Editing Bolometer (section)

==Hot electron bolometer==
The hot electron bolometer (HEB) operates at [[cryogenic]] temperatures, typically within a few degrees of [[absolute zero]]. At these very low temperatures, the [[electron]] system in a metal is weakly coupled to the [[phonon]] system. Power coupled to the electron system drives it out of thermal equilibrium with the phonon system, creating hot electrons.<ref>{{Cite journal |doi = 10.1103/PhysRevB.49.5942|pmid = 10011570|title = Hot-electron effects in metals|journal = Physical Review B|volume = 49|issue = 9|pages = 5942–5955|year = 1994|last1 = Wellstood|first1 = F. C.|last2 = Urbina|first2 = C.|last3 = Clarke|first3 = John|bibcode = 1994PhRvB..49.5942W}}</ref> Phonons in the metal are typically well-coupled to substrate phonons and act as a thermal reservoir. In describing the performance of the HEB, the relevant [[heat capacity]] is the electronic heat capacity and the relevant [[thermal conductivity|thermal conductance]] is the electron-phonon thermal conductance.

If the [[Electrical resistance|resistance]] of the absorbing element depends on the electron temperature, then the resistance can be used as a thermometer of the electron system. This is the case for both [[Semiconductor|semiconducting]] and [[Superconductor|superconducting]] materials at low temperature. If the absorbing element does not have a temperature-dependent resistance, as is typical of normal (non-superconducting) metals at very low temperature, then an attached resistive thermometer can be used to measure the electron temperature.<ref name=Richards/>