Identification of spatial averaging effects in vibrational CARS spectra

Accurate temperature measurements with the coherent anti-Stokes Raman scattering (CARS) technique are difficult to perform when temperature gradients occur within the measurement volume. Very often it is even difficult or time consuming to identify the influence of spatial averaging on the measurement. To solve this problem, a weighting procedure based on a combination of least-sum-of-squared-differences-fits (LSF) using different weighting factors was developed and tested by using experimental data, measured in a laminar and in a turbulent premixed methane/air flame. With this evaluation procedure it was possible to identify spatially averaged CARS spectra in order to sort them out avoiding the problems arising from the nonlinear nature of the CARS process. Using this new fitting approach, the expected bimodal temperature distribution near the flame front of the turbulent premixed flame can be confirmed. Copyright (c) 2006 John Wiley & Sons, Ltd.