High-Q surface lattice resonances under normal incidence in asymmetric environments

Abstract High-Q resonances that confine the light energy at subwavelength scales are attractive in various fields such as fluorescence enhancement, nanolasers, and optical sensing. Notably, plasmonic surface lattice resonances (SLRs) exhibit exceptionally enhanced field intensities and substantially elevated Q factors, garnering significant attention. Nevertheless, achieving a high-Q SLR in the visible spectrum within asymmetric -1ractive-index environments remains fraught with numerous challenges. In this study, we introduce a novel high-Q SLR supported by a one-dimensional (1D) asymmetric nanograting, which demonstrates superior performance in asymmetric dielectric settings under normal incidence. This phenomenon stems from interference between the lattice resonance mode and the out-of-plane dipole resonance mode, resulting in a narrow spectral linewidth of approximately 2 nm and a remarkable Q factor of 167 under normal incidence and asymmetric environmental excitation. Furthermore, the 1D asymmetric nanograting achieves a sensitivity of up to 450 nm RIU −1 and a figure of merit ( FOM ) of 165, respectively, for plasmonic refractive index sensing. Our findings not only advance the pathway to effectively manipulate in-plane SLRs but also present a promising candidate for the advancement of high-performance plasmonic sensors.