Absolute Stimulated Raman Cross Sections of Molecules

Stimulated Raman scattering (SRS) is a fundamental optical process that was discovered more than 60 years ago. While the early SRS spectroscopy studies have provided valuable insights into materials systems, the advent of SRS microscopy has launched a rapidly growing field in biological imaging. However, a fundamental understanding of the molecular response under SRS is still lacking. Herein we present a new framework to introduce molecule-intrinsic stimulated Raman scattering cross sections, σ_SRS, in the unit of Göppert-Mayer (GM). The absolute SRS cross sections determined for real molecular systems challenge the conventional wisdom that Raman spectroscopy is always a weak process. The enormous rate acceleration of SRS, captured by an apparent SRS cross section, stems from a synergistic effect between the field and the molecule. Our new framework goes beyond the conventional optics-centric view and presents a molecule-inclusive perspective, thus offering a comprehensive foundation for the future growth of SRS spectroscopy and microscopy.