GB1092094A - Improvements in or relating to photo-cathodes - Google Patents

Abstract

1,092,094. Electron multipliers; image converter tubes. MULLARD Ltd. July 7, 1964 [Aug. 20, 1963], No. 32939/63. Heading H1D. A photo-cathode for an image intensifier or converter tube includes a matrix of insulating material in the form of a plate having an array of channels, each containing a conductive insert, extending between its two faces, the plate being covered on its input face with photoconductive material which contacts the conductive inserts and is itself covered on its exposed face by a transparent conductive layer, the opposite end of each of the conductive inserts being covered by a separate photo-emissive element, and the corresponding output face of the matrix supporting a conductive layer which is apertured in alignment with the inserts, and acts as a grid spaced from the photo-emissive elements. When the grid is maintained positive with respect to the transparent conductive layer, and when an optical image is focused upon the latter and a flooding or scanning beam is incident upon the photo-emissive elements, the density of photoemitted electrons issuing through the grid is modulated by the photoconductive effect of the incident image. The photo-cathode of Fig. 2 is formed by an arrangement of fine glass tubes 16 bonded together and containing copper wires 17, the lead oxide/lead sulphide photoconductive layer 13 being coated with a transparent aluminium layer 11. The other ends of the wires 17 are etched back and coated with photoemissive gold elements 14, which are subjected to ultra-violet flooding radiation F, the aluminium layer 15 on the tubes 16 forming the grid. The photo-cathode may be employed in an image intensifier (Fig. 3, not shown), or in a camera tube (Fig. 4, not shown), in which the photo-emissive elements are scanned by a flying spot, and the emitted electrons are received by an electron multiplier. To improve resolution, layer 13 may be constituted by a plurality of discrete elements. The glass/metal matrix may be prepared either by first bonding together by heat the tubular glass fibres-which may be coated with glaze- and then introducing molten metal by capillary action, or by first forming metal-filled glass tubes by passing tungsten wire through molten glass, and then drawing down the tubes to produce fibres, which are subsequently cut into lengths and bonded together.