Genuine Dynamics vs Cross Phase Modulation Artifacts in Femtosecond Stimulated Raman Spectroscopy

Femtosecond stimulated Raman scattering is a time-resolved vibrational spectroscopic technique able to access sub-picosecond dynamics and providing accurate structural information. Thanks to an appropriate combination of three laser pulses, triggering vibrational coherences delayed with respect to the photoinduced event of interest, it is capable of uncompromised temporal precision (down to 50 fs) and spectral resolution (a few wavenumbers), better than spontaneous Raman. Reaching such extreme time scales requires significant temporal overlap of pulses, which gives rise to undesired nonlinear artifacts, often hampering an immediate interpretation of the Raman spectra. Building on a perturbative expansion of the density matrix, we identify the origin of such artifacts in cross phase modulation effects and show how they can be theoretically evaluated and factored out from the signals. We experimentally benchmark the theoretical predictions in a nonreactive model system, namely cyclohexane.