Hot-electron effect in superconductors and its applications for radiation sensors

Abstract

The paper reviews the main aspects of nonequilibrium hot-electron phenomena in superconductors and various theoretical models developed to describe the hot-electron effect. We discuss implementation of the hot-electron avalanche mechanism in superconducting radiation sensors and present the most successful practical devices, such as terahertz mixers and direct intensity detectors, for far-infrared radiation. Our presentation also includes the novel approach to hot-electron quantum detection implemented in superconducting x-ray to optical photon counters.

Detection mechanism of superconducting nanowire single-photon detectors

“…with ∇ 2 being the Laplace-operator, C e ( r, t) is the probability density to find the excited electron at position r at time t, and C qp ( r, t) is the local density of excess QPs at time t. This simple exponential behaviour for the increase in the number of QPs was used instead of a more detailed description [88,104,107] to avoid unnecessary complexity. The inhomogeneous distribution of QPs may also be interpreted as a continuously varying order parameter of the superconducting condensate.…”

THz radiation sensors

“…Since in YBCO detector layers C p /C e »38, they are mainly the phonon−cooled type, as the energy backflow from phonons to electrons can be neglected and therma− lization time is about an order faster (t ep~1 ps) compared to NbN layers. In YBCO films, excited by fs pulses, non−ther− mal (hot−electron) and thermal bolometric (phonon) pro− cesses are practically decoupled, with the former ones domi− nating the early stage of electron relaxation [128]. To de− couple electrons from phonons, non−equilibrium phonons in the film should escape from it (into the substrate) in time short compared to the phonon−electron time t pe .…”

Review of 20 Years of Research on Microwave and Millimeter-wave Lenses at "Instituto de Telecomunicaço˜es"

“…However, an actual ultrawideband low profile feed is also required, for example, in radio astronomy applications, compatible with simple integration of ultrawideband bolometer detectors [23], [24]. Planar antenna structures printed directly at the lens base [25], [26] are the preferred solution for submillimeter-wave applications where waveguides are difficult to manufacture.…”

“…The same concept of shaped integrated lens antennas was later extended to millimeter and submillimeter imaging systems, in the framework of a project funded by the European Space Agency (ESA-ESTEC). The challenge was to develop lens antennas with an integrated feed to operate over 100% bandwidth, matching similar bandwidths from integrated quasi-optical receivers used in terahertz (THz) radioastronomy reflector antennas [23], [24]. Output beams were required to present Gaussissity value on the order of 90% over the band.…”