Use of a dc superconducting quantum interference device as read-out electronics for radiation detectors based on superconducting tunnel junctions

A new generation of astronomical detectors has recently been developed, on the basis of superconducting tunnel junctions (STJs). STJs are capable of d etecting photons in a wide range of wavelengths, from X-rays to infrared; a lso the counting of single photons in the optical range has been demonstrat ed. Since these detectors operate at very low temperature (down to 100 mK), a natural candidate for the read-out electronics is the de superconducting quantum interference device (SQUID), an extremely sensitive magnetometer t hat is fabricated with a similar technology to the Sn junctions. Biasing th e STJ at a constant voltage, the current pulse caused by the incoming radia tion is passed through the tightly coupled input coil of the SQUID and conv erted into a magnetic flux signal which can be detected. In this paper we p resent measurements on a home-made de SQUID, showing the response of the de vice to current pulses, which simulate the real signals from a Sn. We show how the SQUID performance can be improved by using a superconducting flux t ransformer, which allows us to detect signal amplitudes of fraction of nano amperes, such as the signals coming from irradiation of STJs in the near-in frared range.