Extraordinary optical transmission with coaxial apertures

Recently it has been predicted that “cylindrical” surface plasmons (CSP’s) on cylindrical interfaces of coaxial ring apertures produce a different form of extraordinary optical transmission that extends to ever increasing wavelengths as the dielectric ring narrows. This letter presents experimental confirmation of this CSP assisted extraordinary transmission. Nanoarrays of submicron coaxial apertures are fabricated in a thin silverfilm on a glass substrate and far-field transmission spectra are measured. The experimental spectrum is in close agreement with predictions from finite-difference time-domain simulations and CSP dispersion theory. The role of cylindrical surface plasmons in producing extraordinary transmission is thus confirmed.This work was partially supported by the Office of Naval Research. Computations were carried out under the Department of Defense High Performance Computation Modernization Project. The support of the Australian Research Council through its Centers of Excellence, Federation Fellow and Discovery programs is gratefully acknowledged

Metal-free scanning optical microscopy with a fractal fiber probe

Scanning Near-field Optical Microscopy (SNOM) is the leading instrument used to image optical fields on the nanometer scale. A metalcoating is typically applied to SNOM probes to define a subwavelength aperture and minimize optical leakage, but the presence of such coatings in the near field of the sample can often cause a substantial change in the sample emission properties. For the first time, the authors demonstrate nearfield imaging on a metal substrate with a metal-free probe made from a novel structured optical fiber, designed to maximize optical throughput and potentially remove the need for the metal

Plasmonic nanoresonant materials

Resonant nano structure d 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