Efficient vortex generation in sub-wavelength epsilon-near-zero slabs

TL;DR

This paper demonstrates that epsilon-near-zero slabs efficiently generate optical vortices of order two in reflected and transmitted light, leveraging their unique electromagnetic properties for potential nanophotonic applications.

Contribution

It reveals that epsilon-near-zero materials can produce high-order vortices efficiently in sub-wavelength slabs without complex fabrication, due to their unique electromagnetic response.

Findings

Vortices of order two are generated in reflected and transmitted fields.

Vortex generation is highly efficient in epsilon-near-zero regimes.

The process works effectively even at ultraviolet wavelengths.

Abstract

We show that a homogeneous and isotropic slab, illuminated by a circularly polarized beam with no topological charge, produces vortices of order two in the opposite circularly polarized components of the reflected and transmitted fields, as a consequence of the difference between transverse magnetic and transverse electric dynamics. In the epsilon-near-zero regime, we find that vortex generation is remarkably efficient in sub-wavelength thick slabs up to the paraxial regime. This physically stems from the fact that a vacuum paraxial field can excite a nonparaxial field inside an epsilon-near-zero slab since it hosts slowly varying fields over physically large portion of the bulk. Our theoretical predictions indicate that epsilon-near-zero media hold great potential as nanophotonic elements for manipulating the angular momentum of the radiation, since they are available without resorting to complicated micro/nano fabrication processes and can operate even at very small (ultraviolet) wavelengths.