DEPHASING OF INTERACTING HEAVY-HOLE AND LIGHT-HOLE EXCITONS IN GAAS QUANTUM-WELLS

We describe a novel three-pulse degenerate four-wave mixing configurat ion that permits the direct observation of the coherence between the s igma(+) and the sigma(-) exciton states in a GaAs quantum well excited in a two-photon process. It is found that the phase coherence between the two single heavy-hole exciton states decays with a time constant that is considerably longer than the dephasing time of the coherence b etween these states and the ground state (interband coherence). All th e experimental data are well described by numerical solutions of the o ptical Bloch equations for a phenomenological multilevel model.