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

This paper presents the ponderomotive filamentation (single hot spot) of a laser beam, propagating in a homogeneous plasma in a non-paraxial region. Electron plasma wave coupling in these filaments has been studied. It is found that an 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 4^th power of r, it is observed that the focusing of the laser beams becomes fast in the non-paraxial region. The uneven focusing/defocusing of the axial and off-axial rays leads to the formation of a split 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 laser beam power. The energy of the accelerated electrons on account of laser beam and plasma wave interaction has been calculated by using a distribution function. For typical laser beam and plasma parameters with wavelength (lambda=1064 nm), power flux (10¹⁶ W cm^-2) and initial temperature (T_e= 2.5 keV ), the elevated electron temperature was found to be 4.5 keV, after passing through one wave packet.