Holographic Grating Dynamics In Phenanthrenequinone Doped Poly(Methyl Methacrylate) Polymer

The optical holographic storage is a promising candidate for next generation information storage due to its high storage capacity, high transfer speed, and storage density. For long-term development the holographic storage technology is closed to actual application by compact storage systems and storage materials with low cost. Among storage materials, phenanthrenequinone doped poly-(methyl methacrylate) (PQ-PMMA) photopolymer material is also a candidate for holographic technology due to their excellent ability to form thick medium that exhibit high diffraction efficiency, low cost. However its application for memory is limited by the poor response and high holographic scattering of sample. So far, the photochemical dynamics of the material is not investigated in detailed, despite the experiments focusing on the improvement of the materials are achieved. The improvement of holographic performance by means of analyzing the photochemical process have not much attention. In this thesis, the photochemical reaction diffusion model for PQ-PMMA photopolymer is established, and the formation and evolution dynamics of holographic volume gratings are investigated theoretically and experimentally. This investigation can improve the understanding of photochemical processes and accelerate applicability of the photopolymer, and it is also provided the crucial theoretical and experimental foundation for characterizing the holographic performance of materials.There are several dynamics processes in the grating formation in PQ-PMMA photopolymer, such as dark enhancement of grating after short recording exposure, grating evolution under consecutive exposure, and long-term decaying process of holographic gratings after reaching steady state. By analyzing the corresponding photochemical processes, this thesis advances kinetic diffusion model which is suitable for the photopolymer based on the nonlocal effect and describes the dynamics processes of grating formation experimentally. It is provided a new method from microcosmic reactions to macrographic phenomenon for studying photochemical processes and improving the performances of the materials.The determination of kinetics parameters is significant for describing the photochemical reaction. Two basic kinetics parameters, quantum yield and molar absorption coefficient, are determined by holographic scattering method in the photopolymer. The parameters values are then improved by introducing photobleaching dye process. The dark enhancement dynamics after short exposure are described by the diffusion model. The dependences of PQ's concentration on the rate and increment of the enhancement are achieved, and the dependences of exposure energy on dark enhancement are obtained quantitatively. It is implied that the enhancement can amplify the diffraction efficiency and improve the photosensitive performance.The dark enhancements in multiplexing gratings are observed for the first time. This process is presented as a simple and efficient method to improve response region of the material, bring it into linear region, and further improve the effective storage capacity. Due to the increment differences between strong and weak gratings we can utilize the method to improve the homogeneity of diffraction efficiency only using constant exposure and avoid using complex schedule exposure.In the grating formation under consecutive exposure, the complex photochemical reactions are simultaneously introduced into nonlocal diffusion model. The dynamics of grating formation are described by analytic expressions and nonlocal diffusion model and the one to one attachment process is determined as a primary photochemical reaction. Finally an extended model based on diffusion model is derived by introducing shrinkage for describing photopolymerization dynamics in the photopolymer.After reaching steady state, the influence of environment factors, especially temperature, on the long-term decay dynamics of holographic gratings are analyzed. The diffusion of photoproduct macromolecules is a significant factor bring about the decaying. The quantitative dependence of the diffusion and temperatures is determined and the storage lifetime of holograms is estimated nearly to one year. The uniform incoherent illumination is a effective method for improving the stability. Finally low temperature and uniform incoherent illumination as alternative optimal methods are proposed to optimize the storage stability.