Ultrabroadband two-beam coherent anti-Stokes Raman scattering and spontaneous Raman spectroscopy of organic fluids: A comparative study

Spontaneous Raman spectroscopy isa well-established diagnostic tool,allowing for the identification of allRaman active species with a singlemeasurement. Yet, it may sufferfrom low-signal intensity and fluo-rescent background. In contrast,coherent anti-Stokes Raman scatter-ing (CARS) offers laser-like signals,but the traditional approach lacksthe multiplex capability of spontaneous Raman spectroscopy. We present an ultra-broadband 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 spectroscopyand superiority in fluorescent environments. The spectral resolution provessufficient to differentiate between the complex spectra of L-proline andhydroxyproline. Moreover, decay constants in the sub picosecond range aredetermined for individual Raman transitions, providing an additionalapproach for sample characterization.