Photon counting.

The fundamentals of photon counting using photomultipliers are described, including criteria for selecting suitable photomultipliers, some of the precautions that must be taken in using these devices, and methods of calculating the counting errors that may occur under various conditions of measurement. Problems of determining the time distribution of photons and, in particular, the coincident emission of photons which may be encountered in lasers and other simulated emission sources are also discussed. The question of photon counting with photoconductors is reviewed, and it is shown that it is extremely difficult, if not impossible, to achieve photon counting with simple photoconductors. However, carrier multiplication with photoconductive multipliers should eventually make possible photon counting with photoconductors. Photoconductive multipliers in one form or another have high quantum efficiency and wide spectral response, and will almost inevitably replace photomultipliers for photon counting.