Ultrafast coherent transients due to exciton-continuum scattering in bulk GaAs

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Abstract
Recent two-beam four-wave-mixing experiments on GaAs using pulses of 15 fs in duration have exhibited unusual line shapes that simultaneously show narrow spectral lines with a width of 1 meV and decays in the time-delay domain on a scale of 10 fs. This observation appears to violate time-energy uncertainty and has not been explained so far. Here we present three-beam four-wave-mixing experiments under identical conditions. The data are compared with a model of exciton-continuum coupling that explains the signatures of the three-beam data as well as the two-beam data.