5. Quantum sensors

5.1 Definition and essential properties of the quantum detector

The adjective "quantum" refers to photons, i.e. the granular nature of the energy carried by electromagnetic radiation. For a quantum detector, a photon, provided it carries an energy greater than a limiting value hν (h, Planck's constant and ν, the frequency of the radiation), causes an effect on matter that may be either the ionization of an atom, or a chemical modification, or the ejection of an electron from the medium, or the passage of an electron from the valence band to the conduction band of a semiconductor, and so on. Since the response of a quantum detector is most often the current in a semiconductor, it is proportional to the number of incident photons. For low fluxes, each pulse created by an incident photon...