Giant enhancement of third-harmonic generation in epsilon-near-zero material by an ITO-SiO2 metagrating

Abstract

Thin film of epsilon-near-zero (ENZ) materials always exhibit a maximum of nonlinear response under large-angle oblique illuminations. As a result, the parallel components are hardly helpful during the nonlinear processes. Here, we proposed a new approach for coupling all incident electric field into the ENZ nanostructures at the ENZ frequency. By fabricating ITO, a typical ENZ material, into a grating pattern and filling the gaps with SiO₂, the incident light polarized in the direction of ITO-SiO₂ periodic arrangement were totally coupled into the nanostructure under normal incidence. Compared with a bare ITO film with same height at the ENZ wavelength, numerical simulations demonstrate a 10³-fold THG efficiency enhancement from the proposed ITO-SiO₂ metagrating under the pump intensity of I₀=1.2GW/cm². For better understanding the giant enhanced nonlinear effects, field distributions at ENZ frequency in the metagrating were analyzed. In addition, the angle-dependent THG efficiencies of the proposed metagrating were also investigated.