Principles of the light-amplifier and allied devices

The paper first considers the necessary component parts of a light amplifying system and briefly points out the advantages of using solid state devices. A system is outlined which consists of a photoconducting layer in series with an electroluminescent phosphor layer. The properties of the constituent parts are discussed in detail and the behaviour of the series combination is examined. Various practical coiistructions are described and attention drawn to the difficulties of manufacturing a picture reproducing device of large area. Optical feedback depends on the spectral emission distribution of the electroluminescent layer and the spectral response of the photoconductor. An amplifier with optical feedback such that the loop gain exceeds unity can be triggered by a light pulse and then remains in the light emitting condition until the supply voltage is reduced. Such an electro-optical binary switch is described using ZnS and CdS powder layers or single crystals. Complex combinations of such units could be employed in shift registers, scaling circuits, etc., and novel circuits are suggested which employ light as the means of triggering and coupling. These devices would be of miniature size and need few, if any, associated conventional components. Limitations of switching time and possible future developments are also discussed.