photomultiplier tube

Definition: Device for producing amplified signal from a photo-detector. * Consists of a vaccum tube with a photocathode followed by a cascade of cathodes. * When exposed to light the cathode releases electrons which are accelerated across an electrical gradient to fall upon another metal surface where more electrons are released which are accelerated to yet another cathode, and so on. * The amplification possible is very high -- over ten-fold -- and output is linear. * Used in e.g. drum scanners; densitometers.

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