Kolloquium 17.01.2016 16.30 s.t in Room 222 of the Institute for Applied Physics

Doktorandenkolloquium (Dauer: ca. 30 Minuten pro Vortrag)

Controlling caustics: Weaving catastrophic structures in Airy-, Pearcey-, and swallowtail beams

Catastrophe science is a branch of bifurcation theory in the study of dynamical systems; it is also a special case of more general singularity physics. Bifurcation theory studies and classifies phenomena characterized by sudden shifts in behaviour arising from small changes in circumstances, analysing how the qualitative nature of solutions depends on control parameters. In optics, these dramatic changes manifest as geometrically stable caustics, which, as natural phenomena, are associated with the arcs close to rainbows, or may occur as high-intensity networks on the floor of shallow waters. Similar to their formation behind refractive index lenses with imperfections, the formation of corresponding structures has been observed for numerous kinds of lenses with importance in optics, astrophysics and surface analytics.
The most prominent representative of catastrophe that manifests as wave package is the fold catastrophe that has been realized as paraxial Airy beam, and shows a form-invariant and accelerated propagation. Here, we present higher-order catastrophes as paraxial light, discuss the mapping of corresponding cusp and swallowtail catastrophes to these beams and demonstrate their unique propagation effects. Their often auto-focusing propagation of curved trajectories is well suited to optically induce photonic structures, waveguides to nonlinear photosensitive materials.
Alessandro Zannotti, AG Denz, Institut für Angewandte Physik

Delay-induced Dynamics in a Swift-Hohenberg Model with Spatial Inhomogeneities

We study pattern formation in a Swift-Hohenberg model that, aside from many other applications, describes the evolution of the electric field envelope in the transverse plane of a bistable optical cavity pumped by an external injection beam.
Typical solutions of the Swift-Hohenberg equation are homogeneous, periodic and localized states. Here, we focus on the destabilization of stable localized solutions by time-delayed feedback, which can be implemented by using an external cavity in optical applications. We show that by varying the delay time and the delay strength, one can induce a variety of different dynamics including the drift or the annihilation of the localized solutions as well as travelling wave solutions.
A special focus lies on the introduction of spatial inhomogeneities into the system, e.g., by introducing a spatially inhomogeneous injection beam, which changes the delay-induced dynamics drastically. We report on pinned localized solutions, oscillating solutions and depinning due to timedelayed feedback. The competition of a pinning inhomogeneity and a destabilizing time-delayed feedback is studied both analytically and numerically.
Felix Tabbert, AG Thiele, Institut für Theoretische Physik

Einladender: Dr. O. Kamps

All Termine WS 2016/17

Das CeNoS

Das Center for Nonlinear Science (CeNoS) ist eine zentrale wissenschaftliche Einrichtung der Westfälischen Wilhelms-Universität Münster und besteht aus den beteiligten Arbeitsgruppen die im Moment sechs verschiedenen Fachbereichen angehören. Mitglied kann jede an der Thematik interessierte Arbeitsgruppe oder jede/r interessierte Wissenschafter/in der Universität Münster werden.Das CeNoS versteht sich als Dach für die grundlagenorientierte Forschung und Lehre an Fragestellungen zu nichtlinearen Systemen sowie für Anwendungen der Ergebnisse in verschiedenen Gebieten. Darüber hinaus dient es als Forum des interdisziplinären Dialogs zwischen Wissenschaftlern und Wissenschaftlerinnen verschiedener wissenschaftlicher Fachdisziplinen.