Dynamics of self-focusing and Terahertz generation of Bessel–Gaussian beam in plasma with density ramp

The current investigation examines the spatial dynamics of laser self-focusing and terahertz (THz) generation during the interaction of zeroth-order Bessel–Gaussian (BG) laser beam with the plasma medium. Self-focusing and terahertz generation in the plasma medium are analyzed by considering the combined effects of relativistic and ponderomotive nonlinearities along with a density ramp. The combined effect of these nonlinearities induces a transverse density gradient, stimulating an electron plasma wave (EPW) inside the plasma. The self-focused laser beam interacts with the excited electron plasma wave, producing terahertz radiation in the plasma medium. An expression for the laser beam width and the corresponding yield of terahertz generation is derived using the WKB approximation and the moment theory approach. The study concludes that laser and plasma parameters, along with the density gradient, significantly influence laser self-focusing and the yield of terahertz generation in plasma.