Enhanced second harmonic generation of Hermite–Gaussian laser beam in plasma having density transition

Abstract

Under the combined effect of relativistic and ponderomotive nonlinearity, resonant second harmonic generation of an intense Hermite-Gaussian (H-Gaussian) laser beam in a plasma having upward density ramp profile has been theoretically investigated. Under WKB approximation and with the use of the moment theory approach the coupled differential equations are derived which govern the spot size of the H-Gaussian laser beam. The ponderomotive force creates the density gradient in the background plasma electrons which is responsible for the excitation of the electron plasma wave. The large-amplitude electron plasma wave interacts with the fundamental beam which produces coherent radiations with double the frequency of the incident beam. In addition, the Gouy phase shift is observed for the H-Gaussian laser beam in plasma under the effect of density transition. The analysis shows the vital role of the different modes of the H-Gaussian laser beam and density ramp on the efficiency of generated harmonics and self-phase shift of laser beams in plasma.

Generation of terahertz radiation by a Hermite–Gaussian laser beam inside magnetoplasma with a density ramp

“…Poisson's equation, the adiabatic equation of state, the equation of motion and the continuity equation are the four main equations that govern the excitation of the electron plasma wave. The relativistic-ponderomotive force experienced by the electrons is given by and following Wadhwa & Singh (2020), the expression for perturbed electron density is given as …”

“…Unlike the laser beams with Gaussian profiles which are studied by paraxial theory, its interaction with plasma is studied through the method of moments. This is because for laser beams with super-Gaussian profile such as Laguerre–Gaussian (Kad & Singh 2022 a ,2022 c ), Bessel–Gaussian (Kad et al 2022), HG (Wadhwa & Singh 2020), etc., one needs to take into account the intensity of the off-axial parts along with the axial parts. In paraxial theory, only the axial part of the laser intensity is taken into consideration and the off-axial parts are neglected.…”

Direct Electron Acceleration By An Intense Nonparaxial Cosh-Gaussian Laser Beam Driven Electron Plasma Wave in Plasma

“…Nevertheless, various profiles of laser beams such as super Gaussian beams (Gill et al 2015), elliptic Gaussian beams (Gaur et al 2018), Hermite-Gaussian beams (Wadhwa and Singh 2020), hollow Gaussian beams (Purohit et al 2016), Hermite-cosh-Gaussian laser beams (Belafhal and Ibnchaikh 2000), and q-Gaussian beams (Yadav et al 2020) have been used in a few studies of self-focusing and plasma wave excitation. Such beams having different types of irradiance across their wavefront, which show different features in plasma.…”