Coherent acoustic phonon generation and detection by femtosecond laser pulses in ZnTe single crystals

We report experiments of coherent acoustic phonon generations and detections using a two-color femtosecond pump-probe technique in [001] and [110] oriented ZnTe single crystals. The above-bandgap pump excitation initiates strain waves to yield coherent acoustic phonons. The generation and propagation of coherent acoustic waves not only modulate the intensity of the reflected probe light but also change its polarization periodically due to strain-induced birefringence. The nonuniform excitation due to Gaussian spatial distribution of pump pulses takes an important role in the polarimetric detection of coherent acoustic phonon oscillations.