Editing Bolometer (section)

== Principle of operation ==
[[File:Bolometer conceptual schematic.svg|thumb|alt=Conceptual schematic of a bolometer.|'''Conceptual schematic of a bolometer'''. Power, ''P'', from an incident signal is absorbed and heats up a thermal mass with [[heat capacity]], ''C'', and temperature, ''T''. The thermal mass is connected to a reservoir of constant temperature through a link with [[thermal conductivity|thermal conductance]], ''G''. The temperature increase is Δ''T'' = ''P''/''G'' and is measured with a resistive thermometer, allowing the determination of ''P''. The intrinsic thermal time constant is τ = ''C''/''G''.]]

A bolometer consists of an absorptive element, such as a thin layer of metal, connected to a thermal reservoir (a body of constant temperature) through a thermal link. The result is that any radiation impinging on the absorptive element raises its temperature above that of the reservoir – the greater the absorbed power, the higher the temperature. The intrinsic thermal time constant, which sets the speed of the detector, is equal to the ratio of the [[heat capacity]] of the absorptive element to the [[thermal conductivity|thermal conductance]] between the absorptive element and the reservoir.<ref name=Richards>{{Cite journal | doi=10.1063/1.357128| title=Bolometers for infrared and millimeter waves| journal=Journal of Applied Physics| volume=76| issue=1| pages=1–24| year=1994| last1=Richards| first1=P. L.| bibcode=1994JAP....76....1R| url=https://zenodo.org/record/1232918}}</ref> The temperature change can be measured directly with an attached resistive [[thermometer]], or the resistance of the absorptive element itself can be used as a thermometer. Metal bolometers usually work without cooling. They are produced from thin foils or metal films. Today, most bolometers use [[semiconductor]] or [[superconductor]] absorptive elements rather than metals. These devices can be operated at [[Cryogenic particle detectors|cryogenic]] temperatures, enabling significantly greater sensitivity.

Bolometers are directly sensitive to the energy left inside the absorber.  For this reason they can be used not only for ionizing particles and [[photon]]s, but also for non-ionizing particles, any sort of [[radiation]], and even to search for unknown forms of mass or energy (like [[dark matter]]); this lack of discrimination can also be a shortcoming. The most sensitive bolometers are very slow to reset (i.e., return to thermal equilibrium with the environment). On the other hand, compared to more conventional particle detectors, they are extremely efficient in energy resolution and in sensitivity. They are also known as thermal detectors.