Non-equilibrium plasma generation via nano-second multi-mode laser pulses

TL;DR

This paper presents a comprehensive non-equilibrium plasma model that simulates laser-induced plasma formation using nano-second multi-mode laser pulses, accurately predicting plasma behavior without artificial triggers.

Contribution

It introduces a coupled hydrodynamic and plasma dynamics model that accounts for beam propagation and attenuation, reducing reliance on empirical parameters and improving simulation accuracy.

Findings

Good agreement between simulations and experiments on plasma boundary evolution.

Periodic plasma kernel structures are linked to modulating laser frequency.

Model effectively predicts plasma formation without artificial seeding.

Abstract

A non-equilibrium model for laser-induced plasmas is used to describe how nano-second temporal mode-beating affects plasma kernel formation and growth in quiescent air. The chemically reactive Navier-Stokes equations describe the hydrodynamics, and non-equilibrium effects are modeled based on a two-temperature model. Inverse Bremsstrahlung and multiphoton ionization are self-consistently taken into account via a coupled solution of the equations governing plasma dynamics and beam propagation and attenuation (i.e., Radiative Transfer Equation). This strategy, despite the additional challenges it may bring, allows to minimize empiricism and enables for more accurate simulations since it does not require an artificial plasma seed to trigger breakdown. The benefits of this methodology are demonstrated by the good agreement between the predicted and the experimental plasma boundary evolution and absorbed energy. The same goes for the periodic plasma kernel structures which, as suggested by experiments and confirmed by the simulations discussed here, are linked to the modulating frequency.