A new method for recording femtosecond stimulated Raman spectra was developed that dramatically improves and automatizes baseline problems. Instead of using a narrowband Raman source, the experiment is performed using shaping of a broadband source. This allows locking the signal into carefully crafted watermarks that can be recovered from measured data with high fidelity. The approach uses unique properties of Raman scattering, thus allowing a direct recording of stimulated Raman signals with robust rejection of baselines and fixed-pattern-noise. Low cost technology for generating required pulse-shapes was developed and demonstrated. The methodology is applicable to any Raman experiment but primarily targets Femtosecond Stimulated Raman spectroscopy (FSRS) where a lack of robust methods for parasitic signal rejection has been a major obstacle in the practical development of the field in the last decade. The delivered improvement in FSRS experiments was demonstrated by recording evidence that the so-called S* state of carotenoids in solution corresponds to the optically forbidden S1 state of a sparsely populated carotenoid conformation.

Department of Chemistry University of Connecticut 55 North Eagleville Road Storrs CT 06269 USA

Department of Physics and Astronomy VU University Amsterdam De Boelelaan 1081 1081HV Amsterdam The Netherlands

Department of Physics and Astronomy VU University Amsterdam De Boelelaan 1081 1081HV Amsterdam The Netherlands and ELI Beamlines Institute of Physics Na Slovance 2 182 21 Praha 8 Czech Republic

University of South Bohemia Branišovská 1645 31a 370 05 České Budějovice Czech Republic

References provided by Crossref.org

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A Unified Picture of S* in Carotenoids