Femtosecond stimulated Raman spectroscopy in 1D and 2D — Direct observation of intramolecular motions and intermolecular interactions

Summary form only given. It is exactly half century now since the discovery of stimulated Raman scattering (SRS) (1). Despite numerous proof-of-the-principle experiments it is only about a decade since the mechanism got a general analytical use through the special phenomena called femtosecond stimulated Raman scattering (FSRS). When two strongly different light pulses are time spatially overlapped in a sample, one spectrally ultra narrow and one ultra short in time, the entire Raman spectra of the sample are imprinted on the broad spectral envelope of the ultra short pulse with a high signal gain. While the spectral resolution is determined by the narrow pulse the time gating precision is set by the ultrafast pulse so the time-energy resolution is no longer bound by the time-bandwidth uncertainty principle. This mechanism was recently successfully harnessed in mapping the fastest know bio reactions (2, 3) yet robust FSRS experiment is still under development (4). The supreme time resolution of FSRS opened the door for a fully coherent time domain 2D-Raman experiments (5) where the vibrational motion is mapped beyond the period of single oscillation. After initial optimism 2D Raman signals were discovered to be strongly overwhelmed by parasitic cascading signals (6) and at the moment it is unclear if the problem is fully solvable. Frequency domain 2D Raman experiments were proposed as well and their applicability is currently being evaluated. Never the less 1D Raman techniques are already obtaining strong recognition as an irreplaceable toll for studding of vibrations with low IR cross section.