Mastering Femtosecond Stimulated Raman Spectroscopy: A Practical Guide

Abstract

Femtosecond stimulated Raman spectroscopy (FSRS) is a powerful nonlinear spectroscopic technique that probes changes in molecular and material structure with high temporal and spectral resolution. With proper spectral interpretation, this is equivalent to mapping out reactive pathways on highly anharmonic excited-state potential energy surfaces with femtosecond to picosecond time resolution. FSRS has been used to examine structural dynamics in a wide range of samples, including photoactive proteins, photovoltaic materials, plasmonic nanostructures, polymers, and a range of others, with experiments performed in multiple groups around the world. As the FSRS technique grows in popularity and is increasingly implemented in user facilities, there is a need for a widespread understanding of the methodology and best practices. In this review, we present a practical guide to FSRS, including discussions of instrumentation, as well as data acquisition and analysis. First, we describe common methods of generating the three pulses required for FSRS: the probe, Raman pump, and actinic pump, including a discussion of the parameters to consider when selecting a beam generation method. We then outline approaches for effective and efficient FSRS data acquisition. We discuss common data analysis techniques for FSRS, as well as more advanced analyses aimed at extracting small signals on a large background. We conclude with a discussion of some of the new directions for FSRS research, including spectromicroscopy. Overall, this review provides researchers with a practical handbook for FSRS as a technique with the aim of encouraging many scientists and engineers to use it in their research.

Excited State Dynamics in Unidirectional Photochemical Molecular Motors

“…10 cm –1 ) “Raman pump” pulse. The probe pulse combination generates an instantaneous stimulated Raman spectrum, which has the spectral resolution of the Raman pulse and the temporal resolution of the continuum, which is then measured as a function of pump–probe delay. − The measured signal comprises a number of contributions, which must be carefully measured and separated, and the final spectrum can be complicated by interference with competing signals. , These effects are now quite well understood and can be removed or corrected for as described in detail elsewhere, although this complexity is undoubtedly a limitation of the method. , An advantage of FSRS is that the Raman pulse can be tuned into resonance with a specific transient absorption and the resonance enhancement used to extract state specific transient Raman spectra. , It should be noted that there is a Fourier transform time domain analogue of FSRS, impulsive SRS, which has fewer and simpler background correction problems and can provide outstanding signal-to-noise, but which places high demands on the laser source and experimenter, requiring sub 10 fs pulses, high stability, and long measurement times …”

The Impact of Pulse Shaping on Coherent Dynamics near a Conical Intersection

“…The photoisomerization of stilbene has also been investigated and the structural changes have been revealed by the gradual shift of the torsional mode [18]. Moreover, the twodimensional FSRS has been recently constructed and applied to study the anharmonicity of the vibrational coherence of charge-transfer modes of an artificial dimer system [19][20][21]. In addition, the ultrafast electron pulses have been employed to study the isomerization process, and the gradual changes in structures has been shown when a wave packet passes through the CI [22].…”