High Pressure Experiments and Computer Modeling Studies of Relaxation Mechanisms in Nonlinear Optical Polymers

9705800海登非线性光学(NLO)有机和聚合物材料已被提出用于各种光子系统。对于倍频、电光(EO)调制和光折变(PR)应用的成功实现，需要详细了解这些材料的结构与其线性和非线性光学性质之间的联系。这项工作的重点是确定聚合物中的松弛机制及其对这些聚合物的非线性光学性质稳定性的影响。这项工作将利用一种新的方法，通过对极化和非极化材料的原位二次谐波产生(SHG)和介电弛豫测量，测量极化NLO聚合物在不同温度下非线性光学系数衰减的压力依赖性。先前的研究发现，客体-宿主体系中二阶非线性光学极化率的弛豫是掺杂剂相对于主体的取代基或珠子的相对大小的函数。研究还发现，在玻璃化转变温度Tg以下，在客体-宿主体系中，生色团的重新取向与二次弛豫相耦合。根据发色团的相对大小和主体的侧基的不同，偶联程度也不同。这项研究将测试这些早期结果在侧链和主链NLO聚合物中的普遍性。最有技术前景的类型将被研究：间规聚合物，可交联性聚合物，以及基于聚酰亚胺和多喹啉的高玻璃化温度客体体系。此外，压力研究将被用来研究有助于实现更好稳定性的新的加工技术。此外，还将对掺杂和悬挂发色团的取向动力学进行详细的分子动力学模拟。分子模拟将补充实验测量，试图确定活化体积在分子水平上的含义，从而巩固其作为设计更稳定系统的参数的有用性。随着信息时代的发展，将需要更快的通信和计算资源。通过使用和发展光学器件技术，这些需求正在并将继续得到满足。这项工作的结果将有助于设计更好的材料，用于未来基于光的通信、计算和传感器系统。***

9705800 Hayden Nonlinear optical (NLO) organic and polymeric materials have been proposed for use in a variety of photonic systems. Successful implementation for frequency doubling, electrooptic (EO) modulation, and photorefractive (PR) applications requires a detailed knowledge of the connection between the structures of these materials and their linear and nonlinear optical properties. This work is focused on determining the mechanisms involved in relaxations in polymers and their effects on the stability of the nonlinear optical properties of these polymers. This work will utilize a new method to measure the pressure dependence of the decay of the NLO coefficients at various temperatures in poled NLO polymers by in-situ second harmonic generation (SHG) and dielectric relaxation measurements on poled and unpoled materials. Previous studies found that the relaxation of the second order NLO susceptibility in a guest-host system is a function of the relative size of the dopant compared to the sizes of the substituents or "beads" of the host. It was also found that below the glass transition temperature, Tg, chromophore reorientation is coupled to secondary relaxations in guest-host systems. The coupling varies according to the relative size of the chromophore and the side groups of the host. This study will test the generality of these earlier results in side-chain and main-chain NLO polymers. The most technologically promising types will be studied: syndioregic polymers, crosslinkable polymers, and high Tg guest-host systems based on polyimides and polyquinolines. In addition, the pressure studies will be used to investigate new processing techniques useful for achieving better stability. In addition, detailed molecular dynamics simulations of dopant and pendant chromophore orientational kinetics will be performed. The molecular modeling will complement the experimental measurements in an attempt to determine what the activation volume means on the mol ecular level and hence solidify its usefulness as a parameter in the design of more stable systems. %%% As the information age evolves, faster communication and computing resources will be needed. Increasingly, these needs are being and will continue to be met through the use and development of optical device technologies. The results of this work will be useful in helping to design better materials for use in future optical based communication, computing, and sensor systems. ***