Malallah Ra'ed, Li Haoyu, Qi Yue, Cassidy Derek, Muniraj Inbarasan, Al-Attar Nebras, Sheridan John T
J Opt Soc Am A Opt Image Sci Vis. 2019 Mar 1;36(3):320-333. doi: 10.1364/JOSAA.36.000320.
An experimental and theoretical investigation of the preparation and exposure of multilayer photosensitive materials is presented. It is shown how the recorded change in the refractive index in each layer depends on the dye (photosensitizer) concentrations in each layer. It is also shown how the photosensitive material properties in each layer can be controlled to optimize some recording characteristics for particular applications. To do so, a set of equations, predicting the amplitude of higher harmonics refractive index amplitudes induced in the material layers with depth during exposure, is derived. This results in a technique for varying the dye concentration in each layer of a multilayer, so as to optimize volume diffraction grating performance. In part I of this paper, the 3D nonlocal photopolymerization-driven diffusion (NPDD) model is applied to calculate the resulting combined multilayer absorption and polymerization processes. The NPDD describes the time-varying behaviors taking place during exposure in such photopolymer materials. Simulations are performed for an acrylamide/polyvinyl alcohol-based photopolymer containing erythrosine-B dye. It is predicted that, in general, non-uniform gratings are formed, with the resulting refractive index being distorted both from the ideal sinusoidal cross-sectional spatial distribution and also with depth. This agrees with previous results indicating that increasing the thickness of a single photopolymer layer does not in practice lead to ever-increasing angular selectivity. In part II of this paper, it is confirmed experimentally that a suitably modified multilayer can be used to increase grating angular selectivity, i.e., reduce the width of the off-Bragg replay curve.
本文介绍了对多层光敏材料的制备和曝光进行的实验和理论研究。研究表明了每层中记录的折射率变化如何取决于每层中的染料（光敏剂）浓度。还展示了如何控制每层中的光敏材料特性，以优化特定应用的某些记录特性。为此，推导了一组方程，用于预测曝光期间材料层中随深度诱导的高次谐波折射率幅度。这产生了一种改变多层中每层染料浓度的技术，以优化体衍射光栅性能。在本文的第一部分，应用三维非局部光聚合驱动扩散（NPDD）模型来计算由此产生的多层吸收和聚合过程的组合。NPDD描述了此类光聚合物材料曝光期间发生的随时间变化的行为。对含有赤藓红-B染料的基于丙烯酰胺/聚乙烯醇的光聚合物进行了模拟。预测通常会形成非均匀光栅，其产生的折射率在理想正弦横截面空间分布以及深度方面都会发生扭曲。这与先前的结果一致，即增加单个光聚合物层厚度在实际中并不会导致角度选择性不断增加。在本文的第二部分，通过实验证实，适当改性的多层可用于提高光栅角度选择性，即减小非布拉格重放曲线的宽度。
