Photomultiplier tube (PMT)
It is a vacuum tube that converts light into electrical energy and later amplifies it. Photomultiplier
tubes are highly used in high-end drum scanners, because they are more sensitive to light than the CCD elements used in lower-cost
devices.
Amplification can be as much as 108 which mean that quantifiable pulses can be attained from single
photons. The combination of high gain, low noise, high frequency response and large area of collection have meant that these devices still find applications in particle physics, astronomy and medical imaging. Their substitution by semiconductor devices has long been envisaged but has never been realized. Incident photons hit the photocathode stuff which is there as a thin deposit on the entry window of the device, with electrons being produced as a consequence of the photoelectric effect.