Direct Observation of Third-Sound Mass Displacement Waves in Unsaturated SuperfluidHe4Films

Abstract
We report direct observation of pulsed third-sound film thickness oscillations in unsaturated superfluid He4 films using a capacitance technique. Simultaneous measurements of accompanying temperature oscillations allow the first study of the relative amplitudes of these oscillations and the results are in reasonable agreement with the theory of Bergman although some discrepancies are noted.