Polarization dependence and selection rules of transient four-wave mixing in GaAs quantum-well excitons

We report the experimental results of two-pulse transient four-wave mixing near the first heavy-hole quantum-well exciton. Input pulses with similar polarizations (circular or linear) measure the exciton dephasing rate; opposite circular polarized pulses produce no four-wave mixing signal, while crossed linear polarized pulses generate a weaker signal with a faster dephasing rate. This signal is attributed to the biexcitonic transition, which was directly observed in a separate nondegenerate four-wave mixing experiment. The selection rules for these transitions are discussed and confirm the treatment of the excitonic transition as a three-level system.