Control of optical nano-structure of azo-benzene polymers and its application to diffractive optics

采用激光干涉图样辐照的方法制备表面浮雕全息图。衍射效率和表面浮雕深度取决于写入能量和写入激光束的偏振度。该结构在玻璃化转变温度T_g下非常稳定。我们提出了一种控制地表起伏结构的新技术。在电晕沉积极化装置中，电荷沉积在表面浮雕光栅上。电晕放电前后的一级衍射效率由0.24%左右提高到28%左右。这种衍射效率的提高主要是由于电荷引起的浮雕深度的增加。通过电晕充电，使浮雕深度由20 nm增加到350 nm。采用基于移动粒子半隐式（MPS）方法的计算模型，模拟了偶氮苯聚合物上光致表面起伏光栅（srg）的形成和擦除过程。对于对流计算，提出了一种各向异性扩散模型。电场梯度力和表面张力的影响被认为是光致质量输运的驱动力。在我们的模型中，聚合物薄膜的粘度随光强的变化而变化。计算了SRG形成和擦除过程中的粒子运动，研究了SRG生长和擦除速率对SRG节距和极化的依赖关系。这些理论结果与我们的实验结果在质量上是一致的。

Surface relief holograms are fabricated by means of irradiation of laser interference patterns. The diffraction efficiency and the surface relief depth depend on the writing energy and the polarization of the writing laser beam. This structure is very stable at temperatures under glass transition temperature T_g. We proposed a new technique to control the surface relief structure. The electric charge was deposited on the surface relief grating in a corona-depositing poling setup in an oven. The first-order diffraction efficiency measured before and after corona discharge increased from about 0.24 % to about 28 %. This diffraction efficiency increase is mainly caused by the increase of the relief depth caused by the electric charge. The relief depth is increased from 20 nm to 350 nm by corona charging.The formation and erasure of photoinduced surface relief gratings (SRGs) on azobenzene-containing polymers are simulated using a calculation model based on the moving-particle semi-implicit (MPS) method. For the convection calculation, an anisotropic diffusion model is proposed. The gradient force of the optical electric field and the influence of surface tension are considered as driving forces for photoinduced mass transport. The viscosity of polymer films changes with the light intensity in our model. Particle motions in SRG formation and erasure are calculated and the SRG pitch and polarization dependences of the SRG growing and erasing rates are investigated. These theoretical results coincide qualitatively with our experimental results.