IR filters for high responsivity cryogenic detectors

Modern cryogenic detectors, such as Superconducting Tunnel Junctions and Transition Edge Sensors, provide single photon counting performance, medium to high energy resolution, high count rates and good photon collection efficiency over a wide wavelength range. In order to avoid background limited performance, it is necessary to shield the detectors from any thermal IR radiation originating from the surrounding warm surfaces. In this paper we analyse the contribution of the thermal radiation to the detector performance and describe the IR filters used in the S-Cam camera and in other experimental configurations. Future detectors may require very severe attenuation of the IR flux (λ>1 μm). Solutions to this problem are proposed and their validity demonstrated with experimental results.