Extrinsic spin angular momentum carried by plasmonic vortex in terahertz cylindrical corrugated waveguide

An electromagnetic surface wave carrying orbital angular momentum (AM) is called plasmonic vortex that also carries spin AM originating from evanescent field. In this study, spin and orbital AM of plasmonic vortex in a terahertz cylindrical corrugated waveguide (CCW) are analyzed. We report the extrinsic spin AM of the plasmonic vortex for the first time. The extrinsic spin AM is produced by the rotation of the polarization of the plasmonic vortex whose rotation axis is positioned at the vicinity of the CCW wall. The extrinsic spin AM depends on the intrinsic orbital AM and radius of CCW. The plasmonic vortex with sufficiently large orbital AM carries large spin AM per photon. This large extrinsic spin AM expands degree of freedom of the spin AM and would be applied to various terahertz technologies.