Observation of High-Harmonic Generation from a Subwavelength Dielectric Resonator

Generation of higher-order optical harmonics recently entered the realm of nanostructured solids being observed in optical gratings and metasurfaces with a subwavelength thickness. Structuring materials at the subwavelength scale allows to enhance substantially the efficiency of nonlinear processes and reduces the size of high-harmonic sources. Here we report the observation of up to seventh harmonics generated from a single subwavelength resonator enabled by an engineering of the resonator geometry for supporting an optical mode associated with bound state in the continuum (qBIC) excited resonantly with a structured light. We evaluate the contributions of perturbative and non-perturbative nonlinearities to the generation process. Our work paves the way to on-chip solid-state sources of high harmonics of the subwavelength volumes.