Calculation Of The Signal Time-Profile In Transient Cars Experiments

The expressions for the resonant and non-resonant contributions to the CARS signal in a time-resolved CARS experiment are derived on the basis of a diagrammatic perturbative expansion of the polarization. The laser fields are assumed to be off-resonance with respect to any electronic level of the system. The probe pulse is supposed to be derived from one of the two pump pulses (omega-1). Under this assumption the effect of the noise content of omega-1 laser pulses on the signal time-profile (coherence artefact) is correctly reproduced by modelling the noise as a stationary stochastic process. The choice of appropriate polarization geometries is shown to allow for direct measurement of the individual contributions to the CARS signal; the experiments performed on a KClO4 single crystal fully confirm the results of the calculation based on our theoretical treatment.