Efficient non-perturbative high-harmonic generation from nonlinear metasurfaces with low pump intensity

High-harmonic generation (HHG) from solids in non-perturbative regime has recently attracted great interest due to the high efficiency compared with atomic gaseous media, compact experimental configurations, and promising applications for spectroscopy and coherent extreme ultraviolet sources. However, it needs still high pump intensity in the order of several hundreds GW/cm(2). In this work, we present comprehensive results of efficient HHG with low pump threshold by employing high field enhancements in dielectric metasurfaces and hybrid metasurfaces comprising plasmonic nanoantennae. The numerical results show that ZnO nanodisk arrays supported by gold substrate enable us to generate high-order harmonics with efficiency in the order of 10(-5)-10(-6)% in plateau region and cut-off order of up to 21 by pumping at 1550 nm with a peak intensity below 70 GW/cm(2). When using metasurfaces of plasmonic nanoantennae containing ZnO nanoparticles in their gaps and supported by dielectric substrate, HHG can be realized by using pump with much lower peak intensity and the spatial inhomogeneity of plasmon-induced local field plays an important role, leading to the appearance of even order harmonics. For peak pump intensity of about 0.4 GW/cm(2), the resultant HHG efficiency in plateau region is in the orders of 10(-8)% for odd order harmonics and 10(-9)% for even order ones. In particular, when the plasmonic metasurfaces are supported by dielectric-coated metallic substrate, the local field in the gap region is further enhanced, resulting in HHG efficiency 1-2 orders-of-magnitude higher than the case of using dielectric substrate.

Automated summary

Efficient high-harmonic generation with low pump threshold can be achieved by using dielectric and plasmonic hybrid metasurfaces. ZnO nanodisk arrays supported by dielectric substrate enable efficient generation of high-order harmonics. Plasmonic nanoantennae metasurfaces supported by dielectric-coated metallic substrate can result in orders-of-magnitude higher HHG efficiency compared to using dielectric substrate.