Generation of terahertz (THz) radiation by p-polarised lasers beating in hot plasma with surface density ripple

摘要

The present communication deals with a scheme to generate terahertz (THz) radiation by electromagnetic Gaussian beams beating in a hot collisionless plasma having a density ripple on its surface, parallel to the z-axis. These p-polarised laser beams propagate in the x-z plane, incident obliquely to the density ripple on the plasma surface, and exert a ponderomotive force on electrons. The plasma electrons start oscillating because the plasma neutrality disturbed by the nonlinearity arises due to the ponderomotive force. This oscillatory velocity beats with the density ripple; as a result, an irrotational current density (J) over right arrow (NL) arises at the beating frequency omega(1) - omega(2) (with (del) over right arrow x (J) over right arrow (NL) not equal 0). This nonlinear current density urges a wave whose frequency is in the THz range. Our results show that, for a set of laser and plasma parameters, the power of emitted THz radiation scales as the square of the density ripple amplitude, as well as the amplitude of the emitted THz wave, decreases with the THz frequency and increases with the incidence angle up to an optimum value. In our case, the maximum normalised amplitude of emitted THz radiation is reached up to 0.038 at laser intensity similar to 7 x 10(14) W cm(-2), theta = 30 degrees and electron temperature similar to 5 keV with 30% density ripple.