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Previous: CCDs and their controllers
Up: Overview of the DAS
Next: The Detector Memory System
Previous Page: CCDs and their controllers
Next Page: The Detector Memory System
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 This article is somewhat out-of-date, in that the RCA CCD camera has been replaced by a GEC CCD camera; this affects the pixel size and detector format.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.