Laser light heating for low-noise temperature control in SQUID applications

We have developed a new technique to heat a temperature-controlled stage fo r SQUID measurements without coupling excess noise to the SQUID. We send in frared laser light from a diode laser into a cryostat through an optical fi ber, whose cleaved end is held close to a blackened spot on the stage. The laser current is controlled by a commercial PID temperature controller, whi ch monitors the stage temperature with a diode sensor. Temperature control with the laser heating system is almost as good as that with a resistive he ater, but it is much easier to achieve excellent SQUID noise performance be cause the rapidly oscillating magnetic field of infrared light does not cou ple to SQUIDs' pickup loops, and the optical fiber does not carry RF noise to the SQUID. (C) 2000 Elsevier Science B.V. All rights reserved.