Enhanced Third Harmonic Generation in Thermal Quantum Plasma Driven by Cosh-Gaussian Laser Beams under Relativistic-Ponderomotive Nonlinearities

Abstract

The current study explores enhanced third harmonic generation in thermal quantum plasma driven by cosh-Gaussian laser beams considering relativistic-ponderomotive nonlinear effects. Laser beam propagation in plasma leads to development of strong intensity gradients due to relativistic mass variation of electrons and ponderomotive force. There is an excitation of electron plasma wave at twice the frequency of fundamental wave due to these intensity gradients through \({{\vec {V}}} \times {{\vec {B}}}\) mechanism. The nonlinear coupling of excited plasma wave and fundamental wave produces third harmonic generation. The nonlinear differential equation representing the dynamics of beam waist as a function of propagation distance and analytically expression for conversion efficiency of third harmonics are derived by employing Wentzel–Krammers–Brillouin and paraxial approaches. Further, the impact of key laser-plasma parameters on focusing behavior of beam and conversion efficiency of third harmonics is also explored.