How to avoid reflection losses in superconducting light detectors

The quantum efficiency of superconducting light detectors with film thicknesses ≥ 100 nm is mainly limited by the reflection losses at the superconducting film surface, which are usually higher than 50%. In this work we show that it is possible to reduce the reflection of Ti/Au and Ir/Au films to under 1% at telecommunication wavelengths, by means of properly designed antireflection coatings. The effect of optical cavity structures is also considered in the case of highly transmitting Ti and Ir films with thickness lower than 50 and 70 nm respectively in order to enhance absorption.