Astigmatism in tapered slot antennas

A series of scale model measurements of transverse electromagnetic mode tapered slot antennas are presented. They show that the beam launched by this type of antenna is astigmatic. It is shown how an off-axis spherical mirror can be used to correct this astigmatism to allow efficient coupling to quasi-optical systems. A millimetre wave antenna and mirror combination is described and, with the aid of solid state noise diodes, the coupling of the launched beam to a quasi-optical spectrometer is shown to be in good agreement with that predicted by the scale model measurements.     

Excitation of propagating magnetization waves by microstrip antennas

We discuss the self-consistent theory of excitation of dipole-exchange magnetization waves by microstrip antennas in a metal-dielectric-ferrite-dielectric-metal stratified structure, magnetized under an arbitrary angle to the surface. Spin-wave Green's functions are derived, describing the response of the spin-system to a spatially inhomogeneous varying magnetic field. The radiative resistance of microstrip antenna is calculated. In this case the distribution of surface current density in the antenna is found on the basis of the analytic solution of a singular integral equation. The nature of the effect of metallic screens and redistributed surface current densities in the antenna on the frequency dependence of the resistive radiation is investigated. Approximate relations are obtained, convenient for practical calculations of radiative resistance of microstrip antennas both in a free and in a screened ferromagnetic film. The theoretical calculations are verified by data of experiments carried out on monocrystalline films of iron-yttrium garnet.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 11, pp. 24–53, November, 1988.     

The role of propagating and evanescent waves in scanning near-field optical microscopy

Theoretical study on the image formation in scanning near-field optical microscopy is carried out in the framework of the direct moment method. Information brought, respectively, by the propagating and evanescent components in the optical near field that is collected by a scanning fiber tip with a sub-wavelength aperture is numerically and systematically analyzed in the light of the resolution achieved by the microscope. The analyses reveal that resolutions beyond the diffraction limit can be achieved even in the absence of the evanescent waves. That is, it is incorrect or at least incomplete to believe that a microscope that collects only the propagating waves is limited by the diffraction. Our studies show that a scanning near-field optical microscope can achieve resolutions beyond the diffraction limit by collecting only the propagating waves.     

Resonant transmission of terahertz waves through metallic slot antennas on various dielectric substrates

We report on terahertz electromagnetic field transmission through metallic slot antennas supported on various dielectric substrates. The substrate effect strongly modifies the transmission resonance compared to the free-standing case, while the resonance can be determined systematically by introducing an effective refractive index. The relative contribution of the substrate index to the effective index has been measured for various substrates, and shows a good agreement with theoretical calculations based on a coupled mode method. In addition, the slot antenna arrays embedded in a flexible substrate show a transmission resonance governed by a substrate refractive index.     

基于半导体纳米线/锥形微光纤探针的被动式近场光学扫描成像

本文结合近场扫描结构和纳米线-微光纤耦合技术,提出了一种基于硫化镉纳米线/锥形微光纤探针结构的被动近场光学扫描成像系统.该系统采用被动式纳米探针,保留了纳米探针对样品表面反射光的强约束优势.其理论收集效率为4.65‰,相比于传统的金属镀膜近场探针收集效率提高了一个数量级,可有效地提高扫描探针对样品形貌信息的检测能力;而后通过硫化镉纳米线与微光纤之间高效的倏逝场耦合,将检测的光强信号传输到远场进行光电探测,最终实现对目标样品形貌的分析成像,其样品宽度测量误差在7.28%以内.该系统不需要外部激发光路,利用显微镜自身光源进行远场照明,被动扫描探针仅作为样品表面反射光的被动收集系统.本文基于半导体纳米线/锥形微光纤探针的被动式近场光学扫描成像方案,可有效地降低探针的制备难度和目标光场的检测难度,简化扫描成像的结构,为近场光学扫描显微系统之后的发展提供新的思路.     

基于半导体纳米线/锥形微光纤探针的被动式近场光学扫描成像

本文结合近场扫描结构和纳米线-微光纤耦合技术,提出了一种基于硫化镉纳米线/锥形微光纤探针结构的被动近场光学扫描成像系统.该系统采用被动式纳米探针,保留了纳米探针对样品表面反射光的强约束优势.其理论收集效率为4.65‰,相比于传统的金属镀膜近场探针收集效率提高了一个数量级,可有效地提高扫描探针对样品形貌信息的检测能力;而后通过硫化镉纳米线与微光纤之间高效的倏逝场耦合,将检测的光强信号传输到远场进行光电探测,最终实现对目标样品形貌的分析成像,其样品宽度测量误差在7.28%以内.该系统不需要外部激发光路,利用显微镜自身光源进行远场照明,被动扫描探针仅作为样品表面反射光的被动收集系统.本文基于半导体纳米线/锥形微光纤探针的被动式近场光学扫描成像方案,可有效地降低探针的制备难度和目标光场的检测难度,简化扫描成像的结构,为近场光学扫描显微系统之后的发展提供新的思路.     

利用扫描近场红外显微镜对化学样品组分进行成像研究

介绍了用北京自由电子激光为光源的扫描近场红外显微镜对化学样品组分进行的成像研究，通过所得到的近场微区图像，可以对样品在微区范围内的成分组成，混合的均匀程度等作出比较清晰的判断. 关键词： 自由电子激光 近场光学 扫描近场红外显微镜     

Tunneling of evanescent waves into propagating waves

The tunneling of evanescent waves into propagating waves is related to the convolution of the high spatial frequencies of the source with those of the detectors. Such an approach is demonstrated by treating the evanescent waves which are diffracted from very narrow apertures in a plane screen (with dimensions much smaller than the wavelength) and are converted to propagating waves by tip detectors. The mechanism responsible for the conversion of evanescent waves into propagating waves is explained and a general formula for the conversion of evanescent waves into propagating waves is derived. PACS 42.25.Fx; 42.30.Kq; 42.25.Bs     

Physical principles of plasma dipole and slot antennas

Basic principles of plasma antennas operating on bulk and surface plasma waves are described. It is shown that the efficiency of plasma antennas is highly competitive with that of metal antennas and their controllability is far superior. Two types of plasma antennas are considered, i.e., the dipole ones operating on the surface plasma wave and the waveguide slot antennas operating on the bulk plasma wave.     

Nanoscale near-field infrared spectroscopic imaging of silica-shell/gold-core and pure silica nanoparticles

Spectroscopic near-field imaging of single silica-shell/Au-core and pure silica nanoparticles deposited on a silicon substrate is performed in the infrared wavelength range (λ = 9–11 μm) using scattering-type scanning near-field optical microscopy (s-SNOM). By tuning the wavelength of the incident light, we have acquired information on the spectral phonon–polariton resonant near-field interactions of the silica-shell/Au-core and pure silica nanoparticles with the probing tip. We made use of the enhanced near-field coupling between the high index Au-core and the probing tip to achieve spectral near-field contrast of the thin silica coating (thickness < 10 nm). Our results show that spectroscopic imaging of thin coating layers and complex core–shell nanoparticles can be directly performed by s-SNOM.     

Characterization and optimization of linearly tapered slot antenna pattern

A parametric study of linearly tapered slot antenna (LTSA) in air and a method for optimization of its pattern are presented. A method of moments code is utilized to investigate the behavior of LTSA’s as the length, height and the taper angle varies. It is shown that the antenna pattern can be improved using a top layer of dielectric material with varying permittivity.     

Equivalent source analysis of curved edge tapered slot-line antennas

An equivalent source model for the analysis of curved edge tapered slot-line antenna is developed, which employs effective filamentary currents along the conductor edges of the slot, but forces the electric field produced by the currents to satisfy the boundary condition on the whole conductor surface. This idea is implemented by method of moments with collocation technique, and applied to analyze a tapered slot-line antenna with arbitrarily curved edge.     

Determination of electric-field, magnetic-field, and electric-current distributions of infrared optical antennas: a near-field optical vector network analyzer

In addition to the electric field E(r), the associated magnetic field H(r) and current density J(r) characterize any electromagnetic device, providing insight into antenna coupling and mutual impedance. We demonstrate the optical analogue of the radio frequency vector network analyzer implemented in interferometric homodyne scattering-type scanning near-field optical microscopy for obtaining E(r), H(r), and J(r). The approach is generally applicable and demonstrated for the case of a linear coupled-dipole antenna in the midinfrared spectral region. The determination of the underlying 3D vector electric near-field distribution E(r) with nanometer spatial resolution and full phase and amplitude information is enabled by the design of probe tips with selectivity with respect to E(∥) and E(⊥) fabricated by focused ion-beam milling and nano-chemical-vapor-deposition methods.     

Statistics of waves propagating in a random medium

We present a review of part of the results obtained by the authors for the statistics of coherent radiation propagating in a random medium both in the framework of diagrammatic techniques and random matrix theory. Distribution functions for the total transmission coefficient and the angular transmission coefficient for the diffusive transport and the crossover between the diffusive and ballistic regimes are obtained.The authors acknowledge the financial support of the Israeli Academy of Sciences and of the Schottenstein Center.     

Nano-plasmonic antennas in the near infrared regime

Plasmonic nano-antennas constitute a central research topic in current science and engineering with an enormous variety of potential applications. Here we review the recent progress in the niche of plasmonic nano-antennas operating in the near infrared part of the spectrum which is important for a variety of applications. Tuning of the resonance into the near infrared regime is emphasized in the perspectives of fabrication, measurement, modeling, and analytical treatments, concentrating on the vast recent achievements in these areas.     

Transmission enhancement by conversion of evanescent waves into propagating waves

The convolution between spatial modes of two different parts of an optical system can convert evanescent waves into propagating waves. This principle is applied to different optical systems for analyzing various effects in transmission enhancements experiments. We discuss here the differences between the present principle which is related to broadening of resonances and the near-field optical microscopy based on a tunneling effect by a tip detector. The present analysis is applied in particular to two systems: a) transmission enhancement in one slit by coupling the transmitted radiation with transversal Fabry–Pérot electromagnetic (EM) modes, and b) transmission enhancement by coupling between a metallic film with arrays of holes and surface plasmons (SP). The present approach gives more information on transmission enhancement phenomena than that obtained by conventional treatments and can also solve certain disagreements between different theories. The differences between the present process of converting evanescent waves into propagating waves, and that related to the new development of getting a super-resolution by an hyperlens are discussed. PACS 41.20.Jb; 73.20.Mf; 42.79.Dj     

Interaction of shear waves and propagating cracks

Shear waves generated from an ultrasonic transducer are used to twist dynamically growing crack fronts; the response of crack front to such external perturbations is examined in order to investigate the primary cause of surface roughening in brittle materials. The response of the crack front is found to be linear in amplitude and frequency of the perturbing wave and without persistence. The response to random perturbations, e.g., by localized material inhomogeneities at the free surface, is also discussed.