Radiant-Energy Detection by Superconducting Films

Abstract

Superconducting films offer promise as fast, sensitive detectors at intermediate frequencies from millimeter waves to near infrared. The superconductor's marked temperature dependence of resistance about its transition temperature suggests that it would have a high responsivity as a bolometer, and operation at cryogenic temperatures suggests that a low NEP can be achieved. In addition, placing the sample in the liquid-helium bath should result in very short response times (τ) on the order of 10 nsec. Films have been studied with sheet resistances from 200 Ω/sq to > 1000 Ω/sq. These films achieve NEP ≈ 10−9 W·Hz−1/2 as bolometers with τ≈20 nsec. There is an enhanced microwave response, NEP ≈ 10−11 W·Hz−1/2 with τ = 20 nsec, which is especially pronounced for high-resistance films. This mode shows promise for use in the far-infrared and submillimeter region. The bolometer mode compares favorably with other bolometers.