TRANSVERSE STRUCTURES IN A SODIUM-FILLED FABRY-PEROT RESONATOR .2. INTERPRETATION OF EXPERIMENTAL RESULTS

We provide a heuristic physical interpretation of experimental results given in a preceding paper in this issue, on pattern formation in a n onlinear confocal Fabry-Perot resonator. The basic physical principles governing a resonator with a self-induced, intracavity lens, well app licable to a nonlinear medium dominated by diffusion, are shown to be sufficient to explain the salient features of the structures that can be formed in the nonlinear system for weak nonlinearities, and give us eful guidance in the case of stronger nonlinearities as well. This int erpretation highlights the basics of the interplay between the nonline ar medium and the optical cavity, thereby elucidating the mechanisms t hat control pattern formation in a passive nonlinear resonator. The an alysis of the experimentally observed symmetries, as a function of the beam incoupling and of the other experimental conditions, shows that the crucial parameters that control the topological properties of patt erns are the modal phases, especially the excitation phases.