Fiber bolometer and emitter with negligible reflection for second sound measurements near the lambda-point

Superconducting Pb-Au thin film bolometers for second sound (SS) measurements near the lambda -point have been made on 8 mum diameter glass fibers. The small diameter of the fibers provides negligible cross-section to SS waves as close as similar to 10(-5) K to the lambda -point (for f = 10 kHz), thus eliminating reflections that may unduly complicate the wave distribution in the experimental cell. The bolometers have isotropic sensitivity to SS waves in the plane perpendicular to the fiber. The operating temperature of the bolometers can be adjusted by changing an external magnetic field and/or by varying the bias current, while still maintaining a figure of merit of similar to 30. A SS emitter producing planar waves was made using the same fibers. (C) 2001 Published by Elsevier Science Ltd.