All-angle negative refraction and imaging in a bulk medium made of metallic nanowires in the visible region.

NSF Nanoscale Science and Engineering Center, 5130 Etcheverry Hall, University of California, Berkeley, CA 94720-1740, USA.
Optics Express (Impact Factor: 3.53). 10/2008; 16(20):15439-48. DOI: 10.1364/OE.16.015439
Source: PubMed

ABSTRACT We theoretically demonstrated that all-angle negative refraction and imaging can be implemented by metallic nanowires embedded in a dielectric matrix. When the separation between the nanowires is much smaller than the incident wavelength, these structures can be characterized as indefinite media, whose effective permittivities perpendicular and parallel to the wires are opposite in signs. Under this condition, the dispersion diagram is hyperbolic for transverse magnetic waves propagating in the nanowire system, thereby exhibiting all-angle negative refraction. Such indefinite media can operate over a broad frequency range (visible to near-infrared) far from any resonances, thus they offer an effective way to manipulate light propagation in bulk media with low losses, allowing potential applications in photonic devices.

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    ABSTRACT: A class of strongly anisotropic materials having their principal elements of dielectric permittivity or magnetic permeability tensors of opposite signs, so-called indefinite or hyperbolic materials, has recently attracted significant attention. These materials enabled such novel properties and potential applications as all-angle negative refraction, high density of states, and imaging beyond the diffraction limit using a so-called hyperlens. While several studies identified a few examples of negative refractions in birefringent crystals existing in nature, the majority of optical materials with hyperbolic dispersion relations known to date are engineered composite materials, “metamaterials”, such as metal-dielectric subwavelength multilayered structures or metal nanowires in a dielectric matrix. In this paper, we investigate naturally existing hyperbolic materials with indefinite permittivity for a range of frequencies from terahertz to ultraviolet. These include graphite, MgB2, cuprate, and ruthenate. Spectroscopic ellipsometry is used to characterize the dielectric properties of graphite and MgB2, and a fitting method based on reflectance spectra is used to determine the indefinite permittivity of the cuprate and ruthenate. Lastly, we discuss the mechanisms behind indefinite properties of these materials.
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