NONLINEAR RESPONSE OF LOCALIZED EXCITONS - EFFECTS OF THE EXCITATION-INDUCED DEPHASING

The polarization dependence of the ultrafast nonlinear response of loc alized excitons in GaAs/AlGaAs quantum wells has been investigated by spectrally resolved, transient four-wave mixing. The role of the excit ation-induced dephasing in the delay dependence of the signal is discu ssed in detail. In particular, we show experimentally that the excitat ion-induced dephasing gives rise to a photon echo in inhomogeneous sys tems. We develop a simple analytical model for the delay dependence of the signal, which enables us to deduce the dephasing time from the fo ur-wave mixing decay.