Ultrafast acoustic phonon pulse generation in chromium

The generation mechanisms for longitudinal acoustic-phonon pulses excited in the transition metal chromium with sub-picosecond optical pulses are studied. The temporal and spatial evolution of the electron and lattice temperatures up to several picoseconds after laser photon absorption have a major impact on the final profile of the acoustic-phonon pulses. These phonon pulse shapes can be explained by considering both thermal and electron diffusion, and taking into account the effects of frequency-dependent ultrasonic attenuation.