Optimization of the nonlinear optical response in chiral media

Abstract

This paper describes the development and optimization of chiral, non-polar media with large second-order nonlinear optical responses. We employ molecular engineering, quantum-mechanical sum-over-states theory, and measurements of molecular hyperpolarizability by means of Kleinman-disallowed hyper-Rayleigh scattering in order to understand molecular properties. Then we analyze the appropriate arrangement of the chromophores that produce an optimum axial nonlinear optical medium. Chromophores with large Kleinman disallowed traceless symmetric second rank tensor hyper-polarizabilities β can be aligned so as to result in large susceptibilities, χ (2) , in structures that lack polar order. We found that L-shaped chromophores with C 2v or similar symmetry are good candidates for these materials as they can exhibit large second-rank components of the hyperpolarizability tensor. A wide variety of techniques can be used to fabricate bulk materials belonging to the chiral non-polar symmetry groups, D ∞ and D 2 . The microscopic chromophore alignment schemes that optimize the NLO response in such materials are deduced from general symmetry consideration for both molecules and bulk.