Second harmonic generation and thermally stimulated current measurements: A study of some novel polymers for nonlinear optics

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Abstract
The relaxation of electric field-induced polar orientation in novel side and main chain polymers was measured by simultaneous second harmonic generation and thermally stimulated discharge current techniques. Using this combination of experiments, individual microscopic relaxation mechanisms could be discriminated and identified. The relaxation of a polymer bearing polar chromophores on a side chain polymer was found to occur through local reorientation. For polymers containing the polar chromophore within the main chain, both a local rotation of the chromophores and the reorientation of the end-to-end vectors of the chains could be detected. Physical aging near the Tg of the polymers greatly increased the stability of the poling-induced orientation below Tg. Nonlinear dependencies on the poling field were observed for low fields and are discussed in terms of screening due to space charges. Kirkwood–Frohlich correlation factors were found to be very close to unity.