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

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