TRANSLATING MICROSCOPIC OPTICAL NONLINEARITY INTO MACROSCOPIC OPTICALNONLINEARITY - THE ROLE OF CHROMOPHORE-CHROMOPHORE ELECTROSTATIC INTERACTIONS

It has been commonly assumed that electrostatic interactions between c hromophores that exhibit large second hyperpolarizabilities beta can b e neglected in estimating electro-optic and second-harmonic coefficien ts, which can be achieved by electric-field poling of chromophore-cont aining polymers. Macroscopic optical nonlinearity has been assumed to scale as mu beta/molecular weight, where mu is the dipole moment. Synt hesis of chromophores with mu beta values of the order of 10(-44) esu has led to expectations of electro-optic coefficients for organic mate rials that substantially exceed those of lithium niobate. Expected val ues have not been easily realized; thus the utility of the above-menti oned scaling factor or chromophore figure of merit has been brought in to question. We demonstrate that macroscopic optical nonlinearities ar e attenuated at high chromophore loading for chromophores characterize d by electrostatic interactions that, at close approach distances, exc eed thermal energies (kT) and poling energies (mu F), where F is the e ffective electric field. (C) 1998 Optical Society of America.