Abstract The generation of terahertz (THz) radiation from the propagation of Laguerre–Gaussian (LG) laser beams in a preformed plasma channel is investigated by considering relativistic nonlinearity. The transverse evolution of the laser beam is described using the moment theory approach, incorporating relativistic nonlinearity through the intensity-dependent electron mass variation. A self-consistent beam width equation is derived, accounting for diffraction, plasma channel guiding, and relativistic refractive index modification. The excitation of plasma waves by the non-linear current leads to efficient THz emission, whose yield is analytically evaluated for different LG modes. Higher-order modes exhibit stronger self-focusing and significantly improved THz efficiency due to stronger transverse intensity gradients. The influence of laser intensity, plasma density, and channel depth on beam dynamics and THz output is systematically examined. The obtained scaling shows qualitative agreement with experimental observations and numerical simulations of non-linear focusing behaviour.
Ancy et al. (Mon,) studied this question.