Photonic transducers measure the light intensity by measuring the impulses of finite energy content, generally known as light quanta or photons. In these transducers, the energy of the photons is converted into a proportional electrical output by means of several transduction mechanisms. In this section, in addition to others, we consider the following:
Photoemissive detectors, where the energy of a photon removes an electron from a metal surface placed in a vacuum or a gas-filled environment.
Photoconductive detectors, where the input photons energy creates electronhole pairs which change the conductivity or resistance of a semiconductor by increasing the number of available charge carriers.
Photovoltaic detectors, p-n junction devices where the input photons also generate electron-hole pairs. The electrons and holes provide additional mechanisms for current conduction. These detectors can be operated in the photovoltaic mode or the photoconductive mode.
The energy of a photon, when expressed in electron volts, is given by