Abstract
One of the techniques that has proven to be extremely powerful for studying coherent processes and excitonic effects in semiconductors is the study of the polarization dependence of the degenerate four-wave-mixing (FWM) process. While there have been a large number of studies that have addressed the dependence of the strength of the FWM signal (or its spectrum) on input polarization, there have been few attempts1"3 to monitor the polarization state of the FWM signal itself, and only one study4 completely characterized the polarization state of the FWM signal. In the latter, we measured the time-integrated polarization state, and we found that the time-integrated four- wave-mixing (TI-FWM) signal had a significant unpolarized component and that the polarized portion was highly elliptically polarized. In addition, the degree of polarization, the ellipticity, and the orientation of the polarization ellipse were each strongly dependent on the fluence (i.e., the carrier density) and the incident polarizations. The presence of an unpolarized component in the TI-FWM signal suggests either that (i) the FWM signal has a random component to its polarization or (ii) the integration of a time- varying (but deterministic) polarization yields a degree of polarization less than one. In either case, these results suggest that useful new information would be obtained by time resolving the polarization state of the FWM signal.
© 1996 Optical Society of America
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