Design and development of stimulated Raman spectroscopy apparatus using a femtosecond laser system

We present the design and development of a stimulated Raman scattering (SRS) experimental set-up using a femtosecond laser system. The set-up involves the generation of (i) a picosecond (ps) narrow-bandwidth (5-20 cm(-1)) Raman pump, and (ii) a femtosecond (fs) broadband continuum Raman probe pulse (800-1050 nm) providing the Stokes field, covering vibrations in the range 300-2500 cm(-1). When the two fields interact with the system simultaneously, gain features are observed on top of the probe beam at frequency corresponding to the characteristic molecular vibration frequency of the system. The ratio of the probe spectrum with and without the Raman pump provides a background-free gain spectrum. We present initial studies on some standard systems, viz. benzene, cyclohexane and beta-carotene in CCl4/benzene. These studies indicate that this technique provides a better signal with improved signal-to-noise ratio even for a low acquisition time in comparison with normal Raman spectroscopy.