Second- and third-harmonic generations for a nondilute suspension of coated particles with radial dielectric anisotropy

We derive expressions for the effective nonlinear susceptibility tensors for both the second harmonic generation (SHG) and induced third harmonic generation (THG) of nonlinear composite materials, in which nondilute coated particles with radial dielectric anisotropy are randomly embedded in the linear host. Two types of coated particles are considered. The first is that the core possesses a second order nonlinear susceptibility and the shell is linear and radially anisotropic, while the second is that the core is linear with radial anisotropy and the shell has a second order nonlinear susceptibility. We observe greatly enhanced SHG and THG susceptibilities at several surface plasmon resonant frequencies. For the second model, due to the coating material being metallic, there exists two fundamental resonant frequencies ω_c1 and ω_c2, whose difference ω_c2-ω_c1 is strongly dependent on the interfacial parameter and the radial dielectric anisotropy. Furthermore, in both systems, the adjustment of the dielectric anisotropy results in larger enhancement of both SHG and induced THG susceptibilities at surface plasmon resonant frequencies than the corresponding isotropic systems. Therefore, both the core-shell structure and the dielectric anisotropy play important roles in determining the nonlinear enhancement and the surface resonant frequencies.     

Nonlinear dielectric response and thermodynamic heterogeneity in liquids

If large amplitude time-dependent fields (e.g., dielectric, magnetic, mechanical) are applied to a sample that displays relaxational modes, some energy of the external field is absorbed by the slow degrees of freedom. The weak coupling of these modes to the phonon bath leads to long persistence times of the resulting higher fictive temperature. Assuming heterogeneities regarding dielectric and thermal relaxation times, extremely strong nonlinear dielectric effects are predicted and experimentally verified. For glycerol at T = 213 K, the dielectric loss measured at 280 kV/cm increases by more than 6% over its low-field value. This nonlinearity shows a characteristic frequency dependence and implies that dielectric and thermal time constants are locally correlated in viscous liquids.     

Correlation of magnetic anisotropy with dielectric anisotropy in fluorinated phenyl bicyclohexane liquid crystal

Temperature dependence of magnetic anisotropy of homologous nematic fluorinated phenyl bicyclohexane liquid crystals is measured by a magneto-electric method.The result shows that the diamagnetic property is slightly influenced by the positions and the numbers of fluorine atoms substituted at the phenyl ring.By investigating the correlation of the dielectric anisotropy with the magnetic anisotropy,a novel explanation is proposed for the behaviour of the molecular dipole-dipole dimerization in the polar liquid crystal compounds.     

The effective dielectric response of nonlinear coated granular composites

The dielectric response of a nonlinear composite system, which is composed of coated granular cylinders with nonlinear cores and linear shells or with linear cores and nonlinear shells randomly embedded in a linear host matrix, is investigated. For the concentric cylinders with weak nonlinear core and linear shell embedded in a linear host, the system can be replaced by solid cylinders with weak nonlinearity embedded in the same host under certain conditions. One of the linear partially resonant conditions is ϵ_s + ϵ_h = 0, which associated with two linear components can be extended to this nonlinear composite, the equivalent nonlinear solid cylinders have the same dielectric function as the original cores and radii larger than those of the original coating shells. Another is the linear partially resonant condition ϵ_c + ϵ_s = 0, which associated with one linear component and another nonlinear component cannot be extended to this nonlinear composite, but under this condition the nonlinear dielectric response of whole system will still be greatly enhanced. For another case of concentric cylinders with linear cores and nonlinear shells, we cannot find the equivalent nonlinear solid cylinders embedded in the same host, and the nonlinear partially resonant condition cannot be realized.     

Metal particle size effects in the dielectric response of metal-insulator composites

Metal-insulator composites consisting of nanometer-sized Au particles in a Si0₂ matrix were prepared by a novel technique which, for the first time, allows for control of metal particle size independent of metal volume fraction. Electron energy loss and optical studies show that the effective dielectric function (EDF) of these composites depends not only on metal volume fraction, but also on metal particle size. These results can not be explained by current effective dielectric function theories with size-independent metal dielectric function. However, quantum size effects partly account for the size-dependent properties of these composites.     

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.     

Metal particle size effects in the dielectric response of metal-insulator composites

Metal-insulator composites consisting of nanometer-sized Au particles in a SiO₂ matrix were prepared by a novel technique which, for the first time, allows for control of metal particle size independent of metal volume fraction. Electron energy loss and optical studies show that the effective dielectric function (EDF) of these composites depends not only on metal volume fraction, but also on metal particle size. These results can not be explained by current effective dielectric function theories with size-independent metal dielectric function. However, quantum size effects partly account for the size-dependent properties of these composites.     

Modulation of photonic band structures with dielectric anisotropy

By the multiple scattering method and the extended Mie theory, we have calculated the photonic band structure of the photonic crystals consisting of the dielectric spheres with uniaxial/biaxial anisotropy. The results demonstrate that for fcc lattice structure there exist two partial photonic band gaps which does not appear in the isotropic case. Among them, the lower one, lying between the second and the third bands, exists in one third of the first Brillouin zone, while the upper one, opening between the fourth and fifth bands, can appear simultaneously in the rest two thirds of the first Brillouin zone. The effects of anisotropy on the band structures are studied as well, which suggests the biaxial anisotropy are much more flexible than the uniaxial anisotropy in modulating the band structures.     

Electromagnetically induced magnetochiral anisotropy in a resonant medium

Chirality has been extensively studied for well over a century, and its potential applications range from optics to chemistry, medicine, and biology. Ingenious experiments have been designed to measure this naturally small effect. Here we discuss the possibility of producing a medium having a large chiral effect by using the ideas of coherent control. The coherent fields resonant with appropriate transitions in atomic or molecular systems can be used to manipulate the optical properties of a medium. We demonstrate experimentally very large magnetochiral anisotropy by using electromagnetic fields in atomic Rb vapors.     

金属/电介质颗粒复合介质的非线性交流响应

推广T矩阵法来研究二组分颗粒复合介质的非线性交流响应，解析推导出基频、三次及五次谐波频率下的有效线性介电常数及三阶和五阶非线性极化率的解析表达式.当组分颗粒的介电常数为实数时，表达式同以前微扰理论完全一致.进一步数值计算了金属-电介质复合介质的有效非线性交流响应，数值结果表明，体系的三阶、五阶非线性极化率在表面等离子共振频率附近有明显增强，而且，随着体积分数提高，共振峰增强且伴随着共振频率红移现象.还进一步讨论了维度效应对体系非线性交流响应的影响. 关键词： T矩阵方法 复合介质 非线性交流响应     

Small- and strong-signal dielectric response in a single-crystal film of partially deuterated betaine phosphite

Poly- and single-crystal films of betaine phosphite deuterated to ∼20% have been grown by evaporation on NdGaO₃ (001) substrates with a preliminarily deposited planar interdigital structure of electrodes. The small-signal dielectric response in the 0.1–100.0-kHz frequency range has revealed a strong anomaly in capacitance upon the transition of the films to the ferroelectric state. Application of a bias field brings about suppression and a slight shift of the dielectric anomaly toward higher temperatures. The strong-signal dielectric response has been studied by the Sawyer-Tower method over the frequency range 0.06–3.00 kHz both in the para- and ferroelectric phases. In contrast to the case of a plane-parallel capacitor, in the planar structure studied, the dielectric hysteresis loops exhibit a very small coercivity at low frequencies, which grows with increasing frequency. This difference should be assigned to different domain structures formed in a planeparallel capacitor and in a planar structure in a saturating field. The growth of hysteresis with increasing frequency in a planar structure is considered to be associated with the domain wall motion.     

介质部分填充平行平板传输线微放电过程分析

本文主要研究了介质填充微波部件微放电随时间演变的过程,重点分析了介质微波部件微放电自熄灭机理.以介质部分填充平行平板传输线为研究对象,忽略空间电荷效应,采用自主研发粒子模拟软件模拟微放电过程,并将模拟结果与金属微波部件结果进行对比.结果表明,在一定功率下,金属微放电过程中电子数目呈指数形式增长,而介质微放电过程经历初始电子倍增后发生自熄灭现象,同时发现在电子数目即将下降为0时,介质表面的平均二次电子发射系数大于1或约等于1.另外,在上述模拟结果的基础上对微放电过程中介质表面积累电荷问题进一步分析,模拟结果表明,如果持续向微波部件内注入电子,介质表面的平均二次电子发射系数最终都约等于1.所得结论对研究复杂介质填充微波部件微放电的机理具有一定的理论指导价值.     

Isothermal relaxation current in a dielectric with partially blocking contacts

The continuity and Poisson's equations are solved numerically for a dielectric with partially blocking electrodes in the nonsteady case. The distribution of the mobile-charge-carrier concentration and the electric field strength inside the dielectric is obtained at various times after the potential source is switched on. The time dependence of the isothermal current and the emf of high-voltage polarization of the dielectric with a single type of mobile charge carriers at different values of the contact current is calculated.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 9, pp. 12–16, September, 1985.     

Nonlinear properties of composites based on dielectric layers containing copper and silver nanoparticles

Nonlinear optical characteristics of copper and silver nanoparticles in glass host matrices are studied by the Z-scan method at the wavelength of a Nd:YAG laser (λ=1064 nm) in a field of picosecond pulses. It is found that the third-order nonlinear susceptibility is more pronounced in glasses with copper nanoparticles than in glasses with silver nanoparticles. On the basis of experimental data obtained for samples with copper nanoparticles synthesized by ion implantation, it is shown for the first time that the nonlinear absorption of laser radiation with a wavelength lying out of the plasmon resonance region can be caused by a two-photon effect in metal particles. The character of the optical limiting process in the samples with copper nanoparticles when two-photon absorption is involved is discussed.     

Electric and magnetic optical response of dielectric nanospheres: Optical forces and scattering anisotropy

Nanospheres made of non-magnetic materials are shown to present non-conventional scattering properties similar to those previously reported for somewhat hypothetical magnetodielectric particles. We find a wide window in the near-infrared, where light scattering by lossless submicrometer semiconductor nanospheres is fully described by their induced electric and magnetic dipoles. The interference between electric and magnetic dipolar fields is shown to lead to anisotropic angular distributions of scattered intensity, including zero backward and almost zero forward scattered intensities at specific wavelengths. Interesting new consequences for the corresponding optical forces are derived from the interplay, both in and out of resonance, between the electric- and magnetic-induced dipoles.     

Nematic liquid crystals with positive dielectric and negative diamagnetic anisotropy

p-Alkyl-p′-cyanocyclohexylcyclohexanes CCH represent a new class of thermotropic nematic liquid crystals which no longer exhibit UV absorption abobe 200 nm, are distinguised by an optical anisotropy of less than 0.1, and in contrast to all previously known “dielectric positive”, thermotropic nematic liquid crystals possess a negative diamagnetic anisotropy.     

Dielectric resonance,local field distribution,and optical response in 3D resonant composites

We extend the Greens function formalism in a binary 2D composite to 3D. Using the formalism, we investigate the dielectric resonances, local-field distribution, and effective linear optical responses for one-bond, two-bond and three-bond clusters, as well as for various disordered composites. Due to the different values of Greens function in 2D and 3D, for the same cluster, the values of the dielectric resonances in 3D are smaller than those in 2D, but the fields are more localized than those in 2D. The sum rule of dielectric resonance in three-component composites is extended to d dimensions. For the same resonance, the intensity of the local-field in 3D is also weaker than that in the 2D case, but the fields are more localized than those in 2D. For the disordered composites in 2D and 3D, inverse participation ratios (IPR) with q = 2 are used to represent the localization of the field. When we increase the concentration of impurity bonds, a blue shift of IPR peaks occurs in 3D, while in 2D, these peaks are very stable. Finally, both for 2D and 3D disordered composites, the absorption range broadens with increasing impurity concentration, and a red shift of the absorption peak is observed in 3D.Received: 19 August 2004, Published online: 14 December 2004PACS: 77.84.Lf Composite materials - 42.65.-k Nonlinear optics