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Optimisation of poling parameters for nonlinear optical polymers from their dipolar orientation and relaxation behaviour
Summary form only given, as follows. Nonlinear optical polymers contain molecular dipoles with very large hyperpolarisabilities in a glassy polymer matrix. Two typical examples-a guest-host system of Polymethylmethacrylate (PMMA) and Disperse Red 1(DR1) and a DR1-styrene-maleic-anhydride-based side-chain material kindly provided by SANDOZ Optoelectronics, Huningue, France-were studied with corona-poling experiments, dielectric spectroscopy, thermally stimulated depolarisation (TSD), and electro-optical thermal analysis (EOTA). It was found that the dielectric behaviour of both polymers can be described by the phenomenological Havriliak-Negami equation. The existence of master curves for both materials demonstrated the validity of the time-temperature superposition principle above their respective glass-transition temperatures. Mean relaxation times and calculated relaxation-time distributions for the guest-host and the side-chain polymer permit the selection of optimal polingdurations. The guest-host system's relaxation-time distribution is broader and has more short-time components than that of the side-chain polymer. From the results of short-circuit TSD-current measurements, the overall sample polarisation is obtained by integration. The values agree reasonably well with estimates from the poling-current measurements and with the dielectric data. From the temperature dependence of the polarisation, optimal poling temperatures may be derived.