Generating and detecting phonon solitons in MgO using picosecond ultrasonics

We present an improved method for generating and detecting phonon solitons in a crystalline solid using the picosecond ultrasonics technique. An acoustic strain pulse is generated by a laser pulse in a transducer on the surface of the sample. The transducer is designed so that the generated strain pulse has a known and controlled shape. The strain pulse travels the thickness of the sample to the opposite side where it is detected by another laser pulse. After traveling this distance, the accumulated change in shape of the strain pulse indicates several fully formed phonon solitons. Calculations based on the Korteweg-de Vries equation give results in very good agreement with experiment.