PURE ROTATIONAL CHIRPED-PROBE PULSE FEMTOSECOND CARS OF O2 FOR THERMOMETRY MEASUREMENT

Abstract

We investigate the capability of temperature measurement by pure rotational femtosecond coherent anti-Stokes Raman spectroscopy (fs CARS) of O$_{2}$ through a chirped probe pulse (CPP) technique. The electronic ground state of O$_{2}$ is known to have a $^{3}\Sigma^{-}_{g}$ symmetry. As a result, both total nuclear angular momentum quantum number N, as well as total angular momentum quantum number J=N$\pm$1 are used for O$_{2}$ rotational level characterization. The selection rules for O$_{2}$ pure rotational Raman transitions are $\Delta$N=0, $\pm$2, $\Delta$J=0, $\pm$1, $\pm$2. The simplifications of the theoretical modeling are possible, for example, by neglecting the 3-J splitting structures or by considering only the $\Delta$N=2, $\Delta$J=2 (S$^{S}$ branch) transitions. We validate the accuracy of those assumptions by comparing to the correspondingly simulated rotational CARS spectra as well as by comparing to the experimental measurements. The experimental measurements will be performed in O$_{2}$ jet flow as well as in flames established over a Hencken burner. In the latter case, the interference from N$_{2}$ pure rotational CARS signals will become important, thus it will also be accounted for our spectroscopic analysis. \begin{wrapfigure}{r}{0 pt} \includegraphics[scale=0.8] {Figure.eps} \end{wrapfigure}