The acoustical coupling of two thin superconducting films forming a tunnel junction was measured. The experiment was performed by photoexciting quasiparticles in one film and studying the resulting change in the energy gaps. The results show that the phonon escape parameter from lead to tin agrees with calculated values and there is an indication of an additional escape mechanism in the lead films.

• Received 24 March 1975

DOI:https://doi.org/10.1103/PhysRevB.12.2629