Intensity depending on object distance in a two-dimensional photonic crystal

The propagation of electromagnetic (EM) waves in two-dimensional triangular-lattice photonic crystals (PCs) is investigated through dispersion characteristics analysis and numerical simulation of field pattern. The designed PC structure can exhibit all angle negative refraction in the second band. A flat superlens formed from such a PC has been designed and its imaging properties have been investigated systematically. Good-quality images and focusing, with relative refractive index of ?1, have been observed in this system for TE mode waves. In contrast to the images in near-field region for the lowest valence band, non-near-field images, explicitly following the well-known wave-beam negative refraction law, have been demonstrated. The relation between the intensity of the image and the object distance has also been discussed in this paper. The extensive applications of such a phenomenon to optical devices are anticipated.     

Near-Field Optical Transfer Function for Far-Field Super-Resolution Imaging

The far-field superlens based on surface plasmon polaritons （SPP） has shown great application potential, but it is difficult and time-consuming to reconstruct the far-field image. We derive a near-field optical transfer function （NOTF） of a silver slab and analyse its validity so that accurate information of nano-seale object in the near-field can be computed rapidly. The NOTF is helpful not only for analysing the super-resolution imaging process in far-field, but also for providing a track to describe the transmission of optical information from near-field to far-field by using the optical transfer functions theorv only.     

Sub-diffraction-limited far-field imaging in infrared

We investigated a far-field superlens operating at mid-infrared wavelength that allows resolving subwavelength features in the far-field. By utilizing evanescent enhancement provided by surface plasmon excitation of silver nanorods and Moiré effect, we numerically demonstrated that subwavelength information of an object can be converted to propagating information. This information can then be captured by conventional optical components. A simple image reconstruction algorithm can restore the subwavelength object. A sub-diffraction-limited resolution of 2.5 μm at 6-μm wavelength is demonstrated.     

Sub-diffraction-limited far-field imaging in infrared

We investigated a far-field superlens operating at mid-infrared wavelength that allows resolving subwavelength features in the far-field. By utilizing evanescent enhancement provided by surface plasmon excitation of silver nanorods and Moiré effect, we numerically demonstrated that subwavelength information of an object can be converted to propagating information. This information can then be captured by conventional optical components. A simple image reconstruction algorithm can restore the subwavelength object. A sub-diffraction-limited resolution of 2.5 μm at 6-μm wavelength is demonstrated.     

Coupling effect in a near-field object–superlens system

The coupling effect in a near-field object–superlens system has been studied, where the object is a silver cylinder and the superlens is a silver slab. A semi-analytical formulation has been established to study the system with and without the coupling effect. The analysis shows that the coupling effect significantly changes the field distributions of both the object and the image, leading to the conclusion that such a system must be designed and analyzed as a whole. Our study also suggests that it is possible to design a superlens system with mismatched permittivities.     

突破衍射极限的超级透镜技术及其应用研究

基于超材料的超级透镜能让携带物体高频信息的倏逝波分量参与成像,从而实现对小于半个工作波长的超精细结构的分辨。分析了几种典型的超透镜,如近场、远场和双曲超透镜的工作原理和研究进展,并对超透镜技术在实时生物成像、高密度光存贮、光刻等方面的应用前景进行了分析和总结。     

Dual mode near-field scanning optical microscopy for near-field imaging of surface plasmon polariton

In this paper, we theoretically and experimentally demonstrate that metal coated apertured probes are efficient near-field probes on surfaces with high reflectivity for the scattering as well as for the collection mode near-field scanning optical microscopy (NSOM). We show that a blunt apertured metal coated tip is very effective in suppressing image dipoles which affect strongly the signals scattered from frequently used sharp metal tips or gold nanoparticle attached probes. By using a simultaneous collection and scattering mode (dual mode) NSOM we measure the near-field images of surface plasmon polariton (SPP) launched from a slit. The collection mode measures propagating SPP along lateral distance in a long scan range with high signal-to-noise ratio, and the scattering mode measures the polarization resolved near-field of SPP. Comparisons of the measured data obtained in the dual mode enable to easily characterize SPP and to separate the measured near-field into the propagating SPP and the directly transmitted light.     

Adiabatic transfer of surface plasmons in non-Hermitian graphene waveguides

We investigate the energy transfer of surface plasmon polaritons (SPPs) based on adiabatic passage in a non-Hermitian waveguide composed of three coupled graphene sheets. The SPPs can completely transfer between two outer waveguides via the adiabatic dark mode as the waveguides are lossless and the coupling length is long enough. However, the loss of graphene can lead to breakdown of adiabatic transfer schemes. By utilizing the coupled mode theory, we propose three approaches to cancel the nonadiabatic coupling by adding certain gain or loss in respect waveguides. Moreover, the coupling length of waveguide is remarkably decreased. The study may find interesting application in optical switches on a deep-subwavelength scale.     

银层超透镜光学传递函数的研究

银层超透镜对基于表面等离子体激元的超分辨光刻、 成像和生物传感有着重要作用.利用银层超透镜的光学传递函数详 细研究了银板的表面等离子体激元共振和成像特性, 并利用时域有限差分法计算模拟了银层超透镜的成像过程, 得到与理论推导公式相符合的结果, 证明了光学传递函数的可靠性, 为基于表面等离子体激元的传感器件、 超分辨成像以及辅助增强干涉光刻提供了快速参数优化方法.     

Subwavelength imaging enhancement through a three-dimensional plasmon superlens with rough surface

In this Letter we investigate the subwavelength imaging of a three-dimensional plasmon superlens based on the full vector wave simulations of optical wave propagation and transmission. The optical transfer functions are computed. Comparisons are made between the results of lenses with flat and periodic/random rough surfaces. We also study the problem of practical imaging system geometry using laser as an illumination source. Results show that the lens with periodic or random roughness can reduce the field interference effects, and provide improved focus on the transmission field and the Poynting flux. We illustrate that the subwavelength roughness in a plasmon lens can enhance the image resolution over a flat lens for both matched and unmatched permittivity conditions. The enhancement of resolution occurs because the introduced subwavelength roughness can amplify the evanescent wave components and suppress the surface plasmon resonance peaks.     

A new near-field phase-correction method for superlens

A new phase-correction method in a realistic loss superlens imaging system is theoretically predicted.The image resolution is enhanced using the near-field active phase-correction method.Resolvable separation between two slits has been significantly improved toλ/20 for the symmetrical superlens system andλ/12 for unsymmetrical system.     

The reconstruction of finite extent objects with the superlens

The imaging of three-dimensional source objects with the Veselago–Pendry superlens has not been extensively researched. In this paper, we attempt to answer two fundamental questions. Firstly, can the superlens image an object with non-zero dimension normal to the lens surfaces—at least in principle? Secondly, if the answer is yes, would it be possible to realize such a system, and what are the conditions that it would have to satisfy? To answer these questions, we develop an image reconstruction algorithm based on a spatial Fourier decomposition of the field functions and an optimal sampling technique employing Deslauriers–Dubuc interpolation wavelets. We conclude that it is theoretically possible to image 3-D objects with the superlens, but that real-world limitations impose stringent restrictions on the system.     

Two surface plasmon resonances effects for light through the perforated metal film

Light transmission through perforated metal film has been reported and some investigations have been made into the physical origin of this phenomenon. We show that the transmission assisted with surface plasmon (SP) through a perforated metal film results from two different SP resonances effects: surface plasmon resonance due to the periodicity at the left air/metal and right metal/air interfaces and localized cavities resonance inside rectangular holes. The fields intensity is localized separately on the left and right metal-air surfaces for structure-factor-induced surface plasmon mode. And for localized cavities resonance mode, standing electromagnetic fields can also be entirely localized inside the nanohole region. The aspect ratio of the rectangular holes can affect the transmission.     

数值模拟探针诱导表面等离子体共振耦合纳米光刻

采用有损耗介质和色散介质的二维时域有限差分方法,数值模拟了以光波长514.5nm的p偏振基模高斯光束为入射光源,激发Kretschmann型表面等离子体共振,并通过探针的局域场增强效应实现纳米光刻的新方法——探针诱导表面等离子体共振耦合纳米光刻.分别就探针与记录层的间距以及探针针尖大小,模拟分析了不同情况下探针的局域场增强效应和记录层表面的相对电场强度振幅分布.结果表明,探针工作在接触模式时,探针的局域场增强效应最明显,记录层表面的相对电场强度振幅的对比度最大;当探针针尖距记录层5nm时,针尖下方记录层表面的相对电场强度振幅大于光刻临界值的分布宽度与针尖尺寸相近. 关键词： 纳米光刻 表面等离子体共振 时域有限差分方法     

Angle- and energy-dependent core-level photoelectron energy loss studies in Al and In

Electron energy loss structures of Al and In core-level photoemission spectra, in particular surface and bulk plasmon losses, have been investigated as functions of photon energy (i.e., photoelectron kinetic energy). These studies utilized synchrotron radiation to provide a variable photon source in the ultra-soft X-ray region, thus allowing these loss processes to be studied at photoelectron kinetic energies for which the mean free path of the electrons is minimal. The Al plasmon loss structure was also studied with soft X-ray radiation in an angle-resolved mode, allowing the variation of effective photoelectron sampling depth with different electron take-off (collection) angles. These results for the relative intensity of the bulk and surface plasmons as a function of electron kinetic energy and electron exit angle are in qualitative agreement with the predictions of ?unji? and ?ok?evi?. The core-level binding energies of surface atoms have also been studied with the result that no significant shift has been observed with respect to bulk-atom core levels.     

Experimental study of transmission enhancement of evanescent waves through silver films assisted by surface plasmon excitation

In this paper, we investigated an essential precursor of superlensing: enhancing the transmission of evanescent waves assisted by excitation of surface plasmon. Using natural roughness as a well characterized grating, the transmission of evanescent waves is studied through silver thin films of increasing thickness. Measurements and calculations are performed in the wavelength range of 514.5 nm to 351.1 nm where the real part of the permittivity of silver is negative. Pronounced peaks due to surface-plasmon excitations are observed in the transmission spectra. We found the transmission of evanescent waves rapidly grows with the film thickness up to about 50 nm, after which it decays as loss becomes significant. As the permittivity of a silver slab approaches -1, we experimentally observed a broadening of surface plasmon bandwidth. Our study indicates a pathway to access the deep subwavelength features by metamaterial superlens. PACS 42.79-e; 42.30.Wb; 78.20.Ci; 78.66.Bz     

Enhancing surface plasmon polariton propagation by two-layer dielectric-loaded waveguides on silver surface

We report a study of a two-layer dielectric-loaded surface plasmon polariton waveguide (TDLSPPW) which consisted of two dielectric layers (high-index/low-index) on a silver film. The discontinuity of the electric field at the interfaces resulted in a concentrated field in the low-index region. It efficiently reduced the propagation loss of the surface plasmon polariton mode. The mode fields and corresponding complex propagation constants were calculated by a vector finite-difference method. The propagation properties were measured by a modified near-field optical microscope. It is confirmed that the propagation length of the proposed TDLSPPW was about 1.6 times longer than conventional single-layer SPP waveguides. In addition, a 90^° waveguide turn with 3 μm radius showed that the bending loss was smaller than 2 dB.     

Emission-depth-selective auger photoelectron coincidence spectroscopy

The collision statistics of the energy dissipation of Auger and photoelectrons emitted from an amorphized Si(100) surface is studied by measuring the Si 2p photoelectron line as well as the first plasmon loss peak in coincidence with the Si-LVV Auger transition and the associated first plasmon loss. The Si 2p plasmon intensity decreases when measured in coincidence with the Si-LVV peak. If measured in coincidence with the Si-LVV plasmon the decrease is significantly smaller. The results agree quantitatively with calculations accounting for surface, volume, and intrinsic losses as well as elastic scattering in a random medium. In this way one can determine the average emission depth of individual electrons by means of Auger photoelectron coincidence spectroscopy, which therefore constitutes a unique tool to investigate interfaces at the nanoscale level.     

Long-Range Slot Hybrid Surface Plasmon Waveguide With Long Propagation Distance and Tight Mode Confinement

A long-range hybrid slot surface plasmon waveguiding structure that is capable of achieving ultra-small mode confinement and a long propagation distance simultaneously is proposed in this article. In comparison with the conventional long-range hybrid surface plasmon waveguide, the proposed waveguide can provide one order smaller mode area and a longer propagation distance by introducing a through-slot in the gap region. Meanwhile, the practical fabrication errors have little influence over mode properties of the waveguide. These results indicate that our designed waveguide can be a potential candidate for high-performance nanophotonic circuit and device.     

Collective mode dispersions of organic chain compounds

We investigate the collective mode dispersions for the tight-binding dielectric matrix with two one-dimensional electron bands per donor and acceptor chains, and the three-dimensional long-range Coulomb electron-electron interaction within the random phase approximation. The hybridized collective modes are the result of the strong coupling between the intraband plasmon and the interband dipolar modes due to strong dipole Coulomb interactions. Our calculations show the existence of the low-energy renormalized plasmon mode above the electron-hole quasi-continuum in the long wavelength limit. The obtained modes are brought into correspondence with the optical data of quasi-one-dimensional organic conductor tetrathiafulvalene-tetracyanoquinodimethane (TTF-TCNQ). Namely, the renormalized plasmon and the dipolar mode are assigned to the observed excitations at respective energy scales of roughly 10 meV and 0.75 eV, explaining why lower excitation is eliminated while higher excitation persists below the temperature of the Peierls phase transition.