Terahertz generation by an amplitude-modulated Gaussian laser beam in a rippled density plasma column

Abstract

The nonlinear interaction of amplitude-modulated two-dimensional and three-dimensional laser beams with a cylindrical plasma column and the generation of terahertz (THz) radiation are studied. The plasma column could be formed by a cylindrically symmetric laser pre-pulse impinging on a gas jet target. A two-dimensional Gaussian laser beam propagating through the plasma exerts a ponderomotive force on electrons, imparting on them a resonant transverse velocity at the modulation frequency, Ω, when , where ωp is the plasma frequency of the column. The current produces THz radiation. In the case of a cylindrically symmetric Gaussian laser beam, the electron response to ponderomotive force misses the resonance, yet the phase matching introduced by a density ripple could efficiently produce THz radiation. The power conversion efficiency of the order of the ratio of THz radiation frequency to laser frequency can be achieved at a laser intensity of ≈1015  W cm−2 at 1 μm wavelength.