Infrared detector
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
| 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.