Sub-wavelength resolution in linear arrays of plasmonic particles
TL;DR: In this article, the authors discuss the results of numerical simulations of the imaging of point sources in an optical superlens and show that sub-wavelength resolution can be obtained in much thicker structures than usual.
Abstract: Recently, we suggested the idea of an optical superlens based on the extraordinary dispersion properties of plasmonic nanochains. In the present paper we discuss the results of numerical simulations of the imaging of point sources in this superlens. The simulations show that sub-wavelength resolution can be obtained in much thicker structures than usual. A distance of nearly λ/2 between the source and the image plane is achieved. In addition the effects of stochastic deviations in geometrical parameters are studied.
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TL;DR: Bound and leaky modes with complex wavenumber in chains (linear arrays) of plasmonic nanospheres are characterized for both longitudinal and transverse polarization states (with respect to the array axis) in the proposed method.
Abstract: Bound and leaky modes with complex wavenumber in chains (linear arrays) of plasmonic nanospheres are characterized for both longitudinal and transverse polarization states (with respect to the array axis). The proposed method allows for the description of each mode evolution when varying frequency. As a consequence, full characterization of the guided modes with complex wavenumber is provided in terms of propagation direction, guidance or radiance, proper or improper, and physical or nonphysical conditions. Each nanosphere is modeled according to the single dipole approximation, and the metal permittivity is described by the Drude model. Modal wavenumbers are obtained by computing the complex zeroes of the homogeneous equation characterizing the field in the one dimensional periodic array. The required periodic Green's function is analytically continued into the complex wavenumber space by using the Ewald method. Furthermore, a parametric analysis of the mode wavenumbers is performed with respect to the geometrical parameters of the array.
51 citations
TL;DR: In this paper, the modal dispersion diagrams of planar arrays of silver nanospheres with the ability to follow individual modal evolutions are described using the single dipole approximation technique by including all the dynamic field terms.
Abstract: Two-dimensional periodic arrays of noble metal nanospheres support a variety of optical phenomena, including bound and leaky modes of several types. The scope of this paper is the characterization of the modal dispersion diagrams of planar arrays of silver nanospheres, with the ability to follow individual modal evolutions. The metal spherical nanoparticles are described using the single dipole approximation technique by including all the retarded dynamic field terms. Polarizability of the nanospheres is provided by the Mie theory. Dispersion diagrams for both physical and nonphysical modes are shown for a square lattice of Ag nanospheres for the case of lossless and lossy metal particles, with dipole moments polarized along the x, y, and z directions. Though an array with one set of parameters has been studied, the analysis method and classification are general. The evolution of modes through different Riemann sheets and analysis of guidance and radiation are studied in detail.
42 citations
TL;DR: In this article, the plasmonic modes of a metal nanoparticle circular array were analyzed and closed-form solutions to the particle mode problem were presented, showing that the mode with the highest quality was in antiphase and the remaining radiative linewidth decreases exponen-tially as the number of particle increases.
Abstract: Received 27 December 2007; revised manuscript received 7 April 2008; published 15 May 2008We analyze the plasmonic modes of a metal nanoparticle circular array. Closed-form solutions to theeigenmode problem are presented. For each polarization, the plasmonic mode with the highest quality is foundto be in antiphase. The significant suppression of radiative loss can be understood as the cancellation of thedipolar radiation term in the radiative linewidth. The remaining finite radiative linewidth decreases exponen-tially as the number of particle increases.DOI: 10.1103/PhysRevB.77.205423 PACS number s : 78.67.Bf, 73.22.Lp, 73.20.Mf, 78.70. g
31 citations
TL;DR: In this article, the authors report super-resolution imaging in a metamaterial system comprising spherical silver nanoparticle chain arrays, where each chain consists of nanoparticles with a smaller particle added to the end.
Abstract: We report super-resolution imaging in a metamaterial system comprising spherical silver nanoparticle chain arrays, where each chain consists of nanoparticles with a smaller particle added to the end. Our simulations reveal that silver nanoparticale chains have subwavelength resolution capability at visible wavelengths and that the field intensity in the imaging plane varies with the number of layers of nanoparticles, their polarization, and their coupling. By adding a smaller nanoparticle at the end of each chain, the resolution capability is significantly enhanced, and high-quality super-resolution imaging can be realized for incident waves polarized along the chain direction.
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TL;DR: In this paper, the optical constants for the noble metals (copper, silver, and gold) from reflection and transmission measurements on vacuum-evaporated thin films at room temperature, in the spectral range 0.5-6.5 eV.
Abstract: The optical constants $n$ and $k$ were obtained for the noble metals (copper, silver, and gold) from reflection and transmission measurements on vacuum-evaporated thin films at room temperature, in the spectral range 0.5-6.5 eV. The film-thickness range was 185-500 \AA{}. Three optical measurements were inverted to obtain the film thickness $d$ as well as $n$ and $k$. The estimated error in $d$ was \ifmmode\pm\else\textpm\fi{} 2 \AA{}, and that in $n$, $k$ was less than 0.02 over most of the spectral range. The results in the film-thickness range 250-500 \AA{} were independent of thickness, and were unchanged after vacuum annealing or aging in air. The free-electron optical effective masses and relaxation times derived from the results in the near infrared agree satisfactorily with previous values. The interband contribution to the imaginary part of the dielectric constant was obtained by subtracting the free-electron contribution. Some recent theoretical calculations are compared with the results for copper and gold. In addition, some other recent experiments are critically compared with our results.
17,509 citations
TL;DR: The authors' simulations show that a version of the lens operating at the frequency of visible light can be realized in the form of a thin slab of silver, which resolves objects only a few nanometers across.
Abstract: Optical lenses have for centuries been one of scientists’ prime tools. Their operation is well understood on the basis of classical optics: curved surfaces focus light by virtue of the refractive index contrast. Equally their limitations are dictated by wave optics: no lens can focus light onto an area smaller than a square wavelength. What is there new to say other than to polish the lens more perfectly and to invent slightly better dielectrics? In this Letter I want to challenge the traditional limitation on lens performance and propose a class of “superlenses,” and to suggest a practical scheme for implementing such a lens. Let us look more closely at the reasons for limitation in performance. Consider an infinitesimal dipole of frequency v in front of a lens. The electric component of the field will be given by some 2D Fourier expansion,
10,974 citations
TL;DR: This work demonstrated sub–diffraction-limited imaging with 60-nanometer half-pitch resolution, or one-sixth of the illumination wavelength, using silver as a natural optical superlens and showed that arbitrary nanostructures can be imaged with good fidelity.
Abstract: Recent theory has predicted a superlens that is capable of producing sub–diffraction-limited images. This superlens would allow the recovery of evanescent waves in an image via the excitation of surface plasmons. Using silver as a natural optical superlens, we demonstrated sub–diffraction-limited imaging with 60-nanometer half-pitch resolution, or one-sixth of the illumination wavelength. By proper design of the working wavelength and the thickness of silver that allows access to a broad spectrum of subwavelength features, we also showed that arbitrary nanostructures can be imaged with good fidelity. The optical superlens promises exciting avenues to nanoscale optical imaging and ultrasmall optoelectronic devices.
3,753 citations
TL;DR: A double-periodic array of pairs of parallel gold nanorods is shown to have a negative refractive index in the optical range, which results from the plasmon resonance in the pairs of nanorod for both the electric and the magnetic components of light.
Abstract: A double-periodic array of pairs of parallel gold nanorods is shown to have a negative refractive index in the optical range. Such behavior results from the plasmon resonance in the pairs of nanorods for both the electric and the magnetic components of light. The refractive index is retrieved from direct phase and amplitude measurements for transmission and reflection, which are all in excellent agreement with simulations. Both experiments and simulations demonstrate that a negative refractive index n???0.3 is achieved at the optical communication wavelength of 1.5??m using the array of nanorods. The retrieved refractive index critically depends on the phase of the transmitted wave, which emphasizes the importance of phase measurements in finding n?.
1,567 citations
TL;DR: A nanofabricated medium consisting of electromagnetically coupled pairs of gold dots with geometry carefully designed at a 10-nm level exhibits a strong magnetic response at visible-light frequencies, including a band with negative µ.
Abstract: A great deal of attention has recently been focused on a new class of smart materials-so-called left-handed media-that exhibit highly unusual electromagnetic properties and promise new device applications. Left-handed materials require negative permeability ν, an extreme condition that has so far been achieved only for frequencies in the microwave to terahertz range. Extension of the approach described in ref. 7 to achieve the necessary high-frequency magnetic response in visible optics presents a formidable challenge, as no material-natural or artificial-is known to exhibit any magnetism at these frequencies. Here we report a nanofabricated medium consisting of electromagnetically coupled pairs of gold dots with geometry carefully designed at a 10-nm level. The medium exhibits a strong magnetic response at visible-light frequencies, including a band with negative ν. The magnetism arises owing to the excitation of an antisymmetric plasmon resonance. The high-frequency permeability qualitatively reveals itself via optical impedance matching. Our results demonstrate the feasibility of engineering magnetism at visible frequencies and pave the way towards magnetic and left-handed components for visible optics. © 2005 Nature Publishing Group.
569 citations