Coherent shear phonon generation and detection with picosecond laser acoustics

Measurements on a film of silica on crystalline zinc using picosecond laser acoustics are theoretically analyzed to quantitatively explain the generation and detection of picosecond shear and longitudinal-acoustic waves. The theory encompasses the scattering of obliquely incident probe light of arbitrary polarization by a depth-dependent anisotropic permittivity modulation in a multilayer, including terms arising from the photoelastic effect, interface displacements, and local rotations. Sound velocities, ultrasonic attenuation, and photoelastic constants are experimentally derived.