Modeling of the initiation and evolution of a laser-ionized column in the lower atmosphere - 314.5 nm wavelength resonant multiphoton ionization of naturally occurring argon

A model has been developed to examine the effects of a 314.5 nm wavelength laser pulse directed vertically through the atmosphere on the local ion and electron concentrations in the beam path. The 314.5 nm wavelength was selected to exploit a three‐photon excitation resonance with the 3p54s 1P10 excited state in argon. Absorption of a fourth photon of the same wavelength will ionize the excited atom. Using a rate equation formalism and a detailed collection of atmospheric chemistry reactions the model provides the concentrations of electrons and ions as functions of altitude, time, laser energy, relative humidity, focal characteristics of the pulse, and ambient atmospheric electric‐field conditions. Both linear and nonlinear effects on the propagation of the laser pulse have been taken into account. The calculated charged particle concentrations are used to estimate the conductivity of the ionized column. Results presented indicate peak electron densities up to 108 cm−3 can be created using laser intensit...