IR detectors fall into two broad categories: photon and thermal. In the classical photon detector, photons are absorbed and generate free carriers, which are sensed by an electronic readout circuit. The thermal detector, on the other hand, is a power law detector. The incoming IR photons are absorbed by a thermally isolated detector element, resulting in an increase in the temperature of the element, which is sensed by monitoring a parameter such as resistivity or dielectric constant. The majority of this book is concerned with photon detectors, because of the somewhat more complex and varied materials physics associated with each of the various formats. However, comparisons are made in Chapter 6 between the ultimate forms of both photon and thermal detection.
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