Abstract:A novel approach for measuring the diffusion coefficients in photopolymerisable materials is proposed. The method is based on studying the evolution of the surface relief profile in a single illuminated spot using an interferometric surface profiler. It is shown that the observed postexposure swelling in the illuminated spot is due to mass-transport of monomer from the unexposed to the exposed area driven by a monomer concentration gradient set up by the monomer polymerization in the exposed area. Appropriate choice of the thickness of the studied layers ensures both lateral movement of monomer and negligible contribution from the depth. The diffusion coefficient is retrieved from the standard onedimensional diffusion equation where the height of the profile in the center of the illuminated spot is used instead of the monomer concentration. In contrast to other techniques for measuring the diffusion in photopolymerisable materials, no assumptions or preliminary information about the polymerization rates are required. It is shown how the method can be used for studying the intensity and polymer density dependence of diffusion coefficient.

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The optical properties of photopolymer layers consisting of an acrylamide-based matrix and microporous aluminophosphate nanocrystals of AEI-type are investigated. The compatibility of the photopolymer doped with the nanoparticles is studied. The surface and volume properties of the layers with different levels of doping with microporous nanocrystals are characterized. The effective refractive indices and absorption coefficients of the doped photopolymer layers are determined and used to calculate the refractive index and porosity of pure AEI nanoparticles used as dopants. Volume transmission gratings were recorded in the doped photopolymer layers at different spatial frequencies.By spatial monitoring of the characteristic Raman peak of the AEI particles across the grating vector, the optimal concentrations of the nanocrystals for obtaining highest light induced redistribution of nanocrystals are determined. The optical properties of the photopolymer layers combined with the redistribution of the AEI nanoparticles during holographic recording are the parameters exploited for fabrication of optical sensors. An irreversible humidity sensor based on a transmission holographic grating is designed and fabricated. The diffraction efficiency of the sensor changes permanently after exposure to high humidity.