Electron-bombarded CCD image intensifier with a GaAs photocathode

ITT has an ongoing research program to develop a new generation of image intensifiers that uses a charge-coupled device (CCD) operated in the electron-bombarded mode in order to detect electrons directly from a GaAs photocathode. This type of image intensifier combines signal-to-noise levels typical of microchannel plate (MCP) image tubes with the modulation transfer function (MTF) performance of a diode tube design and generates electronic output compatible with standard video displays. The first successful electron-bombarded CCD (EB- CCD) image intensifier with a GaAs photocathode was demonstrated in August 1991. This photocathode was a standard ITT negative-electron-affinity (NEA) GaAs photocathode. Imagery was obtained from this device. The intensifier incorporated an RCA back-illuminated frame-transfer CCD, designed for electron detection and mounted in a vacuum compatible package. The cathode had a photoresponse of 965 (mu) A/lm at 6 kV -- equivalent to 1,166 (mu) A/lm at an electric field typical of proximity-focused image intensifiers (80 V/mil). A full-well signal was obtained with 2.5 X 10-5 fc photocathode illumination and 6 kV cathode-to-CCD bias. A photocathode life in excess of 280 hours at 1 X 10-4 fc illumination was demonstrated.