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.