POLARIZATION PARTITION NOISE AND INTENSITY FLUCTUATION LINEWIDTH IN ANEARLY SYMMETRICAL VECTOR LASER

We consider the statistical properties of the fluctuations in the orie ntation of the vector laser field for a nearly isotropic laser, addres sing the competition between the randomizing influence of noise and th e preference for linearly or circularly polarized emission induced by saturation in the laser medium and/or cavity anisotropies. We describe , through a nonperturbative analysis, a crossover regime from diffusio n-induced polarization-isotropic emission to emission of nearly fixed polarization characteristics. In this crossover the linewidth of inten sity fluctuations associated with one of the circularly polarized comp onents of the vector field amplitude changes from decreasing to increa sing with output power. This behavior can be expressed in terms of a s ingle parameter that measures the pump or the total output intensity i n terms of the ratio of the noise amplitude to the degree of cross sat uration of the amplitudes of the circularly polarized components of th e vector field amplitude. Analytical results are given for the linewid th of the intensity fluctuations. When the laser has a preference for linearly polarized emission, there is a weakly non-lorentzian spectrum in the crossover region. When the laser has a ''preference'' for circ ularly polarized emission the crossover regime is characterized by a n on-lorentzian spectrum due to fast hopping between two circularly pola rized eigenstates. We also describe ellipticity fluctuations induced b y the diffusion of the direction of the main axis of the polarization ellipse in the presence of cavity birefringence.