Infrared detector
An infrared detector is a photodetector
Photosensors or photodetectors are sensors of light or other electromagnetic energy. There are several varieties:*Active pixel sensors are image sensors consisting of an integrated circuit that contains an array of pixel sensors, each pixel containing a both a light sensor and an active amplifier...

 that reacts to infrared
Infrared light is electromagnetic radiation with a wavelength longer than that of visible light, measured from the nominal edge of visible red light at 0.74 micrometres , and extending conventionally to 300 µm...

 (IR) radiation
In physics, radiation is a process in which energetic particles or energetic waves travel through a medium or space. There are two distinct types of radiation; ionizing and non-ionizing...

. The two main types of detectors are thermal and photonic.

The thermal effects of the incident IR radiation can be followed through many temperature dependent phenomena.
A bolometer is a device for measuring the power of incident electromagnetic radiation via the heating of a material with a temperature-dependent electrical resistance. It was invented in 1878 by the American astronomer Samuel Pierpont Langley...

s and microbolometer
A microbolometer is a specific type of bolometer used as a detector in a thermal camera. Infrared radiation with wavelengths between 7.5-14 μm strikes the detector material, heating it, and thus changing its electrical resistance. This resistance change is measured and processed into temperatures...

s are based on changes in resistance. Thermocouple
A thermocouple is a device consisting of two different conductors that produce a voltage proportional to a temperature difference between either end of the pair of conductors. Thermocouples are a widely used type of temperature sensor for measurement and control and can also be used to convert a...

s and thermopile
A thermopile is an electronic device that converts thermal energy into electrical energy. It is composed of several thermocouples connected usually in series or, less commonly, in parallel....

s use the thermoelectric effect
Thermoelectric effect
The thermoelectric effect is the direct conversion of temperature differences to electric voltage and vice-versa. A thermoelectric device creates a voltage when there is a different temperature on each side. Conversely, when a voltage is applied to it, it creates a temperature difference...

. Golay cells follow thermal expansion. In IR spectrometer
A spectrometer is an instrument used to measure properties of light over a specific portion of the electromagnetic spectrum, typically used in spectroscopic analysis to identify materials. The variable measured is most often the light's intensity but could also, for instance, be the polarization...

s 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
Electrical resistivity is a measure of how strongly a material opposes the flow of electric current. A low resistivity indicates a material that readily allows the movement of electric charge. The SI unit of electrical resistivity is the ohm metre...

 of the detector element is monitored. Photovoltaic detectors contain a p-n junction
P-n junction
A p–n junction is formed at the boundary between a P-type and N-type semiconductor created in a single crystal of semiconductor by doping, for example by ion implantation, diffusion of dopants, or by epitaxy .If two separate pieces of material were used, this would...

 on which photoelectric current appears upon illumination.
A few detector materials:


type Spectral range(μm) Wavenumber(cm-1)
Indium gallium arsenide
Indium gallium arsenide
Indium gallium arsenide is a semiconductor composed of indium, gallium and arsenic. It is used in high-power and high-frequency electronics because of its superior electron velocity with respect to the more common semiconductors silicon and gallium arsenide. InGaAs bandgap also makes it the...

photodiode 0.7-2.6 14300-3800
Germanium is a chemical element with the symbol Ge and atomic number 32. It is a lustrous, hard, grayish-white metalloid in the carbon group, chemically similar to its group neighbors tin and silicon. The isolated element is a semiconductor, with an appearance most similar to elemental silicon....

photodiode 0.8-1.7 12500-5900
Lead sulfide
Lead sulfide
Lead sulfide is an ionic compound of lead and sulfur, having two possible proportions:*Lead sulfide, the ionic compound containing lead in the +2 oxidation state*Lead sulfide, the ionic compound containing lead in the +4 oxidation state...

photoconductive 1-3.2 10000-3100
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
Platinum silicide
Platinum silicide is a semiconductor material used in infrared detectors. It is used in detectors for infrared astronomy.Platinum silicide is capable of operating at 1–5 µm wavelength range. It has a good sensitivity and high stability...

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
Mercury zinc telluride
Mercury zinc telluride is a telluride of mercury and zinc, an alloy of mercury telluride and zinc telluride. It is a narrow-gap semiconductor material....

 (MZT, HgZnTe)
Lithium tantalate
Lithium tantalate
Lithium tantalate , is a crystalline solid which possesses unique optical, piezoelectric and pyroelectric properties which make it valuable for nonlinear optics, passive infrared sensors such as motion detectors, terahertz generation and detection, surface acoustic wave applications, cell phones...

triglycine sulfate
Triglycine sulfate
Triglycine sulfate is a chemical compound with a formula 3·H2SO4. The empirical formula of TGS does not represent the molecular structure, which contains protonated glycine moieties and sulfate ions. TGS with protons replaced by deuterium is called deuterated TGS or DTGS; alternatively, DTGS may...

 (TGS and DTGS)

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
A microbolometer is a specific type of bolometer used as a detector in a thermal camera. Infrared radiation with wavelengths between 7.5-14 μm strikes the detector material, heating it, and thus changing its electrical resistance. This resistance change is measured and processed into temperatures...


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