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G Demeter

Publications and source records attributed to G Demeter.

6 recordsLinked to original sources
PubMed2005

Numerical study of optically induced director oscillations in nematic liquid crystals: transition to chaos via homoclinic gluings and the role of backflow.

We investigate the director oscillations of a homeotropically aligned nematic liquid crystal that are generated by cw laser radiation incident at a slightly oblique angle. The full nematodynamic equations are solved numerically, and it is shown that the inclusion of backflow leads to a qualitative change of the theoretical bifurcation scenario at moderate to high intensities. Very good correspondence is achieved with recent observations. The route to chaos via a sequence of homoclinic gluing bifurcations, whose existence was suggested by simple models, but doubted by recent calculations and experiments, is shown to exist in a parameter region unexplored by experiments.

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PubMed2005

Influence of the backflow effect on the orientational dynamics induced by light in nematics.

We investigate the dynamical phenomena induced by a circularly polarized plane wave incident perpendicularly on a homeotropically aligned nematic layer. We study theoretically the influence of the velocity field (backflow effect) on the bifurcation scenario. Whereas backflow leads to substantial quantitative changes of secondary bifurcation thresholds, the overall bifurcation scenario remains unchanged. In the regime of uniform precession of the director with large reorientation, an unanticipated spatial oscillation of the flow field across the layer is found. Quantitative comparison with experimental large-aspect ratio systems is now possible.

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PubMed2002

Pattern-forming instability induced by light in pure and dye-doped nematic liquid crystals.

We study theoretically the instabilities induced by a linearly polarized ordinary light wave incident at a small oblique angle on a thin layer of homeotropically oriented nematic liquid crystal with special emphasis on the dye-doped case. The spatially periodic Hopf bifurcation that occurs as the secondary instability after the stationary Freedericksz transition is analyzed.

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PubMed2001

Numerical investigation of optically induced director oscillations in nematic liquid crystals.

We present a theoretical study of the effects induced by the passage of a linearly polarized light beam through a thin cell of homeotropic nematic liquid crystal. The light is incident at a slightly oblique angle and is polarized perpendicular to the plane of incidence. Experiments in this geometry have revealed a rich variety of complex, time dependent director motion. We solve numerically the director equations for the nematic and compare the results with existing experimental findings.

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PubMed2000

Complex nonlinear behavior in optically excited nematic liquid crystals.

We present a study of the passage of a monochromatic, linearly polarized cw laser beam through a cell of homeotropically aligned nematic liquid crystal at a slightly oblique angle. The light is polarized perpendicular to the plane of incidence. Experiments in this geometry have revealed the existence of complex, time-dependent dynamics of the director motion. We present a model for the director dynamics derived from the basic equations that shows both periodic and chaotic behavior at different light intensities as observed in the experiments. The model we derive exhibits a variety of complex behaviors, among them an uncommon route to chaos via gluing bifurcations that has not yet been observed in any real physical system.

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