Second-order nonlinear optical response of thin films containing organic chromophores. Theoretical aspects

This paper discusses some theoretical aspects associated with the unusual s econd-order nonlinear optical response of chromophoric self-assembled stilb alzolium superlattices, and of (N,N-dimethylamino)-4-nitrostilbene (DANS)-d oped glass polymers poled in an "in-plane" configuration. It is found that the bulk nonlinearity of such materials strongly depends upon specific chro mophore interactions. While for the stilbalzolium superlattices the supramo lecular hyperpolarizability is strongly affected by the ion-pair configurat ion, the formation of (formally) centrosymmetric charged chromophore aggreg ates is likely responsible for the observed anomalous strong nonlinearity i n DANS-doped in-plane poled polymers. The simple "chromophore gas" model is thus inadequate to describe the nonlinearity of such materials.