COHERENT NONLINEAR EXCITONIC EFFECTS AND PULSE-PROPAGATION

Carrier-polarization scattering (off-diagonal dephasing) was shown to be indispensable for a correct description of the dephasing-processes in a laser excited semiconductor. We demonstrate that a correct descri ption of the exciton which undergoes only a weak shift with increasing excitation up to the Mott transition requires also the consideration of the corresponding real parts of the scattering integrals. Particula rly for low temperatures the observed weak blue shift of the exciton i n ZnSe, which is in contradiction to the prediction of a. theory with simple static screening approximation. can be explained. Including spa tial dispersion of the exciton propagation effects of a probe pulse (p olariton beats) are in investigated. With our results for the Mott tra nsition of tile exciton we are able to describe tile experimentally ob served vanishing of polariton beats with increasing number of carriers generated by a preceding pump pulse.