US2227018A - Photoelectric storage device - Google Patents

Description

1940- K. SCHLESINGER 3 PHOTOELECTRIC STORQGE DEVICE Filed June 11, 1937 fnrepfar;

Patented Dec. 31, 1940 rno'roELEo'r PATENT OFFICE mo STORAGE DEVTCE Kurt Schlesinger, Berlin, Germany, assignor, by

mesne assignments, t

poration of New York Application June 11,

In Germany June 16, 1936 1 1 Claim.

The applicant has formerly proposed to employ a device. for storing, and scanning photoelectric charges which device consists in substance of a coherent andan incoherentphotoelectric plate electrode,.for example a mesh and a mosaic screen. The two plates are situated opposite and parallel to I one another, and the photo-electric condenser thus formed is from the one side illuminated by the image light and from the other side scannedby a moving spot of light, which in turn may be produced, as a projection of the luminous screen image of a television cathode ray tube. Thisarrangement, while yielding quite satisfactory effects in the television transmission of scenes, is still subject to internal losses. These losses are due primarily to the fact thatthe two illuminations influence one another because none of them is completely absorbed by the electrode on which it impinges and each of them causes,

.29 partly reflected, a spurious discharge of the other electrode, so that the storage duced. 1

"An object of the present invention is. a tube construction avoiding the above disadvantage.

A further object of the invention is a tube act- 'ing in itself as an electronic amplifier of 'the current obtained by scanning the image.

The invention will be explained by 'meansof the accompanying drawing of which Fig. 1 shows an arrangement according to the invention, 1 I

Fig. 2 is a detailed cross-section of electrodes according to the invention includingthe circuit connectedtherewith, Fig. 3 shows a modified circuit connection of the electrodes of the device according to :Fig. 1, and

Fig. 4 the structure illustrated'in Fig. 1 as com bined with an electron amplifier system.

In Fig. 1, I is a network having a number of meshes which corresponds at least to the number of image points. The network consists of silver, or is silver-coated, and is photo-electrically activated in the usual manner by means of caesium. 45 It functions as photo-electric cathode. In close proximity opposite to 1 there is provided a mosaic screen 2, which consists of at least as many small rods as there are image points to be transmitted. The rods are photo-electrically activated on its 50 rear side and are well insulated one against the other. Behind the screen 2, at a somewhat larger distance, there is arranged an anode 3 consisting of a wide network of thin wires. The whole assembly is enclosed within the vacuum vessel 4. 55 The image or scene 5 is projected onto the front output will be reo Loewe'RadioJncs a cor- 1937, Serial No.147,7 99

side of the'net I by way of a lens 6, whilst the rear side of the screen2 is scanned by a light spot projected onto it by means of the lens I from the luminousscreen of a Braun tube 8 operated in the well known manner with constant ray inelectron emission of the corresponding point of I according to the light intensity of each point, and this emission is absorbed the. rods 2 forming anodes with respect to I.. The positive charges of the rods are due to the scanning light spot freeing electrons from the rods. Thuseach rod facingan illuminated part of the net I will, when recharged bythe scanning spot, cause a current push through'resistance 9 which is coupled at 2| to the videoamplifier (not shown). c c It is accordingly on the one hand necessaryto make the. capacity between I and 2 very. large, whilst on the other hand 'it is very detrimental to 'allovv'jalarge capacity between the different rods 2.. In practice it would be very diificult to fulfil this condition without employing the .construction ofthe screen according to Fig. 2. I a In Fig.. 2,. 2a is a cross section through a coherent net or sieve insulated on all sides. An appropriate insulation, when employing a sieve of aluminium, may be produced advantageously by an electrical oxidizing process. It is, however, also possible toemploy. any other'metal and to glaze the same," for example with enamel. The insulation of the. sieve is represented by the surrounding curves II. After this operation. metallic silver is introduced into the intermediate spaces of the sieve, so as to completely fill out the previously open meshes. The silver is designated I 212. It replaces the rods 2 inFig. 1'. The introe ,ductionfof the silver may take place, for example, by reducing a paste of silver compound at high temperature or electrolytically or by atomization. After the introduction of the metallic plugs 2b the same are photo-electrically activated on the side facing the anode 3. The supporting sieve 2a is, by means of lead I2, electrically connected with the net I and this way earthed, this screening-off the singled rods 2b against each other. The spacing between screen 2 and net I must, accordingly be equal to or smaller than the mesh width in order to avoid a straying of the primary electrons from one image point location to adjacent ones. In practice, even with the maximum number of lines presently used, i. e., with 400 lines, a spacing of mm. will be found suiliowing to the fact that the scanning light drops off the area. In this way novel effects maybe obtained in the transmission of images.

Instead of coupling the amplifier tothe anode 3 it may also, with the reciprocal efiect be coupled at 3| by means of a resistance 22 to the net I, according to Fig. 3, with the disadvantage that a condenser l3 must be inserted in order toblock-' off the direct current.

A particularly important feature is the possibility of directly amplifying the electron currents supplied by plate 2 before they are conducted to a tube amplifier. In contradistinction' to the known ikonoscope this screen plate supplies electron currents instead of voltage impulses, which electron currents may be directly multiplied by secondary current multiplication. whereby the ratio between signals, andinoises is considerably reduced. For this purpose itis firstly necessary to concentrate the electrons, which'are leaving the largearea 2 by means of an electron-optical collecting lens on to a comparatively small focus point. As the applicant has found, this may be effected by, the use offtwo co-axial ringslfi, l (Fig. 4) in conjunction with an anode ring I6. The height of the rings I4 is approximately equal totheir radius. Thev first ring M is connected with a weak positive potentialofabout volts relatively to earth. The next ring l5. and the anode ring 5 are furnished with increasing potentials By adjusting of the intermediate potential IE it is possible to concentrate all electronic raysiust in or behind the aperture of i6 into a space ten times smaller than the area 2. At this point there may be provided a small intermediate anode. H, which becomes the origin of an. amplifiednumber of electrons. Methodsof magnetically 'or electrically separating the primary and secondary electron rays. are already known. An. electric or magnetic deflection of the primary rays may also take place before the impinging on IT, for example, tothe extent of 90, by means of a magnetic fieldinot shown) disposed perpendicularly, to the plane of the paper, so that the next intermediate. anode is situated at is and the. secondary electrons emitted from the latter impinge ,on 2 3. The last anode is connected to thefmost positive'term'inal of the battery It, the intermediate anodes to progressive intermediate potentials, and'theoutput 2| to the signal amplifier. Infthis arrangement the anodes are so disposed that the screen 2 is freely accessible to the light from the scanned area projected into the tube by the lens 1.

I claim:

A television system comprising an evacuated tube member, a photoelectrically activated meshlike electrode element within the tube, a connection from said element to a point 'ofequilibrium potential, means to illuminate said element with the light of an optical image to release photoelectrons therefrom, a mosaic electrode element within the tube in close proximity to and substantially parallel to said mesh-like element to collect electrons released from the mesh-like element under the influence of light, said mosaic element also comprising a mesh-like support and having an insulating coating about the mesh and metallic elements extending within and protruding through the interstices of the mesh to a plane at least, co-planar with the plane of the mesh, said metallic elements being insulated one from the other by" the insulatingcoating, a photoelectric coating upon the ends of the metallic elements which are remote from the photoelectrically activated mesh-like electrode, an apertured anode element, a source of scanning light to illuminate the photoelectrically activated areas of the mosaic according to a. predetermined light traversal pattern and to release electrons therefrom at areas of light impingement, thequantity of electrons'instantaneously released by the scanning light being measured by the amount necessary to raise the potential of the mosaic element to substantially anode potential from a more negativevalue due to collecting photoelectrons from the mesh-likeelectrode element, a second anode element of an area relatively smallcompared to the mosaic electrodeelement, means to maintain the second anode positive withres'pect to the first anode, focusing electrode. means intermediate the mosaic and the first anode to focus the electrons released from the mosaic by the scanning light through the first apertured anode and upon the second anode so that the electron stream released from the relatively large mosaic area is concentrated upon the reduced .area' second anode and secondary electrons. are released therefrom by the impact thereon'ofthe said initialy released electrons, said second anode being in non-parallel relation relative to the mosaic to redirect the electron flow reaching said second anode along a diverted path, electrode means for producing by secondary emissionfurther intensification of the electron flow, an output electrode and a direct connected load circuit for amplifying the resultant output energy available at theoutput electrode. 1 I 1 KURT S CHLESINGER.

Images