In-situ CARS investigation of vibrational temperature of SF6 in discharge plasmas

In-situ real time CARS (coherent anti-Stokes Raman spectroscopy) spectra of the nu(1) mode of SF6 were recorded in a discharge tube with varying delay times between the discharge pulse and the CARS detection pulse. Theoretica l CARS spectra were calculated for the nu(1) mode of SF6 at various vibrati onal temperatures. Based on relationships between line width, frequency shi ft, and temperature, a best fit method was developed to extract the tempera tures from experimental line shapes instead of peak intensities. The kineti c behaviour of the vibrational temperature of SF6 during the discharge puls e was thus obtained. This method is useful for examination of chemical and physical processes in which the total population in a specific vibrational mode changes.