Self-focusing and defocusing phenomena of super-Gaussian laser beams in plasmas carrying density gradient

Abstract

Considering nonlinearities due to relativistic mass variation and ponderomotive force driven depression in the electron density, a model is developed for the self-focusing of a super-Gaussian laser beam in inhomogeneous plasmas. Since paraxial ray approximation is not appropriate for the beams of super-Gaussian profile, the formulation is developed based on the moment theory. To have an in-depth understanding of self-focusing and defocusing phenomena and to develop generalized treatment, three different types of plasma density profiles namely linear, tangent and exponential density profiles, are considered and the results are compared. Due to the saturating nature of nonlinear permittivity with laser intensity, the beam is found to undergo periodic focusing because of competition between the diffraction divergence and nonlinear self-focusing effects. The ponderomotive nonlinearity enhances the self-focusing. As the super-Gaussian beam moves into higher density plasma region up to several Rayleigh lengths, stronger self-focusing is achieved and the value of minimum spot size decreases.

Electron Acceletaion by Laser Driven Electron Plasma Wave in Plasma with Density Ramp: Cosh Gaussian Laser Beam

“…Along with ideal Gaussian beams a few investigations have been reported on electron acceleration by Gaussian like beam pro les i.e., -Gaussian laser beams [18][19]. The irradiance cross-section of Gaussian beams decreases symmetrically with increasing distance from the center; in contrast, at-top beams, also known as top-hat beams, maintain a constant irradiance value through a beam cross-section, providing a consistent intensity across the target of a laser system [20,21]. This results in more accurate and predictable results in applications such as semiconductor wafer processing, other materials processing, and nonlinear frequency conversion with high-power beams.…”