Proceedings PaperQuantum Limited Imaging
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Optical imaging at high light levels is adequately described by the diffraction or wave theory of image formation as, for example, expounded in Reference 1. The directly observable quantity in this case is the wave intensity. At low light levels, however, the intensity is not measurable: real detectors respond to the light field by emitting phot2-electrons randomly in space and time. According to the semi-classical model, due originally to Mandel , the photo-electrons form a doubly stochastic point process which embodies the statistics of the classical intensity and those of the detection process. In particular, the probability of photo-electron emission in the region of the space-time coordinate (x,t) is simply proportional to the intensity averaged over the same space-time region. This semi-classical model is sufficient for most purposes in low light level imaging and in the following we shall refer to the photo-electrons as detected photons or quanta.