Abstract
Intense picosecond stimulated emission from the face of a thin GaAs film is studied. The emission is observed when GaAs is pumped with high-power picosecond optical pulses. It is found that the dependences of the emission energy on the photon energy, the picosecond delay between two pump pulses, and the distance between the active region and the face are modulated. Modulation is taken to mean the appearance of protrusions or peaks in any of the mentioned dependences. The modulation parameters for the dependences under consideration are found to be related by expressions that make it possible to suggest the following. The modulation of characteristics is caused by a common (not yet conclusively identified) mechanism of self-modulation of the emission spectrum. This mechanism is related to an ultrafast nonlinear interaction between a highly photoexcited semiconductor and the pump radiation and stimulated emission. There is indirect evidence that this mechanism also gives rise to an amplitude modulation of the emission in a picosecond time interval.