Transition-edge sensors

In recent years, superconducting transition-edge sensors (TES) have emerged as powerful, energy-resolving detectors of single photons from the near infrared through gamma rays and sensitive detectors of photon fluxes out to millimeter wavelengths. The TES is a thermal sensor that measures an energy deposition by the increase of resistance of a superconducting film biased within the superconducting-to-normal transition. Small arrays of TES sensors have been demonstrated, and kilopixel arrays are under development. In this Chapter, we describe the theory of the superconducting phase transition, derive the TES calorimeter response and noise theory, discuss the state of understanding of excess noise, and describe practical implementation issues including materials choice, pixel design, array fabrication, and cryogenic SQUID multiplexing.