Coherent shear phonon generation and detection with ultrashort optical pulses

Picosecond shear and quasishear coherent acoustic phonon pulses were generated and detected in time domain using an optical technique. A mode-locked Ti:sapphire laser beam of pulse duration ∼400 fs, repetition rate 76 MHz and wavelength 814 nm was focused onto the SiO₂-Zn interface. Pure shear phonon pulses propagating in an isotropic material were detected with oblique optical incidence by an interference technique. The generation was shown to be intricately tied to the symmetry properties of the tensors representing the relevant physical properties.