CARS studies of vibrationally excited nitrogen at low pressures

Coherent anti-Stokes Raman spectroscopy (CARS) was used to measure the vibrational temperature of microwave-excited nitrogen in a N₂–CO–He mixture. CARS spectra, originating from the N₂-vibrational levelsv=0 up tov=3, have been recorded by both narrowband scanning of the resonance region as well as by broadband OSA detection. For the microwave-excited N₂ molecules a vibrational temperatureT _v (N ₂ = (2130±110K) and a lower limit of detection forN ₂(v = 3) = 1.2 x 10¹⁵ cm^–3 was established. The CARS results were independently confirmed by simultaneously recorded and spectrally resolved CO infrared fluorescence studies.