Annular Aperture Arrays Research Articles

Large-area, infrared nanophotonic materials fabricated using interferometric lithography

In this paper, we discuss the characterization and fabrication of two nanophotonic materials for the infrared region by using IL—realizing a negative refractive index material and enhancing transmission through annular metallic coaxial aperture arrays.

Annular aperture arrays: study in the visible region of the electromagnetic spectrum

Baida and Van Labeke recently proposed a structure that exhibits a supertransmission of light through an array of nanometric coaxial apertures in a metallic film that has been named an annular aperture array (AAA) [Opt. Commun. 209, 17 (2002); Phys. Rev. B 67, 155314 (2003); J. Microsc. 213, 140 (2003)]. We present the first experimental study, to our knowledge, of an AAA structure in the visible region. For technological reasons, the structure under study does not produce a supertransmission of 80% as in Baida and Van Labeke [Opt. Commun. 209, 17 (2002)]. We built the nanostructure and experimentally recorded its far-field spectral response. This transmission shows only one broad band with a maximum around lambda = 700 nm, giving a maximum efficiency around 17%. A finite-difference time-domain simulation reproduces quite well the obtained transmission spectrum.

Origin of the super-enhanced light transmission through a 2-D metallic annular aperture array: a study of photonic bands

Recently a new structure showing a super-enhanced transmission [Optics Commun. 209, 17–22 (2002); Phys. Rev. B, 67, 155314, (2003)] has been proposed. The origin of this phenomenon was not clearly explained. In this paper, by using a numerical Order-N FDTD spectral method, we study the eigenmodes, the band structure and the dispersion curves of a photonic 2-D crystal made with coaxial circular cavities and made from a real metal. We show that the super-enhanced transmission of the finite structure is due to a cavity resonance of a single guided mode. An extensive characterization of this mode is presented, in terms of the spatial mode structure and effective index dispersion curve.

Three-dimensional structures for enhanced transmission through a metallic film: Annular aperture arrays

Light transmission through arranged nanostructures can be increased comparing to what was observed three years ago by Ebbesen et al. [Nature, 391, 667 (1998)]. The results obtained recently by Krishnan et al. [Opt. Commun. 200, 1 (2001)] with gold hole grating are confirmed, but a new design is suggested in order to enhance the light transmission. A three-dimensional finite difference time domain simulation was performed in order to obtain the spectral response of metallic periodic structures in the visible domain. The grating structure is modified by filling the central region of each hole with a concentric cylinder of smaller diameter. The grating now consists of a periodic array of annular apertures. Theoretical simulations were performed with such a subwavelength silver grating. It is shown that the transmission efficiency can reach 80% in the visible spectral range.

Light transmission by subwavelength annular aperture arrays in metallic films

We study the spectral response of a metallic film with an engraved 2D periodic structure of annular apertures. We show that an enhanced transmission can be obtained and can reach 90%. The variation of the spectral response as a function of the film thickness from 150 nm to a value of 1.8 μm is also studied. We show that a guided mode in the subwavelength coaxial structure is responsible for this large transmission. A wavelength cut-off exists. We study the transmission characteristics on the optical and geometrical parameters of the array (period, coaxial radii, incident polarization and dielectric constants) using a 3D-FDTD algorithm.

A time-resolved x-ray ring coded-aperture microscope for inertial confinement fusion applications

For energetic x rays (hv≥3 keV), ring coded-aperture imaging gives better signal-to-noise ratio than equivalent-resolution pinhole cameras for inertial confinement fusion (ICF) targets. We have created a time-resolved ring coded-aperture microscope by combining a 4×3 array of annular apertures with a gated microchannel-plate x-ray imager. The new instrument can produce 500-ps duration sequences of images with a temporal resolution of 80 ps and a spatial resolution of 5 to 6 μm. In demonstration experiments, coded images of imploded targets directly driven by the Omega laser at the Laboratory for Laser Energetics showed the formation and dissolution of the target cores with improved detail. Contour plots of the images indicate that the laser illumination pattern is imprinted in the imploded core region. The gated ring-aperture microscope will be useful in detailed studies of ICF target hydrodynamics.

Bandpass grids with annular apertures

A rigorous theory is developed for describing the diffraction of a plane wave by a doubly periodic array of annular apertures in a thick, perfectly conducting screen. Coaxial waveguide modes are used to describe the fields within each aperture, while the fields above and below the grid are written as plane wave expansions. Appropriate boundary conditions are applied at the upper and lower surfaces of the screen, and the method of moments is used to determine mode and wave amplitudes. Such a structure was found to exhibit excellent bandpass characteristics which can be adjusted by changing the size of the apertures and the thickness of the screen.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>