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20 August 2009 Rewritable Bragg holograms of azobenzene polymers with fast response
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Amorphous copolymers were synthesized with azobenzene methacrylate, cyanobiphenyl methacrylate, and alkyl methacrylate, in which the azobenzene acts as a photoresponsive part to undergo photoisomerization, the cyanobiphenyl is involved in a change in refractive index triggered by the photoisomerization of the azobenzene, and the alkyl methacrylate is to prevent light scattering, respectively. The obtained polymers showed no LC phase in spite of the incorporation of the common mesogenic group. When two writing beams were interfered in the thick polymer films, the diffraction of the probe beam was observed. The first-order diffraction efficiency reached more than 70 % within 500 ms. On the other hand, the intensity of the zeroth-order beam decreased in proportion to the increase in that of the first-order diffracted beam. It is clear that the intensity of the zeroth-order beam is transferred to that of the first-order diffraction with no optical loss due to the formation of the Bragg gratings. When the writing beams were turned off, the diffraction efficiency remained unchanged. When the recorded grating was kept in the dark at room temperature, sufficient diffraction efficiency was generally retained after a year. However, the grating was easily erased when heated up above Tg for several seconds, and rewritability was confirmed more than 100 cycles. No shrinkage was observed through those processes.
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Atsushi Shishido, Hyo-Bok Cha, and Tomiki Ikeda "Rewritable Bragg holograms of azobenzene polymers with fast response", Proc. SPIE 7414, Liquid Crystals XIII, 74140S (20 August 2009);

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