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Self-organized surface relief gratings in azo-polymer thin-films

Abstract : Nature is a beautiful combination of patterns. Natural patterns are self-organized. Well defined self-organized patterns also can appear in laboratory conditions for different systems. In this thesis we present pattern formation via self-organization of azo molecules under light illumination. Illuminated azo molecules undergo a trans-cis-trans photoisomerization and diffuse in the polymer film far from brightness. We show that it is possible to form spontaneous patterns on the surface of azo-polymer films under coherent light exposure. The pattern orientation depends on light polarization and polarization multiplexing for more than two states is possible. The experimental results for different incidence angle are fitted by a simple theoretical model based on stimulated Wood's anomalies. Various patterns were inscribed by varying input beam polarization and incidence angle. Under incoherent beam illumination, diffusion of azo-molecules is random (no correlation between them) and it is impossible to create a well defined pattern. Presence of an additional low power coherent beam causes pattern formation. Information about formed pattern in the coherent region, propagate in a self-organized manner and cover whole region of incoherent beam. Only a few percent of informed molecules is enough for self-organization. In addition, we also studied light induced birefringence and surface relief grating formation in a series of azo-polymers. Some possible applications of these patterns are presented.
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https://tel.archives-ouvertes.fr/tel-00592269
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Submitted on : Wednesday, May 11, 2011 - 6:41:37 PM
Last modification on : Wednesday, October 20, 2021 - 3:18:53 AM
Long-term archiving on: : Friday, August 12, 2011 - 2:55:07 AM

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  • HAL Id : tel-00592269, version 1

Citation

Sohrab Ahmadi-Kandjani. Self-organized surface relief gratings in azo-polymer thin-films. Atomic Physics [physics.atom-ph]. Université d'Angers, 2007. English. ⟨tel-00592269⟩

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