In an optical pattern forming system (sodium vapor with feedback from a single plane mirror) different scenarios for the destabilization of stationary patterns in favor of states that are irregular in space and in time are studied experimentally and numerically. Secondary bifurcations from hexagons to squares occur via a time dependent state whose origin is traced back to noise-driven hexagon–square competition in a region of bistability between the two states. Squares can display a transition to another state with irregular — probably intrinsic — time dependence in which a whole band of wave vectors is excited. In real space pentagons are a prominent feature.
['Aric R. Aumann', 'T. Ackemann', 'E Große Westhoff', 'W. Lange']
TRANSITION TO SPATIOTEMPORALLY IRREGULAR STATES IN A SINGLE-MIRROR FEEDBACK SYSTEM