High harmonic generation from a subwavelength dielectric resonator

TL;DR

This paper demonstrates high harmonic generation up to the seventh order from a single subwavelength AlGaAs resonator, enabled by engineered optical modes supporting a quasi-bound state in the continuum, showcasing miniaturization of nonlinear light sources.

Contribution

It reports the first observation of high harmonic generation from a single subwavelength dielectric resonator with engineered resonant modes supporting a quasi-bound state in the continuum.

Findings

Achieved up to seventh harmonic generation from a subwavelength resonator.

Engineered resonator geometry supports optical modes for efficient harmonic generation.

Proved the feasibility of miniaturizing high-harmonic sources to subwavelength scales.

Abstract

Higher-order optical harmonics entered the realm of nanostructured solids being observed recently in optical gratings and metasurfaces with a subwavelength thickness. Structuring materials at the subwavelength scale allows for resonant enhancing of the efficiency of nonlinear processes and reducing the size of high-harmonic sources. Here we report the observation of up to a seventh harmonic generated from a single subwavelength resonator made of AlGaAs material. This process is enabled by careful engineering of the resonator geometry for supporting optical modes associated with a quasi-bound state in the continuum in the mid-infrared spectral range at around {\lambda}=3.7 {\mu}m pump wavelength. The resonator volume measures ~ 0.1 {\lambda}^3. The resonant modes are excited with an azimuthally polarized tightly focused beam. We evaluate the contributions of perturbative and non-perturbative nonlinearities to the harmonic generation process. Our work proves the possibility to miniaturize solid-state sources of high harmonics to the subwavelength volumes.