ABSTRACT
In general, infrared detectors fall into two categories: photon detectors (also named photodetectors) and thermal detectors (see figure E.l). In photon detectors the incident photons are absorbed within the material by interaction with electrons, either to lattice atoms, or to impurity atoms or with free electrons. The observed electrical signal results from the changed electronic energy distribution. The photon detectors show a selective wavelength dependence of the response per unit incident radiation power. In thermal detectors, the incident radiation is absorbed and raises the temperature of the material. The output signal is observed as a change in some temperature-dependent property of the material. In pyroelectric detectors a change in the internal electrical polarization is measured, whereas in the case of bolometers a change in the electrical resistance is measured. The thermal effects are generally wavelength independent since the radiation can be absorbed in a 'black' surface coating.
