Optical Properties of Metal-Insulator Fibonacci Quasi-Periodic Superlattice

Based on the hydrodynamic theory and the transfer-matrix method, we have studied the optical properties by taking account of damping effects to the system of the metallic. and dielectric Fibonacci quasi-periodic superlattice for s-polarized soft x-rays and extreme ultraviolet. The analytical expression for the reflectivity is formally given. From our numerical results, we find that besides the reflection intensity spectrum has a very rich structure of self-similarity, the stronger reflection peaks appear at the region of soft x-rays and ultraviolet compared with metal-metal superlattice, and the width of the maxima is dependent on the dielectric functions of metallic and dielectric media. By using the periodic condition approximation, we also distussed the electromagnetic normal modes in the system, which explains the reflection spectra, and we found that with the increasing of the generation number, the electromagnetic modes all become localized.     

A damping boundary condition for atomistic-continuum coupling

The minimization of spurious wave reflection is a challenge in multiscale coupling due to the difference of spatial resolution between atomistic and continuum regions. In this study, a new damping condition is presented for eliminating spurious wave reflection at the interface between atomistic and continuum regions. This damping method starts by a coarse–fine decomposition of the atomic velocity based on the bridging scale method. The fine scale velocity of the atoms in the damping region is reduced by applying nonlinear damping coefficients. The effectiveness of this damping method is verified by one-and two-dimensional simulations.     

Exciton reflection of ZnSe single crystals with account for the effect of the surface electric field

The mechanism of formation of an exciton reflection band is analyzed using a multilayer model of the near-surface region of ZnSe single crystals. It is shown that the appearance of a fine structure (a spike) in the reflection spectra at large damping parameters of the exciton is due to the surface electric field and the Stark exciton effect. The exciton-resonance energies and the damping parameters of free excitons for temperatures ranging from 12 to 100 K are determined by comparing experimental and predicted contours of the reflection spectrum. The surface concentration of charged centers and the characteristics of the space-charge region are evaluated within the framework of the model employed. Brest Polytechnic Institute, 267, Moskovskaya Str., Brest, 224017, Belarus. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 66, No. 3, pp. 401–407, May–June, 1999.     

Method of Images direct mapping of one-dimensional heat flow patterns in an arbitrarily layered solid

A new method for direct analysis and visualization of one-dimensional heat flow patterns in an arbitrarily layered impulse-heated solid is presented. This analysis is based on the Method of Images in which the surface temperature/time response is described as the superposition of a free medium temperature field and additional image field contributions which account for the effects of thermal reflection and damping at subsurface interfaces. Through the introduction of a simple set of constraint rules, all sequences of thermal reflection and transmission at sample interfaces which return significant energy to the material surface in a given observation time may be systematically mapped and directly visualized.     

A theory of the bion in a one-dimensional sine-Gordon system: II. AC conductivity

A linear response theory is developed for the ac conductivity due to one-dimensional sine-Gordon bions within a semiclassical approximation. As a damping mechanism we consider the diffusive motion of the phase of the internal motion of the bion due to collisions with other bions. The line shape is either Lorentzian or asymmetric Lorentzian with a lower frequency tail. The lower frequency tail has its origin in the bion to bion transition accompanying one-photon annihilation; a new process other than one-bion creation from the vacuum. The effect of an extrinsic damping is also examined, which, in some cases, results in an asymmetric Lorentzian with a higher frequency tail. The results of the far infrared reflection experiments on quasi-one-dimensional conductors TTF-TCNQ and KCP are reanalyzed in the light of the present theory.     

Perfectly matched layers for the heat and advection–diffusion equations

We design a perfectly matched layer for the advection–diffusion equation. We show that the reflection coefficient is exponentially small with respect to the damping parameter and the width of the PML and this independently of the advection and of the viscosity. Numerical tests assess the efficiency of the approach.     

Spin damping correction to electrostatic modes in kinetic plasma theory

The effect of spin of particles is studied using a semi-classical kinetic theory for a magnetized plasma. No other quantum effects are included. We focus in the simple damping effects for the electrostatic wave modes. Besides Landau damping, we show that spin produces two new different effects of damping or instability which are proportional to ?. These corrections depend on the electromagnetic part of the wave that is coupled with the spin vector.     

GaN载流子浓度和迁移率的光谱研究

用红外反射光谱的方法对生长在蓝宝石衬底上的α-GaN外延薄膜的载流子浓度和迁移率进行了研究.通过测量蓝宝石衬底和不同Si掺杂浓度的一系列GaN外延膜的远红外反射谱并进行理论计算和拟合,得到GaN中的声子振动参量和等离子振荡的频率及阻尼常量,并由此计算得到其载流子浓度和迁移率.计算结果,红外方法得到的载流子浓度与Hall测量相一致,但迁移率比Hall迁移率要低约二分之一.同时红外谱与喇曼谱上明显观察到LO声子与等离子体激元耦合模,(LPP)随掺杂浓度的变化. 关键词： α-GaN外延薄膜 红外反射光谱 载流子浓度 迁移率 LO声子与等离子体激元耦合模 Raman光谱     

Damping of flexural vibrations in rectangular plates using the acoustic black hole effect

The reduction of flexural vibration in plate structures has been investigated using the recently reported acoustic black hole effect for flexural wave reflection in plates with the local thickness varying according to h(x)=εx^m and m≥2. Since sharp edges of such plates (wedges) are always truncated before x=0, the real reflection coefficients are relatively high, therefore the application of a small amount of damping is required to achieve large reductions in vibration amplitude. This paper presents a numerical model of a plate incorporating an acoustic black hole wedge, with predictions for vibration amplitudes. These are compared to equivalent experimental measurements for a range of applied damping layers. It is concluded that the above-mentioned power-law wedges can be used as effective vibration dampers in plate structures over a wide frequency range of interest.     

Computational prediction of modal damping ratios in thin-walled structures

Modal analysis in finite element packages gives natural frequencies and mode shapes, but not modal damping values. Given a constitutive relation for specific material dissipation, volume integrals of the per cycle dissipation can be used to estimate the modal damping. Here, we adopt a well known power law model for such specific dissipation. We develop a modal damping estimation procedure for thin-walled components using shell elements in a commercial finite element package. We validate our shell element results against both analytical results and a solid elements approach developed elsewhere. Our computational approach allows complex geometries in a study of the effects of shape on damping. Finally, we demonstrate the efficacy of both stress concentrations and small tuned resonant appendages in increasing damping.     

Effect of phonon damping on the resonance reflection of a transverse sound wave from a planar defect in a crystal

Resonance scattering of a transverse sound wave by a planar defect in an elastic isotropic medium is studied in a wide range of values of the ratio of the damping length and the size of the region of localization of longitudinal oscillations. The transition between two limiting cases is described. The character of the transition is demonstrated by typical plots of the dependence of the reflection and transmission coefficients on the parameter relating the wavelength of the incident wave and the strength of the defect. It is shown that renormalization of total reflection into conventional dissipative passage occurs for values of this parameter below a certain critical value.     

基于等效参数反演的敷设声学覆盖层的水下圆柱壳体声散射研究

应用了一种等效方法计算敷设声学覆盖层无限长圆柱壳体水下声散射特性.等效方法的核心是忽略复杂声学覆盖层内部的声学结构,将其作为具有等效材料参数的均匀阻尼层进行建模,该均匀阻尼层具有和原覆盖层相同的复反射系数.进而,应用COMSOL Multiphysics软件建立敷设均匀阻尼层圆柱壳体的有限元模型并求解其声散射特性.等效方法的关键是等效材料参数的获取.采用充水阻抗管实验和有限元数值实验两种方法获取声学覆盖层贴敷在与壳体具有相同厚度、相同材料背衬条件下的复反射系数,在此基础上,基于遗传算法反演材料的等效参数.研究表明,等效参数具有频变特性,且尽管等效杨氏模量和等效泊松比在频率范围内存在较大波动,但是等效前后复反射系数仍保持一致.为了验证等效方法求解壳体声散射特性的准确性,同时建立了敷设声学覆盖层壳体的完整有限元模型,将覆盖层内部声学结构进行精细建模,并求其声散射特性.结果表明,两种方法求得的形态函数符合得较好,在整个频率范围内平均误差大约为1 d B.     

Influence of the nonradiative decay of qubits into a common channel on the transport properties of microwave photons

The influence of nonradiative damping of qubits on the microwave transport of photons propagating in a onedimensional microstrip line has been considered. Expressions for the transmission and reflection coefficients for two qubits have been obtained within the non-Hermitian Hamiltonian formalism. The indirect interaction between qubits caused by nonradiative decay into a common channel is explicitly taken into account in these expressions. It has been shown that this interaction leads to results significantly different from known results.     

Refractive damping of Fraunhofer diffraction in light ion-nucleus elastic scattering at high energy

Angular distributions for elastic scattering of 100 MeV and 140 MeV alpha particles by heavy nuclei are characterized by strong damping of the Fraunhofer diffraction oscillations at large angles. This effect is attributed to refraction by the real part of the alphanucleus potential. It is shown that this can be accounted for through a technical modification of Frahn's closed formalism for strong absorption scattering together with a suitable parameterization of the nuclear scattering coefficients. The result exhibits not only the characteristic filling in of the Fraunhofer minima at large angles, but also a subtle interplay of Coulomb and nuclear effects which produce a characteristic dip and hump in the lower Fraunhofer envelope at smaller angles. It is shown that less structured 180 MeV proton-nucleus elastic angular distributions can also be accounted for. Finally, it is suggested that the refractive damping of the Fraunhofer oscillations does not appear at lower energies because of the masking of refraction by quantal surface reflection from the complex nuclear potential, and it is shown how this effect can be included in the formalism.     

Normal-incidence exciton transmission and reflection spectra of semiconducting plane-parallel slabs

Summary Exciton transmission and reflection spectra of thin semiconducting crystals in the spectral region of excitonic polaritons are calculated by the Stahl's coherent wave approach. The influence of the crystal thickness and of the intrinsic damping is discussed. Calculations are performed for the lowest state of theA-exciton in CdS. Experimental results of Broseret al. (1985) are reproduced by inserting an appropriate energy-dependent damping. The research was supported by the Polish Ministry for Science and Higher Education, Program CPBP01.03.     

Numerical studies of surface and bulk modes in attenuated total reflection spectra

The dispersion relations of normal modes in the layered constructions are studied. In the frequency region with negative permittivity, we investigate the normal modes near the air--metal and the air--matematerial interfaces and compare them. An extra bulk mode appearing in a pass band of two media is found near the air--matematerial interface, which is different from the air--metal case. Moreover, the bulk mode will be further proved by the attenuated total reflection (ATR) technique, in which the coupling between the incident electromagnetic waves and the normal modes is studied. For p-polarized incident waves, the ATR spectra based on the Otto and the Kretschmann configurations are obtained numerically, where the dips present the excitations of the surface and bulk modes. Furthermore, we also discuss the influences of the middle layer thickness, the incident angle and the damping term on the reflection in detail. It is found that the coupling frequencies and the maximum strength are strongly dependent on the above media parameters.     

Two-Photon Jaynes-Cummings Model Governed by Milburn Equation with Phase Damping

In this paper, we find an analytic solution of the master equation of a non-resonant two-photon JaynesCummings model (JCM) with phase damping with the help of the super-operator technique. We study the influence of phase damping on non-classical effects in the JCM, such as oscillations of the photon-number distribution, revivals of the atomic inversion, and sub-Possion photon statistics. It is demonstrated that the phase damping suppresses the revivals of the atomic inversion and non-classical effects of the cavity field in the JCM.     

Effect of coherence property of incident light on prism waveguide coupling

The accurate reflection coefficient of prism waveguide coupler that takes coherence property of incident light into account is obtained at first. Based on the reflection coefficient, the effect of coherence property of incident light on prism coupling is discussed in this work. It is shown that extra damping in waveguide caused by the coherence property is larger for high-order resonant mode than that for low-order mode. For 100 fs Gaussian pulses incidence, the reflected spectra at different resonant modes are obtained theoretically and experimentally, which show that coherence property has a strong effect on prism coupling at high-order modes.     

Quantum Phase and Nonlocal Correlations for a Three-Level System Interacting with Laser Light in a Nonlinear Kerr Medium Under Decoherence

In this paper, we study the time evolution of the geometric phase and nonlocal correlations for a three-level atom interacting with the quantum field emerged in a nonlinear Kerr medium. We discuss the dependence of the physical quantifiers on the phase damping effect. We examine the effects of the initial state and different system parameters on the evolution of the nonlocal correlation and geometric phase with and without the phase damping effect. Furthermore, we explore the link between the geometric phase and the nonlocal correlation during the time evolution. Finally, we show that the model proposed will be very useful to avoid the phase damping effect by a proper choice of the physical parameters in the field for both cases of the initial pure and mixed states of the three-level atom.     

Theory of surface polaritons in n-type silicon in the presence of a dc current,including the electron thermal pressure gradient

A theoretical investigation has been made of the effect of a drift current, including the electron thermal pressure gradient, on surface polaritons in n-type Si. The polariton propagation and drift current directions are taken to be either parallel or antiparallel. Retardation is included, but damping is neglected. The specular reflection approach of Kliewer and Fuchs is used to obtain the polariton dispersion relation. The results show that the drift current and surface polaritons interact, leading to evanescent waves for certain frequencies. However, no wave amplification is obtained.