Degree and state of polarization of the time-integrated coherent four-wave mixing signal from semiconductor multiple quantum wells

All four of the Stokes parameters of the time-integrated degenerate four-wave mixing signal from a GaAs/${\mathrm{Al}}_{\mathit{x}}$ ${\mathrm{Ga}}_{1\mathrm{-}\mathit{x}}$As multiple quantum well are measured as a function of the relative angle between the linear polarizations of the pump and the probe and of the incident fluence, thus completely characterizing the polarization state of the signal. The degree to which the signal is polarized, the ellipticity, and the orientation of the polarization ellipse are found to be strongly dependent on the orientation of the incident polarizations and on fluence. The principal features can be qualitatively understood in terms of a simple model that includes density-dependent dephasing and local-field corrections.