Resonant nanostructured metallic devices have attracted considerable recent attention through phenomena such as
extraordinary transmission and their potential application as sensing elements, metamaterials and for enhancing
nonlinear optical effects. Here we report on the investigation of the geometry and material properties on the performance
of periodic and random arrays of coaxial apertures in thin metallic films. Such apertures in perfect conductors have been
shown to resonate at a wavelength governed by the geometry of the apertures leading to enhanced transmission. This
resonant wavelength is dictated by the cutoff wavelength of the fundamental mode propagating in the corresponding
coaxial waveguide and, as a consequence, is largely independent of whether the apertures are isolated or in random or
periodic arrangements. In the case of periodic samples, however, these resonances can coherently couple to surface
waves to produce an analogue of the enhanced optical transmission seen in arrays of circular and other apertures. We
have previously shown that as the width of the rings decreases, there are substantial red-shifts in the resonant wavelength
from that predicted for perfect conductivity when the optical properties of the metal are considered. Here we report on
recent developments in fabrication, design and modelling of metallic resonant structures and their near- and far-field
optical characterisation. In particular, we consider the relationship between random and regular arrangements of
apertures.
The near and far-field transmission characteristics of nanoscale annular array metamaterials fabricated using ion beam
lithography are investigated both computationally and experimentally. Experimental results in the far-field regime
demonstrate high transmission efficiencies in the near infra-red region of the electromagnetic spectrum for these devices,
in excellent qualitative agreement with a previously developed numerical model. The diffractive near-field behavior of
such structures is discussed, with a particular emphasis on the implications associated with verifying such predictions
experimentally.
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