Beaming of helical light from plasmonic vortices via adiabatically tapered nanotip

TL;DR

This paper presents a method to generate and direct optical beams with specific orbital angular momentum using a tapered plasmonic structure, combining theoretical modeling, numerical simulation, and experimental validation.

Contribution

It introduces an adiabatically tapered gold nanotip with a spiral slit for efficient mode transformation from plasmonic vortices to free-space Laguerre-Gaussian beams, validated by fabrication and measurements.

Findings

Successful generation of far-field optical beams with desired orbital angular momentum.

Excellent agreement between experimental measurements and theoretical predictions.

The structure enables localized excitation and beaming of plasmonic vortices.

Abstract

We demonstrate the generation of far-field propagating optical beams with a desired orbital angular momentum by using a smooth optical mode transformation between a plasmonic vortex and free space Laguerre-Gaussian modes. This is obtained by means of an adiabatically tapered gold tip surrounded by a spiral slit. The proposed physical model, backed up by the numerical study, brings about an optimized structure which is fabricated by using highly reproducible secondary electron lithography technique. Optical measurements of the structure excellently agree with the theoretically predicted far-field distributions. This architecture provides a unique platform for a localized excitation of plasmonic vortices followed by its beaming.