Abstract

There is presently a large interest in the study of pattern formation. In nonlinear optics, the system consisting of a thin slab of nonlinear medium and a feedback mirror¹ is particularly interesting because it appears to be relatively easy to handle both from a theoretical and an experimental point of view. In particular, the possibility to vary the distance between the cell and the nonlinear medium is an easy and reliable way to check the validity of a model. We present the results of an experiment where the nonlinear medium consists of Rubidium atoms. A striking result of our experiment is the observation of new patterns completely different from those considered before (hexagons, rings, and stripes) for passive nonlinear media. These patterns look like flowers with a number of petals, which varies with the distance between the feedback mirror and the Rubidium cell. This experiment differs from those performed with Kerr media because the nonlinearity is very different from a quadratic nonlinearity and the pattern selection is associated with the strong saturation of this nonlinearity.

© 1994 IEEE