Srivastava Prasenjit, Stierwalt David A, Elles Christopher G
Department of Chemistry, University of Kansas, Lawrence, Kansas 66045, United States.
Anal Chem. 2023 Sep 5;95(35):13227-13234. doi: 10.1021/acs.analchem.3c02298. Epub 2023 Aug 21.
Two-photon absorption (2PA) spectroscopy provides valuable information about the nonlinear properties of molecules. In contrast with single-wavelength methods, broadband 2PA spectroscopy using a pump-probe approach gives a continuous 2PA spectrum across a wide range of transition energies without tuning the excitation laser. This contribution shows how stimulated Raman scattering from the solvent can be used as a convenient and robust internal standard for obtaining accurate absolute 2PA cross sections using the broadband approach. Stimulated Raman scattering has the same pump-probe overlap dependence as 2PA, thus eliminating the need to measure the intensity-dependent overlap of the pump and probe directly. Eliminating the overlap represents an important improvement because intensity profiles are typically the largest source of uncertainty in the measurement of absolute 2PA cross sections using any method. Raman scattering cross sections are a fundamental property of the solvent and therefore provide a universal standard that can be applied any time the 2PA and Raman signals are present within the same probe wavelength range. We demonstrate this approach using sample solutions of coumarin 153 in methanol, DMSO, and toluene, as well as fluorescein in water.
双光子吸收（2PA）光谱学提供了有关分子非线性特性的宝贵信息。与单波长方法不同，采用泵浦-探测方法的宽带2PA光谱学无需调谐激发激光，就能在很宽的跃迁能量范围内给出连续的2PA光谱。本文献展示了如何将来自溶剂的受激拉曼散射用作一种方便且可靠的内标，以便使用宽带方法获得准确的绝对2PA截面。受激拉曼散射与2PA具有相同的泵浦-探测重叠依赖性，因此无需直接测量泵浦光和探测光强度相关的重叠情况。消除这种重叠是一项重要的改进，因为在使用任何方法测量绝对2PA截面时，强度分布通常是不确定性的最大来源。拉曼散射截面是溶剂的一种基本特性，因此提供了一种通用标准，只要2PA和拉曼信号出现在相同的探测波长范围内，就可以随时应用。我们使用香豆素153在甲醇、二甲基亚砜和甲苯中的样品溶液，以及荧光素在水中的样品溶液来演示这种方法。
