Statistics of multimode YAG laser radiation with implications for quantitative coherent anti-Stokes Raman scattering spectroscopy in combustion diagnostics

The autocorrelation coefficient of frequency-doubled YAG laser radiation for different operating conditions and two different laser systems is determined by measurement of the nonresonant coherent anti-Stokes Raman scattering (CARS) intensity as a function of the time delay between two correlated excitation beams. The YAG laser radiation is modeled as the sum of two components, following coherent and Gaussian statistics, respectively. Based on the autocorrelation coefficient and the YAG second-harmonic conversion efficiency, the intensity ratio of these two components is determined, yielding a larger coherent than Gaussian component for all configurations examined. The results and some implications for quantitative CARS spectroscopy are discussed.