Polarization dependence of dephasing processes: A probe for many-body effects

The spectra of the diffracted wave in femtosecond-four-wave mixing and their dependence on the polarization of the driving fields are shown to be a very sensitive probe for the fundamental scattering processes that govern the coherent dynamics in a semiconductor. We demonstrate that the total dephasing rate is the result of a delicate balance between self-energies and vertex corrections. Particle interactions of the polarization scattering type are shown to be important contributions to the nonlinear optical response in the coherent regime.