Terahertz Generation and Nonlinear Propagation of Laguerre–Gaussian Laser Beams in Plasma Channel with Relativistic-Ponderomotive Effects

In this article, we carry out a theoretical investigation of the self-focusing and propagation characteristics and terahertz (THz) radiation generation of Laguerre–Gaussian (LG) laser beams in an inhomogeneous plasma channel, considering the effects of relativistic and ponderomotive nonlinearities. The analysis is carried out by the method of moments to derive the equation for the evolution of the width of LG laser beams propagating in a preformed parabolic plasma channel. From the results, it is observed that the overall effect of relativistic mass variation and intensity-dependent ponderomotive force results in a significant modification in the plasma refractive index, which in turn affects self-focusing and confinement. The self-focusing is observed to be sensitive to various parameters such as intensity, plasma density, channel depth, and order of LG modes. It is also noted that the most efficient generation of THz radiation occurs in the regime where self-focusing is strongest, which suggests an intrinsic connection between beam confinement effects and plasma low-frequency responses. It is also noted that the THz signal increases with increasing laser intensity and channel depth, which suggests that relativistic ponderomotive effects are key to understanding the overall efficiency of the process. It is also noted that the presence of a preformed parabolic plasma channel enhances the guiding effects, which supports the interaction process. On the whole, the study suggests that structured LG beam modes, especially of higher orders, can be a promising way of controlling self-focusing and boosting THz generation in plasmas, and this may have implications for the creation of a new generation of radiation sources.