Far-field measurements of vortex beams interacting with nanoholes

TL;DR

This study investigates how vortex beams interact with nanoholes, revealing that angular momentum is conserved while helicity is not, and that vortex beams significantly influence the transmitted helicity ratios.

Contribution

It provides the first detailed analysis of vortex beam transmission through nanoholes, highlighting the dependence on helicity and angular momentum, and demonstrating the enhancement of helicity ratios with vortex beams.

Findings

Total angular momentum is preserved during transmission.

Helicity is not conserved in the process.

Vortex beams increase the helicity ratio compared to Gaussian beams.

Abstract

We measure the far-field intensity of vortex beams going through nanoholes. The process is analyzed in terms of helicity and total angular momentum. It is seen that the total angular momentum is preserved in the process, and helicity is not. We compute the ratio between the two transmitted helicity components, $\gamma_{m,p}$. We observe that this ratio is highly dependent on the helicity ($p$) and the angular momentum ($m$) of the incident vortex beam in consideration. Due to the mirror symmetry of the nanoholes, we are able to relate the transmission properties of vortex beams with a certain helicity and angular momentum, with the ones with opposite helicity and angular momentum. Interestingly, vortex beams enhance the $\gamma_{m,p}$ ratio as compared to those obtained by Gaussian beams.