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理想的存储材料一直是体全息技术发展的关键。光致聚合物材料具有高灵敏度,高信噪比和制造成本低廉等诸多优点,是高密度全息存储最有希望首先获得突破的材料。PQ-PMMA 光聚物以其较低的曝光收缩性和较大的厚度受到了人们的广泛关注,但是人们对其光致聚合机理和全息性能的认识并不充分.分析了材料曝光后内部的光反应过程以及扩散作用对信息的永久存储造成的影响,通过光反应过程建立了适合此类材料的扩散方程.在曝光条件下,PQ 分子吸收光子,形成自由基,然后该自由基引发 MMA 单体形成活性自由基。PQ 分子与 MMA 分子的一对一加成是主要的反应,同时可能有少量的低聚物产生,这是由PQ 引发 MMA 发生的链式反应引起的。通过分析光反应速率,得到了 PQ 的扩散方程,并将其推广为描述自由单体扩散的一维非局域方程。对该方程进行数值求解较好地描述了光栅的建立过程,通过优化方法得到了材料的主要性能参数如聚合速率,扩散速率和有效链长度等。利用上述方法,得到 PQ 分子扩散系数的数量级为10~(-21)m~2/s,与相关文献的报道一致。由于 PQ 分子在常温下的扩散系数较小,曝光结束后随着放置时间的增长,PQ 分子的扩散作用将导致材料的光栅轮廓变模糊,折射率调制度下降。采用过曝光方法能够很好地保持存储图像的长期稳定性.在实时探测过程中,首次在光致聚合物中观察到动态自增强效应.光折变材料的动态自增强效应是由于两记录光在材料内部形成光栅,然后挡住其中一束用另一束记录光进行读出。读出的衍射光会发生增强现象.这是由于读出光与其自身的衍射光发生干涉形成的光栅加强了原光栅,使衍射增强。在文中的光致聚合物中,光栅形成机制不同于光折变材料,因此衍射效率自增强也有所不同.当两束记录光进行光栅记录的同时,由于材料的收缩效应使原光栅与光强光栅间产生偏移,相干光会继续消耗单体记录新的光栅,这使得衍射效率曲线先上升达到最大值后下降,并再次出现上升和下降过程,并最终趋于稳态。文中考虑材料在光反应过程中的收缩,利用多光栅叠加的原理对上述实验现象进行了解释。
The ideal storage material has been the key to the development of volume holography. Photopolymer materials with high sensitivity, high signal to noise ratio and low manufacturing costs and many other advantages, is the most promising high-density holographic storage material first breakthrough. PQ-PMMA photopolymer has drawn much attention due to its lower exposure shrinkage and larger thickness, but its photopolymerization mechanism and holographic properties are not fully understood.Analysis of the internal Photoreaction process and diffusion effect on the permanent storage of information, a diffusion equation suitable for such materials is established through photoreaction process. Under exposure conditions, PQ molecules absorb photons to form free radicals, and then the free radicals initiate MMA single Body forms active free radicals. The one-to-one addition of PQ molecules to MMA molecules is the main reaction with the possible presence of a small amount of oligomers as a result of the chain reaction of PQ-initiated MMA. By analyzing the photoreaction rate, we obtain the diffusion equation of PQ and generalize it as a one-dimensional nonlocal equation describing the diffusion of free monomer. The numerical solution of the equation well describes the process of grating establishment, and obtains the main performance parameters of the material such as polymerization rate, diffusion rate and effective chain length through the optimization method. Using the above method, the order of magnitude of PQ diffusion coefficient was found to be 10 ~ (-21) m ~ 2 / s, which is consistent with the reports of related literatures. Due to the small diffusion coefficient of PQ molecules at room temperature, the diffusion of PQ molecules will cause the grating profile of the material to be blurred and the refractive index modulation to decrease as the exposure time is increased. The overexposure method can well preserve the long-term stability of stored images.Firstly, dynamic self-enhancement effect is observed in photopolymers during real-time detection.The dynamic self-enhancement effect of photorefractive materials is due to the two recording light A grating is formed inside the material, and one of the beams is blocked by reading the other beam of recording light. The read diffracted light is intensified, which is due to the interference of the read light with its own diffracted light, which intensifies the original grating and enhances the diffraction. In the photopolymer herein, the grating formation mechanism is different from the photorefractive material, so the diffraction efficiency self-enhancement is also different.While two beams of recording light raster recording at the same time, due to the material shrinkage effect of the original grating and light intensity The shift between the gratings will cause the coherent light to continue to consume a single record of a new grating. This will cause the diffraction efficiency curve to rise first and then decrease and then rise and fall again and eventually become steady. In this paper, the material shrinkage during the photoreaction process is considered, and the above experimental phenomena are explained by the principle of multi-grating superposition.