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The stimulated Raman scattering time-domain analogue, in which a full scan of the temporal delay between two ultrashort pulses is required to record a single Raman spectrum in the time domain. The addition of an actinic pump turns impulsive stimulated Raman into a time-resolved technique capable of probing excited-state dynamics, similarly to femtosecond stimulated Raman scattering.

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Nature Reviews Methods Primers thanks Chong Fang, David McCamant and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

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A signal in which various frequencies arrive at different time delays. In optical pulses, chirp commonly stems from the chromatic dispersion caused by transmitting optics, leading to red-shifted spectral components arriving earlier (positive chirp) or later (negative chirp) than the blue-shifted ones.

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Edmund Optics

The authors are grateful to G. Cerullo, P. Kukura, S. Mukamel and M. H. Vos for several inspiring discussions. They acknowledge early contributions by E. Pontecorvo to the planning and development of their first FSRS prototype. G.B. acknowledges funding from the PRIN 2022 Project (Dynamat) (grant number 2022PR7CCY).

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Amplification of a desired, weak, optical signal (ES) by its mixing with a strong field (EL), leading to the measured intensity \(I={{\rm{| }}{E}_{{\rm{L}}}{\rm{| }}}^{2}+{{\rm{| }}{E}_{{\rm{S}}}{\rm{| }}}^{2}+{E}_{{\rm{L}}}{E}_{{\rm{S}}}^{* }+{E}_{{\rm{S}}}{E}_{{\rm{L}}}^{* }\).

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Present address: Physical Measurement Laboratory, National Institutes of Standards and Technology, Gaithersburg, MD, USA

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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.

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Introduction (T.S., G.B., C.F., G.F. and M.M.); Experimentation (T.S., G.B., C.F., G.F. and M.M.); Results (T.S., G.B., C.F., G.F. and M.M.); Applications (T.S., G.B., C.F., G.F. and M.M.); Reproducibility and data deposition (T.S., G.B., C.F., G.F. and M.M.); Limitations and optimizations (T.S., G.B., C.F., G.F. and M.M.); Outlook (T.S., G.B., C.F., G.F. and M.M.); overview of the Primer (T.S.).

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A nonlinear optical effect that occurs when the refractive index of a material changes, typically in a quadratic manner, in response to an applied electric field. Such a modification can affect the propagation of pulses and their spectral profiles.

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