Femtosecond transient-grating experiments in quantum wells

Using degenerate four-wave mixing (DFWM) with subpicosecond timeresolution, we demonstrate the following phenomena: (I) a novel coherent interaction of excitonic polarizations and (II) quantum beats of excitons in quantum wells due to interference of light-hole (lh) and heavy-hole (hh) excitons or hh excitons of different confinement.