Coherent excitation phenomena in time-resolved experiments

We report on the influence of coherent phenomena on femtosecond pump-probe experiments in molecular systems. The signature of Coherent Population Return (CPR) has been observed, and satisfactorily simulated, by following the dynamics of the on and off resonance excitation of the S-0-S-1 transition of aniline. While for the on resonance experiments the system dynamics can be described in terms of the simple incoherent rate equations, for the off resonance experiments a more detailed analysis based on the time-dependent Schrodinger equation that takes into account coherent effects is needed. This fact points out the necessity of considering coherent effects during and after the interaction process, even in systems where ordinarily they have been neglected, for a rigorous description of laser mater interaction.