Spin-orbit interaction in a high-power laser irradiated micro-scale plasma waveguide

Light carries angular momentum as spin and orbital components. The spin-orbit interaction (SOI) of light refers to phenomena in which the spin (left or right circular polarisation) affects the spatial degrees of freedom. Recently, interest in SOI has surged, as it provides physical insight into the behaviour of polarised light at subwavelength scales, and allows for spin-controlled manipulation of light. Most studies are performed with low intensity, leaving the role SOI plays in the relativistic laser-plasma interaction, characterised by nonlinearity, less understood. Here, using 3D particle-in-cell simulations, we report SOI effects in this unprecedented regime. Specifically, a circularly polarised Gaussian laser irradiating a micro-scale plasma waveguide drives a spin-controlled chiral surface wave, allowing the reflected harmonic photons to gain orbital angular momentum (OAM). These effects produce intense optical vortices in the extreme ultraviolet regime - an area of significant fundamental and applied physics potential.