Polarized patterns in sodium vapor with single mirror feedback

In a simple nonlinear optical system consisting of a sodium vapor cell and a single feedback mirror, the spatial and polarization degrees of freedom are simultaneously unstable if the incident light is nearly linearly polarized. The instability results in the formation of spatially separated domains of opposite elliptical polarization. For initially linearly polarized light, we find square patterns that give way to positive or negative hexagons if the polarization is elliptical. This confirms a recent theoretical prediction based on a purely dispersive model [Scroggie and Firth, Phys. Rev. A 53, 2752 (1996)]. However, absorption has to be accounted for to reproduce the experimentally observed threshold behavior.