Switching in a structure composed of a photoconducting semiconductor and an oriented liquid-crystal film

An investigation was made of the light-switching action of a structure consisting of a CdS film and an oriented liquid-crystal film, both enclosed between transparent electrodes. The spatial modulation of the conductivity in the photosensitive CdS film, produced by a helium–cadmium laser control beam, altered the voltage across the liquid-crystal film and thus changed its birefringence. Positive and negative images could be obtained, depending on the static field applied to the structure. These images could be read with the aid of a helium–neon laser and polaroids. The method was characterized by a fast response and a high sensitivity to the action of light and electric fields. The resolution of the oriented liquid-crystal film was better than 30 lines/mm. A possible use of reverse-blased p–n junctions was considered.