ULTRAFAST COHERENT TRANSIENTS DUE TO EXCITON-CONTINUUM SCATTERING IN BULK GAAS

Recent two-beam four-wave-mixing experiments on GaAs using pulses of 1 5 fs in duration have exhibited unusual line shapes that simultaneousl y show narrow spectral lines with a width of 1 meV and decays in the t ime-delay domain on a scale of 10 fs. This observation appears to viol ate time-energy uncertainty and has not been explained so far. Here we present three-beam four-wave-mixing experiments under identical condi tions. The data are compared with a model of exciton-continuum couplin g that explains the signatures of the three-beam data as well as the t wo-beam data.