PHASE MEASUREMENT IN A COLLINEAR PUMP-PROBE EXPERIMENT - APPLICATION TO MOLECULAR-DYNAMICS STUDIES IN LIQUIDS

We propose a novel approach of nonlinear resonant spectroscopy based o n a collinear and degenerated pump probe experiment. This particular s cheme leads to an oscillating time-resolved signal superimposed to the usual transient absorption signal. We have performed both amplitude a nd phase analysis of this oscillating signal as a function of the pump probe delay for different laser wavelengths. As an example, results o n the resonantly excited dye molecule hexamethylindotricarbocyanine io dide (HITCI) in ethylene glycol at room temperature have been exploite d in the framework of the phenomenological Brownian oscillator model. The corresponding numerical simulations have been carried out with a s pecial emphasis on the phase sensitivity versus pump probe delay and d etuning. The chromophore dynamical parameters obtained from phase vari ations of our signal are compared with other available spectroscopic s tudies. (C) 1998 American Institute of Physics. [S0021-9606(98)01541-4 ].