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It has been commonly assumed that electrostatic interactions between chromophores that exhibit large second hyperpolarizabilities β can be neglected in estimating electro-optic and second-harmonic coefficients, which can be achieved by electric-field poling of chromophore-containing polymers. Macroscopic optical nonlinearity has been assumed to scale as μβ/molecular weight, where μ is the dipole moment. Synthesis of chromophores with μβ values of the order of 10-44 esu has led to expectations of electro-optic coefficients for organic materials that substantially exceed those of lithium niobate. Expected values have not been easily realized; thus the utility of the above-mentioned scaling factor or chromophore figure of merit has been brought into question. We demonstrate that macroscopic optical nonlinearities are attenuated at high chromophore loading for chromophores characterized by electrostatic interactions that, at close approach distances, exceed thermal energies (kT) and poling energies (μF), where F is the effective electric field.
Harper et al. (Thu,) studied this question.