Electro-optic characterization of nonlinear-optical guest–host films and polymers

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Abstract
The Pockels coefficients r33 of four dyes for electro-optic applications are reported, including ones with stilbene, butadiene, azo, and hexatriene linkages between the charge donors and acceptors, with the charge donor being the amino group and the acceptor groups being the nitro and dicyanovinyl groups. r33 are reported for dyes as guest–hosts in poly(methyl methacrylate) and 50/50 copolymers with methyl methacrylate. The largest r33 is observed for the copolymer containing the amino donor, hexatriene linkage, and the dicyanovinyl acceptor group with a value of r33 = 18 pm/V at 140 V/µm at a wavelength λ = 1.3 µm. We also find evidence that the dicyanovinyl hexatriene dyes in the copolymer are interacting with one another, causing a relative decrease in the copolymer’s electro-optic efficiency compared with its value as a guest–host in poly(methyl methacrylate). The Pockels coefficient is measured by the ellipsometric reflection technique. We derive approximate analytic equations to analyze the reflected intensity and verify the validity of these approximations when the analyzing wavelength is far from the absorption of the dye. We also derive an approximate analytic expression for the optical retardation as a function of the ratio of the off-diagonal to the diagonal components of the Pockels coefficients r13/r33 and also the finite birefringence of the poled film. We show that accurate knowledge of the ratio r13/r33 is critical to obtaining accurate values of r33.