= Photomultiplier
{wiki}
A <photomultiplier> detects weak <light> by converting a <photon> into a <photoelectron> at a photosensitive <cathode>, then multiplying <electrons> through successive <dynodes>. Each impact can release several secondary <electrons>, and an <anode> collects the amplified packet as an electrical pulse.
If each of $m$ stages has mean multiplication $\delta$, the mean gain is approximately $\delta^m$. This amplification makes small signals measurable but does not eliminate <photon shot noise> or fluctuations in multiplication. <Quantum efficiency> controls the probability of producing an initial useful <photoelectron>, while <dark current> and background produce additional signals. Optical shielding, stable applied voltages and a blocked-light measurement are therefore essential to interpreting a weak-light count.<Photomultiplier Tubes by Hamamatsu Photonics>[Photocathode and dynode operation, multiplication and spectral sensitivity]{ref}
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