Forward scattering theory of electric-field-gradient-induced birefringence

We attempt to resolve the discrepancy between the Buckingham—Longuet-Higgins (BLH) and Imrie—Raab (IR) theories of linear birefringence induced in a gas of dipolar molecules by an electric field gradient. To this end we present a new calculation of the effect, based on forward scattering of a light beam incident on a thin lamina of gas molecules. We work to electric quadrupole—magnetic dipole order. The beam undergoes a time delay which is proportional to the thickness of the lamina and the electric field gradient, and can therefore be interpreted in terms of a contribution to the refractive index of the gas due to the field gradient. The birefringence is obtained by considering appropriate polarizations of the incident beam. To avoid the occurrence of a divergent quantity, such as appears in the BLH theory, it is essential to take account of the finite beam width. Calculations are performed using both primitive (traced) and traceless molecular quadrupole moments; as required on basic grounds, these results are equivalent. They are also identical to the BLH result. By contrast, the IR result is physically unacceptable because it is not invariant with respect to the use of traced and traceless moments. The source of error in the IR theory remains unclear.     

Diffraction of Elastic Waves from a Cylindrical Infinite Cavity with Circular Cross Section Filled by a Liquid

Based on the equations of elasticity theory and hydroacoustics, we calculated the field structures arising when a plane wave is incident on an infinite cylindrical cavity with circular cross section filled by a liquid. The variable pressure component on the cavity axis for longitudinal and shear incident waves is determined.     

Numerical simulation of optical bi-stability in antiferromagnetic sandwich structure

The magnetically optical bi-stability, a third-order nonlinear response, is investigated on an antiferromagnetic (AF) sandwich structure, where an AF film is sandwiched between two dielectric films. The configuration with the AF anisotropy axis and external static magnetic field both in the interfaces and normal to the incident plane is used. The incident wave is taken as a TE wave with its electric component transverse to the incident plane. We find that bistable switches can appear only in a finite frequency range and an incident angle range for a given regime of incident power, which means that there are the critical incident angle and frequency. The power threshold value for the bi-stability increases with the incident angle. In addition, the bi-stability also easily is modulated by the external magnetic field.     

Die paraxiale elektronenoptische Abbildung in Quadrupolsystemen auf wellenmechanischer Grundlage

The paraxial electron optical imaging in a system of quadrupoles on the wave mechanical basis. For a system of electrostatic round lenses and electrostatic and magnetic quadrupoles it was investigated, how the intensity distribution in any arbitrary plane may be found from the wave function in the object plane on the basis of paraxial and wave mechanical approximation. The paraxial wave mechanical imaging in electrostatic cylindrical lenses and in exact quadrupole lenses is contained as a special case.     

地面附近的高空核爆电磁脉冲环境

 主要研究在高空核爆的双指数类型电磁脉冲平面波入射时，地面附近的电磁脉冲环境。计算给出了在不同入射波状态，不同地表介质电气特性和距地面不同高度等条件下的电磁脉冲环境参数，归纳了一些规律性认识。结果显示：地面附近的电场会随距地面高度的不同而发生显著的变化，对于水平场分量，其反射场总是试图抵消入射场，而对于垂直场分量，其反射场叠加在入射场上，使得地面附近的垂直场强幅值一般大于入射波场强幅值；当入射波仰角增大时，合成电场波形的脉冲宽度会变宽；地表介质的电气特性参数不同也会对地面附近电场的波形和幅值造成一定的影响。     

基底性质对二维层状电子气感应电场的影响

采用线性化量子流体动力学模型,研究了载能粒子与二维层状电子气相互作用时的集体静电激发现象。在适当的边界条件下推导出感应电势,入射粒子所受的阻止力和侧向力的一般表达式,讨论了存在绝缘基底情况下基底介电常数对感应电势、阻止力及侧向力的影响。结果表明:当入射粒子速度较小时,基底的极化电场较弱,其介电常数的变化对感应电场几乎无影响,而当速度较高时因极化电场较强而影响很大;入射粒子距离与基底相连的电子气平面越近,基底介电常数对各物理量的影响越大。     

Spectroscopic measurements of the evanescent wave polarization state

We applied optogalvanic spectroscopy to observe Zeeman effect in the evanescent wave in Ar gas with the help of a single-mode diode laser. The use of an homogenous external magnetic field enabled us to observe different π and σ Zeeman split lines contribution. We studied two orthogonal directions of external magnetic field and two orthogonal polarizations of the incident wave with respect to the plane of incidence. The analysis of relative line strengths leads to the determination of the polarization state of the evanescent wave.     

矩形槽光栅矢量模式理论的数值计算

本文根据矩形槽光栅的矢量模式理论进行了数值计算。对于任意入射方向及任意偏振态的入射场，计算了其衍射效率和偏振特性变化，并详细研究了光栅结构参数（周期、槽宽、槽深等）对衍射场的影响。     

Frequency shifts of spectral lines induced by scattering from a rotational anisotropic particle

We investigate the scattering of a polychromatic plane light wave incident upon an anisotropic particle. It is different from light wave scattered by an isotropic particle that the frequency shifts of spectral lines will be induced by the rotation of the anisotropic particle. The analytical expression for the spectrum of the scattered field is derived and numerical examples are also illustrated. We suggest an application that the angular speed of rotation of the anisotropic scatterer can be scaled by measurement of the spectrum of the scattered field.     

Anisotropy in Borrmann spectroscopy

In this paper we introduce Borrmann Spectroscopy as a method for measuring X-ray absorption spectra under conditions of an exotic wave field, namely, a coherent superposition of two plane waves. The essential features of the Borrmann Effect (also known as anomalous transmission) are outlined. We show that the Borrmann Effect can lead to a very strong relative enhancement of quadrupole absorption. After describing some early results in this field, and some general considerations of multiple-wave absorption, we contrast recent results on anisotropy in Borrmann spectroscopy with normal absorption. Despite the qualitative success of a simple model for quadrupole enhancement, temperature dependence and anisotropy, a general theory of the Borrmann Effect is required which includes anisotropic and non-dipolar scattering. We outline some first steps towards such a theory.     

光盘光学系统的矢量衍射理论分析

本文以完整的矢量衍射理论分析了光盘光学系统。首先将入射的聚焦光束分解为平面波谱 ,得到每个平面波的振幅矢量 ;然后计算光盘对每个平面波的衍射 ,得到衍射波的振幅矢量 ,从而得到了整个衍射波场的空间频谱 ;最后计算物镜光瞳上的能通量 ,得到光盘系统的读出信号。在衍射计算中 ,光盘被定义为二维金属光栅 ,根据信息符的不同模型 ,选用坐标变换方法、耦合波方法或模态方法。对于典型的 DVD光学系统来说 ,矢量理论的结论与标量理论相差甚远 ,要得到正确的结果就必须采用矢量衍射理论     

相位光栅分离双波长宽角度光线的理论分析

使用衍射光栅的分色分光方式一般以平行光入射情况为讨论基础,对于非平行光入射的情况讨论较少.本文基于菲涅尔衍射理论和角谱理论,将球面波与平面波的衍射波场联系起来,从而在传播函数中引入角度参量,结合分数泰伯效应的理论基础,推导出双波长宽角度入射光线经相位光栅衍射后的波场分布函数,并对推导出的函数进行数值模拟,得到像面不同位置衍射波场分布.与平行光入射时的标准波场分布相比较,得到宽角度入射时的衍射波场的横向展宽量和偏移量.通过调节光栅台阶的宽度,改变衍射场的展宽和偏移,使各个单一波长的衍射波场宽度小于光栅周期的一半,从而减少双波长光衍射波场的混叠.同时本文给出波场宽度与光栅台阶宽度的变化关系,选取光栅面上多个位置作为台阶宽度的计算点,并对整个光栅的台阶宽度进行曲线拟合,得到可以使双波长宽角度入射光实现良好空间分离的光栅参量.该结果可用于各类宽角度入射光线的光谱分离场合,如双波长成像、液晶显示和液晶投影等.     

Absorption of flexural waves by a pair of mechanical resonator chains mounted on a plate

The scattering of flexural waves by two chains of mechanical resonators characterized by effective admittances is considered. In the first (lower) chain, the effective admittance is represented by a susceptance, whereas, in the second (upper) chain, the resonators are characterized by a complex admittance. The spatial periods of the chains are identical. A plane harmonic flexural wave is obliquely incident on the upper chain, and the scattered field formed by the chains is expressed as a superposition of homogeneous and inhomogeneous Bragg spectra. Intense scattering of the incident wave only occurs in the case of mutual compensation of the resonator susceptance and the radiation admittance. A pair of chains with periods not exceeding the half-wavelength of the flexural wave represents an effective insulator for this wave. In the half-space behind the first chain, the zeroth spectral component of the scattered field completely cancels the resonance-frequency incident flexural wave. Let the second chain be positioned at one of the displacement antinodes of the total field formed by the incident field and the zeroth scattered spectrum. Then, if the active components of the effective admittance of resonators belonging to the second chain are identical to the radiation admittance, the incident flexural wave is completely absorbed by the resonators.     

A reciprocal phase-perturbation theory for rough-surface scattering

We study the scattering of a scalar plane wave from a two-dimensional, randomly rough surface, on which the Dirichlet boundary condition is satisfied. The scattering amplitude is obtained in the form of the Fourier transform of an exponential, in which the exponent is written as an expansion in powers of the surface profile function. It is shown that the latter expansion can be written in such a way that the corresponding scattering matrix is manifestly reciprocal. Numerical results for the reflectivity, and for the contribution to the mean differential reflection coefficient from the incoherent component of the scattered field, are obtained and compared with the predictions of small-amplitude perturbation theory and the Kirchhoff approximation. As the wavelength of the incident wave is varied continuously the results of the phase-perturbation theory change continuously from those of the small-amplitude perturbation theory to those of the Kirchhoff approximation.     

Reflective optical bi-stability of antiferromagnetic films

We investigate one magnetically nonlinear response of antiferromagnetic (AF) films to incident electromagnetic waves, or the reflective optical bi-stability (ROB). Such geometry is used, where the AF anisotropy axis and external static magnetic field both are parallel to the film surfaces and normal to the incident plane. For TE incident waves with the electric component transverse to the incident plane, the ROB of the AF film with the absorption is calculated, but the case of TM incident waves is neglected since no magnetic nonlinearity is induced in this geometry. The bi-stability is completely different in the two resonant-frequency vicinities. Two kinds of bi-stability are found in the higher vicinity, and their features versus incident power are opposite. We also find that there are critical incident angle and critical film thickness for the existence of bi-stability. The bi-stability disappears when the film thickness or incident angle exceeds its critical value. Because the properties of bi-stable reflection sensitively depend on the external field and the incident angle, this bi-stability can be easily modulated by means of changing these quantities.     

The role of the longitudinal component of the electric field vector in two-wave mixing in photorefractive BaTiO3

It is shown that for waves incident with a polarisation in the plane of the grating the component of the electric field in the direction of propagation must be included in the calculations. Coupled differential equations for both the transverse and longitudinal components are derived for wave interaction in photorefractive BaTiO₃. Analytic solutions for the electric field of the signal wave are obtained under the assumption that the pump wave is undepleted. For the parameters considered the longitudinal component is shown to be negligible.     

Scattering-induced attenuation of an ultrasonic beam in austenitic steel

The scattering-induced attenuation coefficient of a beam of longitudinal waves propagating through an austenitic steel plate is measured as a function of the texture angle. The experimental data were obtained by mapping the incident and the transmitted ultrasonic field, and by evaluating the energy loss experienced by each plane wave component of the beam. Contrary to the behavior of data obtained by means of conventional techniques, that of the data reported in this work agrees qualitatively with the theoretical predictions. The reasons for the disagreement between theory and data obtained by means of conventional techniques are also discussed.     

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分析了电磁波以任意角度入射到有限磁场中的激光等离子体通道天线(LPCA)时的电磁散射特性。根据LPCA的工作原理建立了其电磁分析模型,推导出广义柱坐标系下各向异性磁化等离子体中纵向分量所满足的波动方程和纵向场与横向场的关系,得到LPCA和周围媒质中的电磁场,利用边界切向电磁场连续,得出了散射系数方程。通过计算实例,将结果与文献结果比较,吻合较好。该研究结果预期可应用于高功率微波武器系统的研究。     

A reciprocal phase-perturbation theory for rough-surface scattering

Abstract

We study the scattering of a scalar plane wave from a two-dimensional, randomly rough surface, on which the Dirichlet boundary condition is satisfied. The scattering amplitude is obtained in the form of the Fourier transform of an exponential, in which the exponent is written as an expansion in powers of the surface profile function. It is shown that the latter expansion can be written in such a way that the corresponding scattering matrix is manifestly reciprocal. Numerical results for the reflectivity, and for the contribution to the mean differential reflection coefficient from the incoherent component of the scattered field, are obtained and compared with the predictions of small-amplitude perturbation theory and the Kirchhoff approximation. As the wavelength of the incident wave is varied continuously the results of the phase-perturbation theory change continuously from those of the small-amplitude perturbation theory to those of the Kirchhoff approximation.     

双折射晶体入射、折射光电场矢量的琼斯描述及界面处菲涅耳方程的修正

为了用琼斯矢量更明确地表示双折射晶体入射光和折射光的偏振状态,利用波法线椭球和物质方程,将入射光和折射光的电场矢量均视为由o振动和e振动两个方向的分量叠加而成,并将之投影到垂直于和平行于入射面的两个方向上。其中,入射光和折射光电场分量之间的关系用菲涅耳方程中的透射系数表示。考虑到e光电场矢量与电位移矢量的差别,对菲涅耳方程进行了一定的修正以满足e光的边界条件。最终给出了入射光和折射光电场矢量的琼斯矢量形式。并通过具体的数值计算说明,菲涅耳方程修正前后e光的透射系数有一定的差别,且e光的电场矢量和电位移矢量之间的分裂不可忽略。