Hannover 2003 – wissenschaftliches Programm

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Q: Quantenoptik

Q 24: Poster: Nichtlineare Optik

Q 24.2: Poster

Dienstag, 25. März 2003, 16:30–18:30, Lichthof

Pattern formation in a single-mirror experiment using an elliptic input beam — •M. Bölscher, F. Huneus, T. Ackemann, and W. Lange — Institut für Angewandte Physik, Universität Münster, Corrensstrasse 2-4, D-48149 Münster

‘Single mirror feedback systems’ consisting of a thin slice of a nonlinear medium and a feedback mirror show a surprising richness of spontaneously formed structures. Due to power restrictions, however, the ‘aspect ratio’ is typically low, i. e. the diameter of the input beam used in the experiments is by no means many times larger than the characteristic length of the evolving structures. As a consequence finite-size effects can play an important role. Here we report on experiments using sodium vapor in a transverse magnetic field as the nonlinear medium. Now the spherical cross-section of the input beam used before was replaced by an elliptical one. In this way a large aspect ratio is obtained in one direction, while maintaining a sufficient intensity level. The set-up provides a rich variety of patterns and dynamics. It is remarkable that now patterns with a length-scale belonging to a self-defocusing nonlinearity occur which are expected from plane-wave theory but were not observed when using a spherical cross-section. A characterization of these and further patterns and their dependence on parameters is presented. Investigations of bright spots, one of the observed structures, indicate that they can be interpreted as bistable localized states. Noise induced bi- and trimodality of this structure is shown as well as the transient behavior of switch-on processes.