Extraordinary optical transmission (EOT) is the phenomenon of greatly enhanced transmission of light through a subwavelength aperture in an otherwise opaque metallic film which has been patterned with a regularly repeating periodic structure. Generally when

light Light, visible light, or visible radiation is electromagnetic radiation that can be visual perception, perceived by the human eye. Visible light spans the visible spectrum and is usually defined as having wavelengths in the range of 400– ...

of a certain

wavelength In physics and mathematics, wavelength or spatial period of a wave or periodic function is the distance over which the wave's shape repeats. In other words, it is the distance between consecutive corresponding points of the same ''phase (waves ...

falls on a subwavelength aperture, it is diffracted isotropically in all directions evenly, with minimal far-field transmission. This is the understanding from classical aperture theory as described by Bethe. In EOT however, the regularly repeating structure enables much higher transmission efficiency to occur, up to several orders of magnitude greater than that predicted by classical aperture theory. It was first described in 1998. This phenomenon that was fully analyzed with a microscopic scattering model is ''partly'' attributed to the presence of surface plasmon resonances and

constructive interference In physics, interference is a phenomenon in which two coherence (physics), coherent waves are combined by adding their intensities or displacements with due consideration for their phase (waves), phase difference. The resultant wave may have ...

. A surface plasmon (SP) is a collective excitation of the

electron The electron (, or in nuclear reactions) is a subatomic particle with a negative one elementary charge, elementary electric charge. It is a fundamental particle that comprises the ordinary matter that makes up the universe, along with up qua ...

s at the junction between a conductor and an insulator and is one of a series of interactions between light and a metal surface called

Plasmonics Plasmonics or nanoplasmonics refers to the generation, detection, and manipulation of signals at optical frequencies along metal-dielectric interfaces in the nanometer scale. Inspired by photonics, plasmonics follows the trend of miniaturizing op ...

. Currently, there is experimental evidence of EOT out of the optical range. Analytical approaches also predict EOT on perforated plates with a

perfect conductor In electrostatics, a perfect conductor is an idealized model for real conducting materials. The defining property of a perfect conductor is that static electric field and the charge density both vanish in its interior. If the conductor has excess ...

model. Holes can somewhat emulate

plasmons In physics, a plasmon is a quantum of plasma oscillation. Just as light (an optical oscillation) consists of photons, the plasma oscillation consists of plasmons. The plasmon can be considered as a quasiparticle since it arises from the quant ...

at other regions of the

electromagnetic spectrum The electromagnetic spectrum is the full range of electromagnetic radiation, organized by frequency or wavelength. The spectrum is divided into separate bands, with different names for the electromagnetic waves within each band. From low to high ...

where they do not exist. Then, the plasmonic contribution is a very particular peculiarity of the EOT resonance and should not be taken as the main contribution to the phenomenon. More recent work has shown a strong contribution from overlapping evanescent wave coupling, which explains why

surface plasmon resonance Surface plasmon resonance (SPR) is a phenomenon that occurs where electrons in a thin metal sheet become excited by light that is directed to the sheet with a particular angle of incidence (optics), angle of incidence, and then travel parallel to ...

enhances the EOT effect on both sides of a metallic film at optical frequencies, but accounts for the terahertz-range transmission. Simple analytical explanations of this phenomenon have been elaborated, emphasizing the similarity between arrays of particles and arrays of holes, and establishing that the phenomenon is dominated by

diffraction Diffraction is the deviation of waves from straight-line propagation without any change in their energy due to an obstacle or through an aperture. The diffracting object or aperture effectively becomes a secondary source of the Wave propagation ...

Applications

EOT is expected to play an important role in the creation of components of efficient photonic integrated circuits (PICs). Photonic integrated circuits are analogous to electronic circuits but based upon photons instead of electrons. One of the most ground-breaking results linked to EOT is the possibility to implement a Left-Handed

Metamaterial A metamaterial (from the Greek word μετά ''meta'', meaning "beyond" or "after", and the Latin word ''materia'', meaning "matter" or "material") is a type of material engineered to have a property, typically rarely observed in naturally occu ...

(LHM) by simply stacking hole arrays. EOT-based chemical and biological sensing (for example, improving ELISA based antibody detection) is another major area of research. Much like in a traditional

sensor, the EOT efficiency varies with the wavelength of the incident light, and the value of the in-plane wavevector component. This can be exploited as a means of transducing chemical binding events by measuring a change in the local

dielectric constant The relative permittivity (in older texts, dielectric constant) is the permittivity of a material expressed as a ratio with the electric permittivity of a vacuum. A dielectric is an insulating material, and the dielectric constant of an insul ...

(due to binding of the target species) as a shift in the spectral location and/or intensity of the EOT peak. Variation of the hole geometry alters the spectral location of the EOT peak such that the chemical binding events can be optically detected at a desired wavelength. EOT-based sensing offers one key advantage over a Kretschmann-style SPR chemical sensor, that of being an inherently nanometer-micrometer scale device; it is therefore particularly amenable to miniaturization.

References

{{reflist, 2 Quantum optics Electromagnetism Plasmonics Metamaterials Diffraction