Hybrid Plasmonic Coupled‐Mode Metasurface Design for Shot‐Noise Limited Ppb‐Level Hydrogen Detection

Plasmonic hydrogen sensors have enabled hydrogen detection below parts‐per‐million (ppm) range by boosting the sensitivity using localized surface plasmonic resonant (LSPR) structures. However, the intrinsic optical losses of Palladium (Pd), the primary plasmonic metal used for hydrogen detection, result in a low quality (Q) factor LSPR, which fundamentally hinders further improvement. In this work, a hybrid plasmonic metasurface is proposed that couples Pd‐based LSPR structure with an Au film supporting surface plasmon polariton mode (Au‐SPP). The coupled near‐perfect absorber resonance yields a spectrally narrow, high Q response that retains strong sensitivity to hydrogen while improving resonance localization. Numerical analysis shows that, under shot‐noise‐limited conditions, the limit of detection (LoD) can be improved by over threefold compared to the state‐of‐the‐art designs. This hybrid plasmonic coupled‐mode metasurface thus presents a promising pathway to achieve parts‐per‐billion‐level (ppb‐level) hydrogen detection with enhanced spectral precision and robustness.