LAUSR

The nonlinear optical response of materials under high-intensity electromagnetic fields is key to advancing THz optical technologies. This study introduces a theoretical approach to estimate the nonlinear refractive index coefficient, , of complex molecules in the THz range by summing individual vibrational bonds contributions, which are extracted from structurally simpler molecules that predominantly consist of the corresponding type of bond. Using water, -pinene, and CO as reference materials, we predict for isopropanol as . Z-scan measurements with pulsed THz radiation yield , validating our model. This bond-based decomposition links microscopic bond vibrations and macroscopic nonlinear coefficients, offering a framework for understanding molecular nonlinear optics and guiding the design of THz nonlinear devices.