Experiments with acoustic solitons in crystalline solids

We have used the picosecond ultrasonic technique to study the formation of acoustic solitons. In these experiments, a longitudinal acoustic pulse is generated at one surface of a sample. After the pulse has propagated across the sample, its shape is modified as a result of phonon dispersion and nonlinearity. We have found that the change in the pulse shape can be described by the Korteweg--de Vries equation. The experiments have been performed on Si, MgO, {α}-quartz, and sapphire. For each sample, we have observed fully developed acoustic solitons, with pulse shapes that are in reasonable agreement with the results of computer simulations.