Electromagnetic wave propagations in a 3-dimensional (3D) left-handed (LH) metamaterial composed of periodic wired metallic spheres are studied numerically. It is shown that the metamaterial supports the dominant 3D LH wave with negative refractive indices. Parametric studies of dependencies of the dispersion characteristics on the unit cell structure are carried out and it is shown that the isotropy can be enhanced by tuning the diagonal wire diameter and the sphere diameters. Keywords: metamaterials, left-handed materials, negative refractive index, super lens Classification: Microwave and millimeter wave devices, circuits, and systems References [1] V. G. Veselago, "The electrodynamics of substances with simultaneously negative values of ε and μ,"

We report on Raman spectroscopy of few quintuple layer topological insulator bismuth selenide (Bi2Se3) nanoplatelets (NPs), synthesized by a polyol method. The as-grown NPs exhibit excellent crystalline quality, hexagonal or truncated trigonal morphology, and uniformly flat surfaces down to a few quintuple layers. Both Stokes and anti-Stokes Raman spectroscopy for the first time resolve all four optical phonon modes from individual NPs down to 4 nm, where the out-of-plane vibrational A(1g)(1) mode shows a few wavenumbers red shift as the thickness decreases below ~15 nm. This thickness-dependent red shift is tentatively explained by a phonon softening due to the decreasing of the effective restoring force arising from a decrease of the van der Waals forces between adjacent layers. Quantitatively, we found that the 2D phonon confinement model proposed by Faucet and Campbell cannot explain the red shift values and the line shape of the A(1g)(1) mode, which can be described better by a Breit–Wigner–Fano resonance line shape. Considerable broadening (~17 cm(–1) for six quintuple layers) especially for the in-plane vibrational mode E(g)(2) is identified, suggesting that the layer-to-layer stacking affects the intralayer bonding. Therefore, a significant reduction in the phonon lifetime of the in-plane vibrational modes is probably due to an enhanced electron–phonon coupling in the few quintuple layer regime.

Hyperlenses have generated much interest recently, not only because of their intriguing physics but also for their ability to achieve sub-diffraction imaging in the far field in real time. All previous efforts have been limited to sub-wavelength confinement in one dimension only and at ultraviolet frequencies, hindering the use of hyperlenses in practical applications. Here, we report the first experimental demonstration of far-field imaging at a visible wavelength, with resolution beyond the diffraction limit in two lateral dimensions. The spherical hyperlens is designed with flat hyperbolic dispersion that supports wave propagation with very large spatial frequency and yet same phase speed. This allows us to resolve features down to 160 nm, much smaller than the diffraction limit at visible wavelengths, that is, 410 nm. The hyperlens can be integrated into conventional microscopes, expanding their capabilities beyond the diffraction limit and opening a new realm in real-time nanoscopic optical imaging.

Far-field optical lens resolution is fundamentally limited by diffraction, which typically is about half of the wavelength. This is due to the evanescent waves carrying small scale information from an object that fades away in the far field. A recently proposed superlens theory offers a new approach by surface excitation at the negative index medium. We introduce a far-field optical superlens (FSL) that is capable of imaging beyond the diffraction limit. The FSL significantly enhances the evanescent waves of an object and converts them into propagating waves that are measured in the far field. We show that a FSL can image a subwavelength object consisting of two 50 nm wide lines separated by 70 nm working at 377 nm wavelength. The optical FSL promises new potential for nanoscale imaging and lithography.The discovery of Ernst Abbe in 1873 set the fundamental far-field resolution limit for an optical lens known as the "diffraction limit", which typically is about half a wavelength. 1,2 Although shorter wavelength electron beams and X-ray sources have improved resolving power, 3,4 the diffraction limit remains a formidable barrier. Near-field scanning optical microscopy (NSOM) forms images by scanning a sharp tip in close proximity to an object. The near-field profile is thus collected "point-by-point", which is a rather slow process that is incapable of projecting realtime images in the way lenses do. [5][6][7] Other techniques, based on nonlinear optical effects, have been proposed to improve resolution. 8 Recently, stimulated emission depletion fluorescence microscopy has emerged as one of the most successful techniques for subdiffraction-limited imaging, which cleverly uses saturation transitions between energy states of a fluorescence dye immersed in the object in shaping a subdiffraction spot. 9 However, this approach also requires time-consuming scanning of the object, in addition to the use of dyes and high illumination intensities to achieve the necessary nonlinear response. Recently, a remarkable perfect lens concept has been proposed that has the potential to recover lost evanescent information. 10 This is accomplished by coupling evanescent waves from the object to surface excitations on a slab of negative refractive index material. The lens compensates for evanescent wave decay in free space using the strong enhancement provided by the surface excitations, thereby restoring the evanescent components and projecting a perfect image. This effect has been studied for a wide range of frequencies in both composite metamaterials 11-14 and photonic band gap crystals. [15][16][17][18] Recently, optical superlensing has been successfully demonstrated using a silver 19 or SiC slab. 20 However, the superlenses experimentally demonstrated so far are only capable of projecting an image in the near field; due to the intrinsic losses, a simple slab superlens is "near-sighted". 21 Far-field imaging with a superlens still remains a great challenge to many exciting applications. In this Letter, we demonstrate a f...

We report here the design, fabrication and characterization of optical hyperlens that can image sub-diffraction-limited objects in the far field. The hyperlens is based on an artificial anisotropic metamaterial with carefully designed hyperbolic dispersion. We successfully designed and fabricated such a metamaterial hyperlens composed of curved silver/alumina multilayers. Experimental results demonstrate far-field imaging with resolution down to 125nm at 365nm working wavelength which is below the diffraction limit.

Optical imaging and photolithography promise broad applications in nano-electronics, metrologies, and single-molecule biology. Light diffraction however sets a fundamental limit on optical resolution, and it poses a critical challenge to the down-scaling of nano-scale manufacturing. Surface plasmons have been used to circumvent the diffraction limit as they have shorter wavelengths. However, this approach has a trade-off between resolution and energy efficiency that arises from the substantial momentum mismatch. Here we report a novel multi-stage scheme that is capable of efficiently compressing the optical energy at deep sub-wavelength scales through the progressive coupling of propagating surface plasmons (PSPs) and localized surface plasmons (LSPs). Combining this with airbearing surface technology, we demonstrate a plasmonic lithography with 22 nm half-pitch resolution at scanning speeds up to 10 m/s. This low-cost scheme has the potential of higher throughput than current photolithography, and it opens a new approach towards the next generation semiconductor manufacturing.

We report that two-dimensional (2D) sub-diffraction-limited images can be theoretically reconstructed by a new metamaterial far-field superlens. The metamaterial far-field superlens, composed of a metal-dielectric multilayer and a one-dimensional (1D) subwavelength grating, can work over a broad range of visible wavelengths intrinsically. The imaging principle and the reconstruction process are described in detail. The 2D sub-diffraction-limited imaging ability enables more applications of the far-field superlens in optical nanoimaging and sensing.

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