Optimizing Second Harmonic Generation in Metasurfaces: The Mode Overlap Factor

While considerable effort has been dedicated to enhancing the quality factor (Q‐factor) of resonances to improve second‐harmonic generation (SHG) in metasurfaces, the role of the mode overlap factor () has lacked systematic and experimentally investigation. In this study, we investigate the influence of on SHG efficiency through numerical simulations and experimental validation under well‐controlled Q‐factor conditions. To isolate and demonstrate the role of in governing nonlinear conversion efficiency, we design and optimize three metasurfaces with distinct values, while maintaining comparable Q‐factors at the FF resonance and no pronounced resonance at the SH wavelength. A higher enhances field confinement within the nonlinear material and facilitates more efficient near‐field interaction between the fundamental and second‐harmonic waves, thereby significantly boosting SHG efficiency. These findings offer deeper insight into the interplay between modal overlap and resonant characteristics, and suggest a practical route to improve SHG performance through optimization.