4 May 2012 Self-trapping waveguiding structures in nonlinear photorefractive media based on Plexiglas with phenanthrenequinone molecules
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The paper presents theoretical and experimental investigations of light beam self-trapping in a photorefractive medium based on Plexiglas (polymethylmethacrylate, PMMA) with photosensitive phenanthrenequinone (PQ)- molecules. It is shown that the self-trapping of a laser beam is generated due to the self-interaction of the propagating light wave under the conditions of a well balanced concurrence of the effects of light diffraction and nonlinear focusing. A new method for controlling the waveguide cross-section by changing the ratio of two competing mechanisms of the nonlinear refractive-index variation (namely the formation of the photoproducts and the heating of the medium while varying the power of the light beam) is proposed. The recording of self-trapping structures implemented in PQ-PMMA layers has been realized with two laser sources (405 nm and 514.5 nm) with an average power of several mW. It is shown that the photoattachment of the PQ-molecules to the polymeric chains and the formation of the photoproduct play the decisive role for the light-induced increase of the refractive index. Besides, the formation of the waveguide is strongly influenced by heating of the medium, which results in an additional thermal defocusing of the light beam. It has been established that the parameters of the waveguide (cross-section and length) are strongly dependent on the wavelength and the power of the laser radiation, as well as on the concentration of the PQ-molecules. Waveguiding structures with a diameter of 100 μm were recorded in samples with a high PQ-concentration (up to 4 mol.%) for the wavelength of 514.5 nm. Reducing the dye-concentration by one order requires shorter (blue) wavelengths (405 nm). The dependence of the waveguide parameters and the optimal laser wavelength on the concentration of PQ-molecules is confirmed by the numerical calculation including a 3D-model of the light self-trapping.
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Elen Tolstik, Elen Tolstik, Oleg Romanov, Oleg Romanov, Vladislav Y. Matusevich, Vladislav Y. Matusevich, Alexei L. Tolstik, Alexei L. Tolstik, Richard M. Kowarschik, Richard M. Kowarschik, } "Self-trapping waveguiding structures in nonlinear photorefractive media based on Plexiglas with phenanthrenequinone molecules", Proc. SPIE 8429, Optical Modelling and Design II, 84290W (4 May 2012); doi: 10.1117/12.922741; https://doi.org/10.1117/12.922741

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