BIEXCITONIC EFFECTS IN TRANSIENT NONLINEAR-OPTICAL EXPERIMENTS IN QUANTUM-WELLS

We present a model for the nonlinear optical response of quantum wells , which includes biexcitons. We show that within this model, the inter action of two laser pulses, mediated by the nonlinear susceptibility, results in oscillations and in coupling between sigma+ and sigma- exci tons. This explains the temporal behavior of the differential absorpti on and four-wave mixing in recent experiments [Phys. Rev. Lett. 68, 34 9 (1992); 68, 1880 (1992)]. The oscillations have a frequency equal to the biexciton binding energy, and are different from known interferen ce and quantum beat phenomena.