Low aspect ratio transverse optical patterns indye-doped nematic liquid crystals

Spontaneous transverse two-dimensional optical pattern formation has been observedwith dye-doped nematic liquid crystals in front of a single feedback mirror. It is shown thatphoto-thermally excited dispersive optical nonlinearities are responsible for the observed spatialinstabilities. The appearence and symmetry of the patterns obtained within finite diameter laserbeams in low aspect ratio regimes are discussed in terms of Bessel function modes. Furthermore,a comparision of self-focussing versus self-defocussing nonlinearities has been performed by usingordinary or extra-ordinary polarized input beams.