Strong interactions between resonant structures in the near-field occur at length scales shorter than the wavelength, and can be exploited for modifying the propagation of electromagnetic radiation. Dolmen-like structures, formed by a rod supporting a dipolar (bright) resonance and two orthogonal rods with a quadrupolar (dark) resonance at the same frequency, represent a geometry of significant interest for near-field electromagnetic coupling. These structures demonstrate electromagnetically induced transparency (EIT) through coupling between these resonances, concurrently providing a sharp spectral selectivity in transmission and large group velocity reduction. We use near-field terahertz scanning microscopy to map the electric fields in the vicinity of a metallic dolmen in both amplitude and phase. In this way, we directly measure the interaction between bright and dark modes in the time-domain, revealing the physics resulting in EIT. We experimentally demonstrate the hybridization of bright and dark modes accompanying the near-field coupling, as well as the excitation of the dark mode at the frequency of the far-field transparency.

European Research Council (ERC)
Appl. Phys. Lett.

Halpin, A., Mennes, C., Bhattacharya, A., & Gómez Rivas, J. (2017). Visualizing near-field coupling in terahertz dolmens. Appl. Phys. Lett., 110(10, Article number: 101105), 1–4. doi:10.1063/1.4978031