Analysis of disorder-induced dephasing

Summary form only given. A number of experiments yielded a polarization-dependent decay of the time-integrated four-wave-mixing (TI-FWM). Often, the TI-FWM decays more rapidly for linear perpendicular than for linear parallel polarized incident pulses. It was suspected that this difference in the decay times is related to the inhomogeneous linewidth of the exciton, i.e. to disorder. On the other hand, it was demonstrated that the understanding of polarization-dependent FWM and pump-probe experiments following excitonic excitation requires the treatment of Coulomb correlations beyond the Hartree-Fock level. For not too strong disorder, these correlations still remain important and influence the nonlinear optical response. A meaningful analysis of disorder effects thus has to include correlations. We analyze the origin of the polarization-dependent disorder-induced dephasing in TI-FWM by performing microscopic model calculations which include both energetic disorder and Coulomb correlations. Correlations are treated exactly up to third-order in the field and energetic disorder is taken from random distribution functions over which the optical response is averaged.