Abstract
In this work, we report a numerical investigation of two sets of experimental measurements that were previously carried out to study the breakdown threshold dependence on laser characteristics (wavelength, pulse width, and spot size) in the breakdown of laboratory air at different pressures. The study aimed to inspect the significance of the physical mechanisms in air breakdown as related to the applied experimental conditions. In doing so, we adopted a simple theoretical formulation relying on the numerical solution of a rate equation that describes the growth of electron density due to the joined effect of multi-photon and avalanche ionization processes given in our earlier work [Gaabour et al., J. Mod. Phys. 3, 1683-1691 (2012)]. Here, the rate equation is adapted to include the effect of electron loss due to attachment processes. This equation is then solved numerically using the Runge-Kutta fourth order technique. The influence of electron gain and loss processes on the breakdown threshold is studied by calculating the breakdown threshold intensity and RMS electric field for atmospheric air using different laser parameters (wavelength, pulse widths, and focal length lenses), in correspondence to the experimental conditions given by Tambay and Thareja [J. Appl. Phys. 70(5), 2890 (1991)]. To validate the model, a comparison is made between those calculated thresholds and the experimentally measured ones. Moreover, the effective contribution of each of the considered physical processes to the breakdown phenomenon is examined by studying the effect of laser wavelength and spot diameter on the threshold intensities, as well as on the temporal variation of the electron density. The correlation between the threshold intensity and gas pressure is tested in relation to the measurements of Tambay et al. [Pramana-J. Phys. 37(2), 163 (1991)]. Calculations are also carried out to depict the impact of pulse width on the threshold intensity. Published by AIP Publishing.