The Imperial College System for Photon Event Counting

Publisher Summary A two-dimensional imaging detector for use in astronomy has been developed at Imperial College. The principal objective was to develop a simple, compact, photoelectron event counter for the photometry of extended objects; it was also envisaged that the system could be used as a high-sensitivity linear detector ancillary to other astronomical instrumentation. A requirement for the completed system was that it would be small enough for easy transportation to remote observing sites while being completely self-contained. The instrument can be used without the need for additional support equipment at the observatory. The primary detector consists of a high-gain microchannel plate image intensifier, optically coupled to a charge-coupled device (CCD) camera. The intensifier gain is sufficiently high to produce individual photoelectron scintillations on the output phosphor screen. Each event location detected by the CCD camera is converted into an encoded address and incremented into a 48K X 16-bit memory. An event centroiding procedure is used to find the center of scintillation, and only the event center is stored in the memory.