MOLECULAR-ORIENTATION, PAIR CORRELATIONS AND CASCADING IN NONLINEAR OPTICAL SUSCEPTIBILITIES

Different susceptibility expansions for the polarization density P are compared to identify cascading contributions to the nonlinear response of a medium. In certain liquids pair-correlation dependence of the nonlinear optical susceptibilities has been observed. To isolate the cascading effects that depend most sensitively on pair correlation and near-field effects, a simple statistical model for P is applied to the case of a liquid whose oriented molecules have only first hyperpolarizabilities; then all third-order effects in P are a consequence of cascading.