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1.4 CHEMICAL SCIENCES
Photopolymers have been the subject of special attention in the last two decades. The advantage of being self-developing makes them a practical alternative to silver halide photographic emulsions in holographic interferometry applications. This thesis is aimed at understanding diffusion properties and optimization of an acrylamide-based green sensitized photopolymer material for reflection holographic recording. The composition of the photopolymer includes a green sensitive dye (erythrosine B), acrylamide (monomer), electron donor (triethanolamine) a cross linking monomer (NN’methylenebisacrylamide) and a binder (polyvinyl alcohol). On illumination with light of the appropriate wavelength the dye absorbs a photon and enters into an excited state. The excited triplet state of the dye reacts with an electron donor and generates a free radical. This free radical in the presence of monomer initiates the local polymerization of the monomer. Non-uniform local polymerization arising from illumination by two interfering light beams results in the monomer concentration gradient. This concentration gradient results in the diffusion of monomer from the unexposed regions to the exposed regions replacing the consumed monomer in the exposed regions. As a result of the changes in the density and molecular polarizability which accompany polymerization the refractive index changes in the exposed and unexposed regions. This results in a volume phase grating. In this thesis a detailed characterization of the material and the processes that contribute to the refractive index modulation is reported. The influence of different parameters on diffusion and polymerization processes is also reported. From the results, the diffusion constant for acrylamide in the photopolymer composition is calculated. Raman spectroscopy is used to study the polymerization rate in this acrylamide-based photopolymer and the polymerization rates of acrylamide and bisacrylamide are calculated. Investigations on the suitability of this material for holographic data storage applications are carried out. The results prove that the material is capable of recording reflection holographic gratings. The spatial frequency response of the material is studied and the material is optimized for high spatial frequency holographic grating recording. Demonstration of the suitability of this acrylamide-based photopolymer recording material for reflection holography is presented.
Jallapuram, Raghavendra. (2005). Optimization of an acrylamides-based photopolymer for reflection holographic recording. Doctoral thesis. Technological University Dublin. doi:10.21427/D75C8K