Time-domain radiative properties of a single subwavelength aperture surrounded by an exit side surface corrugation

Using experiment and simulation, we describe the radiative properties of a single subwavelength aperture surrounded by concentric annular grooves on the exit surface using terahertz (THz) time-domain techniques. The approach allows for the unique determination of the contribution from each exit surface annular groove to the radiated THz temporal waveform. Based on a simple model, we discuss why the grooves on the exit surface necessarily enhance the time-integrated THz power radiated from the metal structure relative to an equivalent bare aperture. Each exit side groove is shown to produce a time-delayed replica of the total THz pulse that is evanescently coupled through the subwavelength aperture. These replicas are coherently superposed on each other and temporally shifted from one another in accordance with the spatial distance between the grooves. The use of patterns incorporating double-sided surface corrugation therefore allows for greater flexibility in generating complex temporal THz pulse shapes.