Transition edge superconducting (TES) bolometers, are an incredibly sensitive broadband detector, offering a higher sensitivity, greater linear dynamic range, lower susceptibility to background noise and a faster speed compared to more traditional Germanium/Silicon bolometers. Their operating principle relies on channelling EM radiation onto an absorber, causing its energy to be deposited as heat. This propagates through the semiconducting crystal until it reaches a superconducting ring, which is operated at a temperature where it is making the transition from the normal state to the superconducting (zero resistance) state. The resistance thus changes sharply over a very small temperature range, making it an extremely sensitive thermometer. This resistance is monitored by the read-out system.

​

The bolometer is most commonly mounted in an optical integrating cavity behind a Winston Cone coupling optics along with low-pass filters which ensure that unwanted higher frequencies are efficiently rejected. It is important that the field of view of the coupling optics be matched to the incoming beam geometry. This ensures not only that all available signal power is available for detection but also that the bolometer is not unduly de-sensitised by exposure to an unnecessarily high background power.