Time-dependent nonlinear optical properties of pyroelectric liquid crystalline polymers |
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Authors: | Jonas Ö rtegren,Philippe Busson,Ulf W. Gedde,Anders Hult,Anders Eriksson,Mikael Lindgren,Per-Otto Arntzé n,David S. Hermann,Per Rudquist,Sven T. Lagerwall |
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Abstract: | Highly oriented pyroelectric liquid-crystalline polymers were prepared by photopolymerization under the influence of a static electric field from binary mixtures of two acrylate monomers exhibiting chiral smectic C mesomorphism. Both monomers contained nitro groups to yield second order nonlinear optical properties (second harmonic generation) and one of the monomers had two functional groups to yield a crosslinked polymer. The room temperature second order nonlinear susceptibility of the polymers showed during the first two hours a 10 % decrease after which it remained constant during the next 48 days. At elevated temperatures there was a significant difference in the nonlinear optical properties over time between crosslinked and uncrosslinked polymers. The uncrosslinked polymer showed a pronounced loss of second order nonlinear optical activity with time at ≥38°C. The crosslinked polymer showed a much smaller and basically a temperature independent decrease rate in the second order nonlinear optical properties at all the ageing temperatures (23-130°C). Both the loss in mesogen order parameter, very evident for the uncrosslinked polymer, and conformational changes occurring within the mesogens (β mechanism), may account for the observations made. |
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Keywords: | pyroelectric liquid crystalline polymers second harmonic generation long-term properties |
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