The development of the Weibel-like instability in the optical breakdown of a dilute neutral gas by an intense laser field is investigated. The ionization mechanism for the gas atoms is governed by tunneling of the bound electrons of atoms. The electron distribution function (EDF) formed during the breakdown process is derived from the electron kinetic equation using a simple model for atomic tunneling ionization. The dielectric permittivity tensor is obtained and the plasma stability is discussed by the solution of the dispersion equation for small electron perturbations. With close attention to the dominant role of the longitudinal ponderomotive force in the laser and gas atoms interaction, the existence of an oscillatory Weibel-like mode is shown in a mildly relativistic regime. The analytical solution is available only for low frequency limit when . Furthermore, the existence of the Weibel-like mode is investigated by a numerical solution of the dispersion equation, in a wide range of frequencies. It is shown that the numerical results are in good agreement with analytical one in low frequency limit when the instability growth rate γ varies linearly with parameter vE/c.
Electron diffusion due to electromagnetic field fluctuations