High-harmonic generation at the nanoscale boosted by bound states in the continuum

Abstract

Recent progress in nanoscale optics is driven by the physics of electric and magnetic resonances supported by high-index dielectric nanoparticles. Here, we exploit optical bound states in the continuum in a subwavelength particle enhanced by an engineered substrate undergoing an epsilon-near-zero transition from an insulator to a conductor, and uncover how to boost dramatically high-order parametric nonlinear effects. Our strategy makes feasible an observation of a variety of multistep cascaded and multifrequency nonlinear effects in an individual subwavelength resonator. This would expand substantially the range of applications of Mie-resonant dielectric metaphotonics for highly efficient subwavelength optical circuitry, nonlinear metadevices, ultrasensitive hyperspectral sensing, and quantum nanophotonics.