Infrared detector

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An infrared detector is a detector that reacts to infrared (IR) radiation. The two main types of detectors are thermal and photonic (photodetectors).

The thermal effects of the incident IR radiation can be followed through many temperature dependent phenomena. Bolometers and microbolometers are based on changes in resistance. Thermocouples and thermopiles use the thermoelectric effect. Golay cells follow thermal expansion. In IR spectrometers the pyroelectric detectors are the most widespread.

The response time and sensitivity of photonic detectors can be much higher, but usually these have to be cooled to cut thermal noise. The materials in these are semiconductors with narrow band gaps. Incident IR photons can cause electronic excitations. In photoconductive detectors, the resistivity of the detector element is monitored. Photovoltaic detectors contain a p-n junction on which photoelectric current appears upon illumination.

A few detector materials:

Types[edit]

type Spectral range(μm) Wavenumber(cm-1)
Indium gallium arsenide(InGaAs) photodiode 0.7–2.6 14300–3800
Germanium photodiode 0.8–1.7 12500–5900
Lead sulfide (PbS) photoconductive 1–3.2 10000–3200
Lead selenide (PbSe) photoconductive 1.5–5.2 6700–1900
Indium antimonide (InSb) photoconductive 1–6.7 10000–1500
Indium arsenide (InAs) photovoltaic 1–3.8 10000–2600
Platinum silicide (PtSi) photovoltaic 1–5 10000–2000
Indium antimonide (InSb) photodiode 1–5.5 10000–1800
Mercury cadmium telluride (MCT, HgCdTe) photoconductive 0.8–25 12500–400
Mercury zinc telluride (MZT, HgZnTe) photoconductive
Lithium tantalate (LiTaO3) pyroelectric
Triglycine sulfate (TGS and DTGS) pyroelectric

The range of pyroelectric detector is determined by the window materials used in their construction.

Vanadium pentoxide is frequently used as a detector material in uncooled microbolometer arrays.