| With the advent of the era of big data,the amount of information is growing exponentially,which poses a severe challenge and huge resource consumption to the traditional disk array storage,and it is difficult to meet the storage demand for a large amount of data.In recent years,with the increasing improvement of holographic storage technology,holographic storage has broken through the traditional two-dimensional storage paradigm of optical disk and disk storage,and adopted three-dimensional volume holographic storage mode,so the storage density has been improved in many dimensions.The advantages of large capacity and high reliability of optical holographic storage meet the requirements of the information age.The research and development of high-performance optical storage materials has become one of the bottlenecks in the wide application of holographic storage technology.Photopolymer storage materials have the advantages of simple fabrication,low cost and high resolution,so they become the best candidate materials for holographic storage and recording.Phenanthraquinone doped poly(methyl methacrylate)(PQ/PMMA)photopolymer has attracted much attention due to its excellent optical properties,negligible shrinkage,controllable thickness and long-term storage.However,the low diffraction efficiency and refractive index modulation of PQ/PMMA materials have become the key issues for their commercial application.So far,many researchers have improved the diffraction efficiency of PQ/PMMA photopolymer materials via changing the photo-initiator or introducing a composite substrate to enhance the solubility of the photo-initiator in MMA monomers.The addition of other substances in PQ/PMMA photopolymer materials,however,usually induce structural stability issues here.In this paper,while maintaining the original composition ratio of the material,starting from the thermal polymerization process,the optical properties of the material are significantly improved by adjusting the polymerization time and temperature during the thermal polymerization process.In addition,the molecular weight is also used to characterize the degree of polymerization of the material,and combined with the test of the optical properties of the material to determine the main optical products that cause the change in the refractive index modulation of the material,the specific research content of this paper is as follows:(1)The thermal polymerization process is divided into two major stages,namely the pre-polymerization and the baking polymerization.The holographic properties of the material are tested and analyzed by changing the polymerization time and temperature of the different stages,and it is found that the holographic performance of the photopolymer PQ/PMMA largely depends on the pre-polymerization adjustment and baking polymerization adjustment.When the pre-polymerization time and temperature are 75 min and 60?,and the baking time and temperature are 20 h and 60?respectively,the diffraction efficiency and refractive index modulation of the material are the best,which are?50%and?1×10-4,respectively,which provides an effective guide for preparing a large number of PQ/PMMA photopolymer materials with excellent optical properties.(2)Through the detailed analysis of the photopolymerization reaction mechanism of PQ/PMMA materials,it is known that the main factors that cause the change of the refractive index modulation of the material are not only the photo-initiator phenanthrenequinone,but also the concentration of the final photoproducts PQ/PMMA and PQ/MMA.In order to judge the main photoproduct,this paper introduces a means to characterize the degree of polymerization of materials,measuring the molecular weight of PQ/PMMA with different pre-polymerization time and baking time,and combining the change trend of the maximum diffraction efficiency,it is found that the change in molecular weight is positively correlated with the change in maximum diffraction efficiency,thus verifying that the main photoproduct causing the change in refractive index modulation is PQ/PMMA. |
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