Transition edge sensor
A transition edge sensor or TES is a type of cryogenic energy sensor or cryogenic particle detector that exploits the strongly temperature-dependent resistance of the superconducting phase transition.
The first demonstrations of the superconducting transition's measurement potential appeared in the 1940s, thirty years after Onnes's discovery of superconductivity. D.H. Andrews demonstrated the first transition-edge bolometer, a current-biased tantalum wire which he used to measure an infrared signal. Subsequently he demonstrated a transition-edge calorimeter made of niobium nitride which was used to measure alpha particles. However, the TES detector did not gain popularity for about 50 years, due primarily to the difficulty of signal readout from such a low-impedance system. A second obstacle to the adoption of TES detectors was in achieving stable operation in the narrow superconducting transition region. Joule heating in a current-biased TES can lead to thermal runaway that drives the detector into the normal (non-superconducting) state, a phenomenon known as positive electrothermal feedback. The thermal runaway problem was solved in 1995 by K. D. Irwin by voltage biasing the TES, establishing stable negative electrothermal feedback, and coupling them to superconducting quantum interference devices (SQUID) current amplifiers. This breakthrough has led to widespread adoption of TES detectors.
The TES is voltage-biased by driving a current source Ibias through a load resistor RL (see figure). The voltage is chosen to put the TES in its so-called "self-biased region" where the power dissipated in the device is constant with the applied voltage. When a photon is absorbed by the TES, this extra power is removed by negative electrothermal feedback: the TES resistance increases, causing a drop in TES current; the Joule power in turn drops, cooling the device back to its equilibrium state in the self-biased region. In a common SQUID readout system, the TES is operated in series with the input coil L which is inductively coupled to a SQUID series-array. Thus a change in TES current manifests as a change in the input flux to the SQUID, whose output is further amplified and read by room-temperature electronics.
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