Gain-enhanced optical coherence in a high optical gain semiconductor

The propagation of ultrashort pulses in a traveling wave semiconductor amplifier is considered. It is demonstrated that the effective polarization relaxation time, which determines the coherence of the interaction of pulses within the medium, strongly depends on its optical gain. As a result, it is shown that at large optical gains the coherence time can exceed the transverse relaxation time T2T2 by an order of magnitude, this accounting for the strong femtosecond superradiant pulse generation commonly observed in semiconductor laser structures.

► We show that polarization decay time of the medium strongly depends on optical gain.
► Coherency time can exceed the transverse relaxation time by an order of magnitude.
► The effect explains generation of femtosecond superradiant pulses in semiconductors.