Electro-optic determination of the nonlinear-optical properties of a covalently functionalized Disperse Red 1 copolymer

We report the development of a methodology for the comprehensive characterization of the linear- and nonlinear-optical properties of a model copolymer, Disperse Red 1, covalently functionalized to a methyl methacrylate backbone. From refractive-index and electro-optic measurements, we have evaluated both fundamental macroscopic and microscopic nonlinear-optical properties. We have measured the refractive indices of the copolymer as a function of chromophore concentration, wavelength, and poling field. For the linear-optical properties we find that the wavelength dependence is well described by a single-oscillator Sellmeier equation and that the poling-field dependence is well described by a simple theory related to the order parameter. From the observed refractive-index anisotropy as a function of poling field, we have obtained an effective dipole moment for the Disperse Red chromophore. We have measured the linear electro-optic effect in these systems as a function of poling temperature, film thickness, poling-field strength, wavelength, and concentration. We have found that the electro-optic coefficients may be modeled by an independent-response two-level dispersion model, from which an independent determination of the effective dipole moment, nonresonant second-order susceptibility χ(2), and nonresonant molecular hyperpolarizability β have been obtained.