Enhanced second harmonic generation in high-$Q$ all-dielectric metasurfaces with backward frequency conversion

TL;DR

This paper demonstrates enhanced second-harmonic generation in all-dielectric metasurfaces using high-Q quasi-BIC resonances, accounting for backward frequency conversion effects to improve nonlinear efficiency.

Contribution

It introduces a corrected nonlinear polarization model for backward frequency conversion, revealing its impact on SHG efficiency in high-Q dielectric metasurfaces.

Findings

SHG efficiency reaches 2.45×10⁻² at 10 MW/cm²

Backward frequency conversion reduces efficiency by 14.3%

High-Q quasi-BIC resonances significantly enhance nonlinear response

Abstract

Here we employ the quasi-bound state in the continuum (quasi-BIC) resonance in all-dielectric metasurfaces for efficient nonlinear processes in consideration of the backward frequency conversion. We theoretically study the second-harmonic generation (SHG) from symmetry-broken AlGaAs metasurfaces and reveal the efficiency enhancement empowered by high-$Q$ quasi-BIC resonances. By introducing the correction term of nonlinear polarization at the fundamental wave field to the conventional undepleted approximation, we uncover the effect of backward frequency conversion on the nonlinear conversation efficiency. The SHG efficiency as $2.45\times10^{-2}$ with the developed depleted model, shows a $14.3\%$ decrease compared with $2.86\times10^{-2}$ in conventional undepleted approximation, under the incident intensity of 10 MW/cm$^{2}$. Our results are of significant importance for designing efficient nonlinear metasurfaces supporting high-$Q$ resonances.