High-Q quadrupolar plasmonic lattice resonances in horizontal metal–insulator–metal gratings

We propose a plasmonic platform for achieving out-of-plane quadrupolar plasmonic surface lattice resonances (SLRs) with large quality factors. The proposed platform is composed of a horizontal metal–insulator–metal (MIM) grating embedded in a homogeneous dielectric environment. Numerical results based on rigorous coupled-wave analysis show that under oblique incidences, high- Q out-of-plane quadrupolar SLRs can be excited at wavelengths of 1242 nm over a wide range of insulator widths, and the quality factor can reach 1036. As a comparison, under the same conditions, only dipolar SLRs with much lower quality factors of ∼ 300 can be excited in a vertical MIM grating, which has the same period and a quarter-turned unit cell. We expect that the proposed high- Q quadrupolar SLR platform will find applications in light–matter interactions on the nanoscale.