Abstract

Spatial patterns with hexagonal symmetry have been observed in many diferent areas of the natural sciences. These include the Rayleigh-Bénard experiment in fluids, chemical reactions, dishes of granular solids, and nonlinear optics. These diverse physical systems are all characterized by an isotropic nonlinearity in the plane of the pattern. In this work we study the formation of hexagonal spatial patterns in a photorefractive crystal with strongly anisotropic nonlinear coupling. In our experiment the nonlinear coupling is zero along one axis of the observed pattern. The anisotropy breaks rotational symmetry in the plane of the pattern, and clamps the orientation of the participating wavevectors. Nonetheless, we observe rotationally symmetric hexagonal patterns, identical to those seen in isotropic media.

© 1996 IEEE