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Dynamique de la polarisation tout-optique de molécules organiques présentant un photochromisme rapide en phase polymérisée

Abstract : We present a theoretical and experimental investigation of the all–optical poling orientation process in order to obtain the full control of the molecular patterning. It is demonstrated that the coherent superposition of two beams at fundamental and second harmonic frequencies results in the breaking of the centrosymmetry in the medium, permitting to induce a polar orientation of photochromic molecules. For an efficient poling of thin films, the relative phases, amplitudes and polarizations of the two interfering beams must be controlled. We present an original stable one–arm interferometer, which is specific to the recording of two–colour interferences. It permits to induce a periodic nonlinear pattern owing to the index dispersion of glass. This particular interference technique permits true real–time non–perturbative monitoring of the polar orientation process and an easy all–optical poling of thin film materials without need for phase control. This opens the door to the realization of customized phase–matched wave–guided frequency conversion devices for the near infrared. This new technique was applied to several new dye–polymer systems. We also observed the formation of a surface relief grating (SRG) in amorphous polymer films containing azodye molecules in side chain positions using the all–optical poling method. The experiment consists in a seeding–type process. The particular configuration with the prism permits to observe the photoinduced translation diffusion of the azo–chromophores, which is at the origin of the SRG formation. We analysed the gratings recorded using s (TE) and p (TM) polarisations of the writing beams. The whole effect is attributed to the mass transport from regions of high isomerisation activity to the ones of lower activity. We also apply the technique of all–optical poling as a method permitting improvement of the efficiency of organic photovoltaic cells.
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  • HAL Id : tel-00110790, version 1

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Aleksandra Apostoluk. Dynamique de la polarisation tout-optique de molécules organiques présentant un photochromisme rapide en phase polymérisée. Science des matériaux [cond-mat.mtrl-sci]. Université d'Angers, 2003. Français. ⟨tel-00110790⟩

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