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The IPCS-2 is an imaging detector, which counts individual photon events with zero read-out noise. In very general terms, the way in which it does this is similar to the way in which original IPCS (as used on the AAT and INT) operates. However, the camera and electronics for the IPCS-2 have been completely redesigned, and so the detailed operation of the detector is completely different.
The principles of operation of the original IPCS are described by Boksenberg 1982 (Philosophical Transactions of the Royal Society of London A, vol 307, p531). The design of the IPCS-2 is described by Fordham, Bone & Jorden 1986 (SPIE proceedings vol 627, Instrumentation in astronomy VI, p 206). This article is somewhat out-of-date, in that the RCA CCD camera has been replaced by a GEC CCD camera; this affects the pixel size and detector format. For an up-to-date and detailed description of the IPCS-2, see the IPCS-2 Users Manual.
Since the operation of the IPCS-2 is described in detail elsewhere, we only give a brief description of the general principles here: individual photon events are detected by means of an image intensifier, on the front of which is mounted a photocathode. Photons incident on the photocathode result in the emission of an electron. Each of these electrons triggers a cascade of electrons through the image intensifier, producing a signal of about electrons at the output. This splash of electrons is detected by a CCD camera, and passed to an image processing unit which calculates the centroid of each splash, and hence the position on the photocathode of each photon event. The coordinates of each photon event are then passed to the Detector Memory System, which counts the number of photons detected in each pixel by incrementing an appropriate memory location. During the course on an integration, a two-dimensional image or spectrum is built up in the Detector Memory System.