CARS Temperature Measurements and Stability Studies of a D.C. Nitrogen Discharge.

摘要

The vibrational and rotational temperatures of a 30-Torr, normal glow N2 gas discharge have been measured using a coherent anti-Stokes Raman spectroscopy system in the folded BOXCARS configuration. The discharge was set up in slowly flowing nitrogen between two plane parallel molybdenum electrodes. Current densities of O.047 A/sq cm were used with an E/N of approximately 50 Td. The nearly wall-less discharge was stabilized using a Macor ceramic cap covering the cathode with a 9-mm circular aperture in the center. Measurements were made at spatially resolved locations within the discharge both axially and radially. Theoretical spectra were fit to experimental data in order to obtain the rotational and vibrational temperatures and the relative populations. A detailed study of the spectral line shape of the dye laser used as the probe beam in the CARS system was carried out using the optogalvanic effect in a Fe-Ne hollow-cathode lamp. The spectral line width and lineshape under differing dye pumping schemes were obtained. These measured line widths were greater than expected and showed a non-Gaussian profile for the probe laser. Stability of the nitrogen discharge was also studied in order to determine the conditions under which the discharge remains stable. Instability was noted visually, in the behavior of the CARS signal and the electrode voltage, both of which showed hysteresis. In order to make way for changes in the system in the future, a new CARS system was designed which will allow study of various gasses under differing discharge conditions.