Influence of periodic chirp dynamics in radially polarised q-Gaussian laser-plasma interactions for terahertz wave optimization in homogeneous plasma

Abstract

We analytically investigate the generation of terahertz (THz) radiation via interaction of two counter propagating radially polarized q-Gaussian laser beams in homogeneous collisional plasma modulated by periodic (sinusoidal) chirp. In contrast to the linear chirp, the periodic chirp offers an oscillatory modulation of the instantaneous laser frequency that is time dependent, allowing a dynamic synchronization of the nonlinear plasma current with the emitted THz wave. Parametric analysis shows that the maximum THz emission is obtained in the low normalized frequency regime ( ω / ω _p ≈ 1.08–1.15) with the best output at smaller chirp modulation indices ( α ≈ 0.4), higher q-parameter values and intermediate radial beam positions ( r / r ₀ ≈ 0.7–1.0). The THz amplitude is moderately increased with increasing plasma electron density and the emission is suppressed by collisional damping with increasing collision frequency, where the peak normalized field decreases from about 0.62 to 0.31 as ν increases from 0.04 ω _p to 0.08 ω _p . The normalized THz energy analysis reveals a monotonic decrease with increasing chirp index, corresponding to a drop of ∼70–75 % at higher chirp values, implying the existence of an optimal chirp window for phase-coherent energy transfer. These results show that periodic chirp modulation and q-Gaussian beam shaping is an efficient and flexible method to control and optimize plasma-based THz sources.