FORMATION AND CHARACTERIZATION OF HEXAGONAL PATTERNS IN A SINGLE FEEDBACK EXPERIMENT

In a nonlinear optical single feedback system formation of symmetry br oken patterns is observed. We make use of a liquid crystal light valve to experimentally simulate a self-defocusing Kerr-type nonlinearity. Beyond a certain threshold of the power of the input laser beam, brigh t spots appear and arrange themselves into a hexagonal formation. By f urther increasing input power, this ideal order is disturbed and final ly breaks down. The observations are compared with a theory, derived f or a similar setup. Measures for the degree of short- and long-range o rder are introduced, leading to the identification of two distinct sta tes of order.