ABSTRACT
This chapter describes the operating principles, and performance limitations of the types of photodetector commonly found in modern microscopes, while paying particular attention to their quantum efficiency and noise. The photo multiplier tube not only has the high bandwidth required to track the time-varying output of a scanning microscope, it is also the first photodetector capable of producing a detectable signal from the absorption of a single input photon. Although the history of the development of electronic image sensors is long and complex, sensors based on silicon semiconductors have become dominant. The main disadvantages are that some of the pixel area must be devoted to the amplifier, resulting in a lower fill-factor and smaller full-well limits. More to the point, small variations in the gain and offset of each amplifier become a major source of “fixed-pattern noise.” Color sensors can be created by placing a pattern of very small red, green or blue colored filters above the sensitive areas of each pixel.
