Nonlinear surface magneto-optics of ferromagnetic Ni/Cu(001) from first principles

We present first-principles calculations of the nonlinear optical (NLO) response of a Ni/Cu(001) bilayer. The calculations are based on the full potential linearized augmented plane wave (FLAPW) method with the additional implementation of spin–orbit coupling (SOC). On the basis of this set of eigenstates the magneto-optical transition-matrix elements are evaluated. Using the surface-sheet model the optical reflection properties are determined for the cases of the magnetization vector perpendicular to the surface (polar magneto-optical configuration (MOC)) and for the in-plane magnetization (longitudinal MOC). The nonlinear optical susceptibility tensor elements χ⁽²⁾ _ijk for different magnetization directions as well as the spectral dependence of χ⁽²⁾ _ijk, the resulting intensities, and Kerr angles are presented for the Ni/Cu(001) bilayer. The results show that the magnetic tensor elements of the χ⁽²⁾ _ijk tensor are smaller than the nonmagnetic ones by only one order of magnitude, confirming the important role of magnetic properties in the NLO response. Received: 16 October 2001 / Revised version: 8 March 2002 / Published online: 29 May 2002     

磁性颗粒膜法拉第转角的研究

在外磁场作用下,复合介质的法拉第磁光效应依赖于颗粒膜电介质张量。而复合介质的电介质张量的计算相当复杂。运用了有效介质近似理论,利用非均匀复合介质的有效电场等于单个颗粒中局域场的平均值的自恰条件,由电介质张量εe方程及自洽条件导出了计算磁性颗粒膜系统磁光法拉第转角的解析公式。并应用导出的关系,以Cu金属颗粒为例,讨论了颗粒膜中金属颗粒含量及对应的基质、离子浓度、颗粒形状对法拉第转角的影响,结果表明,利用有效介质近似理论计算的结果与实验结果一致。     

Reflection matrix in magneto-optics of multilayer structures

An expression is given for the reflection matrix of a magnetic multilayer, each layer of which is assumed to be uniformly magnetized in an arbitrary direction. The layer permittivity tensor takes into account optical anisotropy along the direction orthogonal to boundaries and is considered in the linear approximation with respect to two magneto-optical parameters. The result obtained makes it possible to study a large number of various configurations of multilayers and magneto-optical effects in them taking into account the effect of optical anisotropy.     

Propagation of electromagnetic soliton in anisotropic biquadratic ferromagnetic medium

The information storage technology based on anisotropic ferromagnets with sufficiently high magneto-optical effects has received much attention in recent years. The magneto-optical recording combines the merits of magnetic and optical techniques. We investigate the magneto-optical effects on a biquadratic ferromagnet and show that the dynamics of the system is governed by a perturbed nonlinear Schrödinger equation. The evolutions of amplitude and velocity of the soliton are found to be time independent, thereby admitting the lossless propagation of electromagnetic soliton in the medium, which may have potential applications in accordance with the soliton based optical communication systems. We also exploit the role of perturbation, which has a significant impact on the propagation of electromagnetic soliton.     

Photoinduced precession of magnetization in ferromagnetic (Ga,Mn)As

Precession of magnetization induced by pulsed optical excitation is observed in a ferromagnetic semiconductor (Ga,Mn)As by time-resolved magneto-optical measurements. It appears as complicated oscillations of a polarization plane of linearly polarized probe pulses, but is reproduced by gyromagnetic theory incorporating an impulsive change in an effective magnetic field due to a change in the magnetic anisotropy. The shape of the impulse suggests a significant nonthermal contribution of photogenerated carriers to the change in anisotropy through spin-orbit interaction.     

磁光非线性光纤中光参量增益的研究

将光纤中磁光效应和非线性效应作为微扰,推导了磁光四波混频的耦合模方程.通过解析解研究了各向同性磁光非线性光纤的参量过程,并指出利用磁光耦合系数的色散特性可以实现四波混频的相位匹配.同时,采用龙格-库塔法分析了在线双折射磁光非线性光纤中,忽略费尔德常量的波长依赖性时,左旋圆偏振光参量增益的磁控特性,指出了实验中采用较高费尔德常量的非线性光纤的必要性.研究表明:1)对于低线双折射磁光非线性光纤,优化双折射大小可以获得最大的参量增益;2)根据参量增益对磁光耦合系数的单调依赖特性,适当选择光纤长度、泵浦功率以及输入导波光的偏振态,可使参量增益的磁可调范围大大提高.     

Strong modification of the nonlinear optical response of metallic subwavelength hole arrays

The influence of hole shape on the nonlinear optical properties of metallic subwavelength hole arrays is investigated. It is found that the amount of second harmonics generated can be enhanced by changing the hole shape. In part this increase is a direct result of the effect of hole shape on the linear transmission properties. Remarkably, in addition to enhancements that follow directly from the linear properties of the array, we find a hot hole shape. For rectangular holes the effective nonlinear response is enhanced by more than 1 order of magnitude for one particular aspect ratio. This enhancement can be attributed to slow propagation of the fundamental wavelength through the holes which occurs close to the hole cutoff.     

Nonlinear magneto-optical Bragg gratings

In magneto-optical gratings the magnetic dipolar coupling superimposed on the electric dipolar one introduces nonreciprocity and spectral discrimination between circular polarization states, measured by a Zeeman-like splitting of the photonic Bragg resonances. In a nonlinear regime the degree of nonreciprocity is modified by the photoinduced interplay of these splittings and their Stark-like shifts. We predict novel magneto-optical modulation schemes for switching between orthogonal circular polarization states of transmission or reflection operated by means of an intense linearly polarized optical pulse train.     

高非线性光纤中四波混频的磁控机理研究

将磁光效应和光纤非线性效应作为微扰,采用导波光耦合理论分析了高非线性光纤中导波光发生磁光四波混频的机理;实验测试了磁场对四波混频偏振依赖性的影响,理论分析与实验结果符合.研究表明,当输入的探测光和抽运光为相互正交的线偏振光时,四波混频的磁控效果最为明显,输出的闲频光功率随磁光耦合系数振荡变化,施加适当的外加磁场可使四波混频效率得到进一步提高.选择适当费尔德常数的光纤材料,利用磁光效应对四波混频偏振依赖性的影响,可实现不同范围的磁场测量.     

Nongyrotropic magneto-optical effects in metal-insulator magnetic multilayer thin films

Nongyrotropic magneto-optical effects are investigated in metal-insulator magnetic multilayer thin films. These effects manifest themselves in changes in the coefficients of transmission and reflection of electromagnetic radiation from the surface of a multilayer film due to the crossover of the magnetic structure from an antiferromagnetic configuration to a ferromagnetic configuration. The nongyrotropic magneto-optical effect observed in reflected light is analyzed theoretically. It is assumed that the multilayer structure is exposed to radiation of a monochromatic plane wave polarized along the direction of magnetization of the film. The magneto-optical effect is described in terms of the permittivity tensor of the multilayer medium, which depends only on the light frequency. The Boltzmann kinetic equation is treated with allowance made for spin-dependent electron scattering both inside conducting layers and at rough interfaces. Using an Fe/C multilayer as an example, it is demonstrated that the nongyrotropic magneto-optical effect is equal in order of magnitude to the equatorial Kerr effect or other strong magneto-optical effects.     

PtMn/Co多层膜的磁光特性研究

采用磁控溅射法制备了一系列的Mn掺杂的PtMn/Co多层膜.通过测量得到的磁光常数和光学常 数,计算介电张量的对角元和非对角元,得到在掺杂较大时,克尔角的变化是由于介电张量 的非对角元引起的;在掺杂量较小时,克尔角的变化是由介电张量的对角元和非对角元以及 光学常数的变化引起的.     

利用法拉第效应进行永磁体磁场二维光学成像

借助于法拉第磁致旋光效应,以ZF6玻璃为磁旋光介质,设计了适当的光学系统,对永磁体磁极附近磁场的分布进行了光学二维成像.利用自编的图像采集软件采集了一系列原始图片,并利用自编的图像处理软件对这些原始图片进行了处理,完成了检偏过程.分别得到了透射成像方式和反射成像方式下永磁体磁场的分布图像,这些图像正确反映了永磁体磁场的实际分布.本研究工作为宏观尺度磁场的观测与测量提供了一种有效的手段.     

Magneto-optical polar Kerr effect in a film-substrate system

The problem of electromagnetic reflection at an arbitrary angle of incidence in a system consisting of an isotropic ambient, a magnetic film and a thick magnetic substrate is studied. The magnetizations in both the film and substrate are assumed normal to the planar interfaces. The results are expressed in terms of the reflection matrix which is directly connected to the experimentally observed quantities: ellipsometric ratio and magneto-optical rotation and ellipticity. The general condition for guided wave propagation in the system is obtained. The theory is applied to the special cases of (a) normal incidence, (b) oblique incidence on a uniaxial film on a uniaxial substrate, both optical axes being normal to the interfaces, and (c) oblique incidence on a system consisting of an isotropic ambient, a magnetic film and a thick magnetic substrate assuming the diagonal elements of the permittivity tensor in a particular magnetic medium (film or substrate) equal to each other and the corresponding off-diagonal elements much smaller with respect to them. The possible practical applications of the present analysis are in the optimum design of film-substrate structures in magneto-optic devices and in the optical studies of the surface effects in magnetic materials.     

Magnetic and magneto-optical properties of epitaxial cobalt films grown on a corrugated CaF<Subscript>2</Subscript>/Si surface

The magnetic properties of CaF₂/Co/CaF₂(110)/Si(001) heterostructures fabricated by molecular-beam epitaxy and having a corrugated CaF₂ buffer surface were studied. The optical and magneto-optical properties of these structures reflect the C _2v symmetry of the corrugated structure surface. The studies of hysteresis loops using the longitudinal and transverse magneto-optical Kerr effects under oblique light incidence and of magneto-optical phenomena under near-normal light incidence demonstrate that the corrugated structure surface leads to optical and magneto-optical anisotropies. The magnetization of such structures occurs via coherent magnetization rotation over a wide magnetic-field range. The magnetic anisotropy of these structures is described using a Gaussian distribution of easy axes of magnetization in cobalt granules about the direction parallel to the groove direction. The asymmetry of hysteresis loops of the rotation of the plane of polarization detected under oblique and normal light incidence is shown to be related to the contributions to the effective film permittivity that are quadratic in the magnetic moment.     

Deformation of magneto-optical structures in radiation of extended sources

Shape distortions of magneto-optical resonances in emission of an extended source are considered. The shape deformation of the magneto-optical structures is shown to be created by a longitudinal spatial inhomogeneity of the magnetic field. A simple procedure of taking into account distortions and of determining positions of resonances on the magnetic field scale and their widths is proposed.     

The nonlinear optical properties of a magneto-exciton in a strained Ga_(0.2)In_(0.8)As/GaAs quantum dot

The magnetic field-dependent heavy hole excitonic states in a strained Ga0.2In0.8As/GaAs quantum dot are investigated by taking into account the anisotropy,non-parabolicity of the conduction band,and the geometrical confinement.The strained quantum dot is considered as a parabolic dot of InAs embedded in a GaAs barrier material.The dependence of the effective excitonic g-factor as a function of dot radius and the magnetic field strength is numerically measured.The interband optical transition energy as a function of geometrical confinement is computed in the presence of a magnetic field.The magnetic field-dependent oscillator strength of interband transition under the geometrical confinement is studied.The exchange enhancements as a function of dot radius are observed for various magnetic field strengths in a strained Ga0.2In0.8As/GaAs quantum dot.Heavy hole excitonic absorption spectra,the changes in refractive index,and the third-order susceptibility of third-order harmonic generation are investigated in the Ga0.2In0.8As/GaAs quantum dot.The result shows that the effect of magnetic field strength is more strongly dependent on the nonlinear optical property in a low-dimensional semiconductor system.     

Application of longitudinal generalized magneto-optical ellipsometry in magnetic ultrathin films

The longitudinal generalized magneto-optical ellipsometry(GME) method is extended to the measurement of threelayer ultrathin magnetic films. In this work, the theory of the reflection matrix is introduced into the GME measurement to obtain the reflective matrix parameters of ultrathin multilayer magnetic films with different thicknesses. After that, a spectroscopic ellipsometry is used to determine the optical parameter and the thickness of every layer of these samples, then the magneto-optical coupling constant of the multilayer magnetic ultrathin film can be obtained. After measurements of a series of ultrathin Fe films, the results show that the magneto-optical coupling constant Q is independent of the thickness of the magnetic film. The magneto-optical Kerr rotations and ellipticity are measured to confirm the validity of this experiment. Combined with the optical constants and the Q constant, the Kerr rotations and ellipticity are calculated in theory. The results show that the theoretical curve fits very well with the experimental data.     

Magneto-optical activity of crude oil and its heavy fractions

We have experimentally studied optical and magneto-optical spectra of solutions of crude oils of different origin and their heavy fractions in the visible spectral range. Magnetic circular dichroism of oil in the wavelength range ??550 nm has been revealed. We show that the shape of the spectra of this dichroism depends on the origin of crude oil, with the magnetic dichroism magnitude being proportional to the concentration of the oil in the solution. A comparison of the data of magneto-optical spectroscopy with electron paramagnetic resonance spectra and chemical composition of samples has allowed us to conclude that the observed magneto-optical activity is determined by the occurrence of VO²⁺ complexes in the oil samples. The revealed magneto-optical activity of crude oil can form the basis of a unique method of analysis of the composition and properties of oils of different origin and heavy fractions thereof.     

Optical and magneto-optical properties of YIG and FeBO3

A survey of characteristic optical and magneto-optical properties of the representative ferrite materials yttrium iron garnet (YIG) and iron borate is presented. The interaction of light with collective magnetic excitations, leading to pronounced magnetooptical phenomena, is discussed. Typical examples for the strong influence of foreign atoms on optical and magneto-optical properties of YIG are also given.     

原子漏斗及其应用

文章简单介绍了磁、光原子漏斗的基本原理，详细综述了各种原子漏斗方案及其实验结果．这些漏斗方案主要包括采用红失谐高斯光束、蓝失谐消逝波光场和空心光束串联而成的光学原子漏斗，采用载流导线的静磁原子漏斗以及采用磁光凝胶构成的磁光原子漏斗．文章最后还简单介绍了原子漏斗在原子光学领域中的潜在应用．