Matching molecular and optical multipoles in photoisomerizable nonlinear systems

We experimentally investigate the coupling rules between molecules and optical fields in the all-optical poling scheme. The efficiency and symmetry of the photoinduced quadratic nonlinearity is shown to be dependent on tensorial selection rules connecting the symmetries of the optical poling fields and the molecular tensors. We show that an optimal poling is obtained by matching the molecular symmetry to either a quasi-dipolar or a purely octupolar poling field, each being engineered by use of circular polarizations. Moreover, we define optimized poling conditions allowing the direct measurement of molecular nonlinear anisotropies. This research can be applied to nonlinear and photoisomerizable multipolar molecular systems.