光电倍增管（Photomultiplier，简称PMT），是一种对紫外光、可见光和近红外光极其敏感的特殊真空管。它能使进入的微弱光信号增强至原本的10倍，使光信号能被测量。

光电倍增管是由玻璃封装的真空设备，其内包含光电阴极 (photocathode)，几个二次发射极 (dynode)和一个阳极。入射光子撞击光电阴极，产生光电效应，产生的光电子被聚焦到二次发射极。其后的工作原理如同电子倍增管，电子被加速到二次发射极产生多个二次电子，通常每个二次发射极的电位差在 100 到 200 伏特。二次电子流像瀑布一般，经过一连串的二次发射极使得电子倍增，最后到达阳极。一般光电倍增管的二次发射极是分离式的，而电子倍增管的二次发射极是连续式的。

Photomultiplier tubes (photomultipliers or PMTs for short), members of the class of vacuum tubes, and more specifically vacuum phototubes, are extremely sensitive detectors of light in the ultraviolet, visible, and near-infrared ranges of the electromagnetic spectrum. These detectors multiply the current produced by incident light by as much as 100 million times (i.e., 160 dB), in multiple dynode stages, enabling (for example) individual photons to be detected when the incident flux of light is very low. Unlike most vacuum tubes, they are not obsolete.