Wednesday, June 28, 2017

Abstract-Terahertz diffraction enhanced transparency probed in the near field

Alexei Halpin, Niels van Hoof, Arkabrata Bhattacharya, Christiaan Mennes, and Jaime Gomez Rivas

Electromagnetically induced transparency in metamaterials allows to engineer structures which transmit narrow spectral ranges of radiation while exhibiting a large group index. Implementation of this phenomenon frequently calls for strong near-field coupling of bright (dipolar) resonances to dark (multipolar) resonances in the meta-molecules comprising the metamaterials. The sharpness and contrast of the resulting transparency windows thus depends strongly on how closely these meta-moleucles can be placed to one another, placing constraints on fabrication capabilities. In this manuscript we demonstrate that the reliance on near-field interaction strength can be relaxed, and the magnitude of the electromagnetic induced transparency enhanced, by exploiting the long range coupling between meta-molecules in periodic lattices. By placing dolmen structures resonant at THz frequencies in a periodic lattice, we show a significant increase of the transparency window when the in-plane diffraction is tuned to the resonant frequency of the meta-molecules, as confirmed by direct mapping of the THz near-field amplitude across a lattice of dolmens. Through the direct interrogation of the dark resonance in the near-field we show the interplay of near- and far-field couplings in optimizing the response of planar dolmen arrays via diffraction induced transparency.

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