Evaluation of nonlinear optical coefficients in uniformly aligned dioxane-based ferroelectric nematic liquid crystals using second harmonic generation

Ferroelectric nematic liquid crystals (FNLCs) are promising soft platforms for nonlinear optics, but quantitative determination of their second-order nonlinear optical coefficients has been hindered by limited alignment control. Here, polarization-resolved second-harmonic generation (SHG) measurements on a uniformly aligned dioxane-based FNLC, combined with Jones-matrix simulations, enable determination of all principal tensor components. The resulting tensor is consistent with the expected $C_{\mathrm{\infty }v}$ and Kleinman symmetries, while the measured coefficients cannot be explained by a simple sum of molecular first hyperpolarizabilities. These results provide a quantitative basis for understanding nonlinear optical responses and guiding the design of FNLC-based nonlinear optical materials and devices.