Bolometer
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A bolometer is a device for measuring incident electromagnetic radiation.
It consists of an "absorber", which is connected to a heat sink (area of constant temperature) through an insulating link. The result is that any radiation absorbed by the absorber raises its temperature above that of the heat sink—the higher the power absorbed, the higher the temperature will be.
A thermometer of some kind, attached to the absorber, is used to measure the temperature, from which the absorbed power can be calculated. In some designs the thermometer is also the absorber; in others the absorber and thermometer are separate; this is known as "composite design".
While bolometers can be used to measure radiation of any frequency, for most wavelength ranges there are other methods of detection that are more sensitive. However, for sub-millimetre wavelengths (from around 200 µm to 1 mm wavelength), the bolometer is the most sensitive type of detector for any measurement over more than a very narrow wavelength range.
Bolometers are therefore used for astronomy at these wavelengths. However, to achieve the best sensitivity, they must be cooled down to a fraction of a degree above absolute zero (typically from 50 millikelvins to 300 mK); this makes their operation technically somewhat challenging.
The term bolometer is also used in high-energy physics (particle physics) to designate an unconventional particle detector. They use the same principle described above. The bolometers are sensitive not only to light but to every form of energy. They can be used to search for unknown forms of mass or energy (like dark matter) as well as normal particles and radiation. They are very slow and they have a high dead time. They lack completely of any sort of discimination. On the other hand, they are extremely efficient in energy resolution and in sensitivity. They can be used to test very high radio-purity. They are also known as thermal detectors.
Their use as particle detectors is still at the developmental stage. Their usage as particle detectors was advice from the beginning of 20th century but the first regular use, even if in a pioneering way, was only in the 1980s because of the difficulty associated with having a system at cryogenic temperature.de:Bolometer it:Bolometro