Analysis and control of heat transfer in laser induced thermal poling process of polymer thin film

本文主要研究了激光诱导热极化聚合物非线性光学薄膜波导图形化工艺的发展和优化。在本研究中，我们主要进行了以下几个方面的工作：1）非线性光学聚合物薄膜热扩散率的测量。为了测量非线性光学聚合物薄膜的热扩散率，我们对光声法的实验装置进行了改进。合成了具有DR 1生色团侧基的PMMA作为NLO聚合物。结果表明，热扩散系数与薄膜厚度和色母粒含量无关，但随外加电场的增大而增大。此外，NLO聚合物薄膜的热扩散率随温度降低。我们的仪器没有能力在高温下测量，超过玻璃化转变温度（约380 K），这会产生突变。 ...更多信息 热扩散率的变化，需要开发另一种方法来测量高温下的热扩散率。2）激光诱导热极化过程的数值模拟我们构建了三维模拟代码来估计热极化过程中NW聚合物薄膜的温度分布。为了阐明均匀偏振分布的优化条件，我们引入了偶极（在非线性光学分子）的取向动力学的温度依赖性，我们的模拟代码。由于没有偶极取向动力学的可用模型，因此使用弛豫动力学模型。首先，Ar^+激光器（波长为488 nm）被用作模拟光源。计算结果表明，激光束直径越小，扫描速度越慢，偏振分布越均匀。由于薄膜的吸收光谱表明He-Ne激光（波长为632 nm）比Ar^+激光更深入地照射薄膜内部，因此He-Ne激光导致更高和更均匀的偏振分布。测量高分子材料在电场中的偶极取向动力学是十分必要的。少

We have focused on the development and the optimization of waveguide patterning process in nonlinear optical (NLO) polymer thin film by laser induced thermal poling. In this research, we have elucidated the following subjects.1) Measurement of the thermal diffusivity of NLO polymer thin film.Thermal properties of NW polymer are an important factor in the thermal poling process. To measure the thermal diffusivity of the nonlinear optical (NW) polymer thin film, we modified the experimental apparatus based on the photoacoustic method. PMMA with DR1 chromosphore side groups was synthesized as an NLO polymer. It was found that the thermal diffusivity is independent on film thickness and percentage of the chromosphore, but increases as the applied electric field increases. Also, the thermal diffusivity of the NLO polymer thin film decreases with temperature. Our apparatus has no capability to measure at high temperature, more than glass transition temperature (about 380K) which gives abrupt … More ly change in thermal diffusivity, It is desired to develop another method to measure thermal diffusivity at high temperature.2) Numerical simulation of laser induced thermal poling processWe have constructed three-dimensional simulation code to estimate temperature profile in NW polymer thin) film on thermal poling process. To elucidate optimized condition for uniform polarization profiles, we introduced the temperature dependence of dipole (in NLO molecule) orientation dynamics to our simulation code. Since there is no available model for dipole orientation dynamics, relaxation dynamics model was used. At first, Ar^+ laser (wavelength of 488 nm) was used as light source on simulation. The calculation results showed that smaller diameter of laser beam and slower scanning speed of laser give more uniform polarization profiles. Since absorption spectrum of thin film suggests that He-Ne laser (wavelength of 632 nm) illuminates the thin film more interior than Ar^+ laser, He-Ne laser results in higher and more uniform polarization profiles. It is necessary to measure the dipole orientation dynamics for polymer materials in an electric field. Less