Ultrafast dynamic reflectivity of vanadium pentoxide

The ultrafast dynamic reflectivity of vanadium pentoxide is measured using 40 fs pulses from a self-mode-locked Ti:sapphire laser. The laser pulses excite acoustic vibrations at wave numbers of 145 and 103 cm−1. The amplitudes of the induced oscillations depend strongly on the orientation between the linear polarization of the laser pulses and the crystal axes, with the largest oscillations observed for an orientation of 45°. The higher-frequency oscillation is induced immediately upon arrival of the laser pulse, while the lower-frequency oscillation appears a few picoseconds later. The oscillations persist for approximately 10 ps after the arrival of the pulse. The oscillations are attributed to transverse acoustic modes propagating along the a-axis of the crystal.