Manifestation of exciton coherence in resonant quantum well emission

Secondary emission from GaAs quantum wells following resonant pulsed excita tion is studied in the time domain. Selective excitation of heavy- and ligh t-hole excitons is accomplished in a two-pulse excitation experiment which preserves sub-ps time resolution. After the initial rise the emission decay s exponentially at a fast rate and then with another much slower exponentia l decay at longer times. The variations in the initial decay times with exc itation density and sample temperature are similar to the variation in deph asing rates measured in four-wave mixing experiments. The decay in the visi bility of heavy- and light-hole exciton beating is consistent with the deca y rates measured for both species separately.