High Quality Phosphor Screens for Cascade Image Intensifies

Abstract

This chapter discuses improvements in the quality of the fluorescent screens used in the development of the three-stage cascade intensifier. This has led to improvements in the image quality of the completed device. The formation of the thin, fine-grain phosphor screen on a very thin mica sheet is of crucial importance in the development of cascade image intensifiers. The layer must be as thin as possible, compatible with high electron-energy conversion efficiency, in order to avoid loss of image definition. Methods for the deposition of continuous layer screens have been reported using either vacuum evaporation or vapor-phase formation. Two principal methods of screen preparation were employed: (a) gravity sedimentation or settling, a technique well known for its use in the manufacture of cathode-ray tube screens and (b) electrophoretic deposition, an old technique but one that has not been used much for the production of phosphor screens. At present, however, these techniques lead to the production of screens of rather low conversion efficiency. In order to ensure that the completed intensifier has the highest possible light gain, it is necessary to use phosphor materials of high intrinsic efficiency. The resolution of completed phosphor screens has been measured in single- and multi-stage intensifiers and also by optical methods.