Simulation study of phase-matched THz emission from an axially modulated magnetized plasma

Abstract

We studied and demonstrated the emission of THz waves by the beating of two CW-laser beams in an axially modulated plasma in the presence of a static magnetic field (applied transversely to the direction of propagation of lasers) from two-dimensional particle-in-cell simulation. The ponderomotive-force-induced nonlinear current drives THz radiation with frequency close to the beat frequency (Δω = ω1 − ω2) that propagates in the forward direction. Inside the plasma, THz radiation consists of a mixture of linear and radial polarization, while outside the plasma, only linear polarization dominates; however, radial polarization is stronger in the case of unmagnetized plasma. When the ripple is used, several modes are excited and the mode excited at Δk = (k1 − k2) − kq that meets the phase matching condition is resonantly enhanced. The THz field amplitude grows resonantly with time and it becomes saturated due to the excited higher-order mode coupling. The saturation level is reached about five times higher than the nonrippled plasma case in the vacuum side.