Transition-metal-dichalcogenide nonlinear dielectric metasurfaces

Nonlinear optical phenomena in nanostructured materials have attracted much attention due to their wide range of applications, ranging from sensing to novel light sources. Here, we demonstrate the enhanced harmonic generation in single-crystal transition-metal-dichalcogenide metasurfaces. Our nonlinear metasurface offers the highest refractive index to date and operation in a sub-diffractive regime for both second- and third-harmonic waves. Importantly, the interplay between the metasurface Mie resonances allows for control of the second-harmonic generation in forward or backward direction in a sub-diffractive regime. Our results open new opportunities for nonlinear light sources based on metasurfaces, including nonlinear mirrors and entangled-photon generation.