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 l inearly polarized. The instability results in the formation of spatial ly separated domains of opposite elliptical polarization. For initiall y linearly polarized light, we find square patterns that give way to p ositive or negative hexagons if the polarization is elliptical. This c onfirms a recent theoretical prediction based on a purely dispersive m odel [Scroggie and Firth, Phys. Rev. A 53, 2752 (1996)]. However, abso rption has to be accounted for to reproduce the experimentally observe d threshold behavior.