Photothermal‐Detected Time‐Domain Stimulated Raman Scattering

ABSTRACT Probing vibrational transitions via the photothermal effect has recently emerged as a promising approach in frequency‐domain vibrational spectroscopy, offering improved sensitivity and significant instrumental simplification. However, the frequency‐domain excitation strategy offers limited bandwidth and spectral resolution, mixes the vibrational signals with backgrounds contributed by electronic responses, degrading spectral fidelity and hindering advanced spectroscopic applications. Here we show that high‐fidelity, photothermal‐detected Raman spectra can be faithfully acquired via impulsive time‐domain excitation, a method we term photothermal‐detected time‐domain stimulated Raman scattering (pTD‐TSRS). By scanning the delay between two impulsive stimulated Raman excitations, we generate quantum interference that modulates the population of vibrational excited states at their eigenfrequencies. The subsequent vibrational relaxation encodes the Raman free‐induction decays (FIDs) into the photothermal response. Fourier transformation of the FIDs yields spontaneous‐Raman‐like spectra with natural‐linewidth‐limited resolution. Importantly, while electronic responses such as multiphoton absorptions exist in signal detection, they are incoherent with the photothermal signal and can be applied as an intrinsic reference for wavenumber‐dependent excitation efficiency, permitting global spectral calibration to the intrinsic form. pTD‐TSRS provides easy access to high‐fidelity and broadband Raman spectrum with time‐resolved vibrational dynamics.