Frequency upshifting of electromagnetic radiation via obliqueincidence on an ionization front

Frequency upshifting of electromagnetic radiation impinging on a relativistically moving ionization front is theoretically investigated. Unlike previous works in this field treating the case of normal incidence and qualitatively similar case of oblique incidence of a transverse electric polarized wave, oblique incidence of a transverse magnetic polarized wave on the front is considered. The peculiarities of the case under consideration are connected with the generation of Langmuir waves behind the front and Brewster's phenomenon. We present a complete analysis of the incident wave transformation including analysis of the frequencies and amplitudes of the waves excited ahead of and behind the front. Special emphasis is made on energy transformation in the case when a wave packet is incident on the front. In particular, we show that even for negligible angles of incidence, energy losses via transformation into Langmuir waves may be very high (up to ~60%). In general, generation of Langmuir waves may play a significant role in the plasma-based radiation sources with relativistic ionization fronts     

Stimulated Brillouin scattering of elliptical laser beam in collisionless plasma

This paper presents an investigation of self-focusing of elliptical laser beam in collisionless plasma and its effect on stimulated Brillouin scattering. The pump beam interacts with a pre-excited ion-acoustic wave leading to Brillouin back-scattered process. The transverse intensity gradient of a pump beam generates a ponderomotive force, which modifies the background plasma density profile in a direction transverse to pump beam axis. This modification in density effects the incident laser beam, ion-acoustic wave and back-scattered beam. Non-linear differential equations for the beam width parameters of pump laser beam, ion-acoustic wave and back-scattered beam are set up and solved numerically. It is observed from the analysis that the focusing of waves enhances the SBS back-reflectivity.     

2019年中国声学学会青年人才托举工程项目交流会在南昌召开

为改善电磁超声换能器(electromagnetic acoustic transducer,EMAT)激发横波的特性,提出一种基于正交试验的优化方法,并利用有限元仿真软件COMSOL Multiphysics建立了横波EMAT的有限元模型,应用正交试验和极差分析法,分析了线圈各参数对电磁超声横波的近场长度和半扩散角的影响,比较了线圈各参数影响程度的大小。结果表明,激励电流的频率和线圈的尺寸对横波的传播特性有着明显影响,提高频率会使得横波的近场长度增大及半扩散角减小;其次,减小导线的宽度及间距,以缩小线圈尺寸能有效改善横波的传播特性。     

Effect of magnon–phonon interaction on transverse acoustic phonon excitation at finite temperature

A magnon–phonon interaction model is developed on the basis of two-dimensional square Heisenberg ferromagnetic system. By using Matsubara Green function theory transverse acoustic phonon excitation is studied and transverse acoustic phonon excitation dispersion curves is calculated on the main symmetric point and line in the first Brillouin zone. On line Σ it is found that there is hardening for transverse acoustic phonon on small wave vector zone (nearby point Γ), there is softening for transverse acoustic phonon on the softening zone and there is hardening for transverse acoustic phonon near point M. On line Δ it is found there is no softening and hardening for transverse acoustic phonon. On line Z it is found that there is softening for transverse acoustic phonon on small wave vector zone (nearby point X) and there is hardening for transverse acoustic phonon nearby point M. The influences of various parameters on transverse acoustic phonon excitation are also explored and it is found that the coupling of the magnon–phonon and the spin wave stiffness constant play an important role for the softening of transverse acoustic phonon.     

Propagation of surface elastic waves in the Cosserat medium

The problem of surface elastic wave propagation in the Cosserat medium (half-space) is considered. The strained state is characterized by two independent vectors: displacement and rotation. Solutions to the equations of motion are sought in the form of wave packets specified by an arbitrary Fourier spectrum. It is shown that, if the solution is sought in the form of a three-component displacement vector and a three-component rotation vector dependent on time, depth, and longitudinal coordinate, the initial system splits into two systems, one of which describes the Rayleigh wave and the other corresponds to a transverse wave decaying with depth. For both waves, analytical solutions in terms of displacements are obtained. It should be particularly noted that, unlike the Rayleigh wave, the solution for the transverse surface wave has no analogues in the classical elasticity theory. The transverse wave solution is numerically compared with the Rayleigh wave solution.     

Transverse wave band gaps and longitudinal wave band gaps in solid phononic crystals

Based on the properties of transverse (divergenceless) waves and longitudinal (irrotational) waves, we divided the transverse wave modes and longitudinal wave modes from the mixed eigen modes in solid phononic crystals. By investigating the transverse wave and longitudinal wave band structures at low frequency, we found that transverse bands and longitudinal bands exhibit different behaviors in solid systems including spherical scatterers. Phononic crystal with a large density ratio of solid spheres to the background can guarantee both the large longitudinal and large transverse band gap, but solid spheres with a small ratio of longitudinal wave velocity to transverse wave velocity can only help to enlarge the longitudinal band gap, and do not help to enlarge the transverse band gap.     

Abrupt change of reflectivity from the strongly anisotropic metamaterial

The wave reflection from a non-magnetic anisotropic metamaterial, whose principal elements of the permittivity tensor have different signs, is investigated in this paper. It is found that, if the orientation of the optical axis is properly chosen, an extremely small change of the transverse wave number will lead to a dramatically change of the reflectivity at the glancing incidence. The physical insight for this abrupt change of reflectivity is also given by the analysis of the imaginary part of the k-surface. Since the metamaterial discussed here have been experimental realized from GHz to optical frequencies, the proposed abrupt change property of reflectivity may find some potential applications in various calibration devices, because of its extremely sensitivity to the transverse wave number.     

弦线上波的传播规律实验装置的改进

对传统的验证弦线上横波的传播规律实验中的波源进行改进，采用单片机控制的可连续调节频率的装置，可以得到横波的波长与弦线中的张力、弦线的线密度及振动频率的关系，使得验证弦线上横波的传播规律的实验内容更加丰富。     

Kinetic study of instability growth rate in a helicon plasma discharge source

In this work, a kinetic model is developed to study the effects of the radio frequency antenna wavenumber, helicon plasma electron density, as well as their drift velocity and temperature on the instability increment rate of the helicon wave in both longitudinal and transverse directions. The ion acoustic (IA) wave frequencies and wavenumbers of the helicon waves are obtained when the maximum wave energy is deposited on the plasma ions. Moreover, it is shown that, at the IA wavenumber and frequencies, while the longitudinal instability increment rates for both the helicon and IA waves are ignorable, the transverse instability increment rate for both the helicon and IA wave increases. Besides, the longitudinal instability increment rate for the helicon or IA wave has non‐zero resonant frequencies. On the other hand, the transverse instability increment rate of helicon or IA wave can be neglected. Furthermore, it is observed that, while both the imaginary part of longitudinal permittivity and longitudinal instability increment rate are not influenced by the electron temperature, their transverse component increases linearly with the electron temperature. In addition, the imaginary part of transverse permittivity increases almost linearly with the drift velocity of the plasma electrons.     

A slow wave with the structure of an electromagnetic wave in piezoelectric and magnetostrictive media

The propagation of elastic waves in piezoelectric and magnetostrictive materials is considered theoretically. It is shown that an elastic wave in a piezoelectric can create not only a longitudinal electric field parallel to the wave normal (longitudinal piezoactivity) but also a transverse field of electric induction (transverse piezoactivity). The presence of a transverse induction field leads to the appearance of a magnetic field perpendicular to the direction of the wave normal and to the induction vector; therefore, the transverse-piezoactive wave is accompanied by a transverse wave having the structure of an electromagnetic wave and propagating with the speed of sound. Transverse-magnetostrictive elastic waves in magnetostrictive dielectrics are accompanied by a similar wave.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 10, pp. 32–36, October, 1976.     

Theory of transverse neutron inelastic scattering in the transition metals

A qualitative analysis of the transverse neutron inelastic cross section for the Hubbard model withs?d hybridization in the framework of RPA is considered. The poles of the transverse generalized spin susceptibility are studied. It is found that the acoustic spin wave pole exists among the set of poles of dynamical spin susceptibility and that the non-interacting susceptibility determines the four quasi-Stoner continuum.     

有限温度下二维Heisenberg铁磁系统的横向声频支声子激发

在二维正方Heisenberg铁磁系统的基础上建立了磁振子-声子相互作用模型.利用Matsubara格林函数理论研究了系统的横向声频支声子激发，计算了布里渊区的主要对称点线上的横向声频支声子色散曲线，发现在第一布里渊区的Σ线上，小波矢区(Γ附近k_xa＜0.2)横向声频支声子有硬化现象，但是在软化区(0.25＜k_xa＜0.7)有横向声频支声子有软化现象，在M附近(0.75＜k_xa)横向声频支声子有硬化现象.在Δ线上没有发生横向声频支声子有软化与硬化现象.在Z线上小波失区(X附近k_xa＜0.65)横向声频支声子有软化现象，但是在M附近横向声频支声子有硬化现象.并且又讨论了各项参数对横向声频支声子激发的影响，发现磁振子-声子耦合与自旋波劲度常数对横向声频支声子软化起很大的作用. 关键词： 磁振子-声子相互作用 横向声频支声子软化 Matsubara格林函数理论 铁磁系统     

Ermakov-Modulated Nonlinear Schrödinger Models. Integrable Reduction

Nonlinear Schrödinger equations with spatial modulation associated with integrable Hamiltonian systems of Ermakov-Ray-Reid type are introduced. An algorithmic procedure is presented which exploits invariants of motion to construct exact wave packet representations with potential applications in a wide range of physical contexts such as, ‘inter alia’, the analysis of Bloch wave and matter wave solitonic propagation and pulse transmission in Airy modulated NLS models. A particular Ermakov reduction for Mooney-Rivlin materials is set in the broader context of transverse wave propagation in a class of higher-order hyperelastic models of incompressible solids.     

Generating ultra wide low-frequency gap for transverse wave isolation via inertial amplification effects

Low-frequency transverse wave propagation plays a significant role in the out-of-plane vibration control. To efficiently attenuate the propagation of transverse waves at low-frequency range, this letter proposed a new type phononic beam by attaching inertial amplification mechanisms on it. The wave propagation of the beam with enhanced effective inertia is analyzed using the transfer matrix method. It is demonstrated that the low-frequency gap within inertial amplification effects can possess much wider bandwidth than using the local resonance method, thus is more suitable for designing applications to suppress transverse wave propagation.     

Transverse plane wave analysis of short elliptical chamber mufflers: An analytical approach

Short elliptical chamber mufflers are used often in the modern day automotive exhaust systems. The acoustic analysis of such short chamber mufflers is facilitated by considering a transverse plane wave propagation model along the major axis up to the low frequency limit. The one dimensional differential equation governing the transverse plane wave propagation in such short chambers is solved using the segmentation approaches which are inherently numerical schemes, wherein the transfer matrix relating the upstream state variables to the downstream variables is obtained. Analytical solution of the transverse plane wave model used to analyze such short chambers has not been reported in the literature so far. This present work is thus an attempt to fill up this lacuna, whereby Frobenius solution of the differential equation governing the transverse plane wave propagation is obtained. By taking a sufficient number of terms of the infinite series, an approximate analytical solution so obtained shows good convergence up to about 1300 Hz and also covers most of the range of muffler dimensions used in practice. The transmission loss (TL) performance of the muffler configurations computed by this analytical approach agrees excellently with that computed by the Matrizant approach used earlier by the authors, thereby offering a faster and more elegant alternate method to analyze short elliptical muffler configurations.     

金属和Kerr非线性介质界面上表面等离子体激元的色散关系

从麦克斯韦方程组出发,结合边界条件,分别得到TM波和TE波在金属和Kerr非线性介质界面上表面等离子体激元的色散关系.由于非线性的存在,TM波的色散关系变得复杂,与光强、非线性系数有关.和线性情况一样,此界面不存在TE波.     

转移矩阵法在负折射率介质材料平板波导中的应用研究

利用严格电磁理论,推导出了适用于负折射率介质材料光波导的转移矩阵,分析讨论了转移矩阵的性质和应用.利用转移矩阵方法,推导出导波层为负折射率介质材料、覆盖层和衬底为右手材料的三层对称介质光波导的本征色散方程.用图解法研究了负折射率介质波导中TE波的异常色散特性.在负折射材料介质波导中没有零阶模,最低阶为1阶模,并且有截止频率,只有波导参量满足一定条件的时候才会存在,导模的横向波数可以为实数和纯虚数,而正折射率介质波导导模的横向波数只能为实数.     

Analysis of measuring features of interferometric methods for studying “weak” optical inhomogeneity with a small transverse size

Comparative analysis of interference methods, which are most promising for studying optical inhomogeneities with a small transverse size, is carried out. It is shown based on analysis of interference fringes for the two most widely used interferometric methods (two-beam interferometry with a reference wave and lateral-shear interferometry) that in the case of a lateral shift exceeding the geometrical size, lateral-shear interferometry shows twice as high sensitivity as that of double-beam interferometry with a reference wave and is more promising for estimating the size of “weak” optical inhomogeneities.     

Two-dimensional anisotropic non-Fermi-liquid phase of coupled Luttinger liquids

Using bosonization techniques, we show that strong forward scattering interactions between one-dimensional spinless Luttinger liquids (LL) can stabilize a phase where charge-density wave, superconducting, and transverse single particle hopping perturbations are irrelevant. This new phase retains its LL-like properties in the directions of the chains, but with relations between exponents modified by the transverse interactions, whereas it is a perfect insulator in the transverse direction. The mechanism that stabilizes this phase is strong transverse charge-density wave fluctuations at incommensurate wave vector, which frustrates crystal formation by preventing lock-in of the in-chain density waves.     

On the possibility of natural formation of a transverse wave with a phase velocity lower than the velocity of light

The formation of a transverse wave with a phase velocity lower than the velocity of light, which can exist in an equilibrium plasma without a slow-wave structure in zero magnetic field, is described. It involves the transformation of a transverse wave with trapped electrons, traveling along the magnetic field, into a slow transverse wave after the removal of the magnetic field. During the evolution of the wave with trapped electrons, the magnetic induction decreases very slowly in the direction of the wave propagation. As a result, the velocity at which electrons are in resonant interaction with the wave increases; therefore, the electrons fall to the bottom of potential wells. Under the influence of the trapped electrons, the phase velocity of the wave decreases and becomes lower than the velocity of light. It becomes equal to the velocity at which the electrons are in resonance interaction with the wave at the instant when the magnetic field vanishes. It is demonstrated that a transverse wave with a velocity lower than the velocity of light can exist in an equilibrium plasma even after the magnetic field vanishes; in this case, the flow of trapped electrons serves as a slow-wave structure.