Nonlinear Light Amplification Governed by Structural Asymmetry

Maneuvering the structural asymmetry in metasurfaces plays an essential role in nonlinear nanophotonics, particularly in sub‐wavelength‐scale harmonic generation. Here, a highly efficient and reproducible plasmon‐enhanced second‐harmonic generation platform for exploring these quantitative contributions of structural asymmetries to the amplification of inherently weak nonlinear responses is experimentally designed. It is discovered that such structural asymmetries can not only quantitatively alter the well‐characterized surface susceptibility, but also contribute to the spectral matching and the spatially symmetrical transition of optical resonant modes in plasmon‐enhanced nonlinear polarizations. Furthermore, this study strives to establish a theoretical model to quantify these structural asymmetry‐induced modifications, indicating the consistency with proposed experimental results. These studies may offer a strategy to the design of efficient nonlinear optical nanodevices with extending applications. Maneuvering the structural asymmetry in 3D cap‐shaped nanoparticles provides efficient ways to not only quantitatively alter microscopic effects of surface susceptibilities, but also facilitate the spectral matching and the spatially symmetrical transition of optical resonant modes in plasmon‐enhanced nonlinear polarizations. Under this circumstance, retrieved second‐harmonic generation emissions can be amplified by nearly two orders of magnitude and featured with well‐defined radiation patterns.