# Polarization Spin Inversion with Nonlinear Plasmon Scattering

## TL;DR

This paper shows how plasmonic particles can invert the handedness of polarized light through nonlinear scattering effects.

## Contribution

The study demonstrates polarization spin inversion using nonlinear plasmon scattering in silvered nanoporous silica microparticles.

## Key findings

- High laser power induces reverse saturated scattering (RSS) in plasmonic particles, enabling handedness conversion.
- Handedness conversion occurs only at wavelengths matching quadrupole plasmon modes.
- Adding ethynylaniline (EA) enables handedness conversion at both low and high laser powers.

## Abstract

We report on circularly polarized Gaussian beam spin
angular momenta
that can be inverted upon scattering with quadrupole plasmon modes.
The conditions for such conversion are met with high-angle collection,
dark-field scattering microscopy on spherical plasmonic particles.
We further report that silvered nanoporous silica microparticles exhibit
a strong nonlinearity in their scattering, specifically a reverse
saturated scattering (RSS), when exposed to high laser power densities
on the sample of ca. 5 GW/cm2. Handedness conversion by
these microparticles is only observed at wavelengths tuned to the
quadrupole modes. Conversely, the scattering remains linear, and the
handedness is unchanged, when the same particles are illuminated with
low laser power densities of ca. 10 W/cm2. We infer that
RSS tuned to the quadrupole modes sufficiently enhances their contribution
so that they dominate the high-angle scattering, thereby justifying
the light spin inversion. Moreover, the addition of a self-assembled
monolayer of ethynylaniline (EA) on the microparticles results in
handedness conversion for both low and high incident power, as expected
from preferable dipole damping and plasmon mode red shift. This demonstrates
that optical nonlinearity in scattering can be exploited for polarization
tuning in plasmonic metamaterials.