Photomultipliers | previous | next | feedback |
Definition: photodetection devices based on the photoelectric effect and charge multiplication by secondary emission of electrons
Photomultipliers are vacuum tubes, where light absorbed on a photocathode generates free electrons, which are subsequently accelerated with a high voltage, generate secondary electrons on other electrodes, and finally a usable photocurrent. Due to this avalanche process, the photocurrent can be orders of magnitude higher than from, e.g., a photodiode. Therefore, photomultipliers can be used for, e.g., single photon counting. Photomultiplier tubes can be highly sensitive detectors with high linearity, high speed, and a wide dynamic range.
Disadvantages of photomultipliers are the large size (compared with e.g. photodiodes), the higher cost, the requirement for a high-voltage supply, and in some cases the typically lower quantum efficiency.
In some cases, photomultipliers can be replaced with avalanche photodiodes, which also exhibit an amplification mechanism, but in that case one which occurs within a solid-state (semiconductor) material, rather than in a vacuum tube.
See also: photodetectors, photodiodes, avalanche photodiodes, photon counting
Categories: metrology, photonic devices
