Abstrakt
Ultrafast and long-distance expansion of electronhole plasma in bulk GaAs crystal at temperatures ranging from 20 K to 300 K is observed by means of the optical pump - THz probe experimental technique. The expansion speed similar to c/50 at 300 K notably exceeds values reported earlier in the literature but it also exceeds the values permitted by the GaAs band structure for a bare electron.
This observation is interpreted in terms of a stimulated emission, fast transport and reabsorption of photons by creation of electron-hole pairs. Theoretical quantitative model, based on the above interpretation, shows a very good agreement with the experimental data, gives a valuable insight into the system dynamics and predicts conditions at which the effect should be observable.
At temperatures below 100 K, further increase of the propagation speed of electron-hole plasma surface (up to similar to c/10) is observed. This effect is interpreted as the direct observation of the optical soliton propagation in the crystal.