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Патент USA US2410115

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0¢t- 29, 1946-
R. H. vARlAN
2,410,115
IMAGE INTENSIFIER
Filed Sept. 2, 1942
3 Sheets-Sheet 1
INVENTOR
‘ R. H. VARIAN
. Oct. 29, 1946.
R_ H, VARIAN
‘
IMAGE
2,410,115
INTENSIFIER
' Filed sept. 2, 1942
`
s sheets-sheet 2>
>TO GRIDS
TO OTHER RHEOSTAT
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R. H. VARIAN
WM w
ATTORNEY
'0¢1.29,1946.
,.
`R,H,VAR,AN
.2,410,115
IMAGE INTENSIFIER A
Filed'vSept. 2, 1942
5 Sheets-Sheet 3
INVENTOR
R. H. VA R‘AN
2,410,115
Patented Oct. 29, 1946
UNITED` STATES lPlrrENT OFFICE
to
Russell H. Varian, V'v’antagh, N. Y., assignor
Brooklyn,
Sperry Gyroscope Company, Inc.,
N. Y., a corporation of New YorkV
Application September 2, 1942, Serial No. 457,097
10 Claims.
1
This invention relates to a novel type of photo
electric device, which utilizes a novel electron
multiplication process in order to amplify the in
tensity of an electron image, and which may be
used in conjunction with a suitable optical sys
tem to amplify the intensity of an optical image.
The intensification of an optical image has
been a much sought after objective in order to
make possible visual detection of the presence of
objects which are too dimly illuminated to be seen
by the eye. It is a well-known principle of optics
that no intensiñcation can ever be realized
through the use of a purely optical system. This
is because any optical system used with the eye
cannot escape the limitations imposed by the ac
tual size and the f value of the human eye, which
is necessarily the last stage in the system. It has
also been attempted to accomplish image intensi
ñcation by the use of orthodox television equip
ment. But, here too, limitations of the known
television systems have prevented any appreciable
gain in sensitivity.
In the present invention a system of lenses is
used to focus an optical image on a photoelectric
surface, which converts the optical image to an
electron image. The electron image is then in
tensiiied as a whole by utilizing the effect of sec
(Cl. Z50-153)
2
Y. types of tubes for converting an optical image
into a television signal. One is the Farnsworth
dissector and the other is the Zworykin icono
scope.
The Zworykin iconoscope uses the storage prin
ciple to increase its sensitivity, that is, the elec
trical impulse generated -by each element of the
photoelectric surface is proportional to all the
light falling on that particular element between
successive scannings. The disadvantage of this
tube is that it is impossible to use any of the
previously known types of electron multiplier in
conjunction with it.
The Farnsworth dissector, on the other hand,
employs the principle of electron multiplication to
increase its sensitivity, but cannot take advan
tage of the storage principle. Hence, neither of
these'tubes achieves the theoretical limit of sen
sitivity which can only be obtained by utilizing
both the storage principle and the principle of
electron multiplication. The reason why it has
heretofore been impossible to combine these two
principles in one tube is that all previously known
electron multipliers were adapted to intensify
if only one element of an electron image at a time,
as previously pointed out.
Since the novel type of electron multiplier of
the present invention can intensify an electron
ondary emission to obtain electron multiplication,
image as a Whole with the electron image remain
after which the intensiñed electron image is con
ing intact, it becomes possible to produce a highly
30
verted back to an intensified optical image.
sensitive television transmitting tube which in
Secondary emission has been used heretofore to
corporatesboth the electron multiplication and
obtain electron multiplication, as in the Farns
the storage principles.
worth and Zworykin electron multipliers. But,
The principal object of the present invention is
because of the spreading tendency of the electrons
to
provide an electron multiplier which will in
as multiplication proceeds, it has only been pos 35 tensify al1 the elements of an electron image si
sible to intensify one element of an electron im
multaneously, thus maintaining the electron im
age at a time. In the novel type of electron mul
age intact during the intensification process.
tiplier incorporated in the present invention, the
Another object of the invention is to provide a
spreading of the electrons has beenV so reduced
that it becomes possible to intensify all the ele
ments of the electron image simultaneously,
maintaining the electron image' as a whole intact,
and still obtain a suñiciently high resolving power
device which is capable of receiving a Visual im
age and amplifying its intensity, Without altering
the characteristics of the image.
A further object is to provide a device which
to produce a satisfactory picture. By using 'this
has a high gain in light sensitivity over that of
suitable lens system, a very high gain in light
jects which are too dimly illuminated to be de
novel electron multiplier in conjunction with' a 45 the human eye so that it will render` visible ob
sensitivity over the human eyeV can be‘obtained.
The novel electron multiplier may also be used
as a basis for a new type of television transmitting
tube.
There are in> present use two principal
tected by the human eye alone.
'
An object of the invention is to provide a de
vice whose intrinsic sensitivity is about equal to
that of the eye and whose characteristics may be
3
2,410,115
made to duplicate those of the eye in dim light.
Another object of the present invention is the
provision of a highly sensitive television trans
mitting tube which incorporates the principles 0i
both electron multiplication and light storage.
A further object of the invention is to provide
4
Wires Iii, which all run parallel to each other in
any particular grid, may have a diameter of
about .010 inch and have a spacing between cen
ters of about .020 inch in the grid. The grids
3, 3’ are insulated from each other by thin mica
spacers I5 placed between successive grid frames
I3. The thickness of the grid frames i3 and the
tensity amplified image of an object, which image
mica spacers i5 are such that the distance be
appears in the same color as the object.
tween the grid wires of successive grids may be
A still further object of the invention is to pro 10 about l millimeter. The direction of the wires
vide a device which will produce an intensity `am
of successive grids is rotated through an angle
pliiied color image of an object, in which image
of 60°, so that the direction of the wires in any
invisible radiations from the object, such as in
particular grid is parallel to that oi' the wires in
fra-red or ultra-violet radiations, are made to ap
every fourth grid only.
pear as any arbitrarily chosen color.
15
Referring to Fig. 5, it is seen that the grid and
Other objects and advantages will become ap
screen assembly I comprises a complete unit in
parent from the speciñcation, taken in connection
itself, which may be assembled outside the tube
with the accompanying drawings wherein the
and then inserted as a whole within the tube
invention is embodied in concrete form.
structure. On top of the first photoelectric grid
In the drawings,
.
20 3, there are placed about I5 secondary emissive
Fig. l is a diagrammatic View of a device em
grids 3’ which may be also somewhat photobodying features of the present invention.
sensitive. The last of these grids may be made
Fig. 2 is an elevation view of the vacuum tube
somewhat less secondary electron emissive in
shown diagrammatically in Fig. l.
order to prevent cold emission caused by the
Fig. 3 is a cross-sectional elevation view taken 25 higher potential diiîerence between it and the
along the line 3-3 of Fig. 2.
layer of metal foil 5. All the grids are separated
Fig. 4 is a perspective View of a detail of Fig. 3.
by mica spacers i5. On top of the last of the
Fig. 5 is an enlarged fragmentary cross-sec
secondary emissive grids 3’ there are successively
tional view taken along the line 5_5 of Fig. 3,
stacked a larger insulating spacer block iii, which
showing the details of construction and method 30 may be porcelain, a metal conducting block il,
of support of the grid and screen assembly.
the opaque guard I2, and the fluorescent screen 6.
Fig. 6 is a partial view taken along the line 6_6
On the top and bottom of the stack are placed
of Fig. 5, with the grid andscreen assembly
the clamping frames I9 which are made of some
removed.
insulating material, such as porcelain. Tie rods
Fig. 7 is a diagrammatic View of another em 35
20, of insulating material threaded at both ends,
bodiment of the present invention.
are inserted through holes in clamping frames
Fig. 8 is a diagrammatic View of still another
I9 and opaque guard l2, and the whole structure
embodiment of the present invention.
is then rigidly clamped together by tightening
Similar characters of reference are used in all
the nuts 2i. Conducting wire IS makes an elec
of the above ñgures to indicate corresponding 40 trical connection b-etween the metal block Il and
parts.
the layer of metal foil 5.
VReferring, now to Fig. 1, there is shown a grid
In Figs. 2 and 3 are shown two cooling tubes
and screen assembly l contained in a suitably
2li. extending vertically downward within the tube
evacuated glass tube 2. The grid and screen
structure 2 and constructed integrally therewith.
assembly I consists essentially of a series of 45 These cooling tubes, when filled with liquid air,
closely spaced grids or electron permeable ele
cool the grids 3, 3' suiñciently so that neither
ments 3, t', and a fluorescent screen i! which is
thermionic emission nor cold discharge will take
a device which is capable of reproducing an in
coated on its inside with a thin layer of metal
place. Besides cooling the grids, these cooling
foil 5. The ñrst grid 3, at least, must be photo
tubes also serve to support the rheostats l, and
electric, and the following grids 3’ are highly 50 to support the grid and screen assembly i within
secondary electron emissive. A direct current
the tube structure 2.
potential difference which may be of the order
The rheostats 'I may be formed by wrapping
of 500 volts or so, is applied between successive
a guard strip spirally around a portion of the
grids from a direct current source, represented
cooling tubes 24, and then allowing a metal suit
by the battery 6 and a rheostat 7. A potential 55 able for evaporation in a vacuum, such as silver,
difference of some 50,000 volts is maintained be
to condense upon the unguarded surface of the
tween the last secondary emitting grid 3’ and
tube. Thus, when the guard strip is removed, a
thin layer of silver 7 in the form of a continuous
in order to adapt a device to color vision, and
spiral strip is produced on the surface of the
for other purposes, as will later be described in 60 cooling tubes, as shown in Fig. 6 very much ex
more detail, the two identical rotating colo-r discs
aggerated in thickness. By connecting the oppo
53, both driven in synchronism with each other
site ends of the spiralled silver strip 'l to an ex~
by constant speed motor 55 through suitable
ternal source of direct current potential 6, a
gearing, may be associated with the» device, one
voltage gradient between turns is produced which
placed in front of the photoelectric grid 3 and 5 may be used to supply the desired voltages to the
the other after the fluorescent screen 4. Each
grids 3, 3’ and the thin metal foil 5.
color disc 53 includes the usual series of color
In order to facilitate making the connection to
filters 54.
the grids, one cooling tube supo-lies voltage to the
In Figs. 2 to 6 there are shown the details of a
metal foil and every other grid, while the alter
preferable construction of the vacuum tube 70 nate grids are supplied from the other cooling
the thin metal foil 5 which acts as an anode.
shown diagrammatically in Fig. 1. Referring to
Fig. 4i, it is seen that the grids 3, 3' consist of »a
square metallic frame I3, the length of each side
of which may be about 6 cm., which frame sup
ports a layer of very iine grid wires I4. The grid 75
tube.
(See Fig. 5.)
Connections between the
spiralled silver strips 'I of the two tubes are made
at such points that the desired voltage diiîerence
019500 volts, or so, is obtained between the succes»
sive grids 3, 3’. The conducting wires to the grids
a41d115
5
are made large enough to also serve as heat con
ductors from the grids 3, 3’ to the cooling tubes 24.
The method iny which the grid and screen as
should, therefore, be considered for light which
penetrates beyond the first photoelectric grid, and
also for secondary electrons in the multiplication
sembly I is supported within the tube structure 2
is shown in Figs. 5 and 6. Two supporting collars
process.
25 are slid over each of the cooling tubes 2li and
of successive grids through 60°, so that only every
fourth grid has parallel wires. A grid four grids
in will receive only about 1/8 as much light as the
first grid, and so, even if its photoelectric sensi
tivity were the same as the first grid, it would
emit only 1A; as many photoelectrons. Also the
electrons it does emit will be subject to three
fewer stages in the multiplication process, which
will give another attenuation factor of at least 8.
Therefore, the photoelectric contribution of the
fourth grid may be neglected insofar as its effect
fastened rigidly thereto. A slot `21 is provided on
an inward extension of the collar 25. The grid
and screen assembly I may then be inserted as a
unit within the tube, the clamping frame I9 slid
ing into the slot 2ï ofthe collar 25. Another slot
Z3 in clamping frame I9 similarly engages the in
ward extension of collar 25, thereby preventing
any movement of the grid and screen assembly l
in any but an axial direction. At the same time
a projection 26 on collar 25 projects through a
similarly positioned slot in the opaque guard I2.
The projection 25 may then be folded over and
j
The effect for light has been eliminated in my
device, by shifting the direction of the grid wires
on the final image is concerned.
Hence, there
will be no screen patterns due to optical causes. i
fastened to the opaque guard I2, thus supporting
Considering now the possibility of screen pat
the grid and screen assembly I rigidly within the 20 terns caused by electron shadowing, it will be
tube.
shown later, when the resolving power of the de
For the sake of simplicity, the following discus
vice is considered, that the total amount of lat
sion of the operation of the device of Figs. 1 to 6
eral displacement, or spreading, of the elements
will be confined to the production of an ordinary
of the electron image between successive grids is
25
black-white intensity amplified image. There
considerably more than the diameter of the grid
fore, it will be assumed for the present that the
wires themselves, so that it is impossible for one
rotating color discs 53 either are omitted or that
grid to shadow the electrons produced on the
ordinary glass has been substituted for the var
preceding grid. Therefore, there can be no screen
ions color ñlters 54.
patterns caused by the electrons themselves.
In operation, an optical image of the object S
The over-all effectiveness of the device as an
is focused on the ñrst photoelectric grid 3 by the
image amplifier will be determined by two fac
lens system II). The lens system Il! might; include
tors: (1) its resolving power, and (2) its rela
a pair of erecting lenses so that the image would
tive sensitivity with respect to the human eye.
appear on the photoelectric grid in the same posi
The resolving power will be dependent on the
tion as the object. The photoelectric grid 3 will 35 amount of lateral displacement which the vari
emit photoelectrons, the number emitted from
ous electrons of the elements of the primary
any particular point on its surface varying in ac
electron image will undergo as they pass from
cordance with the intensity of the optical image
the first photoelectric grid to the fluorescent
at that point, thus producing an electron image
screen. If we assume that the average secondary
40
of the object 8, The emitted photoelectrons, rep
electron is ejected from a grid wire with a ve
resenting> various elements of the electron image,
locity transverse to the field of ñve equivalent
are drawn through the interstices of photoelec
volts, and that the potential difference applied
tric grid 3 to the ñrst of the secondarily emissive
between grids is 500 volts, the ratio of the trans
grids 3', producing a shower of secondary elec
verse velocity to the forward velocity at the suc
45
trons, which in turn are drawn through that grid
ceeding grid is
and strike against the succeeding grid, producing
a new shower of secondary electrons, and so on.
Since the various elements of the electron image
maintain parallel paths, and consequently the
since the velocities are proportional to the square
same relative positions in the electron image, it 50 root of the voltages. However, the transverse ve
is seen that the electron image is maintained in
locity is constant between grids, whereas the for
tact as this multiplication process proceeds. Thus
ward velocity uniformly increases from approxi
an intensified electron image emerges from the
mately zero at the emitting grid to the full for
last of the emissive grids 3' and passes to the thin
ward velocity at the next succeeding grid, so that
55
metal foil 5 with an energy of 50,000 equivalent
the ratio of the average velocities is 1/5. There
volts or so, which is enough to cause the electrons
fore, in traversing the distance of 1 mm. between
to penetrate the thin metal foil 5 and excite the
grids the electrons will undergo a lateral dis
fluorescent screen Il. rI‘hus an intensity amplified
placement of 1/s><1 mrn.=.2 mm., to each side
visible image of the object 3 is produced which
of the center line, or a total displacement be
may be seen by the eye I I.
' 60 tween grids of 2><.2 mrn.=.4 mm. No more
The thin metal foil 5, besides serving as an an
spreading will occur between the final grid and
ode, also prevents light `from the visible image
the fluorescent screen than occurs between suc
formed on screen ¿i from feeding back to the
cessive grids because, although the forward dis
photoelectric grid 3 and producing a self-sustain
tance which must be traversed is much greater,
65
ing discharge. An opaque vguard I2 is also placed
nevertheless the forward velocity is proportion
around the grid and screen assembly I and near
ately greater due to the increased potential dif
the fluorescent screen 4 to prevent any light from
ference. Therefore, if there are 15 grids, the
the outer side of the screen from being reflected
most probable total displacement at the fluo-res
around the grid and screen assembly and back to
70 cent screen caused by the random secondary elec
the photoelectric grid 3.
,
tron emission velocity will -be approximatelyl
Whenever wire screens are superimposed on top
of each other, as the grids are in the present in
vention, a system of light and dark bands, known
There >is another displacement due to the dis
tortion
of the electric field caused by the indi
as screen patterns, may occur due to non-uniform
ityv of the individual wires. Screen patterns 75. vidual Wires of the grid, which should also be
2,410,115
7
considered. The displacement due to this cause,
for the various dimensions chosen, has been
found to be approximately equal to the displace
ment caused by the random secondary electron
emission velocity. The most probable total dis
placement due to both causes will then be of the
Thus, if the fluorescent screen is 6 cm. square,
the visible image produced thereon will be equiv
the auxiliary lens system, Whereas the size of
the retina, the diameter of the iris and the f
value of the eye are all intrinsically limited. Thus
by using a photoelectric grid surface larger than
vthe retina of the eye it is possible to use a longer
focal length than that of .the eye and still retain
the same angular field of view. Assuming a lens
having an f value equal to that of the eye is to be
used, the longer focal length permits the use of
alent in detail 4to about a 3l) line television pic 10 a lens of a greater diameter than that of the eye.
ture. If a greater degree of detail is desired, it
But by employing a lens of greater f value than
can readily be obtained by altering the proper
that of the eye, still another increase in the diam
dimensions. For instance, if detail equivalent to
eter of >the lens may be obtained. The use of a
a 300 line picture is desired, it can be obtained
lens having a much greater diameter than that of
by decreasing the distance between grids to 0.1
the iris of the eye results in the interception of
mm. and decreasing the diameter of the wires to
many more light quanta from a particular light
.001 in. With the grids only 0.1 mm. apart, it has
source, and accounts for the high over-al1 gain
been found that, if the grids are cooled by liquid
in sensitivity of the device, with lens system in
air, a potential difference o-f 500 volts between
cluded, over the eye.
grids may still be retained, without cold emission 20
Because of the fact that a single photoelectron
occurring at the grids.
may be made to produce as bright a spot as de
Having shown the resolving power of the de
vice to be satisfactory, the question of its rela
tive sensitivity with respect to the human eye
sired in this invention, itis the number of quanta
arriving through the optical system from a given
source which determines its visibility. In other
will now be investigated. First, the intrinsic sen 25 words, the problem of getting enough illumina
sitivity of the grid and screen assembly alone,
tion on `the screen to render the object visible
without reference to any lens system, will be
has entirely disappeared, and in its place we have
considered.
About loe quanta of light energy is required to
only the problem of getting enough quanta to
produce suilicient photoelectrons so that the fluc
stimulate o, visual element of the human eye.
tuations in the time and position of their arrival
However, the eye is endowed with the property
will not obscure the shape `and character of the
of being able to change the size of the resolvable
object being viewed. Therefore, it is not the f
elements, thus being able to see in dim light at
value of the lens system used with this device
the expense of definition. It also has the char
which counts in determining the visibility Aof an
acteristic of persistence of vision.
35 object small compared to »the ñeld of View, but
The number of quanta per photoelectron for
only `the diameter of the objective lens.
Cs-Ag-CSO photccells is about the same as the
It would seem then that the over-all relative
number required to excite one resolvable ele
sensitivity of the whole device, including the op
ment of the eye, i. e., 100. It is clear that the
tical system, might be increased to any desired
device, through its electron multiplication proc 40 amount by simply increasing the diameter of the
ess, is capable of making a single photoelectron
objective lens'. However, using the highest Í
emitted from the photoelectric grid visible as one
value lens obtainable, and retaining a 6 cm.
resolvable element at the iiuorescent screen.
square photoelectric grid surface, it will be seen
Therefore,~ the human eye and the grid and
that, >as the diameter of the objective lens is in
screen assembly alone are very nearly equal in
creased the angle of view subtended by the photo
intrinsic sensitivity.
'I‘he single photoelectron produced by any
group of 1GO quanta may be emitted at any point
on the grid, but the probability that it will be
emitted at any particular point is proportional
to the number of quanta striking that particular
point. Thus the device is capable of detecting
the presence of a very dimly illuminated object,
but the detail obtained will depend upon the il
lumination of the object.
The device, then, is
also similar to the eye in that it will sacriñce deli
nition for detection in very dim light.
Also, since the effective persistence of vision
electric grid decreases.
Therefore, it becomes
necessary to assume some arbitrary angular field
of View, which will be large enough so that a
particular object can be located and its character
interpreted, and to compare sensitivities on that
basis.
It can be assumed that 0.75 radian which is
about the angular field of view of an ordinary
camera will be satisfactory. Since the photo
electric grid is 6 cm. square, the focal length of
the lens must be about 8 cm. in order to obtain
such a ñeld .of view. Using a lens of f/l and hav
ing a focal length of 8 cm., the diameter of the
lens that can be used is then fixed at 8 cm. Such
high f values are commonly obtained with
Schmidt cameras.
In an article of Albert Rose entitled “The
of the device may be controlled by giving the
fluorescent material a time lag, it is possible,
when viewing the screen with the eye, to have
the effective persistence of vision equal to that
of the eye in full light, or have it arbitrarily
relative sensitivities of television pick-up tubes,
longer. Hence, the characteristics of the device
photographic film, and' the human eye,” in the
may be made to duplicate those of the eye in
Proceedings ofthe I. R.
June, 1942, p. 293, a
dim light.
number of `constants for the human eye are
In the above discussion it was brought out .that
given. On p. 298, paragraph 4, the f value for
the photoelectric part of the device alone has
the human eye is given as f / 2 for threshold vision,
about the same intrinsic sensitivity as the eye.
That is, it takes about the same number of light 70 Í/3.5 for clear vision, and f/8 for bright light.
The focal length is given as 1.5 om. Therefore,
quanta to produce a visual element in both cases.
using
f/3.5 for clear vision, the effective diameter
The big advantage of the present invention lies
of `the lens of the eye is about 0.43 cm.
in the fact that there are no inherent limitations
Since the intrinsic sensitivity of the present
placed either upon the actual size of the photo
device
is about the same as that of the human
electric grid surface or diameter and f value of 75
eye, the relative sensitivity of the device, with
i)
AV2,410,115
9
the >above lens system, compared with the eye,
with its lens system, will be determined solely
by the amount of light delivered to each from
a particular object. Therefore, the over-all gain
in light sensitivity of the device over the humanA
eye will be proportional to the square of the ratio
of the instrument lens diameter to the veffective
eye lens diameter, or
8
z
shown within a cathode ray tube 30, a grid and
condenser assembly 3| which is identical to the
grid and screen assembly I of Fig. 1 insofar as
the grids 3, 3’ are concerned. In place of the
fluorescent screen 4 and thin metal foil 5 of Fig.
1, however, there is shown an extremely thin di
electric sheet 32, which may be of mica, and a
thin metal sheet 33, which may be simply a coat
ing of beryllium condensed on one side of the
dielectric sheet 32. yVoltages'are applied by the
-430
battery 6 and rheostat 'l similar to those applied
to the grid and plate assembly | of Fig. 1, that
for the particular dimensions chosen.
is, about 500 volts between grids and about 50,000
It is obvious that this over-all rgain in sensi
volts between the last of the secondary'emissive
tivity over the human eye may readily be in
creased by altering certain dimensions. For in 15 grids 3’ and the thin metal sheet 33.
On the other side of the dielectric sheet 32
stance, if the dimensions of the grid and screen
there are shown numerous small globules 34 of
assembly are doubled, the diameter of the ob
some heavy metal, such as gold, each of which
jective lens can be doubled, which would then
is separated from and independent of the others.
give a gain in sensitivity of 4><4S0=1720~ This
same result could obviously be obtained, without 20 Each of these globules 34 may be considered as
forming one plate of _a little condenser, the other
altering the dimensions of the grid `and screen
plate of which is common to all and is formed by
assembly, if it is found possible in any particular
the thin metal sheet 33. Grid 35, which is main
application to get along with an angular ñeld of
tained at a positive potential with respect to the
View of half as muchas was assumed.
cathode 36 by the battery 43, attracts an electron
The detailed construction described vand the di
beam from the cathode 33 toward the globuled
mensions chosen throughout this description are
surface of dielectric sheet 32. Grid 35 may be
replaced by the cylindrical collar 31, or both may
be used. The electron beam may then be caused
were chosen in order to be able to work out re
sults in a particular case so that some idea of 30 to scan the globuled surface of the dielectric sheet
32 by means of the deflecting plates 38. An elec
the capabilities of the device could be shown.
trical connection is made from the thin metal
The above described device can be easily made
sheet 33 through the resistor 4| to the cathode 35.
to see in color by utilizing the two rotating color
The operation of the grid and condenser as
discs 53, one placed in front of the ñrst photo
electric grid 3„and the other placed between the 35 sembly 3| is identical with that of the grid and
screen assembly | of Fig. 1 previously described,
eye I! and the fluorescent screen 4 (see Fig. 1).
vexcept that the intensified electron image which
Thus, at any particular time, the loptical image
emerges from the series of grids in this case
focused on the first photoelectric grid 3 will in
penetrates the thin metal sheet 33 and the thin
clude only that much of the object as emits ra
diation of the same c-olor as the filter 54 which 40 dielectric sheet 32 and is stopped by the globules'
34. In this way a negative charge is stored on
is in front of the first photoelectric grid 3 at
each little globule 34 which is proportional to the
that time. This partial image will be convert
amount of light falling on the corresponding
ed to a corresponding intensity amplified black
elementary area of the surface of the photoelec
white image at the fluorescent screen 4, which
image lwill then be seen by the eye in the proper
tric grid 3.
color due to the action of the color filter 54
As the electron beam from the cathode 36
to be understood as illustrative only, and in no
Way limit the invention. Arbitrary dimensions
which is in front of the eye.
As the two color
strikes against any particular charged globule 34,
discs 53 rotate, the various colors emitted by the
it knocks out secondary electrons, which are then
object are reproduced at the eye in their proper
drawn to the positive grid 35 or cylindrical col
relative proportions in rapid succession, so that 50 lar 31, thus removing the charge accumulated
the effect of seeing a color image will be pro
on the globule 34, and re-establishing the datum
duced at the eye.k Some loss of light sensitivity
potential between it and the grid 35. Since the
will-result in this process, but, since the color
charge on globule 34 is removed in a time lwhich
vision elements of the eye are very much less
is very short compared to the time over which
sensitive `than the black-white elements, the 55 the charge was accumulated, a corresponding
over-al1 relative sensitivity of the device over the
charge is induced on the metal plate 33 which in
eye will be considerably higher for color work
turn causes a voltage drop across the resistor 4|.
than for black-white work. The fluorescent
Since this voltage drop will be proportional to
screen 4 should be given no time lag in this case,
the total charge accumulated on globule 34 be
since any persistency of the image at the fluo
tween successive scannings, it will also be pro
rescent screen 4 would interfere with the next'portional to the amount of light falling on the
succeeding color.
.
,
corresponding element of the surface of the first
Also, Vsince photocells may be highly sensitive
photoelectric grid 3 between successive scan
in the near infra-red and the near ultra-violet,
the device may be given infra-red and ultra
violet color vision by the insertion of an infra
red or ultra-violet filter screen in place of any
one ofthe color filters ed in the first color disc
53. In this way ultra-.violet or infra-red light
nings, and may therefore be used as a television
signal. Thus it iS seen that a television trans
can be made to appear as some arbitrarily chosen
70 fore has a much higher sensitivity than 'any of
visual color. The remaining portion of the pic
ture Awill appear in'its true color except for the
omissi-on of the c-olor of the filter which has been
mitting tube has been produced for converting
an optical image into a television signal, which
tube takes advantage of both the electron multi
plication and the storage principles, and there
the presently used tubes.
The above described device will function sat
isfactorily with the globules 34 removed. In
replaced.
,
_
such case, however, the mica strip would have to
f Referring now to Fig. 7 Yin which another em
be made thick enough to .stop the electron image.
75
bodiment of the invention is illustrated, there is
2,410,115
11
Each elementary area of the dielectric sheet 32
would then form one plate of a little condenser,
and take the place of the corresponding glob
an electron image against and through succes
sive surfaces, said surfaces being mutually spaced
suiiiciently close t0 permit intensification of said
electron image by secondary electron emission
ule 34.
Fig. 8 illustrates a modification of the present Ul at each of said surfaces while minimizing de
invention in which my novel electron multiplier
terioration of said image caused by secondary
is combined with the essential features Vof the
electron emission velocities.
ordinary Farnsworth image dissector. Within an
4. An electron image intensifier comprising a
evacuated glass tube 52, there is shown a series
plurality of secondary electron emissive and elec
of grids 3, s', which produce an intensified elec 10 tron permeable surfaces, said surfaces being sep
tron image of the object 3 in the manner pre
arated only sufliciently to maintain electrical in
viously described. The electron image is drawn
sulation therebetween, and means for driving an
from the last of the grids 3, 3’ t0 the anode ¿i3
electron image against and through successive
as a result of the Voltage applied by battery 45.
surfaces whereby said image is intensified at
The focusing coil 44 produces a uniform axial
each of said surfaces with minimum loss of de
magnetic field so that electrons emerging from
tail caused by secondary electron emission vc
a particular spot on the last of the grids 3, 3’
locities.
will strike the same spot on anode 43.
5. A light ampliñer comprising a lens system
Scanning is accomplished by systematically
for producing an optical image of an object, a
moving the whole electron image across the anode
photoelectrically sensitive cathode for producing
G3 by means of the horizontal deñecting coils
a primary electron stream forming an electron
£9 and the vertical deflecting coils 55. In this
image from said optical image, a plurality of
way successive elements of the electron image
electron permeable and secondary electron cinis
are allowed to pass through the'aperture $6 and
sive grids for producing an intensified electron
strike the collector anode 5|, which is main 25 image from said primary electron image, each
tained at a higher potential than the anode ¿i3
of said grids comprising substantially parallel
by the battery 41, Hence, the resulting voltage
wires lying in a direction which is rotated
drop across the resistor 48 is proportional to the
through a predetermined angle for each succes
amount of light falling on the elementary area,
sive grid, a fluorescent screen, and means pro
which is being scanned at that particular time,
jecting said intensified electron image on said
and may therefore be used as a television signal,
screen for producing an intensified optical image
As many changes could be made in the above
of said object free from grid patterns.
construction and many apparently widely differ
6. An electron multiplier comprising a plurality
ent embodiments of this invention could be made
of secondary electron emissive and electron Der
Without departing from the scope thereof, it is
rneable surfaces having a mutual spacing of the
intended that all matter contained inthe above
order of one millimeter, and means for causing
description or shown in the accompanying draw
an electron image to impinge upon and to be
ings shall be interpreted as illustrative and not
driven through successive surfaces, whereby said
in a limiting sense.
image is intensified by secondary electron emis
What is claimed is:
40 sion at each of said surfaces while remaining
l. A light amplifier comprising means for pro
substantially intact.
ducing an optical image of an object, a photo
’7. In an electron multiplier a plurality of elec
electron emissive cathode for producing a pri
tron emissive and electron permeable surfaces
mary electron stream forming an electron image
each comprising a plurality of closely spaced
filamentary means having diameters of the order
secondary
from said optical
electronimage,
emissive
electron
surfaces
permeable
for produc
of one one-hundredth of an inch or less, and
ing an intensified electron image from the pri
means for driving an electron image against and
mary electron image, said surfaces being sep
through successive surfaces, whereby said image
arated only sufliciently to maintain electrical in
is intensified by secondary electron emission at
sulation therebetween whereby said electron 50 each of said surfaces while remaining substan
stream is intensified with minimum loss of de
tially intact.
tail in said electron image caused by secondary
8. In an electron multiplier a plurality of elec
electron emission velocities, a fluorescent screen,
tron emissive and electron permeable surfaces
and means projecting said intensified electron
having a mutual spacing of the order of one mil
image on said screen for producing an intensiñed 55
limeter,
each of said surfaces comprising a plu
optical image of said object.
rality of closely spaced nne wires having diam
2. A light amplifier comprising means for pro
eters of the order of one one-hundredth of an
ducing an optical image of an object, a photo
inch or less and having spacing between centers
electron emissive cathode for producing a pri
of the order of two one-hundredths of an inch or
mary electron stream forming an electron image 60 less, and means for causing an electron image to
from said optical image, plural electron perme
impinge upon and to be driven through succes
able and secondary electron emissive means for
sive surfaces, whereby said image is intensified
producing an intensiñed electron image from the
by secondary emission at each of said surfaces
primary electron image, said secondary electron
emissive means being mutually spaced sufficiently
close to permit intensification of said electron
stream while minimizing deterioration of said
electron image by secondary electron emission
while remaining substantially intact.
9. A light amplifier comprising means for pro
ducing an optical image of an object, a photoelec
tron emissive cathode for producing a primary
electron stream forming an electron image from
said optical image, unitary electron permeable
jecting said intensiñed electron image on said 70 and secondary electron emissive surfaces for pro
screen for producing an intensified optical image
ducing an intensiñed electron image from the
of said object.
primary electron image, said surfaces being sucn
velocities, a fluorescent screen, and means pro-
3. An electron image intensifier comprising a
cessively adjacent whereby said electron stream
plurality of secondary electron emissive and elec
is intensified with
loss of detail in said
tron permeable surfaces, and means for driving 75 electron image caused by secondary electron
l
1
14
13
emissive means being mutually spaced suñiciently
emission velocities, a fluorescent screen, and
close to permit intensification of said electron
stream While minimizing deterioration of said
electron image by secondary electron emission
means projecting said intensified electron image
on said screen for producing an intensified opti
cal image of said object.
10. A light amplifier comprising means for pro
ducing an optical image of an object, a photo
velocities, a fluorescent screen, and means com
prising a light-opaque anode interposed between
said secondary electron emissive means and said.
screen for projecting said intensîñed electron
electron emissive cathode for producing a pri
mary electron stream forming an electron image
image on said screen for producing an intensified
from said optical image, plural electron permea 10 optical image of said object,
ble and secondary electron emissive means for
producing an intensiñed electron image from the
RUSSELL H. VARIAN.
primary electron image, said secondary electron
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