Description: A simple but accurate theoretical model is developed to describe the growth of avalanche ionization (breakdown) in the blowoff vapor from a laser-irradiated surface. This nonequilibrium model is applicable to laser intensities and wavelengths from approximately 10/sup 7/ to 10/sup 12/ ..mu..m/sup 2/.W/cm/sup 2/ for lambda/sub L//sup 2/.I/sub 0/, the square of the laser wavelength times its peak intensity. The model pertains only to the early stages of laser-target interaction, from the time surface vaporization begins to when first-degree ionization is achieved in the vapor. Approximate analytical solutions are found for the basic differential equations of the model, and such key quantities as breakdown time and threshold values of laser fluence and intensity are expressed in terms of simple formulas. With the model, we can thus easily predict general trends and specific parametric dependences. The analytical solutions are shown to agree well with accurate numerical solutions of the model's equations and with documented data on CO/sub 2/ laser-induced breakdown over aluminum targets.
Date: December 1, 1977
Creator: Harrach, R.J.
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