Fiber bolometer and emitter with negligible reflection for second sound measurements near the λ-point Original Research Article

Superconducting Pb–Au thin film bolometers for second sound (SS) measurements near the λ-point have been made on 8 μm diameter glass fibers. The small diameter of the fibers provides negligible cross-section to SS waves as close as ∼10−5 K to the λ-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 ∼30. A SS emitter producing planar waves was made using the same fibers.