Transport induced patterns in an optical system with focussing nonlinearity

We report the experimental sequence of pattern forming instabilities that a nonlocal interaction, due to a lateral image transport in the feedback loop, induces in an optical system with focussing nonlinearity. As the lateral transport is increased, the transitions between consecutive patterns differ both qualitatively and quantitatively from those already observed in a system with defocussing nonlinearity. In particular, 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. PAC.? 42.65.-k; 03.4O.Kf; 42.6O.Jf; 89.90.+ n