Gas breakdown initiated by laser radiation interaction with aerosols and solid surfaces

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Abstract
The threshold for generation of high-density plasma caused by the interaction of laser radiation with solids is examined theoretically. The developed semiquantitative model is applicable for predicting the threshold for generating laser-supported absorption waves, absorbing plasma produced on surfaces with high-intensity laser radiation, and also for predicting the threshold of aerosol-induced gas breakdown, commonly referred to as dirty air breakdown. In developing the model, the vapor density generated by laser interaction with the solid is calculated and then the intensity required to cascade ionize the vapor to full ionization is calculated. Analytic expressions are derived for the breakdown intensity which show the parametric dependence of the threshold. Since the vapor density is a function of laser intensity, and characteristics of the solid, different parametric dependence of the threshold on wavelength, pulse length, and particle characteristics is predicted compared to those determined by previous theoretical models of gas breakdown. Comparison of the threshold predicted by the model agree within a factor of 2 of experimental data for a wide range of experimental conditions including laser pulse duration from 10 nsec to cw, particle sizes from 0.1 μ to laser spot sizes of 1 cm, and wavelength scaling of 1.06–10.6 μ wavelength. Based on the good agreement between theoretical predictions and experimental data, the model can be used to predict thresholds for plasma production for a wide variety of atmospheric and solid-surface conditions.