Plasmons in double quantum wells in a parallel magnetic field

Collective intraband charge-density excitations in the quasi-two-dimensional electron system of double GaAs/AlGaAs quantum wells in an external parallel magnetic field B_∥ are studied by inelastic light scattering. It has been found that the energy of the excitations under study (acoustic and optical plasmons) exhibits anisotropy depending on the mutual orientation of B_∥ and the excitation quasi-momentum k. It is shown theoretically that, in a strong parallel magnetic field, the effects associated with the finite width of the quantum wells dominate over the effects associated with interlayer tunneling and determine the anisotropy of plasmons. The experimental data are compared with a theoretical calculation.     

Enhanced scattering efficiencies in spherical particles with weakly dissipating anisotropic materials

This paper discusses light scattering by a small spherical particle with low dissipation rate and radial anisotropy in optical and magnetic properties, according to the extension of the Mie theory to the diffraction by an anisotropic sphere. It is shown that near plasmon (polariton) resonance frequencies anisotropy can lead to an additional increase in field enhancement.     

Plasmon dispersion in a layered structure

Dispersion of plasmons in a superlattice of finite thickness plasma layers is calculated. Good agreement with dispersion from light scattering experiments is obtained.     

Propagating anti-symmetrically coupled plasmons generation by electron beams

Propagating anti-symmetrically coupled plasmons that usually cannot be excited with incident light and radiate to far field can be efficiently generated by electron beams. An electron beam is proposed as a practical propagating anti-symmetrically coupled plasmon source due to that it couples differently to the surface plasmons than free radiation. Specifically, whispering-gallery anti-symmetrically coupled plasmons with the character of symmetrical coupled dipoles are excited by an electron beam in a nested ringlike waveguide, which is consistent with the dispersion of electron excited plasmons in an infinite-long nanowire pair.     

Near-field magneto-optics and microscopy in resonant scattering of light from a linear nanoprobe

A theory is presented for the polar near-field magneto-optical Kerr effect in scattering of light from a linear nanoprobe. In the framework of Green’s function technique, a solution is obtained for the problem of near-field magneto-optics and apertureless scanning microscopy of lateral magnetic inhomogeneities (domains) with nanometer scale. The probe in the form of a nanowire and the sample with a near-surface magnetic nanolayer are considered to support surface plasmons. Electromagnetic coupling between a nanow-ire and a sample surface (polarizability of the complex “probe plus image charges”) is taken into account self-consistently. Magneto-induced polarization of an ultrathin near-surface layer is treated within linear approximation in magnetization which is perpendicular to the layer. The polarization, spectral and angular characteristics of light scattering modulated by magnetization and resonantly enhanced by surface plasmons are examined. Dependence of the near-field magneto-optical response on the probe-domain distance along the sample surface is obtained. The resolution power of scanning near-field microscopy is estimated and the factors to influence it are pointed out.     

Mie理论在生物组织散射特性分析中的应用

根据等效颗粒散射模型，运用经典的Mie理论，对生物组织的散射相函数、各向异性因子及散射系数进行了数值计算.计算结果表明：可见光照射生物组织时，各向异性因子、散射系数随等效颗粒直径增大而增大；等效颗粒直径较小时，各向异性因子、散射系数随入射光波长增大而单调减小；随着等效颗粒直径增大，各向异性因子、散射系数随入射光波长变化不再具有单调性.上述计算结果可合理解释公布的实验结果. 关键词： 生物组织 散射 Mie理论 等效颗粒     

Magnetooptical Kerr effect in the near field of a nanowire supporting surface plasmons

In terms of Green’s functions, a theory is developed describing the resonant magnetooptical Kerr effect in light scattering by a linear probe that is parallel to the surface of a magnet and placed at a subwavelength distance from it. The probe is supposed to be a metal nanowire supporting long-lived surface plasmons and forming the near field of the “probe + image” complex. The resonant interaction between the probe and the sample is taken into account within a self-consistent approximation of multiple-scattering theory, and the magnetooptical interaction is included in the linear approximation in magnetization. The problem of scanning near-field magnetooptical microscopy with a linear probe is solved analytically in the case where the magnetization is parallel to both the magnet surface and the plane of incidence of light (longitudinal magnetooptical Kerr effect). The polarization, spectral, and angular characteristics of scattered light modulated by magnetization are discussed. It is shown that the magnetooptical modulation of the scattered light intensity is significantly enhanced when surface plasmons are resonantly excited in the nanowire.     

Plasma oscillations in nanotubes and the Aharonov-Bohm effect for plasmons

We theoretically analyze the collective oscillations of 2D electrons in nanotubes. In the presence of a magnetic field parallel to the tube axis, the plasmon frequencies undergo Aharonov-Bohm oscillations. The effect can manifest itself in infrared absorption and in Raman scattering. We calculate the cross sections for inelastic light scattering by plasmons.     

Frequency dependence of the inversion layer conductivity in the metallic and localized regimes

Surface plasmons have been excited with the prism method at sinusoidally modulated silver surfaces. The scattered light intensity of the first diffraction order has been investigated for gratings with different modulation heights H. The scattered light intensity increases up to modulation heights H of ca. 70 Å with the square of H. We discuss the limits for applying first order scattering theories to surface plasmon scattering experiments.     

The observation of the localized surface plasmons and its coupling

The surface plasmons properties on gold film composed of inverted square pyramidal pits were investigated. The near‐field scanning optical microscopy image showed that the surface plasmons were mainly located in the cavity of the pits; this is consistent with the mapping image obtained using the Raman scattering intensity of Rhodamine 6G. The calculation results obtained by using the finite element method showed that the electric field mainly located in the pyramidal pits and the field distribution was not affected by the adjacent pits around it. Compared with the single pyramidal pit, the localized electric field intensity increased in the condition of the structure array because of the surface plasmons coupling effect. The surface‐enhanced Raman scattering spectra intensity decreased as the incident angle of the excited laser increased except that there are two peaks at around 5° and 17.5°, which can be attributed to the Bragg scattering of the surface plasmons. The reflectance spectra collected by a microscope at different magnifications were different. The intensity variation between surface‐enhanced Raman scattering spectra obtained using ×20 and ×50 objective illustrated that the adsorption peak in the reflectance spectra corresponded to the surface plasmons coupling effect. Copyright © 2011 John Wiley & Sons, Ltd.     

Depolarized light scattering,flow birefringence and local order in molecular liquids

We propose a generalization of De Gennes' theory of flow birefringence [3] to the case of two distinct local anisotropy variables and also some extensions to the existing three variable theories of light scattering spectra. We show that the application of the theories with one or with two local anisotropy variables to analyse flow birefringence and light scattering spectra give numerically different results. We also show that it is possible to determinewhether the second local anisotropy variable is a primary or a secondary variable.

The VH and HH light scattering spectra of a number of symmetric top molecules are analysed. They show an unambiguous ‘shear mode coupling’ down to very small values of (q ²η/ρΦ). These results are discussed and compared to flow birefringence experiments in the light of our theoretical considerations. The three variable correction is shown to be small and within experimental error for all liquids studied except one (pyridine). The flow birefringence coefficient for CCl₄ is measured and found to be negative as predicted by our theory. Limitations to the formalism of generalized hydrodynamics are also discussed briefly.     

Anisotropy‐assisted non‐scattering coherent absorption of surface plasmon‐polaritons

The ability to control propagation of electromagnetic guided modes lies at the heart of integrated nanophotonics. Surface plasmon‐polaritons are a class of guided modes which can be employed in integrated optical systems. Here, we present a theoretical design of a coherent surface plasmon absorber which can perfectly harvest energy of coherently incident surface plasmons without parasitic scattering into free space modes. Excitation of free space modes which usually accompanies scattering of a surface plasmon by an interface boundary is avoided due to specially tailored anisotropy of the absorber. The concept of coherent SPP absorber is analyzed numerically for spatially non‐uniform and finite‐size structures. We believe that our results will be important for the development of integrated nanoplasmonic systems.     

Turbid media optical properties derived from the characteristics of propagating laser radiation beams

The possibility is studied to develop a straightforward analytical approach to the determination of the optical properties of liquid turbid media having forward-peaked scattering indicatrices. The approach is based on investigating the in-depth behavior of the radius and the axial intensity of a laser radiation beam propagating through the turbid medium. Based on the small-angle approximation, the detected forward-propagating light power spatial distribution, at relatively small or large optical depths along the beam axis, is obtained asymptotically in analytical form allowing one to derive relatively simple expressions of the extinction, reduced-scattering and absorption coefficients and the anisotropy factor of the medium through the characteristics of the propagating light beam. Preliminary experiments have also been performed, using Intralipid dilutions of different relatively low concentrations and measuring the cross-sectional radial distribution of the detected light power at different depths along the beam axis. The corresponding on-axis detected light power profiles have been measured independently as well. The experimental results are consistent with the analytical expressions obtained that allow one to estimate the optical coefficients and the anisotropy factor of the investigated media on the basis of the measured beam characteristics. The values obtained are near those predicted by other researchers.     

Maximizing scattering by coated spheres with radial anisotropy

The plasmonic resonant condition, associated with scattering maximization, is analytically established for core-shell spheres with radial anisotropy in the small-radii and low-dissipation limit. A generalized expression of the effective permittivity of the scatterers is also formulated. The derived closed-form results are validated with full-wave numerical analysis. The effects of dielectric anisotropy, mode of resonance, size, and loss are further discussed.     

Influence of the optical axis distribution in the anisotropic layer surrounding a spherical particle on the scattering of light

The problem of light scattering from an anisotropic layer with a spherically symmetric distribution of the optical axis is solved exactly. The dependence of the scattering efficiency on the particle size, the anisotropy parameter, and the layer thickness is studied numerically for various anisotropy types. It is shown that the scattering cross section is strongly affected by the type of anisotropy and that the presence of disclinations increases the scattering efficiency. As an additional effect specific to anisotropic scatterers, it is found that, in the case of configurations with broken central symmetry, the scattering amplitudes contain a phase shift that scales logarithmically with the thickness of the anisotropic layer.     

Optical properties of -doped semiconductors: Plasmon–phonon coupling and Raman spectra

Collective excitations and their coupling to optical phonons have been studied for a two-dimensional electron gas in -doped polar semiconductors within the random-phase approximation. The inelastic light scattering spectrum due to the coupled plasmon–phonon modes are calculated for the multisubband two-dimensional electron systems. Our calculation shows that, due to the high electron density in these systems, both intrasubband and intersubband plasmons are strongly coupled to the optical-phonons. On the other hand, due to the high impurity concentration, level broadening modifies the inelastic light scattering spectrum significantly.     

Improving metal-enhanced photoluminescence by micro-pattern of metal nanoparticles: a case study of Ag–ZnCdO system

Micro-pattern of Ag nanoparticles and Ag film is inserted between ZnCdO film and the substrate to enhance the photoluminescence (PL) of ZnCdO films, achieving enhancement ratio of 21.2 and 7.1, respectively. Time-resolved photoluminescence shows that the PL lifetime of Ag/ZnCdO films is longer than that of bare ZnCdO, which is attributed to surface modification and surface plasmons coupling. The improved enhancement in the sample with Ag pattern is attributed to the fact that periodic Ag structure offers additional scattering mediums and thus increases the light extraction efficiency.