Evolution of Laser Thermal Written Diffraction Gratings in Liquid-crystal Polymer Films

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Abstract
Laser writing of diffraction gratings in a liquid-crystal polymer film are studied where the optical changes take place owing to laser heating of the material above the glass transition temperature. The peak diffraction achieved is small (much less than 1%), but the evolution of the diffraction efficiency is well reproduced by theory, and it is seen that the low values obtained are due to thermal diffusion. It is shown that writing on the film with high powers or using a pulsed laser could lead to larger efficiencies.