Ambient air plasma acceleration in tightly-focused ultrashort infrared laser beams

• Main Authors: Lytova, Marianna, Fillion-Gourdeau, François, Vallières, Simon, Fourmaux, Sylvain, Légaré, François, MacLean, Steve
• Format: Journal Article
• Language: English
• Published: 16-08-2024
• Subjects: Physics - Computational Physics; Physics - Optics; Physics - Plasma Physics
• DOI: 10.48550/arxiv.2408.09052

Recent experimental and theoretical results have demonstrated the possibility
of accelerating electrons in the MeV range by focusing tightly a few-cycle
laser beam in ambient air. Using Particle-In-Cell (PIC) simulations, this
configuration is revisited within a more accurate modelling approach to analyze
and optimize the mechanism responsible for electron acceleration. In
particular, an analytical model for a linearly polarized tightly-focused
ultrashort laser field is derived and coupled to a PIC code, allowing us to
model the interaction of laser beams reflected by high-numerical aperture
mirrors with laser-induced plasmas. A set of 3D PIC simulations is performed
where the laser wavelength is varied from 800 nm to 7.0 $\mu$m while the
normalized amplitude of the electric field is varied from $a_{0} = 3.6$ to
$a_{0} = 7.0$. The preferential forward acceleration of electrons, as well as
the analysis of the laser intensity evolution in the plasma and data on
electron number density, confirm that the relativistic ponderomotive force is
responsible for the acceleration. We also demonstrate that the electron kinetic
energy reaches a maximum of $\approx1.6$ MeV when the central wavelength is of
2.5 $\mu$m.