Photomultiplier tube

A typical photomultiplier tube contains a light-entry window, a photosensitive photocathode, an electron-multiplying structure and an anode inside an evacuated enclosure. When a photon is absorbed by the photocathode, the external photoelectric effect can release an electron. An electric field guides and accelerates the electron toward a dynode; impact can release several secondary electrons. Repeated stages multiply the electron population, which is collected at the anode as an electrical signal.

The multiplication process allows a PMT to register very weak light, in suitable systems down to individual photon events. Performance depends on such factors as photocathode response, electron-collection efficiency, dynode design and operating conditions. PMTs are used in scientific and technical instruments, including photon-counting and radiation-detection systems, as well as biological and medical applications. Their high sensitivity is useful when light is faint, although detector choice depends on wavelength, efficiency, noise, speed and other requirements.

The abbreviation PMT means photomultiplier tube. Some technical references also use “photomultiplier” or “photon multiplier” for the device. The name describes amplification of an initial photoelectron signal; the device is a photodetector, not a light source.