Laguerre-Gaussian beam and plasma interaction under relativistic and ponderomotive nonlinearities

Abstract

Self-focusing of the laser plays a decisive role in achieving higher intensity. This article investigates the beam width evolution of the Laguerre-Gaussian laser beam in an underdense, cold, and collisionless plasma in the presence of weakly relativistic and ponderomotive nonlinearities. We consider pure radial mode of the LG beam (LG10) as it plays a key role in phenomenon like higher harmonic generation and can dominate diffraction effect in the self-focusing. Wentzel–Kramers–Brillouin (WKB) approach under paraxial approximation is used to reduce the nonlinear wave equation to a differential equation for the beam width parameter to study the self-focusing and defocusing phenomena. The optimum values of the initial intensity and beam waist of the laser beam are then calculated and plotted, for which the diffraction divergence is cancelled out by the self-focusing.