Direct determination of non-Boltzmann vibrational level populations in electric discharges by CARS

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Abstract
The direct measurement of nonequilibrium vibrational level populations of N2 at the center of an electric discharge has been demonstrated by a new diagnostic technique: coherent anti‐Stokes Raman spectroscopy (CARS). On the assumption of a Boltzmann equilibrium among only the lowest vibrational levels, a method has been developed and utilized for the direct determination of vibrational populations of all other levels, even in the case of extreme deviations from a Boltzmann equilibrium. Limitations of the method are discussed and illustrated.