Transmissivity and reflectivity of spatially dispersive thin films

We calculate the transmission and reflection coefficients for electromagnetic radiation incident normally on the surfaces of thin, spatially dispersive, absorbing, dielectric films. Results are obtained for four models of spatially dispersive dielectrics and for the case in which spatial dispersion is neglected. For each model the effects of spatial dispersion are to introduce additional fine structure into the transmission and reflection coefficients, regarded either as functions of frequency or of the thickness of the film. In addition, the results reveal an interleaving between the maxima and minima of the spectra for different models, which may provide a basis for an experimental discrimination between different phenomenological models for the nonlocal dielectric constant of a spatially dispersive dielectric medium.     

Theory of the Relaxation spectra of polymer networks with included hard rodlike particles manifested in NMR

A theory of nuclear magnetic resonance relaxation of¹³C nuclei and nuclear Overhauser effect (NOE) of polymer networks with included rodlike particles is developed for the case when the length of each rod is comparable or greater than the average distance between neighboring crosslinks. The long-scale dynamics of the network is described by means of a regular cubic “coarse-grained” model. The effects of entanglements of long rods in the network are described by a quasi-elastic potential acting between rods and network fragments. The frequency dependences of 1/T _1C and NOE are calculated for the case when the internuclear vector is directed along each rodlike particle. The frequency dependences of 1/T _1C and NOE for rods included into a polymer network are shifted to high frequencies as compared with these dependences for free rods due to quasi-elastic interactions between rods and network fragments. At strongly different viscoelastic parameters of rods and network fragments, the frequency dependences of 1/T_1C and NOE may have two maxima. The high-frequency maximum corresponds to localized motions of rods at immobile network domains. The low-frequency maximum is caused by involving rods in long-scale network motions. The intensity of the low-frequency maximum increases when the degree of interactions between rods and the network increases.     

Focusing of a diverging ultrasonic beam by a 2D periodic structure into two foci

A preliminarily focused (spherically diverging) ultrasonic beam was directed to a structure of metal rods having two-dimensional periodicity and bounded by reflecting surfaces in a dimension in which this periodicity was absent. For the ultrasound frequency taken at the upper boundary of the “transmission” band of the structure, the splitting of the acoustic image of the focus object into two maxima arranged in the sample homogeneity direction is obtained.     

On the transmission coefficient for the double delta-function potential embedded in a crystalline lattice

The solution of the Schrödinger–Wannier equation is examined for the potential that is defined as a sum of the two delta functions of unequal strengths. The analytical expression for the transmission coefficient is derived from the solution. The transmission coefficient is shown to exhibit maxima and minima. Moreover, it is proved that the transmission coefficient in its maxima is larger and in its minima is smaller than the transmission coefficient for the corresponding single delta-function potential. Some differences between the transmission coefficient of particles with the quadratic energy spectrum and the transmission coefficient of particles with the Kane energy spectrum are presented.     

Flow birefringence,stress optical rule and rheology of four micellar solutions with the same low shear viscosity

The flow birefringence and the rheological properties of four viscoelastic solutions having nearly the same zero shear viscosity and subjected to shear flows are investigated in the linear and non-linear domains. The surfactant used for the samples is the cetyltrimethylammonium chloride in water at the concentration of 100 mmol/l with an organic salt, the sodium salicylate. The low shear viscosity curve versus the salt concentration is non-monotonic and has two maxima separated by a minimum forming four domains in which the salt concentration is chosen. For the two solutions belonging to the inner branch, i.e. between the two maxima, a simple Maxwellian behaviour is observed and shear banding occurs as confirmed by the flow birefringence pictures. Contrary to the results of P. Fisher (1996) where the unstable flow regime is restricted to the first decreasing part of the low shear viscosity curve of a cetylpyridinium chloride solution, we show that shear banding exits in a wider domain of the salt concentration. Received 18 November 2002 / Published online: 1 April 2003 RID="a" ID="a"e-mail: Decruppe@lpli.sciences.univ-metz.fr     

Imaging contrast under aperture tip–nanoantenna array interaction

Periodic arrays of paired and single gold nanorods were imaged in the near field using reflection and transmission modes of a near-field scanning optical microscope at various wavelengths and polarizations of light in the visible range. The paired nanorods act like nanoantenna, and an array of them was initially designed as a negative-index material for the near infrared. Reverse contrast in reflection and transmission images is observed under illumination from the small aperture of a metal-coated fiber probe. By changing the relative orientation of the rods to the polarization, the reverse contrast switches to the normal contrast of near-field imaging. Coupling between the aperture and the nanorod array makes the contrast higher. Transmission through the aperture is enhanced if the aperture probe is positioned between the nanorods. The average near-field transmission exhibits an opposite sign of anisotropy relative to the far-field case. Aperture probes with larger diameters always show normal imaging contrast. The results demonstrate that the broad angular spectra of small-aperture sources play a crucial role in near-field interactions with nanorod arrays. The results also show that angular redistributions of these spectra after transmission or reflection from the nanorod array are likely due to excitation of localized and propagating plasmons.     

Optical properties of one-dimensional photonic crystals fabricated by photo-electrochemical etching of silicon

The optical properties of one-dimensional photonic crystals (1D PCs), fabricated by electrochemical etching of periodic wall arrays on n-type (100) Si substrates, are investigated in this study. Several 1D PCs were fabricated with lattice periods varying from 4 to 7 μm and with trench depths in the range 160–210 μm. In-plane reflection spectra of the photonic structures at different depths were registered over a wide spectral range of 1.5–15 μm using Fourier Transform Infra-Red (FTIR) micro-spectroscopy. Some of the features observed in the reflection spectra of the structures investigated are believed to be as a result of interface roughness. A corrugated side-wall surface, an artifact of the fabrication technique, results in the degradation of optical reflection characteristics, principally mainly in the near IR spectral range, and the emergence of optical anisotropy. As a result of the periodicity, modulation of the reflection spectra, that is, the difference between the maxima and minima of the interference fringes, reached a value of 95% in the mid-infrared. The optical properties of the structures investigated indicate that they show promise for microphotonics applications.     

Electromagnetic properties of ice near the water-ice phase transition temperature

Freshwater ice in a cavity was studied under heating to 0°C followed by cooling at a frequency of 6.3 GHz. Splitting of a resonant transmission line at 60–70 MHz was detected. This effect may be associated with the existence of two vibrational modes in ice, with the coupling between them increasing near 0°C. In such a medium, two waves with identical polarizations and similar wavenumbers can exist. This assumption was confirmed experimentally by measuring the 13-GHz radiation transmission through a natural freshwater ice cover. These measurements detected signal oscillations caused by the interference of two waves, with alternation of maxima and minima with a period of 4.6 m, which corresponds to a beat frequency of ～37 MHz.     

The twice ferromagnetic resonance in hexagonal ferrite single rod and paired rods

The microwave electromagnetic properties of Co₂-Y hexagonal ferrite single rod and paired rods are demonstrated using a standard waveguide method. With the sweeping of the bias magnetic field, the ferromagnetic resonance occurs twice in the transmission spectra of single ferrite rod, which are induced by the self-bias magnetization and the external field magnetization, respectively. The zero/low-field resonance is determined by the shape anisotropy mainly, and disappears as the rod?s aspect ratio is relatively low. For the paired rods, when the interval between two parallel rods is small, the zero/low-field resonance vanishes due to the dipolar interaction between two rods.     

Determination of the magnetic fluid parameters from the microwave radiation reflection coefficients

The interaction of microwave radiation with a magnetic fluid that completely fills a waveguide and is bounded by a dielectric insertion is studied at frequencies between 20 and 40 GHz. The frequency dependence of the alternating interference maxima and minima that are associated with the reflection from the front and back walls of the dielectric insertion is found. The reason for such a dependence is the variation of the complex magnetic susceptibility of the magnetic fluid. The inverse problem, i.e., the determination of the ferromagnetic particle diameter and the volume content of the solid phase in the magnetic fluid, is solved based on the frequency dependence of the reflection coefficient.     

Measurement of viscoelastic properties from the vibration of a compliantly supported beam

A laboratory method is presented by which the viscoelastic properties of compliant materials are measured over a wide frequency range. The test setup utilizes a flexible beam clamped at one end and excited by a shaker at the free end. A small specimen of a compliant material is positioned to support the beam near its midpoint. The deformation from gravity is minimized since the specimen is not loaded by an attached mass. Forced vibration responses measured at two locations along the beam are used to derive a transfer function from which the dynamic properties of compliant materials are directly determined by use of a theoretical procedure investigating the effects of specimen stiffness on the propagation of flexural waves. Sensitivity of the measured properties to experimental uncertainties is investigated. Young's moduli and associated loss factors are determined for compliant materials ranging from low-density closed-cell foams to high-density damping materials. The method is validated by comparing the measured viscoelastic properties to those from an alternative dynamic test method.     

Solvent Polarity and Excitation Wavelength Dependence of the Dual Fluorescence in N,N-Diethyl-4-Nitrosoaniline

Dual fluorescence in N,N-Diethyl-4-nitrosoaniline (DENA) has been studied employing absorption, excitation and emission spectroscopic techniques and computational methods. The absorption and fluorescence spectra of DENA were measured in solvents of various polarities at room temperature. The emission spectra of DENA were found to exhibit a single emission band in non polar solvent (cyclohexane) and in a highly polar solvent (acetonitrile). In the contrary, two emission bands were observed in medium polar solvents (tetrahydrofuran, 1,2-dichloroethane and dichloromethane) whereby the short (local excited; LE) and long (charge transfer; CT) emission maxima correspond to the emission maxima of the compound observed in cyclohexane and acetonitrile solutions, respectively. Moreover, the two emission bands have shown strong excitation wavelength dependence, and area normalization resulted in an iso-emissive point. The two emission maxima were in addition found to correspond to two excitation maxima in 3D fluorescence spectra. Further, two minima were obtained in potential energy surface calculation of DENA. From the experimental and computational results it was concluded that the dual fluorescence may be attributed to the presence of two different ground state structural conformers of DENA in equilibrium that are stabilized through solute-solvent interaction.     

珍珠层独特的反射光谱特征及其成因

采用反射光谱、扫描电镜及理论模拟计算对大珠母贝珍珠层的结构色及微结构进行了系统的研究。结果表明:(1)大珠母贝珍珠层文石板片厚度从生长端到壳中区显著减小, 从540减至340 nm, 导致同级别反射峰波长呈现明显的蓝移现象;(2)大珠母贝珍珠层的结构色是由文石板片和蛋白质层构成的多层薄膜结构和黄色素的共同作用决定的。     

微纳跨尺度ZnO结构的紫外发射机理研究

利用气相输运的方法在Si(100)衬底上生长了ZnO的微纳跨尺度结构.扫描电镜照片可以明显地看到样品表面为椎顶六角微米柱-纳米棒的复合结构.样品在室温下的光致发光谱出现了很强的紫外发射峰,没有观察到与杂质或缺陷相关的深能级发射,表明样品有很好的光学质量.通过详细的研究样品的紫外发射谱与温度(83—307K)的依赖关系,发现在室温下样品的近带边发射包含两个部分,分别与自由激子发射和自由载流子到施主(受主)的跃迁(FB跃迁)相关,这个施主(受主)束缚态的离化能为124.6meV. 关键词： ZnO微纳跨尺度结构 光致发光谱 自由载流子到施主(受主)的跃迁 自由激子发射     

The exciton luminescence in Zn(Cd)Se/ZnMgSSe quantum wells

We study exciton states in Zn(Cd)Se/ZnMgSSe quantum wells (QWs) with various degrees of diffusion blurring in the interfaces by the methods of optical spectroscopy. We show that at low temperatures the QW emission spectra are determined by free and neutral donor-bound excitons. Blurring of the heterointerfaces leads to the increase in the energy shift between the emission line maxima of free and bound excitons. We explain the nonlinear dependence of the steady-state photoluminescence intensity on the excitation-power density in terms of the neutralization of charged donors at the photoexcitation of heterostructures. We observed a complex long-time dynamics of the reflection coefficient, evoked by the charge-redistribution processes in the heterostructure, near the QW exciton resonances under the irradiation.     

An ultrasonic method for determination of elastic moduli, density, attenuation and thickness of a polymer coating on a stiff plate

An ultrasonic method proposed by us for determination of the complete set of acoustical and geometrical properties of a thin isotropic layer between semispaces (J. Acoust. Soc. Am. 102 (1997) 3467) is extended to determination of the properties of a coating on a thin plate. The method allows simultaneous determination of the coating thickness, density, elastic moduli and attenuation (longitudinal and shear) from normal and oblique incidence reflection (transmission) frequency spectra. Reflection (transmission) from the coated plate is represented as a function of six nondimensional parameters of the coating which are determined from two experimentally measured spectra: one at normal and one at oblique incidence. The introduction of the set of nondimensional parameters allows one to transform the reconstruction process from one search in a six-dimensional space to two searches in three-dimensional spaces (one search for normal incidence and one for oblique). Thickness, density, and longitudinal and shear elastic moduli of the coating are calculated from the nondimensional parameters determined. The sensitivity of the method to individual properties and its stability against experimental noise are studied and the inversion algorithm is accordingly optimized. An example of the method and experimental measurement for comparison is given for a polypropylene coating on a steel foil.     

New version of seven wavelengths demultiplexer based on the microcavities in a two-dimensional photonic crystal

A new two dimensional photonic crystal demultiplexer of wavelength (WDM) is designed by exploiting two Fabry–Pérot reflectors at the end of the bus waveguides. The results show that the light with different wavelengths can be successfully filtered to different ports by setting different radius of the center defect rods in the drop waveguides and high drop efficiency can be achieved by means of reflection feedbacks. The proposed filter has a cross section equal to 9.7 μm × 5.8 μm. In the designed filter, an improvement of the number of channels has been achieved. The normalized transmission spectra of this component have been studied using finite difference time domain (FDTD) method. The important parameters consider for this studies are radius of rods used in Fabry–Pérot reflectors, and radius of center defect rods in the drop waveguides. The demultiplexer we designed can easily separate the light with seven different wavelengths simultaneously. The scope of this paper lies on demultiplexer for communication systems around 1.55-μm wavelength.     

基于衰减全反射式太赫兹时域光谱技术的食用油光谱特性研究

食用油是人类营养和能量的重要来源,为人体提供必需的脂肪酸,研究食用油在太赫兹波段光学特性,对食用油成分分析及品质评价具有重要价值。衰减全反射式太赫兹时域光谱技术是一种新型的太赫兹时域光谱技术,通过样品与倏逝波的相互作用,获取样品的太赫兹光谱。与透射式或反射式太赫兹时域光谱技术相比,该技术能有效地避免测量食用油等液体样品时样品池对光学参数的影响,并能获得样品的精确光学参数。分别利用透射式太赫兹时域光谱技术和衰减全反射式太赫兹时域光谱技术测量了大豆油的吸收光谱。结果表明,与透射式太赫兹时域光谱技术相比,衰减全反射式太赫兹时域光谱技术能更有效地提取大豆油的吸收系数、吸收峰分布等光学特性。进一步利用衰减全反射式太赫兹时域光谱技术研究了大豆油、核桃油、葡萄籽油在太赫兹波段的光学特性,获得了三种食用油在1~1.8 THz范围内的折射率谱和吸收光谱。利用密度泛函理论计算了食用油中四种主要成分(软脂酸、硬脂酸、油酸和亚油酸)在太赫兹波段的振动、转动模式,理论计算结果同实验测量结果吻合较好。研究表明,在太赫兹波段食用油的吸收峰与所含脂肪酸分子种类与含量有关,其主要来源为脂肪酸分子的低频振动和转动。研究成果对食用油成分定性定量分析及品质检测等具有指导意义。     

Reflection of structural waves at a solid/liquid interface

This paper investigates the reflection characteristics of structural or guided waves in rods at a solid/liquid interface. Structural waves, whose wavelengths are much larger than the diameter of the rod, are described in a first approximation by classical one-dimensional wave theory. The reflection characteristics of such waves at a solid/liquid (melting) interface has been reported by two different ultrasonic measurement techniques: first, measuring the fast regression rate of a melting interface during the burning of metal rod samples in an oxygen-enriched environment, and second, monitoring the propagation of the solid/liquid interface during the slow melting and solidification of a rod sample in a furnace. The second work clearly shows that the major reflection occurs from the solid/liquid interface and not the liquid/gas interface as predicted by plane longitudinal wave reflectivity theory. The present work confirms this observation by reporting on the results of some specially designed experiments to identify the main interface of reflection for structural waves in rods. Hence, it helps in explaining the fundamental discrepancy between the reflection characteristics at a solid/liquid interface between low frequency structural waves and high frequency bulk waves, and confirms that the detected echo within a burning metallic rod clearly represents a reflection from the solid/liquid interface.     

High amplitude acoustic transmission through duct terminations: Theory

Recent experimental measurements have demonstrated that net acoustic energy dissipation can occur when sound waves interact with free shear layers, which are produced either by boundary layer separation in mean fluid flow at sharp edges, or by separation of the boundary layer in the acoustic flow at an edge in the absence of mean flow. This paper presents theoretical results which are offered in an attempt to explain these observations quantitatively. Comparison is made between the predicted and measured net energy loss which occurs upon transmission of high amplitude impulsive acoustic waves through various duct terminations, and also between calculated and measured reflection coefficients in the duct. The agreement is generally at least qualitatively good, and would appear to justify the physical assumptions on which the theoretical arguments are based.