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Патент USA US2411715

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Nov. 26, 1946.
2,411,715
G. L. DIMMICK
APPARATUS FOR THE PRODUCTION OF REFLECTION REDUCING COATINGS
Filed Dec. 14, 1942
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Patented Nov. 26, 1946
- #2,411,115
UNlTsDsTA'rss PAT ENTÍOFFICBÈ
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2,411,115
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APPARATUS Foa THE PRODUCTION-0F .
-REFLEo'rroN REDUCING coA'rrNGs
Glenn L. Dimmick, Indianapolis, 1nd., assigner to”
Radio Corporation of America, a corporation yof
Delaware
, Application December 14, 1342, serai-"No.sissßis
3 claims. l (orsi-12.2)
'1
tion'would result in an evaporated’ñlm of uni
This invention relates to an apparatus for pro
form thickness upon a spherical surface with the '
ducing evaporated coatings such,l for example, as!
boat or coil at its center. In practice rit is very
desirable to .arrange thel evaporating `>system so
'that a coating vof' uniform thickness can `be de
reflection reducing coatings or coatings of evap
orated meta-1 on optical elements. The production `
of evaporated reñectionreducing coatings is de-`
scribed, for example, in Cartwright et al. Patent
No. 2,207,656. In the actual production of such4
coatings many dimculties are encountered. One
of the difficulties is due to the fact that the coat
ing material when evaporatedy in vacuum either
from a coiled filament or from an evaporating
posited on a flat surface. In his book “Proce
dures in Experimental Physics” (page 179), Dr.
"'John Strong shows how to obtain this condition
by >Placing fa large number of evaporators in -a
circle whose radius is equal to the distance from
the evaporators to the fiat object being. coated.
This has many practical objections. First it as
boat travels uniformly in alldirectîons like radi
sumes a large number >of evaporators with identi
ant energy. As a consequence, the quantity of
coating material reaching a given area ofsurface
varies approximately inversely as the square of
cal characteristics and which will vaporize exactly
the same amount of material when heated with
the same current. This is diilicult to' realize in
the distance of the surface from the evaporator.
The present invention provides an apparatus for
practice.
l
.
l
_
y
In a lens coating equipment, Iit; is desirable to
rendering the coating thickness approximately
coat several lenses at one time and these are often
One object of the invention is to provide `an 20 in tubular mountings so that they can receive the
vaporized material from only a limited angle.
improved evaporating apparatus for the evapora
Fig. »1 shows why those lenses which are in deep
tion of thin films.
,
mountings could not receive the same quantity of
Another object of the-invention is to providey 1
the evaporating‘apparatus which will compensate l » evaporated material on all portions of the lens
for the normal irregularity in distribution of 26 surface. It will be apparent from this figure that
the material from the evaporating coil-I2 will be
evaporated material.
obstructed by the mountings of the lenses Il so
Other and incidental objects of the invention
that a uniform coating will not be produced.
will be apparent to those skilled in the> art from
The improved apparatus according to the pres
a reading of the following specification and an
inspection of the accompanying drawing in 31 ent invention as shown in Fig. 2 produces much
uniform over a plane surface of considerable area.
more unifrom coatings on flat'surfaces and on
which:
.
A»
.
,
Figure 1 shows one way in which it has here
tofore been attempted to secure- uniform coatings
on optical surfaces.
Figure 2 is a perspective view of my improved 35
lenses in deep mountings. In thearrangement
illustrated, three evaporating boats are placed in
a> triangular arrangement and a triangular wire
screen is placed `at the proper distance above the
boats. This screen obstructs` a portion of the
evaporated material and permits the rest to reach ’
Figure 3 is a top view of the evaporators and
the lens plate or »holder L carrying the lenses Il
screen from the center of the lens holder.`
in the -upper end of the `bell jar. lli.v vThe evap
Figure 4 is a view of thel evaporators and screen
taken from the outside edge of the lens holder 40 orating boats I3 are made of platinum or other
appropriate material and are heated by electric `
on a radius _whose vertical .projection passes
, currents passed through them. The-‘bell jar I0
’ through an apex of the screen i4.
,
Figures is a diagram inustreting the relation ' is of course air .tightA and is evacuated to an
evaporating apparatus.
between lens distance and coating thicknesses,
and
`
.
«
v
Figure 6 is a curve showing the corrected re
appropriate degree before thecommencement of
45
evaporation.
,
„
.
„
z
As viewed from the center of >the lens fplate,
Figure 7 is a view of the evaporators and'screeny
' that is, »from the'plane of the‘lenses at a point
v on the common axis passing through the `centers
when viewed from the edge of the lens holder on
of the evaporatorassembly, the screen and the
the center of any side of screen I4.
When a. material is evaporated from a small
boat or coil placed in a vacuum, the evaporated
appear as shown in Fig. 3. It will be apparent
that at this point, which is the nearest to the
sults secured by the use of my improved apparatus. Y
' a. radius whose vertical projection passes through 60 lens plate, the' screen I4 and the evaporators I3
particles travel in straight lines very much like
light rays‘ from a luminous source. 'I'his condi
evaporators, all of the evaporators are shielded -
bythe screenl and only such evaporated material
can reach the surface as passes through the
2,411,715
3
4
screen. As the viewpoint recedes from the c'en
ter of the lens plate, the area of the evaporating
boats to which the surface is directly exposed
increases until, at the edge of the circular lens
holder the equivalent of two evaporating boats
are completely exposed. Figure 4 showsthe rela
tion between the boats and screen as‘vievved from
appropriately shaped piece of magnetic material
I6 counterbalanced by a membe;- Il, preferably
of non-magnetic material. After the optical ele
ments Il have been appropriately coated on one
side, the lensl plate L is rotated with the shaft
I5 by manipulation of a magnet outside of the bell
jar so as to attract'the member I6 which is fas
tened to the shaft' I5 and causes rotation of the
lens plate L through 180 degrees to expose the
the'edge of the lens holder on a radius whose ver
tical projection intersects any one oi’ the apices of
opposite side of the lens to the evaporators.
the screen. In this case one boat is completely
uncovered and two boats are each half uncovered.
Ijclaim as my invention:
1‘.VV In a vacuum evaporating device for produc
the edge of the lens holder on a radius whose ver
ing thin ñlms on the surface oi’ an object, in
tical projection passes through the center of any
1 combination, a holder for said object, three elon
side of the screen. In`this case, vone boat is corn v15 gated evaporating elements equidistant from and
pletely covered, and the other two-are each fully
in opposed relation to said holder and arranged
exposed, producing, as before, the same totalex- '
symmetrically along the sides of an equilateral
Figure 7 is a similar illustration of the viewfrom f , i
, posed area.
At any other point on the edge of
triangle, a foraminous screen in theIorm o1' an
the circular lens holder, the equivalent of two
equilateral triangle `placed between the evaporat
20 ing elements and said holder for procuring uni
.boats are uncovered. Furthermore, the compen
sation is constant for all points on any circle with ì
its center on the common axisv passing vthrough
the center of the lens holder, screen and -b‘oat as
sembly,` an'dfproportional to the radius of the j
`circle from which the view is taken. Conse 25'
quently, the evaporation is substantially constant
over the- whole area within the limits of the lens'v
holder.
`
~
y
ao
`
r2
lwhere To is the corresponding thickness at '
point Po.
-
Fig. 6 shows how the ñlm thickness decreases as
the distance b (from the center of the plate) is
increased.
«
40
As an example, if we make h=6" and R‘=21/2" '
' .
»
mounted-between said evaporating elements and
said holding means ‘and positioned in such a man
-
’ ner- that said evaporating elements are at an
TheA method of compensation described A‘above
is linear with b (Fig.` 5) but the attenuation in
. iilm thickness is not linear.
`
»
alternately expose opposite sides of said objects '
to said evaporating means, and a foraminous
screen in the lform ofl an equilateral triangle
then the ñlm thickness at the edge of the plate
would be 72.6 percent of the Lthickness at the
centerf'
2. In a vacuum vevaporating apparatus for pro
ducing thin viilms on the surface of an object, a ’
elongated evaporating means arranged symmetri
cally along the sides oi' an equilateral triangle,
means for holding objects to ‘be coated with one
side exposed to and substantially equidistant from
said'evapora‘ting means, 'means pivotally mount
ing said holding means, magnetic means con
nected to said holding means whereby the position
of said holding means may be changed to thereby
thickness of the evaporated film at thispoint is
h2 .cos2
just covered by said screen when viewed from the
center of said- holder on the common axis of said
container adapted to be evacuated, a plurality of
_ Vis the radius of a'point P1 on the lens plate, the
u
elements being at an angle to the sides of said
screen', the position and'size oi' said screen kbeing
so selected that said -evaporating elements are
holder, screen and evaporator assembly. `
n
In Fig.v 5 there is diagrammatically illustrated
an evaporating source S placed at a distance h
` below the lens plate'L having a radius R. If b
form thickness of the'evaporated material over
the whole surface of said object, said evaporating
_angle to the sides of said screen and so’thatsaid
screen just covers said elements when' viewed
from the center of said holding means.
3. >In a vacuum evaporating‘apparatus for de
‘
curvek (a) (Fig. 6)` shows the actuai attenua
- tion- While line (c) shows a close approximation 50
positing a thin film on the surface of one or more
to this. Since only two of the boats areuncovered
when viewed from the edge ofthe plate as vshown
objects, a container adapted to be evacuated,
three elongated evaporating boats-lying in a plane
inFigs. 4 or '7, the transmission of the compensat- ,
and arranged symmetrically along the vsides of an
ing screen would have to be 72.6‘X 66.6:481/2 per
equilateral triangle, a holdery for said objects
cent. A triangular piece of '-'No. 40 mesh brass 55. adapted
to expose the surfaces to be treated to
screen may be usedvfor this purpose. Its size was
said evaporators and hold them ina plane par
determined from the arrangement shown in Fig.
allel to the plane of said boatsl and spaced there
2, the size of the screen being determined from
from; ‘a foraminous screen having the form'of an
lthe diameter of the lens plateand the position
Aoi' the boats'in'dicatedin-Fig. 2.
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"
’
equilateral triangle', positioned between said boats
Y
It will be apparent to those skilled in the art . 60 and said holder, parallel to the plane’of said boats,
oriented> so that ' said _ boats lie symmetrically
'that my invention is not limited to the use of
f evaporating boats but that the'same general ar- Y
rangement may be used with other types of evap-` "
.orators such as wire helices, straight wire fila
ments or the like.
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from said holder that said screen just covers said
65 boats when viewed from the point of intersection
In Fig. 2, the’lenses Ill are vsupported on an ap
' propriate lens plate L which is mounted on a shaft
l5.
across the corners of the projection of said screen
on the plane of said boats’ and at such a distance
shaft carries onl its 'opposite end an " `
of the plane of said objects and an axis perpen
dicular to the plane of said boats andpassing
through the center of said screen. v
` GLENN L. DIMMICK.
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