Multifocal THz Emission with Multiple Resonances

Abstract

This analytical study shows an interesting mechanism for the emission of THz radiation due to the production of an extra transverse component of the nonlinear ponderomotive force when an external periodic electric field is applied to a plasma having density ripples. Three components of the nonlinear ponderomotive force; one due to the beating of the incident lasers and two others due to the coupling of the external electric field with the incident lasers’ field are responsible for the generation of different nonlinear currents. These nonlinear currents excited at different resonances lead to the emission of multifocal THz fields. The periodicities of density ripples (β) and external electric field help in attaining the multiple resonance conditions for the emission of multiple THz fields. The amplitude of emitted THz radiation can be tuned via the magnitude of the external electric field, laser beam and plasma parameters. The magnitude of the beat wave-enabled field is 102 times higher than the magnitude of THz fields induced due to external electric fields.