Population pulsations and nondegenerate four-wave mixing in semiconductor lasers.

The theory of nondegenerate four-wave mixing (NDFWM) in semiconductor lasers is presented with particular emphasis on the physical processes that lead to population pulsations. In the case of nearly degenerate four-wave mixing, modulation of the carrier density at the beat frequency omega of the pump and probe waves creates a dynamic population grating whose effectiveness is governed by the spontaneous carrier lifetime tau sub s. Such a grating affects both the gain and the refractive index of the probe wave. In particular, the probe gain exhibits features analogous to those observed in a detuned atomic system arising from the optical Stark effect. Both the gain and index gratings contribute to NDFWM with dominant contribution coming from the index grating. For detunings such that omega tau sub s >> 1, population pulsations correspond to modulation of the intraband population resulting from spectral hole-burning.