Terahertz Wave Enhanced Transmission through a Single Subwavelength Aperture with Periodic Surface Structures

We demonstrate resonantly enhanced transmission of terahertz (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 phenomenon is caused by the resonant excitation of surface waves, which are known as surface plasmon polaritons in the optical region, generated by the concentric periodic grooves. Strongly enhanced transmission of THz-wave radiation is observed through the single subwavelength circular aperture (diameter d = 100 µm). We also show that introducing the Bragg reflector to the bull's eye structure results in the further increase of the enhanced transmission.