Femtosecond stimulated Raman spectroscopy

First demonstrated in 1994, femtosecond stimulated Raman scattering (FSRS) has gained popularity since the early 2000s as an ultrafast pump-probe vibrational spectroscopy technique with the potential to circumvent the time and energy limitations imposed by the Heisenberg uncertainty principle. This Primer explores whether, why, when and how the temporal precision and frequency resolution of traditional time-resolved spontaneous Raman spectroscopy can be surpassed by its coherent counterpart (FSRS), while still adhering to the uncertainty principle. We delve into the fundamental concepts behind FSRS and its most common experimental implementations, focusing on instrumentation details, measurement techniques, data analysis and modelling. This includes discussions on synthesizing the Raman pump beam, artificial intelligence (AI)-assisted baseline removal methods and analytical expressions for reproducing experimental data and extracting key parameters such as relaxation times and out-of-equilibrium temperature profiles. Recent applications of FSRS from physics, chemistry and biology are showcased, demonstrating how this approach has facilitated cross-disciplinary studies. We also address the technical and conceptual limitations of FSRS to aid in designing optimal experiments based on specific goals. Finally, we explore future directions, including multidimensional extensions to address vibrational couplings and the use of quantum light to untangle temporal and spectral resolution.Femtosecond stimulated Raman scattering (FSRS) is an ultrafast pump-probe spectroscopy method for investigating the vibrational dynamics of molecules. In this Primer, Batignani et al. introduce the fundamental concepts behind FSRS, its current utility and future integrations of artificial intelligence and quantum light.