Orbital-to-Spin Angular Momentum Conversion Employing Local Helicity

Abstract

Spin-orbit interactions in optics traditionally describe an influence of the polarization degree of freedom of light on its spatial properties. The most prominent example is the generation of a spin-dependent optical vortex upon focusing or scattering of a circularly polarized plane-wave by a nanoparticle, converting spin to orbital angular momentum of light. Here, we present a mechanism of conversion of orbital-to-spin angular momentum of light upon scattering of a linearly polarized vortex beam by a spherical silicon nanoparticle. We show that focused linearly polarized Laguerre-Gaussian beams of first order ($\ell =\pm 1$) exhibit an $\ell$-dependent spatial distribution of helicity density in the focal volume. By using a dipolar scatterer the helicity density can be manipulated locally, while influencing globally the spin and orbital angular momentum of the beam. Specifically, the scattered light can be purely circularly polarized with the handedness depending on the orbital angular momentum of the incident beam. We corroborate our findings with theoretical calculations and an experimental demonstration. Our work sheds new light on the global and local properties of helicity conservation laws in electromagnetism.

8 pages, 6 figures, 1 table

References in corpus (11)

• Optical spin-to-orbital angular momentum conversion in inhomogeneous anisotropic media
• Chiral Quantum Optics
• Chiral nanophotonic waveguide interface based on spin-orbit coupling of light
• Observation of the spin-based plasmonic effect in nanoscale structures
• Angular Momenta and Spin-Orbit Interaction of Nonparaxial Light in Free Space
• Characterizing optical chirality
• Conservation of the spin and orbital angular momenta in electromagnetism
• Angular momentum-induced circular dichroism in non-chiral nanostructures
• Beaming of helical light from plasmonic vortices via adiabatically tapered nanotip
• Note on the helicity decomposition of spin and orbital optical currents
• Non-zero helicity extinction in light scattered from achiral (or chiral) small particles located at points of null incident helicity density

Cited by in corpus (2)

• Mimicking Chiral Light-Matter Interaction
• Sectoral Multipole Focused Beams