Wavelength-modulated femtosecond stimulated raman spectroscopy—approach towards automatic data processing

• Published in: Physical chemistry chemical physics : PCCP 2011-01, Vol.13 (40), p.18123-18133
• Main Authors: KLOZ, Miroslav, VAN GRONDELLE, Rienk, KENNIS, John T. M
• Format: Article
• Language: English
• Subjects: Aromatic compounds; Carotenoids; Chemistry; Exact sciences and technology; Femtosecond; Filtering; Fourier analysis; General and physical chemistry; Shapers; Vibration
• ISSN: 1463-9076; 1463-9084
• DOI: 10.1039/c1cp21650c

A new wavelength modulator based on a custom-made chopper blade and a slit placed in the Fourier plane of a pulse shaper was used to detect explicitly the first derivative of the time-resolved femtosecond stimulated Raman spectroscopy (FSRS) signals. This approach resulted in an unprecedented reduction of the non-coherent background that results from population transfer by the Raman pump inherent to FSRS experiments. The method of Fourier peak filtering was implemented as a powerful tool for reducing both the remaining non-coherent and coherent background associated with FSRS experiments. The method was demonstrated on β-carotene and a similar synthetic aryl carotenoid. The experiments confirm earlier FSRS results on β-carotene but suggest some reinterpretation. Strong bleaching signals of ground state vibrations were observed and interpreted as an inseparable part of the time-resolved FSRS experiment. New long-lived Raman features were observed in β-carotene and the synthetic aryl carotenoid and assigned to a combination of conformational changes and solvent rearrangement. More complex wavelength modulation methods are proposed in the development of more robust FSRS experiments.