Thermal effects and shockwave formation due to filaments in air

Abstract

A filament forms through a balance of self-focusing (Kerr effect) and plasma self-defocusing. The heat generated as the electron-ion recombine produces a cylindrical shock wave behind which a low-density channel is formed. High-energy UV filaments are used to study the shock wave by shadowgraphy. The shock is seen to start supersonic, before transitioning after microseconds to a constant velocity acoustic wave. Computational models of the gas-dynamics evolution are presented that agree with a well known empirical formula for shockwave velocity, as well as with experimental observations. We determine the profile of induced changes to the refractive index of air due to these thermal effects. We then simulate a vortex filament creating a parabolic index of refraction that can serve as a waveguide for successive filaments.