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

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