Time-domain analysis of enhanced transmission through a single subwavelength aperture.

We have measured the enhanced transmission properties of a single subwavelength aperture surrounded by periodically spaced annular grooves using time-domain techniques. While the present measurements utilize terahertz time-domain approaches, with appropriately scaled device parameters, the general observations should be applicable to other spectral ranges. In contrast to measurements that rely on continuous wave excitation and frequency domain measurements, we are able to determine the contribution of each individual groove to the transmitted terahertz waveform. Using structures containing only a single annular groove surrounding the aperture, we find that each groove can couple a large fraction of the incident terahertz bandwidth in the form of a surface wave pulse. When multiple annular grooves surround the aperture, we observe oscillations in the time-domain waveform that are temporally delayed from the initial bipolar waveform in direct relation to the distance of the groove from the aperture. This is further demonstrated by using structures containing defects (absence of annular grooves).