Driven nonlinear cavities
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Dr. Thorsten Ackemann
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Collaboration with: Prof. Dr. G. L.
Lippi (lippi@inln.cnrs.fr), Institut Non Linéaire de
Nice, France
- Former group members: Dr. Andreas Gahl, Dr. L.M. Hoffer, Dr. Michael Möller, Dr. Jürgen Nalik, Dipl.-Phys. Christoph Vorgerd
The group performed experiments on the transverse mode structure of
sodium-filled confocal or close to confocal resonators. The resonator was
driven by a smooth rotationally symmetric Gaussian beam whose beam parameters
did not necessarily coincide with the beam parameters of the fundamental
mode of the cavity. The effective Fresnel number was of the order 1 to
3. We observed
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excitation of (superpositions of) high order modes of the cavity, often
accompanied by symmetry breaking,
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switching and bistability between different spatial field distributions
(transverse optical bistability),
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the spontaneous appearance of optical vortices.
An interpretation was given based on the creation of a self-induced lens
in the vapor by the inhomogeneous pump beam. By a Galerkin method a simple
model based on ordinary differential equations is derived for the focal
power of this lens which reproduces qualitatively the observed behavior.
The observed vortices are indicators of the symmetry breaking. Nevertheless
they do not have solitonic character, but are simply the nodes of the nonlinearly
generated mode superpositions. Features of pattern formation in stable
nonlinear resonators which originate from basic symmetries and which are
independent of the details of the nonlinearity are discussed by Möller
and Gahl. The analysis reveals
basic differences between ring and Fabry-Pérot cavities which are
due to a kind of selection rules for transverse mode excitation.
 List of publications
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