Plasmonic surface lattice resonances (SLRs) supported by metal nanoparticle arrays have a range of appealing characteristics such as extremely narrow linewidths and greatly enhanced near fields, and thus are attractive in diverse applications. Improving the quality factor of SLRs is important for many applications and thus it has been the focus in this field. In this work, we report high quality out-of-plane SLRs supported by two-dimensional metal nanohemisphere arrays embedded in a symmetric dielectric environment. These SLRs, excited under oblique incidence with TM polarization, can have an ultra-narrow resonant linewidth (∼ 0.9 nm) at visible wavelengths around 715 nm. This corresponds to an exceptionally high quality factor of 794, which is ten times that of the widely-adopted nanorods. We attribute this striking performance to the nanohemisphere geometry, which greatly relaxes the stringent requirement on the height of nanoparticles for supporting out-of-plane SLRs, reducing the absorption loss, and in which the out-of-plane oscillations are much stronger than in-plane ones, leading to stronger inter-particle coupling. The tuning of the resonance wavelength and the quality factor can be explained by a qualitative approach based on the detuning between the Rayleigh anomaly and the localized surface plasmon resonance of an isolated nanoparticle. We expect this work will advance the engineering and applications of high quality SLRs.
Terahertz sensors are promising for biomedical, environmental and security applications. Challenges in terahertz sensing have been the limited sensitivity and small figure of merit. Here we propose an ultra-sensitive terahertz sensing platform based on the Rayleigh anomaly in hyperbolic metamaterial gratings, which are composed of periodic slits patterned in paired metal-dielectric multilayers. Simulation results show that, under normal incidence with TM polarization and designed with proper parameters, the proposed structure has a super-high quality factor of 516, an ultra-high sensitivity of 1.56 THz/RIU (or 9.06×104 nm/RIU, and extremely large figure of merit of 355 RIU-1 at frequency of 2.272 THz, corresponding to a large normalized sensitivity of 0.69 RIU-1. By comparing with other multilayered gratings, we attribute this exceptionally high sensing performance to the strong local field enhancement over an extremely large area in the sensing region at the Rayleigh anomaly frequency, which is found to be unique for hyperbolic metamaterial gratings. We further show that the resonance frequency decreases linearly with the grating period, following the Rayleigh anomaly equation, whereas the large normalized sensitivity keeps constant. We expect this work provides a novel strategy to design extremely sensitive sensors in terahertz as well as other frequency regimes.
Nanoarray structures can support plasmonic surface lattice resonances (SLRs) with extremely narrow linewidths and huge electric field enhancement features, which are attractive applications in nanolasers, biochemical sensors, and nonlinear optics. However, current nanoarray structures located in an asymmetric dielectric environment with a refractive index contrast of 1.00/1.52 of the superstrate/substrate excite much poorer SLRs under normal incidence, which largely limits their application range. In this work, we report extremely narrow SLRs supported by one-dimensional metal-insulator-metal (MIM) nanograting in asymmetric dielectric environments. The simulation results show that an SLRs with linewidth of 3.26 nm and quality factor of 233.2 can be excited under normal incidence. This high-quality SLRs is attributed to the interference formation between the out-of-plane dipole resonance mode and the out-of-plane quadrupole resonance mode. We also show that the resonance wavelength and quality factor can be tuned by changing the structure geometry and period, and we calculate the normal incidence SLRs quality factor to be up to 248 in 1.33/1.52 and 250 in 1.45/1.52. We expect the SLRs of this work to find potential applications in asymmetric dielectric environments.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.