Theory of pulse propagation and wave-mixing processes under intense resonant excitation

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Abstract
We study the temporal and spatial evolution of a pump, test, and signal field generated in a four-wave-mixing process for resonant excitation of a nonlinear medium by nanosecond pulses. The propagation effects for the pulses are taken into account beyond the usual mean-field approximation. The model is then applied to a three-level system, describing CuCl at low temperatures. A great deal of new information concerning the temporal and spatial structures of the different fields propagating through the sample is obtained. We show, for instance, that the temporal shapes of the interacting fields are well established after propagation through the first few micrometers of the sample. Beyond this, they propagate with a diminishing amplitude. We also show that these structures are due to the dephasing of the fields throughout their propagation as well as to the temporal evolution of the absorption and generation function of the sample.