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

This paper combines the concept of bound states in the continuum with engineering of epsilon-near-zero substrates to boost multi-frequency and multi-step cascaded nonlinear processes at the nanoscale. High-order nonlinear processes such as four-wave mixing, third- and fifth-harmonic generation in all-dielectric subwavelength resonators are shown to be enhanced in comparison with the state-of-the-art results.