Picosecond ultrasonic study of phonon reflection from solid-liquid interfaces

We have studied the reflection of longitudinal-acoustic phonons with frequencies between 100 and 300 GHz from solid-liquid interfaces using a picosecond ultrasonic technique. Acoustic phonons were generated by absorption of a picosecond light pulse in a metal film. After propagating through a dielectric layer, the phonons were reflected at the solid-liquid interface. We have measured the reflection coefficient at a series of interfaces between dielectric solids and organic liquids for temperatures from 265 to 300 K. The reflection of 205 GHz phonons was also measured between aluminum and liquid argon and nitrogen. The experimental results were compared with the predictions of the classical acoustic-mismatch model.