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

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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. ***