Pure rotational coherent anti-stokes Raman scattering: comparison of evaluation techniques for determining single-shot simultaneous temperature and relative n(2)-o(2) concentration.
The accuracy and precision of time-resolved simultaneous temperature and O(2)-concentration measurements in binary N(2)-O(2) mixtures by single-pulse dual-broadband pure rotational coherent anti-Stokes Raman scattering (CARS) have been investigated. We present a detailed comparison of the applicability of six evaluation procedures to measurements of air in a temperature range 300-2050 K. Special emphasis is put on the dependence of the results on experimental restrictions and distortions. This comparison includes the least-sum-of-squared-differences fit (LSF) in the frequency space obtained by use of three different kinds of weighting with respect to signal intensity and in Fourier space by use of the complex or the cosine Fourier transformation, both of which permit a great reduction in the number of data points necessary for multidimensional evaluation. Additionally, a cross-correlation technique is tested that, to the best of our knowledge, was not previously applied to pure rotational CARS. We also present the results of measurements directed to the determination of low O(2)-concentration levels that were performed for various binary mixtures (1.0-15.6% O(2)) and for natural air within a temperature range of 300-773 K. A comparison is given for the three evaluation techniques that have proved most promising for the high-temperature investigations, i.e., the constant and the inverse weighted LSF in frequency space and the Fourier analysis technique.
Schenk
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M
Thumann
A
A
Seeger
T
T
Leipertz
A
A