US2160510A - Cathode ray tube with photocell mosaic - Google Patents

Description

May 30, 1939; R. MOLLER ET )AL I 2,150,510

CATHODE RAY TUBE WITH PHOTO CELL MOSAIC Filed NOV. 6, 1956 ai ymwa Elf? Patented May 30, 1939 I UNITED STATES PATENT OFFICE oa'rnonn my me wrm rno'roceu. MOSAIC I many Application November 6, 1936, Serial No. 109,577 In Germany November 14, 1935 3 Claims. (01. 250-215) In electron ray tubes which have a photocell mosaic and especially those which are used for inertia-less scanning and transmission, the optical image to be transmitted is thrown on the 5 photocell mosaic by means of a lens. The photocell mosaic consists of a thin insulating plate having a very high dielectric constant of which one side has a continuous conducting layer whereas the other side consists of a large number of mosaic-like adjacently lying photo-electrically sensitive elemental surfaces which, however, are insulated from each other as well as possible. Under the influence of the light which strikes the mosaic plate a quantity of electrons becomes set free at the individual photo elements in an amount corresponding to the intensity of the light, if a magnetic attractive field is disposed infront of the mosaic plate. The mosaic particles thus become positively charged.

The mosaic side of the plate is controlled (swept) by a cathode ray in grid-like fashion whereby all mosaic elements are brought to a potential which is positive with respect to the cathode and independent of their existing transient photo electric charge. The degree of this positive equilibrium potential against the cathode is a constant of the material of the photo-cell layer and is independent of the anode voltage. In order that an adequately high attractive field strength shall always be present in front of the mosaic, the

acceleration voltage for the controlling (sweeping) ray must exceed the equilibrium voltage to a certain amount (e. g., several volts) said amount being large with respect to the strongest photoelectric (positive) charge of an element. Only in that case is the anode always sufliciently positive with respect to each individual plate element.

In the embodiments of such tubes hitherto known, there was the drawback that the ray V accelerating voltage could not be chosen appreciably higher than the equilibrium voltage exerted towards the cathode and which mounted, e. g.,

to several hundred volts, since otherwise the plate which is. strongly negative with respect to the anode would have rendered a clean ray crosscontrol impossible.

In order to attain a high strength of attractive field in front of the mosaic surface and without disturbing the cross control, a fine meshed gauze made, e. g., of platinum, molybdenum, or tungsten is placed, in accordance with the invention, a

short distance before the mosaic surface and has a higher potential than the equilibrium potential exerted towards the cathode. The potential of the accelerating eiectrode of the cathode ray may, for example, be identical with this potential. If an anode voltage is used which is very much higher, say more than one hundred volts higher than the equilibrium voltage, that is, if a ray of very rapid electrons is directed upon the mosaic surface, then its basic potential will assume a strongly negative position with respect to the superimposed anode gauze so that a high attractive voltage and, owing to the small separation of the gauze from the plate, a very high attractive field strength will be produced without in any way influencing the control of the ray.

The drawing illustrates an embodiment of the subject matter of the invention. The cathode ray tube has the usual ray producing system I, an evacuated housing 2 and a screen which is so positioned that an optical image can be produced thereon by aid of a lens system 3. The screen consists of a highly insulating plate 4, which on the side facing away from the ray carries a conducting layer 5. 0n the side facing the ray there is disposed a photocell mosaic 6 and at a short distance therefrom, say several tenths of a millimeter, is disposed a gauze or grid 1..

The. gauze consists for example of a woven structure made of silver, platinum, molybdenum, or tungsten wires, and has about 10-100 meshes per square millimeter. The wires for example have a size of the order of .1 to,.02 mm. The accelerating anode of the tube may be formed as a wall coating 8 and preferably carries the same potential as the net I. 'The voltage source shown supplies .the anode voltage. The impulses which correspond to the luminosity of the individual image points are taken oil at a resistance In and may be amplified in any desired manner. It is preferable for this purpose to use an amplifier which is as free from crackling tube noise effects as possible (i. e., a photo-cathode type).

In order that no light loss shall occur at the mosaic surface due to the fact that the wires of the gauze lie above the photoelemental surfaces and prevent access of light at these points by shadow action, it is further proposed to spread the gauze prior to producing the light sensitive mosaic layer, at the desired distance from the insulating plate and to cause the insulating plate to become coated by sputtering the material through the gauze. Thus the support, e. g., silver,

is first sputtered into place and the individual mosaic squares are thus obtained in separate to avoiding loss of light. elementary surfaces are obtained which are very clearly insulated from each other and hence charging losses are obviatplate and against an abutment. However, brackets may be used to hold the gauze on the insulating plate against the pressure of the springs. The brackets after the substance desired has been sputtered are released by magnets or by inertia or their own weight so that the springsare able to lift the gauze from the plate. In this case care must be taken that the gauze as it becomes raised is not displaced laterally to any extent.

We claim: v

1. A method for producing a photo-cell mosaic plate for a cathode ray tube, comprising covering an insulating plate with a refractory metal wire gauze having amesh of 10-100 per millimeter, sputtering a silver backing onto said insulating plate through said gauze, oxidizing said silver backing, sputtering a caesium coating through said gauze on the oxidized silver backing, lifting said gauze in a direction normal to said plate to a position several tenths of a millimeter from said insulating plate, whereby said gauze will permit substantially unobstructed access of light to said mosaic elements from a direction normal to said plate.

2. A method of producing a photo-cell mosaic plate within a cathode ray tube, which comprises supporting a refractory wire gauze having a mesh of 10-100 per millimeter parallel to an insulating plate and separated therefrom by several tenths of a millimeter by resilient means, clamping said gauze tightly against said plate, sputtering a silver backing on said insulating plate, oxidizing 'said silver backing, sputtering a. caesium coating thereon through said gauze, and unclamping said gauze from said insulating plate to permit a piano-parallel separation therebetween, enabling unobstructed access of light to the mosaic elements from a direction normal to said plate.

3. A method for producing a photocell mosaic plate for a cathode ray tube. comprising covering an insulating plate with a refractory metal wire gauze, sputtering an oxidizable metal onto said insulating. plate through said gauze to form a backing, oxidizing said metal backing, sputtering a photosensitive coating through said gauze on the oxidized metal backing, and lifting said gauze to a position spaced from and parallel to said plate with the openings in said gauze in alinement with the mosaic elements produced by sputtering material through said openings, whereby said gauze will enable unobstructed access of light to the mosaic elements from a direction normal to said plate. e

\ ROLF MGLLER. mms'r RUSKA.

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