共查询到20条相似文献,搜索用时 15 毫秒
1.
In this Letter, we propose an engineered design of optical cloaks based on the scattering cancellation technique and intended to reduce the observability of cylindrical objects. The cover, consisting of a periodic arrangement of core-shell nanospheres, is designed in such a way to exhibit near-zero values of the real part of the homogenized effective permittivity at optical frequencies. Full-wave numerical simulations, considering the measured data of the dielectric function of the plasmonic material composing the shell, show that the cloak is able to reduce by about 6 dB the scattering cross section of a finite-length cylinder at around 740 THz with a -3 dB fractional bandwidth of about 7%. We show also that this result is not significantly affected by the perturbation of the periodic alignment of the core-shell nanospheres, due to possible fabrication issues or to an amorphous arrangement. 相似文献
2.
We numerically demonstrate that properly designed plasmonic covers can be used to enhance the performance of near-field scanning optical microscopy (NSOM) systems based on the employment of apertureless metallic tip probes. The covering material, exhibiting a near-zero value of the real permittivity at the working frequency, is designed in such a way to dramatically reduce the undesired scattering due to the strongly plasmonic behavior of the tip. Though the light scattering by the tip end is necessary for the correct operation of NSOMs, the additional scattering due to the whole probe affects the signal-to-noise ratio and thus the resolution of the acquired image. By covering the whole probe but not the very tip, we show that unwanted scattering can be effectively reduced. A realistic setup, working at mid-IR frequencies and employing silicon carbide covers, has been designed and simulated to confirm the effectiveness of the proposed approach. 相似文献
3.
There is significant motivation to develop media with negative refractive indices at optical frequencies, but efforts in this direction are hampered by the weakness of the magnetic response at such frequencies. We show theoretically that a nonmagnetic medium with two atomic or molecular constituents can exhibit a negative refractive index. A negative index is possible even when the real parts of both the permittivity and permeability are positive. This surprising result provides a route to isotropic negative-index media at optical frequencies. 相似文献
4.
Zeyad I. Al-SahharHala J. El-Khozondar Mohammed M. Shabat 《Journal of magnetism and magnetic materials》2012,324(6):1100-1105
The dispersion relation in a system that consists of a lossy metamaterials (MTMs) film surrounded by a linear substrate and a nonlinear cladding with an arbitrary nonlinearity is derived. The surface plasmonic (SP) wave at the interfaces between metamaterials (MTMs) and the nonlinear cover is recovered by taking certain limits. Lossy MTMs have simultaneously complex-negative permeability μ and complex-negative permittivity ε. Results are presented by plotting the SP frequency as a function of the nonlinearity at chosen damping factors. Both the real and imaginary parts are studied. Results also display the wave frequency as a function of plasma frequency. For comparison, the imaginary part is set to zero and curves are reproduced. 相似文献
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Hala J. El-Khozondar Rifa J. El-Khozondar Said Zouhdi 《Applied Physics A: Materials Science & Processing》2014,115(2):439-442
Metamaterials (MTMs), which have both negative permeability and negative permittivity, have potential applications in optoelectronics and communications. These materials are fabricated in laboratories which is an added advantage. The focus of this work is on the propagation of surface waves at the interface between nonlinear MTMs and anisotropic materials in the optical range. The dispersion equation is derived from Maxwell’s equations. The dispersion equation is solved numerically to study the characteristics of the propagated wave. Only TE modes are considered. The results display the dependence of the propagating waves on the characteristics of the structure composite materials. 相似文献
7.
E.V. Ponizovskaya A.M. Bratkovsky 《Applied Physics A: Materials Science & Processing》2007,87(2):161-165
One of the most important modern problems in modern electromagnetics is a design and study of negative index metamaterials
that may enable sub-wavelength imaging at optical frequencies. Plasmonic periodic metal-dielectric nanostructures present
one interesting possibility for both 2D and 3D negative index medium (NIM) systems. The displacement current near plasmonic
resonance excitations may produce both negative permittivity and negative permeability (most difficult) in a NIM with e.g.
“fishnet” metal-dielectric composite type structure. One obvious problem with a metallic NIM is that the response is strongly
dispersive and lossy. Both of these effects are detrimental to sub-wavelength imaging. One way of mitigating losses is to
use a gain medium. We address the question of sub-wavelength resolution in the fishnet NIM with and without gain medium.
PACS 42.79.-e; 42.79.Dj; 42.81.Dp; 74.78.Fk; 78.66.Bz 相似文献
8.
Boubacar Kanté André de Lustrac Jean-Michel Lourtioz 《Photonics and Nanostructures》2010,8(2):112-119
Metamaterial building blocks from microwave to optical range are mainly based on metal-dielectric composites. In almost all structures with true negative index (not coming from losses), two kinds of meta-atoms (electric and magnetic) are mixed to drive simultaneously the effective permittivity and permeability to negative values leading in turn to a negative index of refraction. In this paper, we show that two coupled structures with localized plasmons modes (e.g. cut-wires or split ring resonators) can exhibit negative refractive index by their own, by appropriately controlling the hybridization scheme of the plasmons modes. Because of small metal filling factor and reduced optical losses, the resulting structures may pave the way to realistic applications of metamaterials at optical frequencies. 相似文献
9.
An analytical theory is developed for parametric interactions in metamaterial multilayer structures with simultaneous nonlinear electronic and magnetic responses and with a near-zero refractive index. We demonstrate theoretically that electromagnetic fields of certain frequencies can be parametrically shielded by a nonlinear left-handed material slab, where the permittivity and permeability are both negative. The skin depth is tunable, and even in the absence of material absorption, can be much less than the wavelength of the electromagnetic field being shielded. This exotic behavior is a consequence of the intricate nonlinear response in the left-handed materials and vanishing optical refractive index at the pump frequency. 相似文献
10.
E. S. Kolodeznyi S. S. Rochas A. S. Kurochkin A. V. Babichev I. I. Novikov A. G. Gladyshev L. Ya. Karachinskii D. V. Denisov Yu. K. Bobretsova A. A. Klimov S. A. Blokhin K. O. Voropaev A. S. Ionov 《Optics and Spectroscopy》2018,125(2):238-242
Results of investigation of 1550 nm range stripe semiconductor lasers fabricated from heterostructures with different designs of the gain medium are presented. It is shown that the proposed designs of the gain medium allow obtaining the effective lasing at high level of total optical losses, comparable with the typical optical losses in the vertical-cavity surface-emitting lasers. The evaluation of modal gain in different types of the gain mediummade it possible to estimate the possible frequencies of the small-signal modulation of vertically emitting lasers and proposed the ways to increase them up to 20 GHz or more. 相似文献
11.
We show that recent claims of experimental verification of a negative index of refraction in metallic metamaterials, "left-handed" microwave frequencies, are questionable. At these frequencies the imaginary part of the dielectric permittivity is significant or even dominates its real part, and hence the effective medium behaves as a metal, i.e., with losses below the cutoff frequency of relevance. Then, the refractive index is complex, and there is not a distinction between right- and left-handed material because the electromagnetic wave is inhomogeneous. Just by using this idea we explain the transmittivities that were recently obtained in experiments by Shelby et al. [Science 292, 77 (2001) and Appl. Phys. Lett. 78, 489 (2001)]. 相似文献
12.
C. J. Zapata-Rodríguez J. J. Miret 《Applied Physics A: Materials Science & Processing》2011,103(3):699-702
We present a family of p-polarized optical beams that are highly localized around the optical axis and are sustained in a
layered medium. This medium is comprised of a stack of thin films made of a material exhibiting negative permittivity, regularly
placed in a dielectric host. We exploit the excitation of surface plasmon polaritons leading to enhanced localization near
the optical axis. Also we perform an appropriate correction of the 2D wavefront in the vicinity of the beam axis for a perfect
phase matching showing an optimal concentration of light. 相似文献
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The effect of temperature and dc magnetic field variations on effective electromagnetic parameters of metamaterials (MTMs) containing spherical semiconductor particles is studied theoretically. The effect of temperature is taken into account through its influence on semiconductor carrier density and mobility. The effect of dc magnetic field is included using an extension of the Mie theory, describing the interaction of a plane wave with a gyrotropic sphere. The effective parameters such as relative permittivity and permeability are calculated by proper application of the Maxwell Garnett (MG) theory and its extensions to quasi-static condition and multi-phase structures. Based on these theories, the temperature and dc magnetic field tunability of three different MTM structures is investigated. First a single phase medium is considered which contains spherical semiconductor particles of one kind, randomly dispersed in a dielectric host. Then two multi-phase structures containing (a) two kinds of spherical semiconductor particles or (b) spherical particles with core-shell topology are investigated. The two multi-phase MTM structures can exhibit negative index of refraction in far-infrared spectral region. The measure of the temperature and dc magnetic field tunability of effective parameters such as relative permittivity and refractive index of the structures is evaluated and it is shown specifically that the real part of refractive index can be tuned to get negative, zero or positive values in far-IR or THz regimes, but the imaginary part of the index and the Figure of Merit (FOM) are also quite sensitive to the temperature and magnetic field variations. The tunable MTMs can find new applications in THz devices such as switches, tunable mirrors, isolators, converters, polarizers, filters and phase shifters. 相似文献
15.
Dongho Kim Wangju Lee Jaeick Choi 《Applied Physics A: Materials Science & Processing》2009,97(2):461-467
We propose a very simple design method of negative refractive index (NRI) materials that can overcome some drawbacks of conventional
resonant-type NRI materials. The proposed NRI materials consist of single or double metallic patterns printed on a dielectric
substrate. Our metamaterials (MTMs) show two properties that are different from other types of MTMs in obtaining effective
negative values of permittivity (ε) and permeability (μ) simultaneously; the geometrical outlines of the metallic patterns are not confined within any specific shape, and the metallic
patterns are printed on only one side of the dielectric substrate. Therefore, they are very easy to design and fabricate using
common printed circuit board (PCB) technology according to the appropriate application. Excellent agreement between the experiment
and prediction data ensures the validity of our design approach. 相似文献
16.
In nature, some molecules have broken conjugate symmetry configurations, which might result in a special optical phenomenon called negative refraction. Under such circumstances, both permittivity and permeability are negative simultaneously. When light at certain frequency is transmitted through a transparent medium (e.g., slide glass) in which a psychoactive drug with negative indexes has been deposited, the refracted light is detected at different locations in the transparent medium. This is because the refracted light travels in a direction opposite to the expected path when it passes through material with a negative index. Using this method, it is possible to distinguish synthetic cannabinoids from other abusive psychoactive drugs in the UV-vis region. In this study, we use a tight-binding model to calculate the permittivity and permeability of pentagonal configurations with different broken symmetries. Furthermore, a qualitative analysis of the negative refraction with respect to heptagonal models is discussed. 相似文献
17.
The engineering in artificial inclusions of metamaterials has immense potential to explore in the field of electromagnetic wave manipulation that created enormous opportunities in the design of millimetre or sub-millimetres structures. In this research paper, Parabolic Split Ring Resonator (PSRR) based MNZ (Mu-Near-Zero) metamaterial with a wider refractive index is introduced for WiFi/WiMax/Wireless/ISM band applications and printing on Rogers RT-5880 lossy substrate with a copper-based metallic structure at 5.8 GHz within the microwave frequency region. The resonant frequency, negative permittivity, near-zero permeability, and negative refractive index are between 5.5-6.3 GHz. This proposed metamaterial structure is analysed with array structures, different substrate material, different orientations, and split gaps. 相似文献
18.
Nadia Mattiucci Giuseppe D’Aguanno Neset Akozbek Michael Scalora Mark J. Bloemer 《Optics Communications》2010,283(8):1613-23710
Classical theory of crystals states that a medium to be considered homogeneous must satisfy the following requirements (a) the dimension of the elementary cell must be much smaller than the incident wavelength; (b) the sample must contain a large number of elementary cells, i.e. it must be macroscopic with respect to wavelength. Under these conditions, macroscopic quantities can be introduced in order to describe the optical response of the medium. We analytically demonstrate that for a symmetric elementary cell those requirements can be relaxed, and it is possible to assign a permittivity and a permeability to a composite structure, even if the metamaterial cannot be considered homogeneous under the requirements stated above. However, the effective permittivity and permeability in some cases may give rise to unphysical, effective behaviors inside the medium, notwithstanding the fact that they satisfy requirements like being Kramers-Kronig pairs, for example, and are consistent with all the linear properties outside the structure (i.e. reflection, transmission, and absorption at all frequencies). In some situations the medium is assigned a magnetic response even though the medium is not magnetically active. In particular, we demonstrate that the homogenization procedure can lead to a medium that locally violates the second principle of thermodynamics. We also show that, in the non-homogeneous regime, it is not possible to describe the nonlinear behavior of the structure using an effective parameters approach, despite the possibility to assign an effective linear refractive index. 相似文献
19.
E. O. Liznev A. V. Dorofeenko Liu Huizhe A. P. Vinogradov S. Zouhdi 《Applied Physics A: Materials Science & Processing》2010,100(2):321-325
The employment of epsilon-near-zero material (ENZM) has been demonstrated to be the key to cloak designs. Furthermore, methods
for designing such materials at any frequency have been discussed. It has been shown that an ENZM may be manufactured for
any wavelength where the real part of silver permittivity is negative. Depending on the frequency, the ENZM is a dielectric
matrix filled with silver inclusion or silver foam. The losses in the ENZM may be even smaller than the losses in silver at
the wavelength where real part of silver permittivity is equal to zero. 相似文献
20.