SPONTANEOUS OPTICAL-PATTERNS IN AN ATOMIC VAPOR - OBSERVATION AND SIMULATION

Optical pattern formation in an experiment with single mirror feedback is described. The nonlinear medium is sodium vapor in a buffer gas at mosphere. A microscopic model is given and a stability analysis and nu merical simulations are performed. Good agreement between the results of the experiment and the simulation is obtained. By numerical treatme nt of the model for the case of a plane incident wave (large aspect ra tio), the results obtained with a narrow Gaussian beam (small aspect r atio) are traced back to the transition from hexagon to roll formation via 'mixed' states.