Giant Second Harmonic Generation from 3R-MoS$_2$ Metasurfaces

TL;DR

This paper demonstrates giant second harmonic generation in 3R-MoS$_2$ metasurfaces using quasi-bound states in continuum, achieving a 2000-fold enhancement and a 1% conversion efficiency, surpassing traditional bulk material metasurfaces.

Contribution

The study introduces a novel qBIC-based design for 3R-MoS$_2$ metasurfaces that significantly enhances SHG efficiency through high-Q resonances and strategic twist angles.

Findings

2000-fold enhancement in SHG intensity

SHG conversion efficiency of ~1%

Optimal twist angle of 30° boosts efficiency

Abstract

Metasurfaces have long served as a cornerstone technique to enhance nonlinear processes, enabling frequency conversion, efficient light manipulation and integrated photonic devices. However, traditional bulk materials often suffer from high absorption losses, hindering the second harmonic generation (SHG) efficiency. Here, we develop a novel approach exploiting quasi-bound state in continuum (qBIC) to achieve giant SHG efficiency in metasurfaces utilizing 3R-MoS$_2$, with high index, superior damage threshold and inherent nonlinearity. The high refractive index of 3R-MoS$_2$, facilitates the high-quality factor (Q) metasurfaces, leading to reduced radiation leakage and localized light confinement within qBIC resonances, with which a remarkable 2000-fold enhancement in SHG intensity has been experimentally demonstrated. Additionally, the twist angle between the lattice orientation and the metasurface unit geometry exhibits a 120$^\circ$ periodicity in its influence on SHG behaviour. By strategically designing to realize the qBIC and exciton dual resonances and optimized twist angle (30$^\circ$), SHG conversion efficiency was boosted to ~1%, which is around 2 orders of magnitude higher than those of the best metasurfaces on traditional bulk materials. This approach enables potential applications in various areas of nonlinear optics, including frequency conversion, light manipulation, integrated photonics, and quantum communications.