High-sensitivity plasmonic sensing of Au-Ag alternating nanograting with Kretschmann configuration

Abstract

We theoretically investigate an Au-Ag alternating nanograting integrated with a Kretschmann prism-coupled configuration for high-performance plasmonic refractive-index (RI) sensing. Finite-element simulations show that TM-polarized light incident from the BK7 prism side can efficiently excite surface plasmon resonance (SPR) through prism-assisted momentum matching and grating-induced wave vector compensation. The proposed structure is optimized using wavelength interrogation, and its performance is comparatively evaluated against that of traditional single-metal gratings. The alternating design enhances localized plasmonic fields at the ridge vertices, reaching approximately 3.1 × 109 V/m. The strengthened field confinement and plasmonic coupling further improve the sensing performance. For refractive indices of 1.30–1.35, it achieves an average sensitivity of 6454.5 nm/RIU and a maximum figure of merit (FOM) of 73.17 , representing 32.1% and 19.7% improvements, respectively, compared with single-metal gratings. These results suggest that the proposed structure may provide a useful design approach for improving the performance of plasmonic RI sensors.