High-Q plasmonic surface lattice resonance in the ultraviolet region

Surface lattice resonances (SLRs) arise from the long-range dipolar interaction in periodic plasmonic metallic nanostructures and exhibit higher quality factors (Q-factors) compared to plasmon resonances supported in isolated metallic nanostructures. In this Letter, we report a significant improvement in the Q-factor of SLR by a factor of three via modulating the efficiency of a long-range dipolar interaction, which can be achieved by varying the thickness or refractive index of the coating layer on the top of the metallic nanostructures. Under the condition of a weak long-range dipolar interaction, we observe a nascent state of SLR located directly at the Rayleigh cutoff wavelength. Due to the absence of an in-plane diffraction mode at shorter wavelengths, the nascent-SLR dip exhibits an asymmetric shape with a high Q-factor. We experimentally monitor the evolution trend at the onset of the SLR and demonstrate a plasmonic resonance reaching an experimental Q-factor exceeding 100 in the ultraviolet region, outperforming other resonance modes in metallic nanostructures. The reported nascent SLR holds promise for boosting the performance of nano-optic devices.