Photomultiplier tube

A vacuum device that converts faint light into an electrical signal and amplifies it through secondary electron emission. Its staged dynodes produce large gain from a small number of detected photons.

Photoelectric effect: The emission of electrons from a material when it absorbs light of sufficient energy. Light releases electrons from the photocathode, beginning the signal chain.
Scintillation detector: A radiation detector that converts deposited energy into flashes of light and measures them with a photosensor. A photomultiplier commonly reads the faint flashes produced by its scintillator.
Silicon photomultiplier: A solid-state photosensor made from many avalanche photodiode microcells operating in Geiger mode. It offers photon-counting gain without a vacuum tube, but has different noise and operating constraints.
Quantum efficiency: The fraction of incident photons that produce detected charge carriers in a photosensitive device. It sets the probability that light at a given wavelength starts a detectable event.
Leonid Kubetsky: A Soviet physicist associated with an early multi-dynode photomultiplier design. His 1930s design established the staged secondary-emission principle used in photomultipliers.
Photocathode: A photosensitive electrode that emits electrons when it absorbs photons. Its material and quantum efficiency determine how often incident photons start a pulse.
Photomultiplier tube in astronomy: The use of photomultiplier tubes to measure weak optical signals in astronomical instruments. Their sensitivity and rapid response suit measurements of faint or rapidly varying sources.
Avalanche photodiode: A semiconductor photodiode that internally amplifies photocurrent through impact ionization. It provides internal gain in a compact solid-state device rather than through dynodes.
Gain (electronics): The ratio of an output signal to its corresponding input signal in an electronic system. Tube gain describes the electron multiplication between photocathode and output.
Vladimir Zworykin: An inventor and engineer whose work helped develop electronic imaging and vacuum-tube technology. His research group developed early practical photomultiplier tubes in the 1930s.

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