THz anomalous transmission in plasmonic lattices; incidence angle dependence

The phenomenon of anomalous transmission through subwavelength aperture arrays in metallic films (plasmonic lattices) is thought to be mediated by surface plasmon polaritons (SPP) on the film surfaces. Using terahertz time-domain spectroscopy we systematically studied the anomalous transmission spectrum through plasmonic lattices as a function of the incidence angle, 6 of the impinging beam. We observed splitting of the various transmission resonances into two resonance branches when 6 deviates from normal incidence that depends on the polarization direction of the beam respect to the plane of incidence and 6. We show that the transmission resonance splitting is not related to dispersion relation of different SPP branches, but rather is associated to the interference properties of the SPP waves on the metal surface. The dependence of the split resonant frequencies vs. 6 is fit with a theoretical formula that takes into account the effective dielectric function of the plasmonic lattice vs. 6, which emphasizes the important role of the Fanotype anti-resonances in the transmission spectrum. Finally, we introduced a simple way for making an efficient notch filter with high Q factor exploiting the splitting of transmission resonance under rotation.