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.[6] 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 conductance is the electron-phonon thermal conductance.
If the 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 bothsemiconducting and 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.