Picosecond optical excitation of phonons in amorphous As2Te3.

We present a novel method of creating phonon excitations in a thin film of a chalcogenide glass. Phonon generation and the detection is done optically and thus allows measurement with picosecond time resolution. Current methods of studying phonon propagation involve ultrasonics or heat-pulse techniques. These use electronics, and the time resolution is limited to nanoseconds. Our picosecond method is a promising tool for studying propagation of phonons with extremely short mean free paths. As a demonstration of this method we measured the sound velocity in a film of a-Si02 and compared it with a computer simulation.