Broadband Two-Photon Absorption Spectroscopy with Stimulated Raman Scattering as an Internal Standard

Two-photon absorption(2PA) spectroscopy provides valuable informationabout the nonlinear properties of molecules. In contrast with single-wavelengthmethods, broadband 2PA spectroscopy using a pump-probe approachgives a continuous 2PA spectrum across a wide range of transitionenergies without tuning the excitation laser. This contribution showshow stimulated Raman scattering from the solvent can be used as aconvenient and robust internal standard for obtaining accurate absolute2PA cross sections using the broadband approach. Stimulated Ramanscattering has the same pump-probe overlap dependence as 2PA,thus eliminating the need to measure the intensity-dependent overlapof the pump and probe directly. Eliminating the overlap representsan important improvement because intensity profiles are typicallythe largest source of uncertainty in the measurement of absolute 2PAcross sections using any method. Raman scattering cross sections area fundamental property of the solvent and therefore provide a universalstandard that can be applied any time the 2PA and Raman signals arepresent within the same probe wavelength range. We demonstrate thisapproach using sample solutions of coumarin 153 in methanol, DMSO,and toluene, as well as fluorescein in water.

Automated summary

Two-photon absorption (2PA) spectroscopy is used to study the nonlinear properties of molecules. A broadband 2PA spectroscopy using a pump-probe approach is proposed to obtain a continuous 2PA spectrum without tuning the excitation laser. This research demonstrates the use of stimulated Raman scattering as an internal standard to accurately measure absolute 2PA cross sections.