Axial Inhomogeneous Ponderomotive Plasma Dynamics in Entire Spatial Intense Laser Fields

Abstract

This study investigates the effects of axial inhomogeneity on the ponderomotive force within a plasma subject to intense laser fields. The nonlinearity in the dielectric constant arises because the self-focusing problem of nonlinear interaction of intense laser beams has been analysed considering the entire spatial characteristics of the laser beam without any paraxial ray approximation and Taylor series expansion of the dielectric constant—the effect of the axial inhomogeneity on the ponderomotive force for an arbitrary magnitude of intensity. The propagation characteristics of laser beams have been discussed. An appropriate expression for the nonlinear dielectric constant has been used considering the entire spatial characteristic of plasma in the analysis of laser-beam propagation in the non-paraxial approximation for a circularly polarised wave. Various types of inhomogeneity are discussed for plasma. The variations of the beam width parameter with the propagation distance, the self-trapping condition and the critical power have been evaluated. The saturating nature of the nonlinearity for the critical power for beam self-focusing. It is seen that the laser beam width tends to attain a constant value depending on the plasma inhomogeneity and the initial laser intensity. Numerical estimates are made for typical values of the laser-plasma interaction applicable for under-dense and over-dense plasmas, and the results are compared with the paraxial ray approximation method.