| Optimum recording materials play an important role in optical volume holographic storage technology. It is generally believed that photopolymer is a potential recording material because of its high sensitivity, high signal-to-noise ratio and cheap manufacturing cost, and great breakthroughs might be made firstly in this kind of materials, in which PMMA(PQ) photopolymer draws extensive attention because of its low exposure shrinkage and large thickness. But it also has the weakness of low diffusion coefficient. Long-term diffusion is negative for stored holograms, so this is one of the main obstacles for its application. The reaction process in material after exposure and the diffusion under different conditions of exposure and placing time are important for understanding the influence of diffusion on volume holographic storage.By analyzing the photochemical process of PMMA(PQ) photopolymer materials in detail, we present a non-local diffusion model in this thesis. FDTD method was applied to solve the diffusion equations and the dynamic process of grating formation in PMMA(PQ) materials was simulated numerically, and the time evolution of grating profile and refractive index is presented.The permanent storage experiment was carried out to study the negative effect of diffusion of PQ molecule on the quality of volume holographic recording. The diffusion coefficient of PQ molecule was obtained numerically, whose magnitude is in the order of 10 ?2 1 m 2s. To keep the long-term stability of the recorded holograms, the uniform incoherent light was used to illuminate the samples after exposure. This method can overcome the disadvantageous influence of diffusion on the quality of the recorded images effectively.The exposure schedule was deduced from the non-local diffusion model in photopolymer. By using this exposure schedule, 30 holograms were recorded in one point and the uniformity of their diffraction efficiency is much better than that in isochronous exposure scheme.
|
PDF Full Text Request