Surface Lattice Resonance with an Ultra-High Unloaded Q-Factor in Capacitive Metal Meshes at Terahertz Frequencies

Abstract

We investigated the surface lattice resonance (SLR) occurring in capacitive metal meshes (CMMs) in the terahertz (THz) range. CMMs, which comprise two-dimensional periodic arrays of square metal patches on thin quartz substrates, are one of the simplest metasurfaces. Experiments and theoretical simulations performed at frequencies around 0.1 THz show that the SLR in such CMMs has an extraordinarily high unloaded Q-factor of greater than 1000, when the ratio of the length of the metal patch to the mesh period of the CMM and the thickness of the quartz substrate are optimized. An intense and sharp dip in transmission in excess of -60 dB at the SLR frequency was produced with this high unloaded Q-factor in the CMM. Using the CMM as a refractive index sensor, a figure of merit of greater than 340 for frequency interrogation and a refractive index resolution of better than 1.9×10− 6 refractive index units for phase interrogation were experimentally demonstrated. These results indicate that CMMs are superior sensors with high performance in the THz-wave region.