# Freestanding metasurfaces for optical frequencies

## TL;DR

This paper introduces ultrathin, freestanding optical metasurfaces fabricated via focused ion beam milling, capable of functioning as lenses and phase plates to manipulate light at optical frequencies.

## Contribution

The work demonstrates a novel fabrication method for freestanding metasurfaces with integrated optical functionalities at nanometer scale.

## Key findings

- Successfully fabricated 40 nm thick freestanding metasurfaces
- Demonstrated a metasurface lens with 1 mm focal length
- Created a phase-plate transforming Gaussian beam into Laguerre-Gaussian mode

## Abstract

We present freestanding metasurfaces operating at optical frequencies with a total thickness of only 40$\,$nm. The metasurfaces are fabricated by focused ion beam milling of nanovoids in a carbon film followed by thermal evaporation of gold and plasma ashing of the carbon film. As a first example, we demonstrate a metasurface lens based on resonant V-shaped nanovoids with a focal length of 1$\,$mm. The second example is a metasurface phase-plate consisting of appropriately oriented rectangular nanovoids that transforms a Gaussian input beam into a Laguerre-Gaussian ${LG_{-1,0}}$ mode.