Generation and detection of plane coherent shear picosecond acoustic pulses by lasers: Experiment and theory

摘要

Hypersound generation and detection by laser pulses incident on the interface of an opaque anisotropic crystal are theoretically and experimentally investigated in the case where the symmetry is broken by a tilt of its axis of symmetry relative to the interface normal. A nonlocal volumetric mechanism of plane shear sound excitation is revealed and a modification of the temporal shape of the reflectivity signal with variation in probe light polarization is observed, both attributed to asynchronous propagation of the acoustic eigenmodes. Experiments and theory demonstrate the possibility of using polycrystalline materials with an arbitrary distribution of grain orientations for the generation and the detection of picosecond shear ultrasound.