Antenna-enhanced high harmonic generation in a wide-bandgap semiconductor ZnO

We demonstrate high harmonic generation (HHG) into deep-UV range in a ZnO single crystal with resonant nanoantennas. Non-perturbative HHG is successfully induced by optical excitation of as low as 20 GW/cm2. The spectral selection rule is found to reflect crystal symmetry, suggesting the possibility of nano-scaled EUV sources and band-structure reconstruction