Photodetectors, their performance and their limitations

With the human eye as a reference, a short survey of man-made photodetectors is given. The smallest number of detectable photons and the “detectivity” of present-day detectors, both as a function of the wavelength, are discussed in more detail. Finally, some special comments on the performance of photoconductive detectors are made since they are at present the most sensitive detectors for middle and far infrared radiation.