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 n2 of complex molecules by summing contributions from individual vibrational bonds, which are extracted from structurally simpler molecules predominantly consist of corresponding type of bond. Using water, alpha-pinene, and CO2 as reference materials, we predict n2 for isopropanol as 4.7*10^(-9) cm^2/W. Z-scan measurements with pulsed THz radiation yield n2 = (2.5+-0.5)*10^(-9) cm^2/W, 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 materials.
Terahertz Time-Domain Spectroscopy and Density Functional Theory Analysis of Low-Frequency Vibrational Modes of a Benzoxazolium-Coumarin Donor-pi-Acceptor Chromophore
Indian Institute of Science Education and Research Kolkata（印度科学教育研究学院加尔各答分校）；Sri Sathya Sai Institute of Higher Learning（斯里萨蒂亚赛高等学习研究所）；Indian Institute of Technology Gandhinagar（甘地纳加尔印度理工学院）
Nonlinear TeraHertz Coherent Excitation of Vibrational Modes of Liquids
我们报道了太赫兹（THz）光场与分子液体的非线性相互作用对分子内振动模的第一次相干激发。太赫兹-太赫兹-拉曼脉冲序列用宽带、高能量、（亚）皮秒太赫兹脉冲准备相干光，然后在太赫兹克尔效应光谱仪中通过相位敏感、外差检测用光脉冲测量相干光。这里报道的光谱仪具有更宽的太赫兹频率覆盖范围，并且相对于先前报道的太赫兹克尔效应实验增加了灵敏度。在液体二碘甲烷中在3.66 THz（122 cm $^{-1}$）和四氯化碳中在6.50 THz（217 cm $^{-1}$）观察到振动相干性，与这些分子内模式的文献值完全一致。这项工作打开了2D光谱学的大门，在太赫兹领域的非线性，可以研究凝聚相分子系统的动力学，以及在太赫兹频率的相干控制。
Analysis of Dispersive Fourier Transform dataset using Dynamic Mode Decomposition: evidence of multiple vibrational modes, and their interplay in a three-soliton molecule
Addressing intramolecular vibrational redistribution in a single molecule through pump and probe surface-enhanced vibrational spectroscopy
Centro de Física de Materiales (CFM-MPC), CSIC-EHU（材料物理中心）；Donostia International Physics Center (DIPC)（多诺西亚国际物理中心）；Department of Electricity and Electronics, FCT-ZTF, UPV-EHU（巴斯克国立大学电气与电子工程系）；Department of Polymers and Advanced Materials, Faculty of Chemistry, The University of the Basque Country, UPV/EHU（巴斯克国立大学化学学院高分子与先进材料系）；IKERBASQUE, Basque Foundation for Science（伊克尔巴斯基克科学基金会）
