Observation of optical precursors at pulse propagation in GaAs.

Abstract

We have observed optical precursors by studying propagation of ultrashort optical pulses with a steeply rising and an exponentially decaying trailing edge through a 0.2-\ensuremath{\mu}m-thick GaAs crystal near the exciton resonance. The appearance of a fast pulse front---the precursor---independent of the detuning with respect to the resonance, was accompanied by a delayed main pulse. The delay of the main pulse varies with detuning in according with theoretical predictions.