Molecular alignment and orientation in short pulse laser fields

An analytical expression for the propagator associated with impulsive excitation is derived based on the Magnus expansion. We apply this expression to the excitation of angular motion out of a rotational eigenstate for a linear polar molecule in a plane polarized electromagnetic field. We show that with properly chosen field parameters, the motion of the molecule alternates between orientations in the forward and backward hemisphere, respectively, with respect to the polarization axis of the field.