Femtosecond and picosecond nondegenerate four-wave mixing in GaAs/AlGaAs multiple quantum wells by two independently tunable lasers

Abstract

We have performed femtosecond and picosecond nondegenerate two-beam and three-beam (omega (1), omega (1); omega (2)) four-wave mixing experiments by using two partially synchronized, independently tunable lasers with a simple sample-and-hold switch. When the jitter is compensated for externally, heavy- and light-hole beating is observed with these two mutually incoherent lasers, and the synchronous phases of oscillations with the detuning show that these beats are true quantum beats. We also see the strong completely off-resonant signals, and the below-bandgap signals are stronger than the signals at the continuum for equivalent detunings. This off-resonance signal has a Lorentzian dependence on detuning in both the femtosecond and the picosecond experiments. When omega (2) is completely above or below the excitonic resonance, the spectrum of the diffracted beam is determined mostly by the laser spectrum, which can be explained by semiconductor Bloch equations.