Breakdown phenomena in rare and in molecular gases using pulsed carbon dioxide laser radiation
Cooper, Alf W.
Woehler, K. E.
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Light from an atmospheric pressure, double-discharge CO(2) laser was focused in monatomic and in diatomic gases at pressure from 0.01 atm to 10 atm in order to produce optical breakdown. The gases under investigation were Ar, He, N(2), H(2), and air. Measurements of the transmitted laser intensity were obtained and the properties of the resulting spark were studied by means of an open face camera and spectroscopic techniques. For all gases studied the threshold power density was on the order of tens of gigawatts per square centimeter and decreases with increasing focal volume or gas pressure. The theoretical model was based on classical microwave cascade theory. The importance of loss terms other than electron diffusion loss was discussed. In the presence of preionization the threshold was on the order of hundreds of megawatts per square centimeter and showed no volume dependence. Emission spectra consisted of a strong continuum superimposed with strong lines due to neutral and ionized atoms. Results of this study were in good agreement with data published in the current literature.