Strong-field impulsive alignment in the presence of high temperatures and large centrifugal distortion

We achieve impulsive alignment in a 400 K sample of diatomic iodine. This alignment results in an ensemble of coherent rotational wave packets with revival structures at 220 and 440 ps. The revivals contain many more oscillations than are typically seen in rotational wave packets. The high-temperature sample contains a very large distribution in J, with strong centrifugal distortions. We find that the high initial temperature, rather than the strength of the laser impulse, gives rise to the centrifugally distorted revival oscillations. We present polarization measurements of this rotational wave packet together with semiclassical simulations showing the importance of the thermal distribution of population in both rotational and vibrational states. Our results show that excitation of coherent rotations is possible even in a system where the thermal energy is large compared to the energy exchanged with the laser field.