Excitation front propagation in a semiconductor induced by high-intensity femtosecond laser pulses

摘要

We report on the excitation and propagation of an exciton density front inside a semiconductor that is characterized by high absorption and large optical nonlinearity. Femtosecond optical pulses are used for both the excitation of the density front and the probe of the front propagation. We analyze in detail the spectra of reflected probe pulses that carry information about the propagating density front due to partial internal reflection of light at the boundary between regions of high and low excitation density. Time resolved data show that the Doppler shift of the internal reflection is limited to the duration of the pump pulse indicating the highly transient character of the exciton front propagation.