The transmission of phonons from liquid He to crystalline NaF

The angular distribution of phonons transmitted through the interface between liquid He and a single crystal of NaF has been measured in both directions. There are two channels; a q/sub ///-conserving channel and a non-classical channel which carries most of the energy at high phonon frequencies. However, the ratio of the energy carried in these two channels is quite different in the two directions for similar heater powers. At low powers the differences are due to the low characteristic temperature of the phonons injected into the He by a thin-film metal heater. At high power the differences are attributed to the saturation of the transmission channels from He to a solid.