Strong terahertz radiation generation by cosh-Gaussian laser beams in axially magnetized collisional plasma under non-relativistic ponderomotive regime

摘要

We propose a scheme for terahertz (THz) radiation generation by non-linear mixing of two cosh-Gaussian laser beams in axially magnetized plasma with spatially periodic density ripple where electron-neutral collisions have been taken into account. The laser beams exert a non-linear ponderomotive force due to spatial non-uniformity in the intensity. The plasma electrons acquire non-linear oscillatory velocity under the influence of ponderomotive force. This oscillatory velocity couples with preformed density ripples (n′ = n0αeiαz) to generate a strong transient non-linear current that resonantly derives THz radiation of frequency ~ωh (upper hybrid frequency). Laser frequencies (ω1 and ω2) are chosen such that the beat frequency (ω) lies in the THz region. The periodicity of density ripple provides phase-matching conditions (ω = ω1 ? ω2 and $ec k = ec k_1 - ec k_2 + {m ec lpha} $) to transfer maximum momentum from laser to THz radiation. The axially applied external magnetic field can be utilized to enhance the non-linear coupling and control various parameters of generated THz wave. The effects of decentered parameters (b), collisional frequency (νen), and magnetic field strength (B0 = ωcm/e) are analyzed for strong THz radiation generation. Analytical results show that the amplitude of THz wave enhances with decentered parameters as well as with the magnitude of axially applied magnetic field. The THz amplitude is found to be highly sensitive to collision frequency.