DC-Squid Readout for STJ Astronomical Detectors

The new generation of astronomical detectors based on Superconducting Tunnel Junctions (STJs) is capable of detecting photons in a wide range of wavelengths, and, in some cases, even of counting single photons. Since these detectors operate at very low temperature (down to 100 mK), a natural candidate for the readout electronics is the dc-SQUID, a superconducting device that can work as a current preamplifier, reaching very good noise performance. In this paper we present measurements on a homemade dc-SQUID, showing the response of the device to small current pulses, which simulate the real signals from an STJ. An optimal filtering processing of the data is performed, in order to extract from the noisy data the best estimate for the pulse height, which, in a real experiment with single optical photons, would be the parameter that carries the spectroscopic information.