This review provides a perspective on the recent developments in the transmission of light through subwavelength apertures in metal films. The main focus is on the phenomenon of extraordinary optical transmission in periodic hole arrays, discovered over a decade ago. It is shown that surface electromagnetic modes play a key role in the emergence of the resonant transmission. These modes are also shown to be at the root of both the enhanced transmission and beaming of light found in single apertures surrounded by periodic corrugations. This review describes both the theoretical and experimental aspects of the subject. For clarity, the physical mechanisms operating in the different structures considered are analyzed within a common theoretical framework. Several applications based on the transmission properties of subwavelength apertures are also addressed.

http://digital.csic.es/bitstream/10261/47904/1/Light%20passing.pdf

Light passing through subwavelength apertures

This Colloquium analyzes the interaction of light with two-dimensional periodic arrays of particles and holes. The enhanced optical transmission observed in the latter and the presence of surface modes in patterned metal surfaces is thoroughly discussed. A review of the most significant discoveries in this area is presented first. A simple tutorial model is then formulated to capture the essential physics involved in these phenomena, while allowing analytical derivations that provide deeper insight. Comparison with more elaborated calculations is offered as well. Finally, hole arrays in plasmon-supporting metals are compared to perforated perfect conductors, thus assessing the role of plasmons in these types of structures through analytical considerations. The developments that have been made in nanophotonics areas related to plasmons in nanostructures, extraordinary optical transmission in hole arrays, complete resonant absorption and emission of light, and invisibility in structured metals are illustrated in this Colloquium in a comprehensive, tutorial fashion.

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Colloquium: Light scattering by particle and hole arrays

Extraordinary optical transmission through an array of holes in a metal film was reported by Ebbesen and coworkers in 1998. Since that work there has been abundant research activ- ity aimed at understanding the physics and at the development of the many applications associated with this phenomenon, hence the topic of this review. The study of hole-arrays in a metal is not new - theoretical contributions on a small-hole array date back to Lord Rayleigh's description of Wood's anomaly in 1907 and there has been considerable research on metal meshes and hole- arrays since 1962. Bethe's theory, adapted to treat hole-arrays, is the simplest theoretical description of the transmission reso- nance. Following a description of this basic theory, we present the research on the additional effects from variations in real metal properties at different wavelengths, film thickness, hole- shape and lattice configuration. The many promising applica- tions being developed using hole-arrays are examined, including polarization control, filtering, switching, nonlinear optics, sur- face plasmon resonance sensing, surface-enhanced fluorescence, surface-enhanced Raman scattering, absorption spectroscopy, and quantum interactions. Finally, the various approaches, devel- opments in hole-array fabrication, and integration of hole-arrays into devices are described. (top left) Schematic of resonant transmission through nanohole array using scanning electron microscope image of as-fabricated sample. (top right) Microfluidic chip incorporating nanohole ar- rays. (bottom) Composite image of array of nanohole arrays used as sensors in a immunoassay-like microfluidic device, showing (left to right) schematic of microfluidic layout, microscope im- age of arrays in microfluidic channels, and laser transmission modified by adsorbed molecules.

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Resonant optical transmission through hole‐arrays in metal films: physics and applications

Fabricating plasmonic nanostructures with robust optical and chemical properties remains a challenging task, especially with silver, which has superior optical properties but poor environmental stability. In this work, conformal atomic layer deposition (ALD) of thin alumina overlayers is used to precisely tune the optical transmission properties of periodic nanohole arrays made in gold and silver films. Experiments and computer simulations confirm that ALD overlayers with optimized thicknesses tune and enhance the transmitted intensity due to refractive index matching effects and by modifying the dielectric properties of each nanohole. Furthermore, encapsulating silver nanohole arrays with thin alumina overlayers protects the patterned surfaces against unwanted oxidation and contamination. The ability to precisely tune the optical properties while simultaneously providing robust chemical stability can benefit a broad range of applications, including biosensing and fluorescence imaging.

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Atomic layer deposition of dielectric overlayers for enhancing the optical properties and chemical stability of plasmonic nanoholes.

We investigate transmission efficiency and finite size effects for the subwavelength hole arrays. Experiments and simulations show how the finite size effects depend strongly on the hole diameter. The transmission efficiency reaches an asymptotic upper value when the array is larger than the surface plasmon propagation length on the corrugated surface. By comparing the transmission of arrays with that of the corresponding single holes, the relative enhancement is found to increase as the hole diameter decreases. In the conditions of the experiments the enhancement is one to two orders of magnitude but there is no fundamental upper limit to this value.

Efficiency and finite size effects in enhanced transmission through subwavelength apertures.

Optical transmission through arrays of subwavelength apertures is studied systematically in different metals over the optical spectral range in comparable conditions. The results provide an absolute comparison and thereby highlight the influence of the dielectric constants, surface excitations, interband transitions and different loss mechanisms. Only noble metals such as Ag, Au and Cu give rise to significant transmission in the optical regime. Hole arrays in W transmit very poorly, as expected, since W cannot sustain surface plasmons in the optical range.

http://iopscience.iop.org/article/10.1088/1464-4258/8/5/015/pdf

A. Degiron

Papers

Optical transmission in perforated noble and transition metal films