Nonlinear surface acoustic wave pulses in solids: Laser excitation, propagation, interactions (invited)

Laser techniques enabled generation of very high amplitude pulses with acoustic Mach numbers about 0.01. Such waves drive the medium into the nonlinear elastic regime and shock fronts can be formed during their propagation. As an intense surface acoustic wave (SAW) propagates, the temporal evolution of the wave shape provides information on the nonlinear acoustic parameters and the nonlinear elastic constants of the material. The nonlinear propagation of SAW pulses exhibits different types of nonlinear behavior depending on nonlinear acoustic constants. Changes of a SAW pulse shape were calculated using a nonlinear evolution equation. Measurements of SAW pulses in polycrystalline stainless steel have demonstrated that a compression of the pulse takes place in this material corresponding to a positive parameter of the local nonlinearity, which was evaluated by fitting the parameters of the evolution equation to the experimental data. Numerical simulations of a dispersive propagation of nonlinear SAWs in a system comprised of a substrate with a film were performed. A formation of a relatively stable portion of the waveform was found in agreement with recent observations of soliton-like SAW pulses. © 2003 American Institute of Physics.