Probing impulsive strain propagation with x-ray pulses

Pump-probe time-resolved x-ray diffraction of allowed and nearly forbidden reflections in InSb is used to follow the propagation of a coherent acousti c pulse generated by ultrafast laser excitation. The surface and bulk compo nents of the strain could be simultaneously measured due to the large x-ray penetration depth. Comparison of the experimental data with dynamical diff raction simulations suggests that the conventional model for impulsively ge nerated strain underestimates the partitioning of energy into coherent mode s.