Helicity locking in light emitted from a plasmonic nanotaper

TL;DR

This paper demonstrates how a plasmonic nanocone can produce a circularly polarized light beam with a fixed helicity, due to the intrinsic transverse spin of surface plasmons, combining experimental, theoretical, and numerical approaches.

Contribution

It introduces a simple geometric model predicting the helicity-locking effect in plasmonic nanocones, supported by experimental validation.

Findings

Helicity of emitted light is locked to the transverse spin of surface plasmons.

The nanocone guides plasmonic vortices to produce single-handed circular polarization.

Experimental results confirm the model and numerical simulations.

Abstract

Surface plasmon waves carry an intrinsic transverse spin, which is locked to its propagation direction. Apparently, when a singular plasmonic mode is guided on a conic surface this spin-locking may lead to a strong circular polarization of the far-field emission. Specifically, an adiabatically tapered gold nanocone guides an a priori excited plasmonic vortex upwards where the mode accelerates and finally beams out from the tip apex. The helicity of this beam is shown to be single-handed and stems solely from the transverse spin-locking of the helical plasmonic wave-front. We present a simple geometric model that fully predicts the emerging light spin in our system. Finally we experimentally demonstrate the helicity-locking phenomenon by using accurately fabricated nanostructures and confirm the results with the model and numerical data.