Terahertz twisted beams generation in plasma

Abstract

The resonant vortex terahertz beam generation by the cross-focusing of two twisted coaxial laser beams is investigated. For the resonant excitation of terahertz radiation, the rippled density in plasma and the ripple wave number is suitably chosen to satisfy the phase matching condition. The nonlinear current density at terahertz frequency arises due to the spatial variation of two Laguerre-Gaussian coupled field. The terahertz intensity scales as the ponderomotive force of laser beams which imparts an oscillatory velocity to the electrons and, in fact, input Laguerre-Gaussian laser beams properties such as vortex charge number and beam waist. Various laser and plasma parameters are employed to yield vortex terahertz radiation with higher efficiency. Also, it is shown that when the beating frequency approaches plasma frequency, the amplitude of THz radiation increases.