) .
and Buyers* G u id e , Page T -1 0 2 ,
1330, Beacon S t r e e t , B r o o k l i n e
W .J.M oore, P h v s l e a l C h e m i s t r y , (Longman, London 1 9 7 2 ) .
S . F . P a i k and J . E . C r e e d o n , P r o c . IEEE, 2 0 8 6 , November, ( 1 9 6 8 ) .
H .R a e t h e r , A rch, E l e c t r o t e c h . ( B e r l i n ) , 3 4 , 4 9 ( 1 9 4 0 ) .
Ch.K .R hodes, Excim er L a s e r s , T o p ic s i n A p p lie d P h y s i c s , Volume 3 0 ,
( S p r i n g e r - V e r l a s , B e r l i n , H e i d e l b e r g , New York, 1 9 7 9 ) .
M .Rokni, J . H . J a c o b ,
J.A .M angano,
3 0 (9 ), 458(1977).
and
R .B rochu, A p p l. P hys. L e t t . ,
M.Rokni, J.A .M angano,
J .H ,Ja c o b ,
E l e c t r o n ., 1 4 (7 ), 46 4 (1 9 7 8 ).
and
J.C .H sia ,
IEEE
J,
Quantum
D .E .R o th e and R ,A .G ib s o n , O p t. Commun., 2 2 ( 3 ) , 2 6 5 ( 1 9 7 7 ) .
S . K . S e a r l e s and G .A .H a r t, A p p l, P hys. L e t t . , 2 9 , 4 8 6 ( 1 9 7 4 ) .
M .J.Shaw and J . D . C . J o n e s , A p p l. P h y s . , 14, 3 9 3 ( 1 9 7 7 ) .
G .P .S m ith and D . L . H u e s t i s , J . A p p l. P h y s . , 5 2 ( 1 0 ) , 6 0 4 1 ( 1 9 8 1 ) .
R . D .S u a r t ,
P.H.Dawson,
(1 972).
R .C .S z e ,
K .Y .Tang,
IEEE
( 1981) .
J,
a nd G .H .K im b e ll, J ,
Quantum
R .Q .H u n te r ,
E le c tro n .,
V ol.
A ppl, P h y s . ,
4 3 ( 3 ) , 1022
Q E -1 5 (1 2 ), 1 3 3 8 ( 1 9 7 9 ).
and D . L . H u e s t i s , J , A ppl, P h y s . , 5 2 ( 1 0 ) , 6046
J.T e llin g h u ise n ,
J.M .H offm an,
P h y s ., 6 4 ( 6 ) , 2 4 8 4 (1976).
G .C .T i s o n e ,
and
A.IC.Hays,
J .T e llin g h u is e n ,
P .C .T e llin g h u is e n ,
G .C .T is o n e ,
A .K .Hays, J . Chem. P h y s . , 6 8 ( 1 1 ) , 5 1 7 7 ( 1 9 7 8 ).
J . Chem.
J.M .H offm an,
and
P .C .T e llin g h u is e n ,
J,T e llin g h u is e n ,
J.A .C o x o n , J . E . V e l a z c o ,
D .W .S e t s e r , J , Chem. P h y s . , 6 8 ( 1 1 ) , 5 1 8 7 ( 1 9 7 8 ).
and
D .W .T r a in o r ,
(1 9 8 0 ),
J .H .Ja c o b ,
and
M .Rokni,
J.
Chem, P h y s . ,
7 2 ( 6 ) , 3646
J . E . V a l a z c o and D .W .S e t s e r , J , Chem, P h y s . , 6 2 , 1 9 9 0 ( 1 9 7 5 ) .
J.E .V e la zc o ,
(1976).
J .H .K o lts,
and D .W .S e t s e r , J . Chem. P h y s . , 6 5 ( 9 ) , 3468
J .T .V e r d e y e n , L a s e r E l e c t r o n i c s .
C l i f f s , New J e r s e y 1 9 8 1 ) .
( P re n tic e-H a ll,
In c .,
Englewood
REFERENCES
P . J . K . W i s o f f , A . J . M endelsohn,
S .E .H a rris,
Quantum E l e c t r o n . , 1 8 ( 1 1 ) , 1 8 3 9 ( 1 9 8 2 ).
I70
and
J . F . Young,
J . F . Young, S . E . H a r r i s , P . J . K . W i s o f f , and A . J . M endelsohn,
A p r i l (1982)
M.W.Zemansky,
H e a t and Therm odynam ics,
T o r o n to , London 1 9 5 7 ) .
(M c G ra w -H ill,
IEEE J .
L a s e r F ocus
New
York,
Документ
Категория
Без категории
Просмотров
0
Размер файла
40 340 Кб
Теги
sdewsdweddes
1/--страниц
Пожаловаться на содержимое документа