We numerically investigate second harmonic generation (SHG) in plasmonic metasurfaces composed of periodically arranged vertical split-ring resonators. By tuning a height scaling parameter $\delta$, a continuous transition from localized surface plasmon resonances to nonlocal collective modes dominated by trapped surface plasmon polaritons was observed. Such an evolution enables systematic control over radiative and dissipative losses, resulting in a significantly enhanced $Q$ factor for both bright (in-plane resonance) and dark (out-of-plane resonance) modes. In the localized regime, SHG from bright modes is limited by strong radiation loss, while in the nonlocal regime, field delocalization suppresses nonlinear interactions. We identify an optimal crossover regime where a balance between field confinement (local) and radiation suppression (nonlocal) maximizes SHG efficiency. The SHG efficiency from dark modes, which radiate under oblique incidence, is mainly determined by local field enhancement and far-field radiation efficiency. Although the nonlocal mode exhibits a higher $Q$ factor, it does not yield the strongest SHG response. Instead, the optimal SHG conversion efficiency arises in the local mode, attributed to stronger local field confinement and more effective out-of-plane radiation extraction. Our results reveal a different route toward high-efficiency nonlinear metasurfaces and offer opportunities for low-power, ultracompact photonic devices.

Close

PrevNext

View figure in article

• Nonlinear phenomena in plasmas
• Plasma optics
• Plasma surface high-order harmonics
• Plasmonics
• Surface plasmon polariton
• Metasurfaces
• Split-ring resonators
• Optical second-harmonic generation