# 3D-printed mirror-less helicity preserving metasurface “mirror” for THz applications

## TL;DR

This paper introduces a 3D-printed THz metasurface that acts as a mirror-less, helicity-preserving reflector, useful for communication, sensing, and chirality detection.

## Contribution

A novel 3D-printed THz metasurface design that enables perfect cross-polarized and helicity-preserving reflection without a back-reflector.

## Key findings

- The metasurface design achieves ideal cross-polarized reflection for linear polarization and helicity-preserving reflection for circular polarization.
- Experimental validation using THz time domain spectroscopy confirms the theoretical predictions.
- Applications in beam steering, focusing, and molecular chirality sensing are demonstrated.

## Abstract

Stimulated by seminal works on generalized reflection and refraction laws, metasurfaces have evolved to a highly promising research direction, as they allow a multitude of different functionalities by optically thin wave-control elements/structures. Among them, structures functioning in the low THz regime are of extensive research interest, due to their high potential in communication and sensing applications. In this paper we propose a simple THz metasurface design that exhibits ideally perfect cross-polarized reflection for linear polarization and perfect helicity-preserving reflection with a geometric (Pancharatnam–Berry) phase for circular polarization, without the presence of any back-reflector. Numerical calculations demonstrating the structure response are justified by analytical models, which provide physical insights on this response. The designed metasurfaces are fabricated using the direct laser writing 3D-printing technology, metallized with electroless silver plating, and are characterized by THz time domain spectroscopy, with the experimental results validating the corresponding theoretical ones. Applications including beam steering and focusing, exploring the Pancharatnam–Berry phase, are also demonstrated numerically. Besides those applications, the helicity preserving mirror response of our metasurfaces can be valuable, among others, also in molecular chirality sensing applications, an issue that is also highlighted here.