We propose an approach, based on wavelet prism decomposition analysis, for correcting experimental artefacts in a coherent anti-Stokes Raman scattering (CARS) spectrum. This method allows estimating and eliminating a slowly varying modulation error function in the measured normalized CARS spectrum and yields a corrected CARS line-shape. The main advantage of the approach is that the spectral phase and amplitude corrections are avoided in the retrieved Raman line-shape spectrum, thus significantly simplifying the quantitative reconstruction of the sample's Raman response from a normalized CARS spectrum in the presence of experimental artefacts. Moreover, the approach obviates the need for assumptions about the modulation error distribution and the chemical composition of the specimens under study. The method is quantitatively validated on normalized CARS spectra recorded for equimolar aqueous solutions of D-fructose, D-glucose, and their disaccharide combination sucrose.

In narrow-bandwidth coherent Raman scattering (CRS) microscopy, efficient signal generation is accomplished with two-color laser sources providing synchronized picosecond pulses whose frequency difference and spectral widths match the molecular Raman frequency and bandwidth, respectively. With vibrational bandwidths of typically 10 cm -1 , the optimum laser pulse durations thus correspond to about 2 ps. Here, we present a new light source consisting of an amplified Yb-fiber oscillator providing 2-ps pulses at 1031 nm and a synchronously green-pumped optical parametric oscillator (OPO). The OPO slightly shortens the pulses to < 2 ps while maintaining a bandwidth of 10 cm -1 . Output power levels of 1 W in both the 1031-nm and the OPO-branch with continuously tunable frequency differences between the two beams covering a broad range from 700 to 4500 cm -1 are achieved. In addition to CARS microscopy, this light source allows for SRS imaging via an integrated electro-optical modulation of the 1031-nm beam at 20 MHz with a depth of >95%, locked to the laser repetition rate of 80 MHz. The OPO noise at 20 MHz was found to be only 60% above the combined detector and laser noise of a conventional Nd:YVO pump source. This represents a significant reduction in laser noise when compared to other fiber-based laser sources previously proposed for SRS microscopy. When SRS imaging with this new light is compared with a Nd:YVO pumped OPO (delivering 7 ps and 5 ps pulses, respectively), a 5-to 6-fold increase in SRS signal strength and signal-to-noise ratio has been achieved. Video-rate SRS and the capability of multi-spectral SRS imaging are demonstrated.

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