Proceedings PaperNonlinear optical properties of main-chain-type liquid crystalline polymers
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The second harmonic generations (SHG) of liquid crystalline main-chain type polymers were investigated. The sample polymers are copolymers of 2-hydroxy-6-naphthoic acid (HNA) with 4-hydroxy-benzoic acid, in various composition ratios. The SHG of the film samples was greatly affected not only by the polymerization conditions, but also by preparation conditions of the films. SHGs for the samples processed by mechanical stretching and for electrically poled samples were compared. The nonlinear optical coefficients dexp evaluated by Maker Fringe method of the electrically poled samples are 2-3 times larger than that of the mechanically oriented same whose dexp is about 5pm/V. The high SHG of the main-chain type NLO polymers mainly originates from the additivity of hyperpolarizeability of the individual unit due to head to tail bonding.