Spin-to-Orbital Conversion of Angular Momentum in Harmonic Generation Driven by Intense Circularly Polarized Beam

TL;DR

This paper introduces a novel physical mechanism for converting spin angular momentum to orbital angular momentum in harmonic generation driven by intense circularly polarized lasers, verified through simulations and theory.

Contribution

It presents the first demonstration of spin-to-orbital angular momentum conversion in harmonic generation via plasma surface oscillations driven by circularly polarized light.

Findings

Vortex harmonics with OAM are generated after CP laser interaction.

The process conserves total angular momentum during harmonic generation.

OAM of harmonic photons can be tuned using initial vortex beams or spiral phase plates.

Abstract

A new physical mechanism to achieve spin-to-orbital angular momentum conversion based on the interaction of an intense circularly polarized (CP) laser beam with a plane foil is presented and studied for the first time. It has been verified by both simulation and theoretical analysis that vortex harmonics carrying orbital angular momentum (OAM) are generated after a relativistic CP laser beam, even a Gaussian beam, impinges normally on a plane foil. The generation of this vortex harmonics is attributed to the vortex oscillation of the plasma surface driven harmonically by the vortex longitudinal electric field of the CP beam. During the process of harmonic generation, the spin angular momenta of fundamental-frequency photons are converted to OAM of harmonic photon because of the conservation of total angular momentum. In addition, if an initially vortex beam or a spiral phase plate is used, the OAM of harmonic photon can be more tunable and controllable.