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

Spontaneous transverse two-dimensional optical pattern formation has been observed with dye-doped nematic liquid crystals in front of a single feedback mirror. It is shown that photo-thermally excited dispersive optical nonlinearities are responsible for the observed spatial instabilities. The appearence and symmetry of the patterns obtained within finite diameter laser beams 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 using ordinary or extra-ordinary polarized input beams. (C) 1999 Elsevier Science Ltd. All rights reserved.