TRANSPORT INDUCED PATTERNS IN AN OPTICAL-SYSTEM WITH FOCUSING NONLINEARITY

We report the experimental sequence of pattern forming instabilities t hat a nonlocal interaction, due to a lateral image transport in the fe edback loop, induces in an optical system with focussing nonlinearity. As the lateral transport is increased, the transitions between consec utive patterns differ both qualitatively and quantitatively from those already observed in a system with defocussing nonlinearity. In partic ular, we show evidence of a new bifurcation leading to the appearance of nonequilateral hexagons, which become equilateral for a particular nonzero value of the lateral transport.