Second harmonic generation by radially polarized laser beam propagating in homogeneous plasma

TL;DR

This paper analytically and numerically investigates second harmonic generation by radially polarized laser beams in homogeneous plasma, revealing enhanced harmonic generation near the beam axis and oscillatory behavior along the propagation direction.

Contribution

It provides the first analytical expressions for SHG fields in homogeneous plasma driven by radially polarized beams, validated by simulations, highlighting their unique efficiency compared to other polarizations.

Findings

SHG amplitudes oscillate periodically along propagation

Radial and axial SHG contributions are enhanced near the beam axis

Radially polarized beams enable efficient SHG in homogeneous plasma

Abstract

This study presents an investigation of second harmonic generation (SHG) resulting from interaction of radially polarized laser beam propagating in homogeneous, unmagnetized plasma. Lorentz force and continuity equations have been used to derive the radial and axial current density components. Further, using these densities in the wave equation leads to analytical expressions for the SHG field amplitudes. These amplitudes exhibit periodic oscillations along the propagation axis, characterized by detuning length dependent on plasma density and laser parameters. Radial and axial contributions to SHG are found to be highly enhanced near the beam axis due to the Gaussian beam profile of the laser. The analytical findings are validated using Fourier Bessel Particle-In-Cell (FBPIC) simulations. Notably, unlike linearly or circularly polarized beams which require either inhomogeneous or magnetized plasma, radially polarized beams facilitate efficient harmonic generation in homogeneous unmagnetized plasmas.