RESIDORI , Stefania

The basic mechanisms of optical pattern formation are reviewed, with particular reference to a system based on a Liquid-Crystal-Light-Valve with optical feedback. The system is described in different configurations, corresponding to the experiments that have led to the most fascinating observations, such as the optical crystals and...

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We show that under laser and white light action, reorientation of the nematic director for azo-dye doped liquid crystals follows a three-dimensional trajectory, composed by in and out-of-plane motion with respect to the incidence plane of the light. We relate the two components to the surface and bulk effects, respectively, and we show that the...

We show that a very large optical response is obtained in azo-dyedoped nematic liquid crystals for low input light intensities (of the order of a few tens of µW/cm2 and that this extreme sensitivity of the nematic film results from a combined action of the photoisomerization process of the azo-dye molecules and the light-induced changes of the...

We show experimentally that large matrixes of localized structures can be stored as elementary pixels in a nematic liquid crystal cell. Based on optical feedback with phase modulated input beam, our system allows to store, erase and actualize the localized structures in the matrix.

We show theoretically that thermomechanical effects in dye-doped nematic liquid crystals when illuminated by laser beams, can become important and lead to molecular reorientation at intensities substantially lower than that needed for optical Fréedericksz transition. We propose a 1D model that assumes homogenous intensity distribution in the...

Experimental evidence of bouncing localized structures in a nonlinear optical system is reported.

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We study the Faraday instability in an elongated rectangular cell and for a range of the forcing frequency for which two nearly degenerate modes enter in competition. We investigate the stability properties of the two modes and we show that they can either coexist in a bistable way or give rise to a mixed mode. We develop a simple model based...

In a disordered medium with Kerr-type nonlinearity, the transmitted speckle pattern was predicted to become unstable, as a result of the positive feedback between the intensity fluctuations and the nonlinear dependence of the local refractive index. We present the first experimental evidence of speckle instability of light transversally...

In a nonlinear optical experiment we report a unique class of localized structures, which appears as localized peaks of a pattern nucleating over another pattern. We show that this occurs when the system is driven through three pattern branches of solutions, accompanied by the appearance of localized peaks with two different amplitudes....

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When bistability and diffraction are simultaneously present, a Liquid-Crystal-Light-Valve with optical feedback shows the appearance of localised structures. We report here new features of their dynamics, such as their appearance on successive and concentric rings and their motion along the rings. Radial and azimuthal dynamics are presented and...

International audience

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We show that the Talbot effect can be used to increase the gaib of two-wave mixing in a stack of this nonlinear media. We demonstrate that a large gain enhancement is achieved for a new nonlinear elements, provided that they are placed at distances that satisfy Talbot recurrences.

We show that the Talbot effect can be used to increase the gaib of two-wave mixing in a stack of this nonlinear media. We demonstrate that a large gain enhancement is achieved for a new nonlinear elements, provided that they are placed at distances that satisfy Talbot recurrences.

International audience

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International audience

We present an experimental method for measuring the nonlinear optical response of a dye-doped liquid crystal cell. We show that a very large response is obtained for a very low input light intensity. The nonlinear optical response as a function of the dye concentration in the liquid crystal host is characterized by the optical nonlinear...

e report new advancements in the experimental investigation of the giant optical nonlinearity observed in azo-dye doped nematic liquid crystals. We show that the extreme sensitivity of the azo-dye doped nematics results from a combined action of the trans-cis photoisomerization process of the azo-dye molecules and the light-induced changes of...

In this article we review the conditions for the appearance of localized states in a nonlinear optical system, with particular reference to the liquid crystal light valve (LCLV) experiment. The localized structures here described are of dissipative type; that is, they represent the localized solutions of a pattern-forming system. We discuss...

In a photorefractive liquid crystal light valve, acting as a Kerr-like nonlinear optical medium, we show the appearance of optical patterns induced by a single mirror feedback. The spatial wavelength of the patterns scales with the distance between the mirror and the valve and the contrast of the patterns decreases for decreasing this distance....

We report a new type of drop instability, where the density difference between the drop and the solvent is negative. We show that the drop falls inside the solvent down to a minimum height, then fragmentation takes place and secondary droplets rise up to the surface. We have developed a theoretical model that captures the essential of the...