Negative reflection of polaritons at the nanoscale in a low-loss natural medium

TL;DR

This paper demonstrates nanoscale negative reflection of polaritons in a natural low-loss medium, revealing broad tunability and enabling new nano-optic devices like hyperbolic nanoresonators for enhanced light control.

Contribution

It provides the first direct visualization of nanoscale negative reflection of polaritons in a natural medium and introduces a novel hyperbolic nanoresonator device.

Findings

Nanoscale polaritons negatively reflect on subwavelength mirrors.

Broad tunability of polaritonic wavelength and propagation direction.

Enhanced intensity in hyperbolic nanoresonator design.

Abstract

Negative reflection occurs when light is reflected towards the same side of the normal to the boundary from which it is incident. This exotic optical phenomenon, which provides a new avenue towards light manipulation, is not only yet to be visualized in real space but remains largely unexplored both at the nanoscale and in natural media. Here, we directly visualize nanoscale-confined polaritons negatively reflecting on subwavelength mirrors fabricated in a low-loss van der Waals crystal. Our near-field nanoimaging results unveil an unconventional and broad tunability of both the polaritonic wavelength and direction of propagation upon negative reflection. Based on these findings, we introduce a novel device in nano-optics: a hyperbolic nanoresonator, in which hyperbolic polaritons with different momenta reflect back to a common point source, enhancing its intensity. These results pave the way to realize nanophotonics in low-loss natural media, providing a novel and efficient route to confine and control the flow of light at the nanoscale, key for future optical on-chip nanotechnologies.