Ultrabroadband two-beam coherent anti-Stokes Raman scattering and
spontaneous Raman spectroscopy of organic fluids: a comparative study
Abstract
Spontaneous Raman spectroscopy is a well-established diagnostic tool,
allowing for the identification of all Raman active species with a
single measurement. Yet, it may suffer from low signal intensity and
fluorescent background. In contrast, coherent anti-Stokes Raman
scattering (CARS) offers laser-like signals, but the traditional
approach lacks the multiplex capability of spontaneous Raman
spectroscopy. We present an ultrabroadband CARS setup which aims at
exciting the full spectrum (300 - 3700 cm -1) of
biological molecules. A dual-output optical parametric amplifier
provides a ~7 fs pump/Stokes and a ~ 700
fs probe pulse. CARS spectra of DMSO, ethanol and methanol show great
agreement with spontaneous Raman spectroscopy and superiority in
fluorescent environments. The spectral resolution proves sufficient to
differentiate between the complex spectra of L-proline and
hydroxyproline. Moreover, decay constants in the sub picosecond range
are determined for individual Raman transitions, providing an additional
approach for sample characterization.