An extremely sensitive light detector that amplifies single photons into measurable electrical pulses through a cascade of electron multiplication. When a photon strikes the photocathode, it releases electrons that are accelerated and multiplied through a series of dynodes, creating a detectable signal from individual photons.
Compound of Greek 'photos' (light), 'multiplier' from Latin 'multiplicare' (to increase manifold), and 'tube' from Latin 'tubus' (pipe). Invented in the 1930s, PMTs became crucial for astronomy in the 1940s-60s when astronomers needed to detect extremely faint light from distant stars and galaxies before CCD technology existed.
Photomultiplier tubes are like cosmic Geiger counters for light - they can detect single photons and amplify them into electrical pulses a million times stronger! These devices were so revolutionary that they enabled the discovery of pulsars, quasars, and the cosmic microwave background radiation, fundamentally changing our understanding of the universe decades before digital cameras existed.
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