# Orbital-to-Spin Angular Momentum Conversion Employing Local Helicity

## TL;DR

This paper demonstrates a novel orbital-to-spin angular momentum conversion mechanism in light scattering using a silicon nanoparticle, supported by theoretical and experimental evidence, advancing understanding of helicity and angular momentum in optics.

## Contribution

It introduces a new orbital-to-spin angular momentum conversion process employing local helicity manipulation with spherical nanoparticles, supported by both theory and experiments.

## Key findings

- Scattering of linearly polarized vortex beams can produce circularly polarized light with handedness dependent on orbital angular momentum.
- Helicity density distribution varies with orbital angular momentum in the focal volume.
- Experimental results confirm the theoretical predictions of angular momentum conversion.

## 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.