DEPHASING AND RELAXATION IN COHERENTLY EXCITED ENSEMBLES OF INTERMOLECULAR OSCILLATORS

The multi-component, subpicosecond dynamics observed in femtosecond nonlinear-optical experiments on transparent liquids are described in terms of a physically intuitive model based on intermolecular vibrational motion. The essential feature of this model is the recognition that underdamped, critically damped, and overdamped motions can all contribute to the dynamics (or lineshape) associated with a single, inhomogeneously broadened, intermolecular vibrational degree of freedom. This unique result arises because dynamic dephasing processes in liquids occur on a time scale comparable to that of the vibrational motions themselves. These considerations are applied to the subpicosecond optical Kerr dynamics of CS2 liquid.