Helical Electric Field-Assisted Circular Polarised Terahertz Wave Generation in Plasma by Beating of Two Lasers

Abstract

We have studied the circular polarised Terahertz (THz) wave emission by mixing of two lasers in plasma when an externally applied helical structured electric field is present. A nonlinear transverse current density at difference frequency emerges on the accounts of ponderomotive nonlinearity. This occurs when the electrons moving under the influence of externally applied helical electric field, couples with the nonlinear plasma density at difference frequency. This transverse current density can be decomposed of two mutually perpendicular vector having equal amplitude and $\pi /2$ phase shift, which drives a circular polarised coherent THz radiation. It turns out that conversion efficiency of THz radiation substantially depends on electron plasma frequency, mismatch phase, polarisation angle between laser beams and externally applied helical electric filed. Numerical simulations show that the conversion efficiency increases as THz frequency approach to plasma frequency.