Generation of optical vortex beam from relativistic channeling by laser pulse in plasmas

This study investigates the generation of second harmonic (SH) vortex beams in relativistic plasma channels driven by circularly polarized Gaussian laser pulses, with an emphasis on the conversion of spin to orbital angular momentum. Using a self-consistent cold fluid-Maxwell model and three-dimensional particle-in-cell simulations, it demonstrates that SH vortex beams can be effectively generated in such plasma channels, with their intensity reaching a maximum near the plasma channel boundaries. In addition, the findings reveal that the conversion efficiency of the SH vortex is closely tied to the background plasma density. Under the same pump laser conditions, higher plasma density results in a lower critical power for relativistic self-focusing, leading to significant self-channeling effects, a sharper electron density gradient at the channel boundary, and consequently the generation of more intense SH vortex beams.