Low Light Level TV Imaging By Intensified CCDS

Abstract

Low Light Level (LLL) TV cameras, based on the association between image intensifier (II) tubes and solid state image sensors (CCD), add to the extreme performance of electronic tubes, the large system flexibility offered by CCD sensors (video signal). Various combinations of image intensifier tubes and CCDs are investigated. First generation II/CCD appears suitable for many applications where the light level is not too low (> 10-5 lux on the photocathode), but very low light levels require second or third generation devices. Electron bombarded CCDs, not commercially available yet, gives promising results in laboratory experiments. Their very high gain (1,500 at 10 keV) and its very low fluctuations allow both counting and integrating detection modes. Cooled CCDs exhibit rather poor performance in TV mode but their high detectivity them very suitable for still picture imaging. An original application, with detectivity improved, has been carried out in a two-color LLL TV camera. This prototype is based on two 2nd generation II/CCD systems respectively sensitive to the visible and the near IR wavelength range. It takes advantage of the variation of the spectral reflection coefficient of materials to enhance the contrast by image coloration.