Dielectric loading method for doubly resonant enhancement of third-harmonic generation from complementary split-ring...

Nonlinear optical response could be greatly enhanced when metasurfaces support plasmonic resonances at both fundamental and harmonic wavelengths. However, it is still challenging to fulfill the doubly resonant condition. Here, we propose a dielectric-loading method, which simply coats a conformal thin dielectric layer onto the plasmonic metasurfaces, to introduce an additional degree of freedom and make the doubly resonant condition easily fulfilled. We demonstrate that by simultaneously tuning the thickness of the coated dielectric layer and the geometrical parameters of the gold complementary split-ring resonators (CSRRs), the doubly resonant enhancement of third harmonic generation (THG) could be achieved for any given fundamental wavelengths. We also experimentally verify this concept and show that the THG intensity in the dielectric-loaded CSRRs under the doubly resonant condition could be further increased about 3 times as compared with the case of the conventional CSRRs.