Enhanced terahertz extinction of single plasmonic antennas with conically tapered waveguides

We demonstrate experimentally the resonant extinction of THz radiation
by a single plasmonic bowtie antenna, formed by two n-doped Si monomers with a triangular shape and facing apexes. This demonstration is achieved by placing the antenna at the output aperture of a conically tapered waveguide, which enhances the intensity of the incident THz eld at the antenna position by a factor 10. The waveguide also suppresses the background radiation that otherwise is transmitted without being scattered by the antenna. Bowtie antennas, supporting localized surface plasmons, are relevant due to their ability of resonantly enhancing the eld intensity at the gap separating the two triangular elements. This gap has subwavelength dimensions, which allows the concentration of THz radiation beyond the diraction limit. The combination of a bowtie plasmonic antenna and a conical waveguide may serve as a platform for far-eld THz time-domain spectroscopy of single nanostructures placed in the gap.