Numerical modeling for investigating the optical breakdown threshold of laser-induced air plasmas at different laser characteristics

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...