Generation of even and odd high harmonics in resonant metasurfaces using single and multiple ultra-intense laser pulses

Abstract

High harmonic generation (HHG) opens a window on the fundamental science of strong-field light-mater interaction and serves as a key building block for attosecond optics and metrology. Resonantly enhanced HHG from hot spots in nanostructures is an attractive route to overcoming the well-known limitations of gases and bulk solids. We demonstrate a nanoscale platform for highly efficient HHG driven by strong mid-infrared laser pulses: an ultra-thin resonant gallium phosphide (GaP) metasurface. The wide bandgap and the lack of inversion symmetry of the GaP crystal enable the generation of even and odd harmonics covering a wide range of photon energies between 1.3 and 3 eV with minimal reabsorption. The resonantly enhanced conversion efficiency facilitates single-shot measurements that avoid material damage and pave the way to controllable transition between perturbative and non-perturbative regimes of light-matter interactions at the nanoscale.

Continuous Wave Second Harmonic Generation Enabled by Quasi-Bound-States in the Continuum on Gallium Phosphide Metasurfaces

“…This also creates an additional limitation due to a limited overlap of the shortpulse laser spectrum with the narrow-band resonances of high-Q metasurface, which further limits the conversion efficiency. 37 In this work, we combine an emerging material platform for non-linear applications, namely gallium phosphide (GaP), 38,39 and a metasurface design supporting a high-Q quasi-BIC mode that exploits the symmetries of the non-linear tensor, to generate continuous wave (CW) SHG at low pumping intensities with reasonable conversion efficiencies. We also show that, in the pulsed regime, we achieve external efficiencies that are higher than the results reported in the literature for dielectric metasurfaces to the best of our knowledge, despite using two orders of magnitude lower pumping intensities.…”