TEMPORALLY AND SPECTRALLY RESOLVED AMPLITUDE AND PHASE OF COHERENT 4-WAVE-MIXING EMISSION FROM GAAS QUANTUM-WELLS

We demonstrate that spectral interferometry can be used together with a well-characterized reference pulse to directly determine the spectra l amplitude and spectral phase of coherent four-wave-mixing (FWM) emis sion from multiple quantum wells. The temporal amplitude and phase are then readily obtained by an inverse Fourier transformation. We illust rate that it is necessary to accurately determine the spectral phase, as well as the spectral amplitude, in order to correctly determine the temporal behavior. We subsequently use this technique to measure disc ontinuities in the temporal phase. Instabilities in the phase occur an d phase jumps of similar to pi are produced when both the real and ima ginary parts of the FWM field are zero. These jumps occur at the minim a in the quantum beats, and this condition requires the excitation of approximately equal numbers of heavy-and light-hole excitons.