An investigation of in situ background normalization for obtaining sensitive and accurate concentration measurements with coherent anti-Stokes Raman spectroscopy (CARS) is reported. Flame species concentrations measured with CARS were in good agreement with IR laser absorption measurements of CO in extracted flame gases and with equilibrium calculations. Time-averaged detectivity for CO at the 1000-ppm level was obtained at 1900 K. Background normalization was also shown to be capable of improving CARS pulse-to-pulse signal reproducibility nearly to the shot-noise limit. We consider factors important for concentration measurements with CARS, including laser-induced Stark effects, accuracy of susceptibility calculations, and effects of different laser linewidth models.
© 1985 Optical Society of America
Roger L. Farrow, Robert P. Lucht, Gary L. Clark, and Richard E. Palmer, "Species concentration measurements using CARS with nonresonant susceptibility normalization," Appl. Opt. 24, 2241-2251 (1985)