Near-field microscopy of electromagnetically induced transparency in terahertz dolmens

Summary form only given. Terahertz (THz) resonant structures present an attractive canvas for the design of novel optoelectronic devices in the far-infrared. By exploiting the strong scattering properties of metallic resonators, effects such as beam steering [1], spectral filtering [2], and enhanced group delays [3] have been demonstrated over very thin optical path lengths with high figures of merit. In many implementations, such effects arise due to interferences occurring in local fields of the resonators via evanescent coupling. We use scanning probe near-field THz time-domain microscopy [4] to present spectral maps of a periodic array of gold dolmen structures. The system consists of a first resonator that supports a bright mode, which couples efficiently to the radiation field, and a second resonator that supports a dark mode which cannot be driven by incident plane wave radiation. The interaction of these two modes in the near-field gives rise to electromagnetically induced transparency, observed in far-field extinction spectra. The coupling between bright and dark modes supported by the structure is visualized through the hybridization of these modes, and by the enhanced field recorded at position of the dark resonator which cannot be directly excited from the far-field. These measurements present a platform for disentangling the local field distribution near more complex optoelectronic devices in the THz range, for applications in the emerging field of THz photonics.