Effect of laser beam filamentation on plasma wave localization and electron heating

Abstract

This paper presents the ponderomotive filamentation (single hot spot) of a laser beam, propagating in homogeneous plasma in a nonparaxial region. Electron plasma wave coupling in these filaments has been studied. It is found that initially launched weak plasma wave (small amplitude) gets excited and becomes highly localized (wave packet) with a broad spectrum. By expanding the eikonal and other relevant quantities up to the fourth power of r, it is observed that the focusing of the laser beams becomes fast in the nonparaxial region. The uneven focusing/defocusing of the axial and off-axial rays leads the formation of the splitted profile of laser beams in the plasma. The effects of wave particle interaction are also included in this formalism. The simulation result confirms the presence of chaotic fields, and the interaction of these fields with electrons, leads to velocity space diffusion. The stochasticity in the system is also verified by estimating the Lypunov exponent by slightly varying the laser beam power. The energy of the accelerated electrons on account of the laser beam and plasma wave interaction has been calculated by using the distribution function. For typical laser beam and plasma parameters with wavelength (λ=1064nm), power flux (1016Wcm−2), and initial temperature (Te=2.5keV), the elevated electron temperature was found to be around 4.5keV, after passing through one wave packet.