We study the transmission of complementary THz split ring resonator (cSRR) arrays with THz time domain spectroscopy. Utilizing complementary THz metasurfaces and, varying the inter meta-atom separation, a regime of resonant coupling to surface plasmon polaritons (SPPs) is entered. The effective medium condition valid for the direct metasurface is not applicable anymore in the complementary case because of the high THz dielectric constant of gold. We observe a normalized strong coupling of 3.5% to the lattice SPP mode when tuned into resonance with the LC-mode of the cSRR at a frequency of 1.07 THz. The lattice constant is varied from 40 um to 160 um. Finite element simulations with CST MWS show the characteristic field distribution of the two modes and the intermixing of the LC-mode with the SPP-mode very clearly. Analytical modeling with a simple two oscillator model well describes the coupling. An effective relative permittivity of 11.6 for the coupled system was extracted. For broader linewidths, an apparent modulation of the effective Quality-factor can be observed which is of crucial importance for designing metasurfaces for applications. Measurements of the broader lambda/2 mode in orthogonal excitation direction reveal instead a Fano-like interaction. Rectangular array configuration reveal the excitation direction of the SPP modes being along the polarization of the exciting THz pulse. We demonstrate that the understanding of the SPP modes is fundamental for research and applications in which the metasurface has to be designed for special needs.
Janine Keller, Gian Lorenzo Paravicini Bagliani, Johannes Haase, Curdin Maissen, Giacomo Scalari, and Jérôme Faist, "Strong coupling of THz surface plasmon polaritons to complementary metasurfaces (Conference Presentation)," Proc. SPIE 10103, Terahertz, RF, Millimeter, and Submillimeter-Wave Technology and Applications X, 101030H (Presented at SPIE OPTO: January 31, 2017; Published: 19 April 2017); https://doi.org/10.1117/12.2249852.5391659197001.
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