Terahertz Near-Field Imaging Using Enhanced Transmission through a Single Subwavelength Aperture

We demonstrate terahertz (THz) near-field imaging using resonantly enhanced transmission of THz-wave radiation (λ∼200 µm) through a bull's eye structure (a single subwavelength aperture surrounded by concentric periodic grooves in a metal plate). The bull's eye structure shows extremely large enhanced transmission, which has the advantage for a single subwavelength aperture. The spatial resolution for the bull's eye structure (with an aperture diameter d =100 µm) is evaluated in the near-field region, and a resolution of 50 µm (corresponding to λ/4) is achieved. We obtain the THz near-field images of the subwavelength metal pattern with a spatial resolution below the diffraction limit.