Anomalous absorption of TM electromagnetic waves by an ultrathin layer: optical analog of liquid friction

A strong maximum of absorption (as much as 100%) of bulk TM electromagnetic waves by an ultrathin film with imaginary dielectric permittivity is shown to exist at some optimal film thickness. This typical thickness is usually much smaller than the wavelength and the wave penetration depth in the material of the film. The absorptivity maximum increases and the typical thickness decreases with increasing dielectric permittivity of the layer. An optical analog of linear (liquid) friction is discussed. A frictional contact approximation for TM electromagnetic waves is analyzed, and relevant boundary conditions with an optical coefficient of friction are derived.     

脉冲激光沉积法制备钛酸锶钡薄膜及其光电性质

用脉冲激光沉积技术制备了钛酸锶钡(Ba0.5Sr0.6TiO3薄膜.用X射线光电子能谱和原子力显微镜分别分析了薄膜的化学组分和表面形貌.在交流信号为50 mV和100 kHz时测量了薄膜的介电系数和介电损耗随外加电场的变化关系,得出最高的介电可调率达到45%.利用单光束纵向Z扫描的方法研究了薄膜的非线性光学性质,得到非线性折射率为5.04×10-6cm2/kW,非线性吸收系数为3.59×10-6m/W,测量所用光源的波长为532 nm,脉宽为55 ps,表明Ba0.5Sr0.5TiO3薄膜有较快的非线性光学响应.     

Local ferroelectricity in SrTiO3 thin films

The temperature-dependent polarization of SrTiO3 thin films is investigated using confocal scanning optical microscopy. A homogeneous out-of-plane and an inhomogeneous in-plane ferroelectric phase are identified from images of the linear electro-optic response. Both hysteretic and nonhysteretic behavior are observed under a dc bias field. Unlike classical transitions in bulk ferroelectrics, local ferroelectricity is observed at temperatures far above the dielectric permittivity maximum. The results demonstrate the utility of local probe experiments in understanding inhomogeneous ferroelectrics.     

Controlling electric field distribution by graded spherical core-shell metamaterials

This paper investigates analytically the electric field distribution of graded spherical core-shell metamaterials, whose permittivity is given by the graded Drude model. Under the illumination of a uniform incident optical field, the obtained results show that the electrical field distribution in the shell region is controllable and the electric field peak’s position inside the spherical shell can be confined in a desired position by varying the frequency of the optical field as well as the parameters of the graded dielectric profiles. It has also offered an intuitive explanation for controlling the local electric field by graded metamaterials.     

On the electromagnetic cloaking of (Nano)particles

We theoretically study the electromagnetic cloaking of small (nano)particles in optical or IRbands by means of multilayered coating simultaneously providing the shielding of cloaked volume and minimizing scattering. Within a quasi-static approximation in sphe rical geometry, we show that two kinds of shielding shells exist with zero and with infinitely large (in the lossless case) values of the dielectric constant. We demonstrate that narrowing of the shielding shell at zero dielectric permittivity leads to the effect of electric field superlocalization when an infinite amount of energy is concentrated inside an infinitesimal volume.     

Enhancement of electron density in the interaction of high-power electromagnetic waves with inhomogeneous magnetized plasma

Propagation characteristics of a high-power electromagnetic wave through an inhomogeneous magnetized plasma is investigated. Considering the momentum transfer equations for electrons and ions and taking into account the ponderomotive force, the distribution of electron density and dielectric permittivity are obtained. Using non-linear dielectric permittivity and Maxwell's equations in the absence of external current and charge densities, non-linear wave equations are achieved. The results indicate that the external static magnetic field can modify the profiles of both the electric and magnetic fields. It is also shown that the external static magnetic field enhances the amplitude of the electron density and the non-linear dielectric permittivity.     

Electric field and force on a conducting sphere in contact with a dielectric solid

This paper presents the analysis of electric field and force on a conducting sphere lying on a dielectric solid under a uniform field. To achieve high accuracy, we have applied the analytical method of successively placing three infinite sequences of point and dipole charges (zero- or first-order multipoles). The electric field is highest at the contact point, called the triple junction, where the conductor, the dielectric solid, and the surrounding medium (gas or vacuum) meet together. Both the contact-point field and the force increase with the permittivity ratio of the solid to that of the surrounding medium. The resulting force always attracts the sphere to the solid, in contrast to the repulsive force in the case of a conducting sphere lying on a plane conductor under an external field. We have given very simple formulae for approximating the contact-point field and the force which agree with the precise values within a difference of 3% for permittivity ratios up to 32 and 64, respectively.     

Dielectric tensor elements for the description of waves in rotating inhomogeneous magnetized plasma spheroids

The dielectric permittivity tensor elements of a rotating cold collisionless plasma spheroid in an external magnetic field with toroidal and axial components are obtained. The effects of inhomogeneity in the densities of charged particles and the initial toroidal velocity on the dielectric permittivity tensor and field equations are investigated. The field components in terms of their toroidal components are calculated and it is shown that the toroidal components of the electric and magnetic fields are coupled by two differential equations. The influence of thermal and collisional effects on the dielectric tensor and field equations in the rotating plasma spheroid are also investigated. In the limiting spherical case, the dielectric tensor of a stationary magnetized collisionless cold plasma sphere is presented.     

Optics of magnetoelectric media in the presence of a magnetic field and a spatial dispersion of the dielectric permittivity

Influence of an external magnetic field and a spatial dispersion of the dielectric permittivity on the irreversibility of waves in magnetoelectric media is considered. Features of the azimuth inhomogeneity at the simultaneous anisotropy of the dielectric permittivity and magnetic permeability in these media are studied.     

Response of the capacitance and dielectric loss of the SrRuO<Subscript>3</Subscript>/SrTiO<Subscript>3</Subscript>/SrRuO<Subscript>3</Subscript> film heterostructures to variations in temperature and electric field

Three-layer epitaxial heterostructures with a 750-nm-thick intermediate strontium titanate layer between two strontium ruthenate conductive thin-film electrodes have been grown by laser deposition. Photolithography and ion etching have been used to form film parallel-plate capacitors based on the grown heterostructures. The capacitance (C) and dielectric loss tangent (tanδ) of the parallel-plate capacitors have been measured in the temperature range T = 4.2–300 K at an applied bias voltage of up to ±2.5 V and without it. At T > 100 K, the temperature dependence of the dielectric permittivity (ε) of the SrTiO₃ intermediate layer is well approximated by the Curie–Weiss law taking into account the capacitance induced by the penetration of an electric field into the oxide electrodes. At T ≈ 20 K, the dielectric permittivity ε of the SrTiO₃ intermediate layer decreases by approximately 20% in an electric field of 25 kV/cm. The dielectric loss tangent of the film capacitor heterostructures decreases monotonically with a decrease in the temperature in the range from 300 to 80 K and almost does not depend on the electric field strength. However, in the range from 80 to 4.2 K, the dielectric loss tangent increases nonmonotonically (abruptly) with a decrease in the temperature and decreases significantly in an applied electric field.     

Effect of a magnetic field on the permittivity of 80%La<Subscript>0.7</Subscript>Sr<Subscript>0.3</Subscript>MnO<Subscript>3</Subscript>/20%GeO<Subscript>2</Subscript> composite

The dielectric properties of a magnetoresistive conducting two-phase 80%La_0.7Sr_0.3MnO₃/20%GeO₂ (wt %) composite have been studied near the percolation threshold in magnetic fields from 0 to 15 kOe at frequencies of the measurement field from 5 kHz to 1 MHz. The samples have inductive impedances; i.e., their permittivities can be considered negative due to a high conductivity in this frequency range. The permittivity increases in magnitude in magnetic field, and the values of the magnetodielectric coefficient reach 23% at room temperature. The reasons for the effect of magnetic field on the dielectric permittivity of samples are discussed.     

Possible implementation of epsilon-near-zero metamaterials working at optical frequencies

Metamaterials (MTMs) exhibiting a near-zero real part of the permittivity function in a given frequency range have been demonstrated to be useful in several application fields, including field localization and focusing. So far, however, the realistic implementations of such materials working at optical frequencies and exhibiting a reasonable level of losses are rare. In this work, we propose a possible implementation of optical epsilon-near-zero (ENZ) MTMs based on the employment of an array of core-shell nano-spheres embedded in a dielectric medium. The core of the nano-spheres and the host medium are both made of silica, while the shell is formed by a plasmonic material (i.e. silver). Using classical homogenization formulas, we show that it is possible to design the array in such a way to exhibit near-zero values of the effective real permittivity with relatively low losses at optical frequencies. These results are supported and confirmed by proper full-wave simulations and design examples.     

Dielectric relaxation of <Emphasis Type="Italic">trans</Emphasis>-4-propyl-(4-cyanophenyl)-cyclohexane liquid crystals

The frequency dependences of the permittivity of a trans-4-propyl-(4-cyanophenyl)-cyclohexane (3PCH) liquid crystal in the nematic phase are measured in the frequency range 1–2000 MHz for different orientations of the director of liquid-crystal molecules with respect to the polarization of an ac electric field. The temperature dependences of the dielectric and optical characteristics are compared in the range of the transition from the nematic phase to the isotropic liquid phase. The dielectric spectra are approximated numerically, and the times of dipole relaxation upon rotation of the molecules about the short and long axes are determined. It is demonstrated that intramolecular motions make a significant contribution to the relaxation. The activation enthalpies are calculated.     

Dielectric and optical properties of a 5-propyl-2-(<Emphasis Type="Italic">p</Emphasis>-cyanophenyl)-pyridine liquid crystal

The temperature dependences of the dielectric and optical parameters for a 5-propyl-2-(p-cyanophenyl)-pyridine (3CP) liquid crystal are investigated in the vicinity of the nematic-isotropic phase transition. The dielectric spectra of the 3CP compound in the crystalline, nematic, and isotropic phases are measured in the frequency range 1–1000 MHz, and the Debye approximations of the measured spectra are obtained. Analysis of the dependence of the static permittivity on the director orientation with respect to the direction of the electric pump field demonstrates that the angle between the dipole moment and the long axis of the molecule is approximately equal to 15°.     

Analysis of the electric field behavior in the vicinity of a triple junction,using finite elements method computational simulations

The authors studied the electric field behavior in the vicinity of a triple junction, composed by metal, vacuum and dielectric parts, using computational simulations. A bi-dimensional model was constructed using ANSYS MAXWELL to analyze the magnitude of the electric field as a function of the contact angles of the materials. The results showed that a field enhancement or reduction could occur in vacuum for certain contact angles. The influence of the dielectric permittivity was also investigated, and the conclusions showed that the maximum electric field enhancement is proportional to the dielectric permittivity.     

High Q calcium titanate cylindrical dielectric resonators for magnetic resonance microimaging

At high magnetic fields radiation losses, wavelength effects, self-resonance, and the high resistance of typical components all contribute to increased losses in conventional RF coil designs. High permittivity ceramic dielectric resonators create strong uniform magnetic fields in a compact structure at high frequencies and can potentially solve some of the challenges of high field coil design. In this study an NMR probe was constructed for operation at 600 MHz (14.1 T) using an inductively fed CaTiO₃ (relative permittivity of 156) cylindrical hollow bore dielectric resonator. The design has an unmatched Q value greater than 2000, and the electric field is largely confined to the dielectric itself, with near zero values in the hollow bore which accommodates the sample. Experimental and simulation mapping of the RF field show good agreement, with the ceramic resonator giving a pulse width approximately 25% less than a loop gap resonator of similar inner dimensions. High resolution images, with voxel dimensions less than 50 μm³, have been acquired from fixed zebrafish samples, showing excellent delineation of several fine structures.     

Effect of low-angle boundaries on the dielectric properties of epitaxial Ba0.8Sr0.2TiO3 films

The effect of low-angle boundaries on the dielectric properties of epitaxial Ba_0.8Sr_0.2TiO₃ films is studied by comparing films differing in crystalline-block size. It is found that the permittivity diminishes considerably when the block sizes are reduced. The maximum of the temperature-dependent permittivity is shifted towards lower temperatures, and the sensitivity of the permittivity to an electric field is reduced. Moreover, it is found that the maximum in the permittivity temperature dependence is displaced towards lower temperatures when the applied measured voltage is increased and becomes higher than the coercive voltage. The width of a hysteresis loop decreases significantly when the frequency of the controlling field is reduced. The reasons for the observed behavior are analyzed.     

间歇性大气湍流中光传播问题的近Gauss极限分析

间歇性是湍流的重要特征，多年来一直是湍流研究的核心内容之一.考虑大气湍流中的光传播问题，一般回避其间歇性，假设大气介电起伏满足Gauss统计.考虑大气湍流（内）间歇性 对光波传播的影响.考虑到大气介电起伏方差较小的事实，将光场统计矩方程在Gauss场附近 展开到四阶累计量，分析其近似解.进一步，以层次结构模型为基础，着重研究了光场二阶 统计矩的间歇性效应.研究表明，大气湍流间歇性对光场的影响很小. 关键词： 光波传播 大气湍流 间歇性     

An assessment of coherent coupling through radiation fields in time varying slab waveguides

This paper presents an analytical methodology for analysing two-dimensional, dielectric slab waveguides where the guiding region is subject to abrupt and arbitrary temporal changes in permittivity. The methodology solves Maxwell’s equations in the frequency domain and recovers the solutions for the guided and radiation fields in the time domain using the Laplace transformation (LT). Explicit separation of the complete field solution into a set of guided modes and a radiation field continuum provides a clearer insight into the transient effects present in time-varying dielectric waveguides. In particular, the method is used to assess and quantify the impact of coherent radiation field coupling for arbitrary time variation of the waveguide permittivity.