GB333548A - Improvements in or relating to photo-electric cells - Google Patents

Abstract

333,548. Walton, G. W. Feb. 14. 19?rJ. Vacuum tubes. - In photo - electric cells, the light-sensitive surface g, Fig. 1, is continuously bombarded by cathode-rays from a heated filament a or other cathode but the dissipation of energy at the surface g is greatly reduced by the emissions of secondary electrons dislodged by the rays. These secondary electrons and also electrons released by light flow from the electrode g to an anode a<2> and a varying current is produced in the circuit of these two electrodes, the surface g being of alkali halide or hydride or other material the light-sensitivity of which is increased by the cathode-ray bombardment. The surface g is maintained negative with respect to the anode a<2> and positive with respect to the filament a so that some electrons from the filament pass through the anode a<2> to the surface g. At zero or a mean light intensity, zero current flows to the surface g. To facilitate the emission of electrons from the surface g, a conductor h separated from the surface by a dielectric e is negatively charged with respect to the surface g. Due to the secondary emission the circuit to the electrode g has a negative resistance which may be balanced by the resistance of an output device z such as a resistance, inductance or transformer primary, augmented current variations resulting. Such variations may be .applied through connections inside or outside the cell, for example, through a conductive, magnetic or electrostatic coupling, to the electrode h or to coils or electrodes outside the cell or to an additional electrode inside the cell, such as a grid between the filament a and anode a<2>, to increase the response of the cell to light. The circuit of the surface g may include a tuned circuit, and a grid within the anode a<2> may be connected to the surface g through a condenser with or without a rejector circuit, oscillations resulting from the negative resistance and being modulated photoelectrically. Alternatively the grid and anode ,circuits may be coupled and the former tuned to produce oscillations modulating the photo-electric current. The output device z may be . attached to or contained in the envelope of the cell or in the base thereof. The electrode h may be a silver film slit to pass light or may be a conducting fluid in an annular chamber, light emerging through the semi-transparent surface g and some being reflected back by the anode. The .dielectric e carrying the electrodes g, h may be part of the bulb as shown in Fig. 1 or a flat plate of glass or mica inside the bulb parallel or at an angle to the direction of the incident light. Two flat plates may be mounted on opposite sides of the cylindrical anode, subdivided photoelectric surfaces resulting and being connected to separate output circuits for use in colour television. The cell is highly evacuated or filled with gas such as argon or helium. The surface g may be formed by cathodic sputtering. The anode a<2> may be perforated or in the form of a grid as in Fig. 1, the filament emitting electrons without emitting light affecting the surface g, or the anode may comprise a thin plate penetrable by electrons, and dividing the cell into compartments evacuated to different degrees or filled with different gases. Separate anodes may be provided for the filament a and the electrode g.