US2433700A

US2433700A - Phototube multiplier

Info

Publication number: US2433700A
Application number: US508895A
Authority: US
Inventors: Christian C Larson
Original assignee: Farnsworth Research Corp
Current assignee: Farnsworth Research Corp
Priority date: 1943-11-04
Filing date: 1943-11-04
Publication date: 1947-12-30
Anticipated expiration: 1964-12-30

Description

Afina, I uu UNITED STATES .PATENT oFFlcE Christian C. Larson, Fort Wayne. Ind., assignor, by menne assignments, to Farnsworth Research Corporation, a corporation o! Indiana application November-4, 1943, sulla No, tosses l This invention relates to electron-optical devices and particularly` to a phototube multiplier for dividing an optical image into any desired pattern. l

In a conventional phototube multiplier for dividing an optical image the photoelectric cathode is divided into the desired pattern. In this manner a number of individual electron streams are emitted .by the cathode and each is separately multiplied by means of an individual electron multiplier. In such a device the image division is secured bysubdividing the cathode in a desired manner. Such devices have not been entir'ely satisfactory for the reason that the formation o! a subdivided cathode is relatively dimcult. i

Another form of phototube multiplier comprises a. solid photoelectric cathode and one or more electron multipliers. Buch devices` however, have not been utilized for the division of an optical image according to a predetermined plan. The usual employment ot devices oi this character has been in modulation systems. The solid photoelectric cathode upon which light is projected serves merely to produce a copious stream oi electrons. Where a plurality or electron multipliers are used in conjunction with a a plurality of the image components.

Itis an object of the present invention, therefore. to provide a novel electron-optical device',

whereby individual signals representative oi pre` determined portions of an optical image may be produced.

Another object of the invention is to provide a novel method of generating signals, whereby to produce simultaneously a plurality of individual signals each representative of a different pre-- determined portion of an optical image.

In accordance with the invention there is provided an electron-optical device having an evacuated envelope within which there is disposed a photoelectric cathode. within the envelope a plurality oi electron multipliers. Each of the multipliers is provided with a secondrryxniissive electrode oi predetermined There also is disposed Schmidt optical system.

s claim. (ci. aso-iis) 2 A form. These electrodes are disposed in a plan spaced from and facing the cathode and arc arranged with respect to one another to form an area substantially similar to the area formed by projecting the cathode surface into the plane of the electrodes.

Apparatus oi this character is one means for carrying out the novel method in accordance with the instant invention. This method oi contemporaneously producing individual signals representative oi different predetermined portions of an optical image comprises the following steps:

An electron image corresponding to the optical image is formed. A division of the electron image into diiIerent predetermined portions is effected. The different portions oi the elecline 2-2 of Fig. l.

Referring now to the drawing, there is disclosed an embodiment of the invention employing an optical system of the reilection type which more particularly is known as the so-called This system comprises a spherically shaped light reflecting member il. There is formed substantially at the center thereof. an aperture i2. A concave surface I3 on the reflector Ii is conditioned by any well known means for the reection of light. A lens Il. having a conilguration suitable to correct for spherical aberration ofthe r'eilector I I, is mounted in spaced relation to the reilector by a plurality oi angular members such as the spacing members I5 and I8. Y Y

A substantially cylindrical transparent evacuated envelope Il is supported in a ,suitable manner so that it extends through the aperture I2 of the reilector II. Sealed through the lefthand end of the tube envelope I1, as viewed in the drawing, is a metallic rod I8. An opaque "metallic backing plate I8 is supported at the inner end of the rod I8 and is provided with a substantially sphericalsuriace conilguration. A

photoelectric surface 2l is formed on the convex surface of the backing plate Il by any suitable process such as deposition by evaporation of a photoelectric material. Such a structure constitutes a photoelectric cathode having a spherical surface facing and substantially parallel to the reflecting surface I3 of the reflector Il. Preferably the cathode is located approximately midway between the reflector Il and the lens Il. The photoelectric surface of the cathode is continuous over the entire area thereof.

There is mounted in the righthand end of the tube envelope l1, as viewed ln the drawing, four multistage electron multipliers. The ilrst stage electrodes, such as 22 and 23l of the respective multipliers, are provide with secondary emissive surfaces facing the photoelectric cathode 2i andare arranged in a plane a acen e reilector il. These first stage electrodes may have any predetermined forms depending upon the pat tern into which it is desired to divide the optical,

image. For the purposes of illustrating the invention, it is assumed that the optical image is to be divided into four equal quadrants.

Fig. 2 illustrates the arrangement of the

electrodes

22 and 23 with respect to one another and wi respect to the other two flrst stage multiplier electrodes 2| and 25., It is seen that the first stage multiplier electrodes are electrically dis` tinct and are arranged with respect to one another to form an area which is substantially similar to the projection of the photoelectric cathode 2i into the plane of the electrodes.

The second stage multiplier electrodes. such as 26 and 21, associated respectively with the

first stage electrodes

22 and 23, are so formed to provide a guide path for the electrons from the cathode-facing surfaces of the ilrst stage electrodes to the rear or righthand sides ofthese electrodes, as viewed in Fig. 1. The remainder of the electrodes of the respective multipliers may be the conventional box type structures, such as 28 and 29. Each of the multipliers also is provided with a final stage electrode which may be in the form of a plate, such as 3i or 32. Additionally. each of the multipliers is provided with a collector electrode which may be in the form of a grid structure, such as 33 or 3l. Electrical connections to the various multiplier electrodes may be made to the exterior of the tube envelope by means of conductors. such as 35 and 36.

A coil 31 is mounted in a manner to surround the space between the photoelectric cathode 2| and the multiplier flrst stage electrodes, such as 22 and 23. Connections may be made from the coil to a suitable source of the direct current (not shown) by means of conductors 38. Energization of the coil produces a magnetic field which is employed to focus the electron image produced by the photoelectric cathode 2|.

Referring now to the operation of the described embodiment of the invention. assume that light forming the optical image, which it is desired to divide into four equal quadrants, is directed from the left as viewed in Fig. 1. This light is transmitted bythe lens i4 and is reflected by the reflecting surface i3 of the member Il., The reilected light is concentrated and directed onto the photoelectric cathode 2i.

The optical image projected onto the photoelectric cathode in the manner described, causes the cathode to produce a corresponding electron stream. The electron stream is focused by means of the coil 3l to form an electron image corresponding to the optical image in the plane of the multiplier first stage electrodes, such as 22 and 23. These electrodes, together with

similar electrodes

24 and 25, are maintained, in a ywell known manner, at suitable positive potentials with respect to the photoelectric cathode 2i The electron image produced by the solid cathode is divided into four equal quadrants by the elec-

l trodes

22, 23, 24 and 25. This division of the electron image corresponds substantially to the pattern of the multiplier first stage electrode arrangement.

Consider, for example. that portion of the electron image impinging upon the secondary emissive surface of the rst stage electrode 22. The secondary electrons produced by the primary impingement are drawn into the input aperture of the second stage electrode 23 by reason of the maintenance of the second stage electrode at a suitably higher positive potential than the nrst stage electrode. The connections of the multiplier electrodes to a source of direct current potential have not been shown foi the reason that such connections are conventional to maintain each succeeding multiplier electrode at an increasingly more positive potential than its pred ecessor. The secondary electrons traversing the second stage electrode 26 emerge from the output aperture thereof and are directed sequentially through successive stages of the multiplier in a conventional manner.

The electrons collected by the collector electrode 33 are employed to develop, in a conventional manner, the signal in an output impedance (not shown) connected to the collector electrode.

A similar process of electron multiplication is eiectedcontemporaneously with that described by the other electron multipliers. In each case the electron multiplication is of that portion of the electron image corresponding in a pattern to the shape of the multiplier rst stage electrode intercepting the electron image portion. Likewise, the signals developed in the respective output circuits connected to the individual multiplier collector electrodes, are representative of the respective portions of the electron image. It is important to note that the individual signal multiplications are effected simultaneously.

It is apparent from the foregoing description of the illustrative embodiment of the invention. together with the described mode of its operation. that a device of this character is susceptible to employment in numerous ways. Also .it is to be noted that it is not essential that an electron-optical device of the character described be used in conjunction with an optical system of the reflection type. It is contemplated to be `within the scope of the invention that a translucent photoelectric cathode may be employed. In such a case. the optical image may be projected upon the surface of such a cathode opposite to the photoelectric surface in a manner well known to those skilled in the art. lSimilarly, it should be noted that it is not essential to the successful operation of a device embodying the invention that the multiplier be arranged in the manner shown. It is considered to be within the skill of those versed in the art to provide an arrangement of a plurality of multistage electron multipliers in substantially any other relationship to the photoelectric cathode so long as the ilrst stage electrodes are disposed in a manner to intercept the electron stream produced by the cathode. Similarly, the configuration of the cathode may be substantially different from that shown so long as the arrangement of the multiplier rst stage electrodes forms an area winch is substantially similar to the projection of the cathode into the plane of the electrodes.

While there has been described what. at present, is considered the preferred embodiment of the invention, it will be obvious to those skilled A in the art that various changesand modifications may be made therein without departing from the invention. and it. therefore. is aimed in the appended claims to cover all such changes and modifications as fall within'the true spirit cathode, each of said multipliers having a secondary emissive electrode, said electrodes being disposed in a plane spaced from and facing said cathode and collectively having substantially the same shape as the projection of said cathode into the plane of said electrodes.

2. In a phototube multiplier device, an evacuated envelope, a photoelect,- ccathode disposed in said envelope, and a plurality of electron multipliers mounted in said envelope opposite to said cathode, each of said multipliers having a sector shaped secondary emissive electrode, said electrodes presenting together a substantially complete circular area in a plane spaced from and facing said cathode.

3. In a phototube multiplier device. a transparent evacuated envelope, a photoelectric cathode disposed in said envelope, and' four electron multipliers mounted in said envelope opposite to said cathode, each of said multipliers having a quadrant shaped secondary emissive electrode.

said electrodes presenting together a substantially complete circular area in a plane spaced from and facing said cathode.

4. A phototube multiplier device comprising, a reflecting member having an aperture therein, a tube having a transparent evacuated envelope extending through said aperture, a photoelectric cathode disposed in said tube, the surface of said cathode facing and being substantially parallel to the surface of said reflecting member, a plurality of electron multipliers mounted in said tube opposite to said cathode, each of said multipliers having a secondary emissive electrode. said electrodes being disposed in a plane adjacent to said reflecting member and facing said cathode and presenting together an, area substantially similar to the projection of said cathode into the plane of said electrodes, and means included with said device for producing a eld in the space between said photoelectric cathode and s'aid multiplier electrodes to focus the electron stream emitted by said cathode substantially in the plane of said electrodes.

disposed aperture therein, a tube having a transparent evacuated envelope extending through said aperture, a convex photoelectric cathode disposed in one c nd of said tube, the surface of said cathode facing and being substantially parallel to the surface of said reflecting member, a plurality of multistage electron multipliers mounted in said tube opposite to said cathode, each of said multipliers having a flat first stage secondary emissive electrode, said first stage electrodes presenting together a substantially complete circular area in a plane adjacent to said reflecting member and facing said cathode. and means included with said device for producing a field in the space between said photoelectric cathode and said multiplier first stage electrodes to focus the electron stream emitted by said cathode substantially in the plane of said first stage electrodes.

6. A phototube multiplier device comprising. a. concave reflecting member having a centrally disposed aperture therein, a lens disposed in spaced relation to said reflecting member and having a configuration suitable to correct for spherical aberration, a tube having a transparent evacuated envelope extending through said aperture. a convex photoelectric cathode disposed in one end of said tube intermediate of said reflecting member and said lens, the surface of said cathode facing and being substantially parallel to the surface of said reflecting member, four electron multipliers mounted in said tube opposite to said cathode, each of said multipliers having a quadrant-shaped secondary emissive electrode, said electrodes presenting together a substantially complete circular area in a plane adjacent to said reecting member and facing said cathode, and electromagnetic means included with said device and located externally of said tube for producing a longitudinal field in the space between said photoelectric cathode and said multiplier quadrant-shaped electrodes to focus the electron stream emitted by said cathode substantially in the plane of said electrodes.

7. A phototube multiplier device comprising, a spherically-shaped reflecting member having a centrally disposed aperture therein. a lens disposed in spaced relation to said reflecting member and having a configuration suitable to correct for spherical aberration, a tube having a transparent evacuated envelope extending through said aperture, a spherically-shaped photoelectric cathode disposed in said tube intermediate of said reflecting member and saidY lens, the surface of said cathode facing and being substantially parallel to the surface of said reflecting member, four multistage electron multipliers mounted in said tube opposite to said cathode, each of said multipliers having a rst stage quadrant-shaped secondary emissive electrode, said first stage electrodes presenting together a substantially complete circular area in a plane adjacent to said reecting member and facing said'cathode, and an electromagnetic coil included with said device and located coaxially with said tube for producing a longitudinal field in the space between said photoelectric cathode 'and said multiplier first stage electrodes to focus the electron stream emitted by said cathode substantially inthe plane of said first stage electrodes.

8. A vphctotube multiplier device comprising, a spherically-shaped reflecting member having a centrally disposed aperture therein, a lens disposed in spaced relation to said reflecting member and having a configuration suitable to correct for 'spherical aberration, a tube having a transparent evacuated envelope extending through said aperture, a spherically-shaped photoelectric cathode disposed in one end of said tube intermediate of said reflecting member and said lens, the surface of said cathode facing and being substantially parallel to the surface of said reflecting member, four multistage electron multipliers mounted in the other end of said tube opposite to said cathode, each of said multipliers having a first stage quadrant-shaped secondary 7 emissive electrode. said nrst stage electrodes being electrically distinct and presenting together a substantially complete circular area in a plane adjacent to said reflecting member and facing said cathode, and an electromanetic coil surrounding the space between said photoelectric cathode and said multiplier nrst stage electrodes to focus the electron stream emitted by said cathode substantially in the plane of said first stage electrodes.

CHRISTIAN C. LARBON.

REFERENCES CITED The following references are of record in the me oi' this patent:

5 UNITED STATES PATENTS Number Name Date 2,141,322 Thompson Dec. 27, 1939 2,239,149 Farnsworth Apr. 22, 1941 2,204,428 Moller et a1 June 11, 1940 1 2,192,579 Morton et a1 Mu. s, 1940- 2,230,134 Colberg et al. Jan. 28, 1941