US3040205A - Electrostatic vidicon - Google Patents

Description

June 19, 1962 H. R. WALKER ELECTROSTATIC VIDICON 2 Sheets-Sheet 1 Filed May 51, 1960 INVENTOR.

HAROLD R. WALKER BY 5 AGENT June 19, 1962 H. R. WALKER ELECTROSTATIC VIDICON 2 Sheets-Sheet 2 Filed May 51, 1960 INVENTOR HAROLD R. WALKER AGENT United States Patent Ofiice 3,040,205 Patented June 19, 1962 3,040,205 ELECTRQSTATIC VIDECGN Harold R. Walker, Corpus Christi, Ten, assignor to the United States of America as represented by the Secretary of the Navy Filed May 31, 1960, Ser. No. 33,064 15 Claims. (Cl. 315-) (Granted under Title 35, US. Code (11 52), sec. 266) The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

The present invention relates to an improved image tube and more particularly to an electrostatically controlled vidicon having improved performance characteristics.

It is the principal object of the present invention to provide an image tube providing good resolution with low power requirements.

It is another object of the invention to provide for use in an image tube novel electron optical systems whereby the resolution of the image tube may be enhanced.

Other objects and many of the attendant advantages of this invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein:

FIG. 1 illustrates schematically an embodiment of the invention;

FIG. 2 illustrates an alternative electron optical system which may be employed in the embodiment of FIG. 1; and,

FIG. 3 illustrates an electron beam decelerating and collimating means which may be used in embodiments of the invention.

Referring now to FIG. 1, there is shown a vidicon generally indicated by the reference numberal 10. Vidicon 10 includes an evacuated envelope 11 which may be of glass or other suitable material closed at one end by a target T.

Disposed within envelope 11 is a conventional electron gun structure comprising an indirectly heated cathode K provided with a filament 12 and enclosed by a coaxial grid g provided with an aperture 14, The filament 1?, of cathode K may be conventionally coupled to a potential source represented by battery 16.

Adjacent the electron gun structure there is provided an aperture lens comprising control grid g and a second grid g provided with apertures 16, 17,

Following the first aperture lens is a second aperture lens comprising electrodes A provided with an aperture 18, A provided with an aperture 19, and A pro vided with an aperture 21.

A deflection system comprising deflection plates 22, 23, 24, and 26 coupled to sweep generators 27 is disposed adjacent the second aperture lens.

Located within envelope 11 between the deflection system and target T are a plurality of conductive beam decelerating and collimating rings 28, 2,9, '31, 32, 33, 34. While for illustrative purposes six rings have been shown, it is to be understood that more or less :may be provided in order to conform to the particular requirements of a specific image tube or the use to which the tube is put.

As shown in FIG. 3, a continuous resistive spiral deposited upon the interior surface of envelope 11 maybe employed in place of the rings, if desired. A potential gradient may be established across the resistive spiral commensurate with that established across the rings as explained more fully below.

Target T comprises a glass plate 36 having a conductive film 37 deposited thereon and electrically coupled through a load resistor 38 to a terminal 39 to which may be applied a positive potential, for example, 30 volts. As indicated, an output terminal 4-1 may be coupled to resistor 38. According to one embodiment of the invention semiconductor materials are deposited upon conducting layer 3 7 and may comprise, for example, a P-type ma terial 42, such as arsenic triselenide, and an N-type material 43, such as antimony trisulphide. The arrangement described provides short duration storage and is suitable for use with fast targets. As will be explained below for some purposes it may be desirable to transpose layers 42, 43, The materials described are photoconductors which respond optimally to radiation in the visible spectrum but which also have a useful response to radiations in the near infrared spectrum. For infrared applications of the present invention, however, single photoconductive or bolometric layers may offer advantages. Multiple layers of P-type and N-type bolometric materials may also be employed utilizing the thermoresistive and thermovoltaic properties of the PN junction in the presence of infrared radiation. When bolometric layers are used, gold black or some other heat absorbing material would be used as the conductive layer.

An object or field represented by arrow 0 may be focused upon target T by an optical system L, represented in FIG. 1 by an elementary lens.

Operating potentials for the tube elements may be provided from a power supply of any convenient type. In the embodiment of P16. 1, as illustrated, grid g is coupled to a battery 45 while grid g electrodes A A A are coupled to a resistive network 46 connected to a battery 44. In a similar manner, for illustrative purposes, collirnating rings 28, 29, 31, 32, 33, 34 are shown coupled to a resistive network 4 3 connected to a battery 47, while in FIG. 3 corresponding resistive spiral 30 is shown connected to a resistor 4'8 connected to a battery 47'.

In one practical embodiment of the invention, apertures 14, 16 may each have a diameter of .040"; aperture 17 may have a diameter of .0015"; apertures 18, 21 may have diameters of .04"; and aperture 19 may have a diameter of .15". Grid g may be maintained at a potential of approximately -20 volts with respect to cathode K. Grid g electrode A and electrode A may be respectively maintained at potentials of +125, +300, and +600 volts. When, as in the embodiment of FIG. 1, it is desired to provide the aperture lens comprising electrodes A5,, A A with a positive characteristic, electrode A should be maintained at a potential negative with respect to the center potential between electrodes A A for example, volts. Ring 28 may be-maintained at a potential of approximately +600 volts while ring 34 may be maintained at a potential of 45 volts. Intermediate rings 29, 31, 32, and 33 should be maintained at intermediate potentials with the incremental voltage variation therebetween uniform, whilethe potential applied to resistive spiral 30 (-FIG. 3) may extend approxi mately from 45 volts to +600 volts. 7 V

The aperture lens comprising grids g g functions to focus the electron beam emanating from cathode K at a crossover point C. The location of crossover point C undesirably fluctuates with changes in the potentials applied to the elements of the vidicon and with the intensity of the beam current making sharp focusing of the electron beam diflicult or impossible. For this purpose the small'limiting aperture 17 is provided in grid g to thereby establish apoint electron source having a fixed location with respect to the second aperturelens and the target T.

The second aperture lens has a positive characteristic, as mentioned above, and functions to sharply focus the point electron source appearing at aperture 17 upon the surface of target T. Focusing may be accomplished by varying either the potential applied to electrode A or the potential applied to electrode A The beam decelerating and collimating rings or resistive spiral function to insure that the electron beam impinges upon the target T at low velocity and normal to the surface thereof to thereby prevent secondary emission from the target materials and to prevent spurious anomalies in the electric field distribution in the vicinity of the target, both of which would degrade image quality.

Deflection plates 22, 23, 24, 26, when suitably energized from sweep generators 27, function in a conventional manner to cause the electron beam to scan the surface of target T in a selected pattern with a selected scan rate.

In order to provide good resolution it is desired to maintain the beam magnification equal to or less than unity. In accordance with Schlesingers rule for beam magnification:

NZZ M2 where:

M represents beam magnification t represents the object drift time and is proportional to the electron velocity between aperture 17 and aperture 19.

t represents the image drift time and is proportional to the electron velocity between aperture 19 and the surface of target T.

Obviously in order to obtain the objective of maintaining the magnification at a minimum, the potential in the object drift space should be maintained relatively low with respect to the potential in the image drift space. However, in order to provide adequate beam intensity and collimation together with the maintenance of low beam velocity at or near the surface of the target, a compromise must be eflfected. The dimensioning of the electron optical elements and the potentials applied thereto, as illustratively set forth above, provide a resolution of between 400 and 600 lines.

The electron optical system illustrated in FIG. 2, to be described below, affords a somewhat better opportunity to effect a more desirable compromise between the factors mentioned above.

In the absence of an image focused on the photoconductive layers 42, 43 of target T by optical system L, layers will become charged uniformly to approximately the potential of cathode K after being scanned by the electron beam. lmage elements focused on the target will alter the conductivity of the corresponding elemental areas of the layers in accordance with the relative intensity of the image elements causing a selective discharge of the elemental areas toward the potential of conductive layer 37. Subsequent electron beam scans will tend to restore the elemental areas to cathode potential. The resultant potential fluctuations appear across load resistor 38 as an output signal.

As mentioned above, the arrangement of layers described above provides short duration storage suitable for fast scan rates. Reversal of the photoconductive layers provides long duration storage and is suitable for low scan rates.

Bolometric materials function in a somewhat similar manner by providing resistivity variation in accordance with relative image element intensity and, as mentioned above, by thermoresistive or thermovoltaic junction effects.

Referring now to FIG. 2 there is shown an electron gun structure comprising a cathode K, a control grid g provided with an aperture 14, and a second control grid g provided with apertures 16, 17.

The structure thus far described is substantially identical to the corresponding portions of FIG. 1.

Grid g electrode A and electrode A comprise an aperture lens having a negative characteristic while electrodes A and A and A comprise an aperture lens having a positive characteristic when the respective lens elements are coupled to suitable potentials. For example, grid g may be maintained at +125 volts and electrode A at +300 volts. Electrode A is maintained at a potential in excess of the center potential between grid g and electrode A for example +250 volts. Electrode A may be maintained at a potential of +300 volts as previously mentioned, while electrode A, may be maintained at a potential of between +600 and +1000 volts. Electrode A should be maintained at a potential less than the center potential between electrodes A A for example, volts. Aperture diameters of the lens elements in the embodiment of FIG. 2 are equal to or of the same order of magnitude as the corresponding lens elements in the embodiment of FIG. 1.

The combination of a negative electron lens with a positive electron lens together with the Schlesinger drift time effect functions to shift the apparent position of the composite lens nearer to the target. With this arrangement more flexibility is afforded in the selection of the velocity, collimation and current intensity of the electron beam while at the same time permitting the maintenance of adequate resolution.

When constructed and energized as set forth above, the electron optical system of FIG. 2 is capable of providing resolution in excess of 600 lines.

Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described.

What is claimed is:

1. A vidicon comprising: an elongated envelope; a target sealing one end of said envelope, said target comprising an insulative member having a conductive layer deposited on the interior surface thereof adapted to be coupled to an external circuit, and a radiation sensitive material deposited on said conductive layer; an electron gun structure mounted in said envelope adjacent the other end thereof, said electron gun structure comprising a cathode and an apertured control grid in close proximity to said cathode; a second control grid mounted within said envelope adjacent said electron gun and provided with an electron beam transit limiting aperture; electrostatic electron beam decelerating and collimating means mounted within said envelope adjacent said target; electrostatic electron beam deflection means mounted within said envelope intermediate said second grid and said decelerating and collimating means; an electron optical means mounted within said envelope intermediate said second grid and said deflection means operative to image the aperture of said second grid upon said target.

2. A vidicon comprising: an elongated envelope; a target sealing one end of said envelope, said target comprising an insulative member having a conductive layer deposited on the interior surface thereof adapted to be coupled to an external circuit, and layers of P-type and N-type photoconductive materials deposited on said conductive layers; an electron gun structure mounted in said envelope adjacent the other end thereof, said electron gun structure comprising a cathode and an apertured control grid in close proximity to said cathode; a second control grid mounted within said envelope adjacent said electron gun and provided with an electron beam transit limiting aperture; electrostatic electron beam decelerating and collimating means mounted Within said envelope adjacent said target; electrostatic electron beam deflection means mounted within said envelope intermediate said second grid and said decelerating and collimating means; and electron optical means mounted within said envelope intermediate said second grid and said deflection means Operative to image the aperture of said second grid upon said target.

3. The combination of claim 2 wherein said P-type material comprises arsenic triselenide and said N-type material comprises antimony trisulphide.

4. A vidicon comprising: an elongated envelope; a target sealing one end of said envelope, said target comprising an insulative member having a conductive layer deposited on the interior surface thereof adapted to be coupled to an external circuit, and a radiation sensitive material deposited on said conductive layer; an electron gun structure mounted in said envelope adjacent the other end thereof, said electron gun structure comprising a cathode and an apertured control grid in close proximity to said cathode, means to apply a reference potential to said cathode, means to maintain said first control grid at a potential negative with respect to the potential of said cathode; a second control grid mounted within said envelope adjacent said electron gun and provided with an electron bean transit limiting aperture, means to maintain said second control grid at a potential positive'With respect to the potential of said first control grid; electrostatic electron beam decelerating and collimating means mounted within said envelope adjacent said target; electrostatic electron beam deflection means mounted Within said envelope intermediate said second grid and said decelerating and collimating means; and electron optical means mounted within said envelope intermediate said second grid and said deflection means operative to image the aperture of said second rid upon said target, said electron optical system comprising first, second, and third apertured electrodes, means to apply to said first and third electrodes potentials successively more positive with resspect to the potential of said second control grid, and means to maintain said second electrode at a potential negative with respect to the center potential between said first and third electrodes.

5. A vidicon comprising: an elongated envelope; a target sealing one end of said envelope, said target comprising an insulative member having a conductive layer deposited on the interior surface thereof adapted to be coupled to an external circuit, and radiation sensitive material deposited on said conductive layer; an electron gun structure mounted in said envelope adjacent the other end thereof, saidelectmn gun structure comprising a cathode and an apertured control grid in close proximity to said cathode, means to apply a reference potential to said cathode, means to maintain said first control grid at a potential negative with respect to the potential of said cathode; a second control grid mounted within said envelope adjacent said electron gun and provided With an electron beam transit limiting aperture, means to maintain said second control grid at a potential positive with respect to the potential of said first control grid; electrostatic electron beam decelerating and coilimating means mounted within said envelope adjacent said target; electrostatic electron beam deflection means mounted Within said envelope intermediate said second grid and said decelerating and collimating means; and electron optical means mounted Within said envelope intermediate said second grid and said deflection means operative to image the aperture of said second grid upon said target, said electron optical means comprising first, second, third, and fourth apertured electrodes, means maintaining said second electrode at a potential positive with respect to said second control grid, means to maintain said first electrode at a potential'positive with respect to the center potential bet-Ween said second control grid and said second electrode, means to maintain said fourth electrode at a potential positive With respect to said second electrode, and means to maintain said third electrode at a potential negative with respect to the center potential between said second and fourth electrodes.

6. A vidicon comprising: an elongated envelope; a

target sealing one end of said envelope, said target comprising an insulative member having a conductive layer deposited on the interior surface thereof adapted to be coupled to an external circuit, and a radiation sensitive material deposited on said conductive layer; an electron gun structure mounted in said envelope adjacent the other end thereof, said electron gun structure comprising a cathode and an apertured control grid in close proximity to said cathode, means to apply a reference potential to said cathode, means to maintain said first control grid at a potential negative with respect to the potential of said cathode; a second control grid mounted Within said envelope adjacent said electron gun and provided with an electron beam transit limiting aperture, means to maintain said second control grid at a potential positive with respect to the potential of said first control grid; electrostatic electron beam decelerating and collimating means mounted Within said envelope adjacent said target; electrostatic electron beam deflection means mounted Within said envelope intermediate said second grid and said decelerating and collimating means; and electron optical means mounted Within said envelope intermediate said second grid and said deflection means operative to image the aperture of said second grid upon said target, said electron optical system comp-rising first, second, and third rapertured electrodes, means to apply to said first and third electrodes potentials successively more positive with respect to the potential of said second control grid, and means to maintain said second electrode at a potential negative with respect to the center potential between said first and third electrodes; said decelerating and collimating means comprising a plurality of conductive rings disposed along the interior surface of said envelope between said target and said deflection means, means to maintain the ring adjacent said target at a potential negative With respect to the potential of said cathode, means to maintain the ring adjacent said deflection means approximately at the most positive potential applied to said electron optical means, and means to maintain intermediate rings at intermediate potentials.

7. A vidicon comprising: an elongated envelope; a target sealing one end of said envelope, said target comprising an insulative member having a conductive layer deposited on the interior surface thereof adapted to be coupled to an external circuit, and a radiation sensitive material deposited on said conductive layer; an electron gun structure mounted in said envelope adjacent the other end thereof, said electron gun structure comprising a cathode and an apertured control grid in close proximity to said cathode, means to apply a reference potential to said cathode, means to maintain said first control grid at a potential negative With respect to the potential of said cathode; a second control grid mounted Within said en'- velope adjacent said electron gun and provided with an electron beam transit limiting aperture, means to'maintain said second control grid at a potential positive with respect to the potential of said'first control grid; electrostatic electron beam decelerating and collimating means mounted within said envelope adjacent said target; e1ectrostatic electron beam deflection means mounted within said envelope intermediate said second grid and said decelerating and collimating means; and electron optical means mounted within said envelope intermediate said second grid and said deflection means operative to image the aperture of said second grid upon said target, said electron optical system comprising first, second, and third apertured electrodes, means to apply to said first and third electrodes potentials successively more positive with respect to the potential of said second control grid,

and means to maintain said second electrode at a potential negative with respect to the center potential between said first and third electrodes; said decelerating and collimating means comprising a resistive spiral disposed" on the interior surface of said envelope with one end thereof adjacent said target, means to maintain the end of said spiral adjacent said target at a potential negative with respect to the potential of said cathode, and means to maintain the other end of said spiral approximately at the most positive potential applied to said electron optical means.

8. A vidicon comprising: an elongated envelope; a target sealing one end of said envelope, said target comprising an insulative member having a conductive layer deposited on the interior surface thereof adapted to be coupled to an external circuit, and radiation sensitive ma terial deposited on said conductive layer; an electron gun structure mounted in said envelope adjacent the other end thereof, said electron gun structure comprising a cathode and an apertured control grid in close proximity to said cathode, means to apply a reference potential to said cathode, means to maintain said first control grid at a potentialnegative with respect to the potential of said cathode; a second control grid mounted Within said envelope adjacent said electron gun and provided with an electronbeam transit limiting aperture, means to maintain said second control grid at a potential positive with respect to the potential of said first control grid; electrostatic electron beam decelerating and collimating means mounted within said envelope adjacent said target; electrostatic electron beam deflection means mounted within said envelope intermediate said second grid and said decelerating and collimating means; and electron optical means mounted Within said envelope intermediate said second .grid and said deflection means operative to image the aperture of said second grid upon said target, said electron optical means comprising first, second, third, and fourth apertured electrodes, means maintaining said second electrode at a potential positive with respect to said secondcontrol grid, means to maintain said first electrode at a potential positive with respect to the centerpotential between said second control grid and said second electrode, means to maintain said fourth electrode at a potential positive with respect to said second electrode, and means to maintain said third electrode at a potential negative with respect to the center potential between said second and fourth electrodes; said decelerating and collimating means comprising a plurality of conductive rings disposed along the interior surface of said envelope be tween said target and said deflection means, means to maintain the ring adjacent said target at a potential negative with respect to the potential of said cathode, means to maintain the ring adjacent said deflection means approximately at the most positive potential applied to said electron optical means, and means to maintain intermediate rings at intermediate potentials.

9. A vidicon comprising: an elongated envelope; a target sealing one end of said envelope, said target comprising an insulative member having a conductive layer deposited on the interior surface thereof adapted to be coupled to an external circuit, and radiation sensitive material deposited on said conductive layer; an electron gun structure mounted in said envelope adjacent the other end thereof, said electron gun structure comprising a cathode and an apertured control grid in close proximity to said cathode, means to apply a reference potential to said cathode, means to maintain said first control grid at a potential negative with respect to the potential of said cathode; a second control grid mounted within said envelope adjacent said electron gun and provided with an electron beam transit limiting aperture, means to maintain said second control grid at a potential positive with respect to the potential of said first control grid; electrostatic electron beam decelerating and collimating means mounted within said envelope adjacent said target; electrostatic electron beam deflection means mounted within said envelope intermediate said second grid and said decelerating and collimating means; and electron optical means mounted within said envelope intermediate said second grid and said deflection means operative to image the aperture of said second grid upon said target, said electron optical at a potential positive with respect to said second control grid, means to maintain said first electrode at a potential positive with respect to the center potential between said second control grid and said second electrode, means to maintain said fourth electrode at a potential positive with respect to said second electrode, and means to maintain said third electrode at a potential negative with respect to the center potential between'saidsecond and fourth electrodes; said decelerating and collimating means comprising a resistive spiral disposed on the interior surface of said envelope with one end thereof adjacent said target, means to maintain the end of said spiral adjacent said target at a potential negative with respect to the potential of said cathode, and means to maintain the other end of said spiral approximately at the most positive potential applied to said electron optical means.

10. A vidicon comprising: an elongated envelope; a target sealing one end of said envelope, said target comprising an insulative member having a conductive layer deposited on the interior surface thereof adapted to be coupled to an external circuit, and photoconductive material deposited on said conductive layer; an electron gun structure mounted in said envelope adjacent the other end thereof, said electron gun structure comprising a cathode and an apertured control grid in close proximity to said cathode, means to apply a reference potential to said cathode, means to maintain said first control grid at a potential negative with respect to the potential of said cathode; a second control grid mounted within said envelope adjacent said electron gun and provided with an electron beam transit limiting aperture, means to maintain said second control grid at a potential positive with respect to the potential of said first control grid; electrostatic electron beam decelerating and collimating means mounted Within saidenvelopeadjacent said target; electrostatic electron beam deflection means mounted Within said envelope intermediate said second grid and said decelerating and collimating means; and electron optical means mounted within said envelope intermediate said second grid and said deflection means operative to image the aperture of said second grid upon said target, said electron optical system comprising first, second, and third apertured electrodes, means to apply to said first and third electrodes potentials successively more positive with respect to the potential of said second control grid, and means to maintain said second electrode at a potential negative with respect to the center potential between said first and third electrodes.

11. A vidicon comprising: an elongated envelope; a target sealing one end of said envelope, said target comprising an insulative member having a conductive layer deposited on the interior surface thereof adapted to be coupled to an external circuit, and photoconductive material deposited on said conductive layer; an electron gun structure mounted in said envelope adjacent the other end thereof, said electron gun structure comprising a cathode and an apertured control grid in close proximity to said cathode, means to apply a reference potential to said cathode, means to maintain said first control grid at a potential negative with respect to the potential of said cathode; a second control grid mounted Within said envelope adjacent said electron gun and provided with an electron beam transit limiting aperture, means to maintain said second control grid at a potential positive with respect to the potential of said first control grid; electrostatic electron beam dccelerating and collimating means mounted Within said envelope adjacent said target; electrostatic clectron beam deflection means mounted within said envelope intermediate said second grid and said decelerating and collimating means; and electron optical means mounted Within said envelope intermediate said second grid and said deflection means operative to image the aperture of said second grid upon said target, said electron optical means comprising first, second, third, and fourth apertured electrodes, means maintaining said second electrode at a potential positive with respect to said second control grid, means to maintain said first electrode at a potential positive with respect to the center potential between said second control grid and said second electrode, means to maintain said fourth electrode at a potential positive with respect to said second electrode, and means to maintain said third electrode at a potential negative with respect to the center potential between said second and fourth electrodes.

12. A vidicon comprising: an elongated envelope; a target sealing one end of said envelope,'said target comprising an insulative member having a conductive layer deposited on the interior surface thereof adapted to be coupled to an external circuit, and photoconductive material deposited on said conductive layer; an electron gun structure mounted in said envelope adjacent the other end thereof, said electron gun structure comprising a cathode and an apertured control grid in close proximity to said cathode, means to apply a reference potential to said cathode, means to maintain said first control grid at a potential negative with respect to the potential of said cathode; a second control grid mounted within said envelope adjacent said electron gun and provided with an electron beam transit limiting aperture, means to maintain said second control grid at a potential positive with respect to the potential of said first control grid; electrostatic electron beam decelerating and collimating means mounted within said envelope adjacent said target; electrostatic electron beam deflection means mounted Within said envelope intermediate said second grid and said decelerating and collimating means; and electron optical means mounted within said envelope intermediate said second grid and said deflection means operative to image the aperture of said second grid upon said target, said electron optical system comprising first, second, and third apertured electrodes, means to apply to said first and third electrodes potentials successively more positive with respect to the potential of said second control grid, and means to maintain said second electrode at a potential negative with respect to the center potential between said first and third electrodes; said decelerating and collimating means comprising a. plurality of conductive rings disposed along the interior surface of said envelope between said target and said deflection means, means to maintain the ring adjacent said target at a potential negative with respect to the potential of said cathode, means to maintain the ring adjacent said deflection means approximately at the most positive potential applied to said electron optical means, and means to maintain intermediate rings at intermediate potentials.

13. A vidicon comprising: an elongated envelope; a target sealing one end of said envelope, said target comprising an insulative member having a conductive layer deposited on the interior surface thereof adapted to be coupled to an external circuit, and photoconductive material deposited on said conductive layer; an electron gun structure mounted in said envelope adjacent the other end thereof, said electron gun structure comprising a cathode and an apertured control grid in close proximity to said cathode, means to apply a reference potential to .said cathode, means to maintain said first control grid at a potential negative with respect to the potential of said cathode; a second control grid mounted within said envelope adjacent said electron gun and provided with an electron beam transit limiting aperture, means to maintain said second control grid at a potential positive with respect to the potential of said first control grid; electrostatic electron beam decelerating and collimating means mounted within said envelope adjacent said target; electrostatic electron beam deflection means mounted within said envelope intermediate said second grid and said decelerating and collimating means; and electron optical means mounted within said envelope intermediate said second grid and said deflection means operative to image the aperture of said second grid upon said target, said electron optical system comprising first, second, and third apertured electrodes, means to apply to said first and third electrodes potentials successively more positive with respect to the potential of said second control grid, and means to maintain said second electrode at a potential negative with respect to the center potential between said first and third electrodes; said decelerating and collimating means comprising a resistive spiral disposed on the interior surface of said envelope with one end thereof adjacent said target, means to maintain the end of said spiral adjacent said target at a potential negative with respect to the potential of said cathode, and means to maintain the other end of said spiral approximately at the most positive potential applied to said electron optical means.

14. A vidicon comprising: an elongated envelope; a target sealing one end of said envelope, said target comprising an insulative member having a conductive layer deposited on the interior surface thereof adapted to be coupled to an external circuit, and photo-conductive material deposited on said conductive layer; an electron gun structure mounted in said envelope adjacent the other end thereof, said electron gun structure comprising a cathode and an apertured control grid in close proximity to said cathode, means to apply a reference potential to said cathode, means to maintain said first control grid at a potential negative with respect to the potential of said cathode; a second control grid mounted within said envelope adjacent said electron gun and provided with an electron beam transit limiting aperture, means to maintain said second control grid at a potential positive with respect to the potential of said first control grid; electrostatic electron beam decelerating and collimating means mounted within said envelope adjacent said target; electrostatic electron beam deflection means mounted within said envelope intermediate said second grid and said decelerating and collimating means; and electron optical means mounted within said envelope intermediate said second grid and said deflection means operative to image the aperture of said second grid upon said target, said electron optical means comprising first, second, third, and fourth apertured electrodes, means maintaining said second electrode at a potential positive with respect to said second control grid, means to maintain said first electrode at a potential positive with respect to the center potential between said second control grid and said second electrode, means to maintain said fourth electrode at a potential positive with respect to said second electrode, and means to maintain said third electrode at a potential negative with respect to the center potential between said second and fourth electrodes; said deceleratingand collimating means comprising a plurality of conductive rings disposed along the interior surface of said envelope between said target and said deflection means, means to maintain the ring adjacent said target at a potential negative with respect to the potential of said' cathode, means to maintain the ring adjacent said deflection means approximately at the most positive potential applied to said electron optical means, and means to maintain intermediate rings at intermediate potentials.

15. A vidicon comprising: an elongated envelope; at

target sealing one end'of said envelope, said target com-' prising an insulative member having a conductive layer deposited on the interior surface thereof adapted to be coupled to an external circuit, and photo conductive material deposited on said conductive layer; an electron gun structure mounted in said envelope adjacent the other end thereof, said electron gun structure comprising a cathode and an apertured control grid in close proximity to said cathode, means to apply a reference potential to said cathode, means to maintain said first control grid at a potential negative with respect to the potential of said cathode; a second control grid mounted within said 1 l envelope adjacent said electron gun and provided with an electron beam transit limiting aperture, means to maintain said second control grid at a potential positive with respect to the potential of said first control grid; electrostatic electron beam decelerating and collimating means mounted within said envelope adjacent said target; electrostatic electron beam deflection means mounted Within said envelope intermediate said second grid and said decelerating and collimating means; and electron optical means mounted within said envelope intermediate said second grid and said deflection means operative to image the aperture of said second grid upon said target, said electron optical means comprising first, second, third, and fourth apertured electrodes, means maintaining said second electrode at a potential positive with respect to said second control grid, means to maintain said first electrode at a potential positive with respect to the center potential between said second control grid and said second electrode, means to maintain said fourth electrode at a potential positive with respect to said second electrode, and means to maintain said third electrode at a potential negative with respect to the center potential between said References Cited in the file of this patent UNITED STATES PATENTS 2,325,865 Litton Aug. 3, 1943 2,572,861 Hutter Oct. 30, 1951 2,728,872 Smith Dec. 27, 1955 2,884,559 Cooper et a1. Apr. 28, 1959 FOREIGN PATENTS 763,745 Great Britain Dec. 19, 1956 794,331 Great Britain Apr. 30, 1958 794,332 Great Britain Apr. 30, 1958

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