Dielectric materials with high indices have recently attracted much attention in the community of nanophotonics. Severe optical losses in visible–ultraviolet (UV) region, however, limit their applications. This article proposes dielectric–metal nanocomposites as alternative high‐index materials for Mie‐resonance‐based applications. Such composite materials have high indices in the range of wavelength longer than plasmon resonance of inclusion metal nanoparticles, while they have much lower losses in the range from blue‐violet down to near‐UV compared with commonly used high‐index materials such as silicon, enabling near‐UV generation with high efficiency based on third‐harmonic generation (THG). The numerical results show that ZnO nanodisk containing silver nanoparticles can generate near‐UV radiation at 351.3 nm via THG with an efficiency about 20 times higher compared with silicon nanodisk under same pumping condition. Significantly high THG efficiency of 0.015% has been predicted with such a composite nanodisk supported by aluminum substrate under pumping with a peak intensity of 20 GW cm−2, a spot size of 0.8 , a duration of 50 fs at 1054 nm, respectively.
This work reports high-harmonic generation (HHG) from 2D monolayer electrides investigated by using ab-initio approach based on time-dependent density functional theory, mainly focusing on monolayer Mg 2 N. Due to low ionization energy and wide potential well, they exhibit distinctively high HHG efficiency and high cutoff energy for out-of-plane pumping, although they also show atomic-like behavior. For out-of-plane pumping with a peak intensity of 40 TW cm −2 at 1550 nm, high harmonics up to 120th order are generated with efficiency 4 orders-of-magnitude higher than monolayer h-BN. For pump intensity below the direct above-threshold ionization (ATI) regime, the tunneling from the ground state and ATI from one-or two-photon resonant state simultaneously contribute to HHG. In the other subnitride monolayers of alkaline earth with larger atomic sizes (Ca 2 N and Sr 2 N), further higher harmonic generation efficiencies are obtained due to the lower work functions and wider potential wells. For in-plane pumping, the intraband transition is the major source of the HHG due to the metallic in-plane responses. The presented results will attract great attention due to the peculiar HHG signature from fundamental aspects and pave the way of obtaining coherent extreme ultraviolet (EUV)/soft-X-ray with high efficiency by using monolayer electrides.
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