Berlin 2005 – scientific programme

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DY: Dynamik und Statistische Physik

DY 30: Spiral Formation and Feedback

DY 30.8: Talk

Monday, March 7, 2005, 12:00–12:15, TU H3010

Selection of the number of spiral-arms in a single-mirror feedback scheme — •Florian Huneus, Thorsten Ackemann, and Wulfhard Lange — Institut für Angewandte Physik, Westfälische Wilhelms-Universität, Corrensstrasse 2/4, 48149 Münster

In the experiment we report on, sodium vapor in an oblique magnetic field is irradiated by a laser beam. A plane mirror feeds the transmitted light back into the vapor.

Beyond a certain input intensity, self-organized inwardly moving targets and spirals emerge in the transverse intensity profile. For the same set of parameters, targets and spirals with different numbers of arms are observed; the system is multistable. In experiments, in which the intensity is switched abruptly from zero to a value beyond threshold, histograms of the number of spiral-arms are obtained. The dependence of the most frequent number of arms on parameters is investigated experimentally and theoretically. A linear stability analysis that regards perturbations of different azimuthal order reproduces the experimental results qualitatively. A correlation is found between the most frequent number of arms and the focal-length of a self-induced lens.