暗中空光束的产生及应用

综述了几何光学、模式变换、光学全息、计算全息、横模选择、中空光纤等几种产生暗中空光束的方法,并简单介绍了暗中空光束在原子光学及其他领域的应用。     

中性原子的激光导引及其应用

文章综述了采用中空光纤中红失谐高斯模式,红失谐高斯激光束,中空光纤中蓝失谐消逝波和蓝失谐暗中空光束实现中性原子激光导引的原理,方法和实验及其最新进展,并简单介绍了激光导引原子技术在原子光学领域中的应用。     

利用具有轨道角动量的光束实现微粒的旋转

采用扭转柱面镜光学系统将半导体激光抽运固体激光器产生的厄米高斯光束变换成为具有轨道角动量的扭转对称光束.利用该光束具有的轨道角动量特性研制成功了“光学扳手”， 利用“光学扳手”实现了对微米量级微粒的俘获和旋转. 关键词： 轨道角动量 扭转对称光束 光学扳手 光束变换     

用波晶片相位板产生角动量可调的无衍射涡旋空心光束

本文提出了一种用波晶片产生无衍射涡旋空心光束的新方案. 根据晶体双折射的性质, 设计波晶片的厚度, 在一块晶体薄片上对o光和e光分别形成各自的四台阶相位板, 线偏振光入射到该相位板后, o光和e光衍射按强度叠加, 利用准伽利略望远镜系统聚焦, 得到近似无衍射涡旋空心光束. 光路简单, 调节方便. 在近轴条件下, 运用菲涅耳衍射理论和经典电磁场角动量理论, 数值模拟计算了周期数不同的两块波晶片相位板衍射光强和角动量的分布, 结果表明: 两块相位板都能在较长距离内产生近似无衍射涡旋空心光束, 光强和轨道角动量的分布与螺旋相位板产生的涡旋光束基本相同. 在衍射光路中加入相位补偿器, 调节o光和e光的相位差可以调节自旋角动量的大小, 从而可以调节总角动量密度和平均光子角动量的大小. 用这种空心光束导引冷原子或冷分子, 原子在与光子相互作用过程中可获得可调的转动力矩.     

产生纳米级暗中空光束的方法研究

用时域有限差分法，给出光纤头近场区电场强度模的空间分布.讨论了当光纤纤芯分别取不同尺寸时，对此空间光场强度的影响.要想得到较大范围的暗中空光束，必须增加光纤纤芯尺寸.并且，对光纤纤芯尺寸取一较大值和光纤中空区域尺寸取一较小值时的情况进行讨论，可得在光纤头附近可以出现与光纤中空区域尺寸大小相当的暗斑(10¹ nm量级).但是，暗中空光束中背景光较强.为此，将光纤的空心设计为金属. 发现此时中心暗斑的背景光明显减弱，在近场区域可获得较为理想的暗中空光束.如进一步缩小光纤中空区域尺寸，可以在光纤头附近获得暗斑更小甚至纳米量级的暗中空光束.为获得一种纳米量级的暗中空光束提供一种方法.     

扭转对称光束的产生及其变换过程中的轨道角动量传递

研究了采用扭转柱面镜光学系统将厄米-高斯光束变换成为具有轨道角动量的拉盖尔-高斯扭转对称光束. 采用本征模式分解的方法分析了扭转柱面镜光学变换系统实现光束变换的原理.利用光束传输矩阵和二阶矩理论分析计算了光束经过扭转柱面透镜变换过程中的轨道角动量传递过程，证明光束与透镜系统的轨道角动量交换发生在第一个柱面透镜处，光束经过第一个柱面透镜后，具有的轨道角动量保持不变. 关键词： 轨道角动量 光束变换 扭转对称光束 轨道角动量传递     

利用光束的轨道角动量实现高密度数据存储的机理研究

光束的轨道角动量本征态可以构建高维Hilbert空间，将之应用于数据存储中，可以实现比传统方法更高的数据存储密度.提出了一种用光束轨道角动量实现高密度数据存储的方法，对存储区域进行相位编码，通过探测透射光束轨道角动量谱(螺旋谱)的特征来区分由相位编码形成的不同数据态.四台阶结构相位编码可以实现57个不同的数据态，有望将数据密度提高为传统方法的近6倍. 关键词： 光束轨道角动量 光学存储 高密度存储     

空心光束的产生及其在现代光学中的应用

近年来,随着激光应用技术的发展,各种中心强度为零的激光束被相继产生,并正在形成一个新颖的所谓空心光束(也称暗中空光束)的大家族。作为激光导管、光学镊子(光钳)和光学扳手,空心光束在微观粒子(如微米粒子、纳米粒子、自由电子、生物细胞和原子或分子等)的精确、无接触操纵和控制中有着广泛的应用。本文将首先给出空心光束的定义及其参数,并详细介绍各种空心光束产生的基本原理、方法及其实验结果。其次,就空心光束的分类及其应用场合进行了简单归纳与讨论。最后就空心光束在微观粒子(包括微米粒子、纳米粒子、生物细胞和自由电子等)的光学囚禁与操控中的应用进行简要综述,并就空心光束的产生与应用及其未来研究与应用前景进行了简短总结与展望。     

利用振幅光栅生成拉盖尔-高斯光束的实验研究

拉盖尔高斯(Laguerre-Gaussian,LG)光束由于其独特的相位结构和轨道角动量特性在微粒旋转操纵和信息处理等方面得到了越来越多的重视.对利用振幅型叉状衍射光栅产生LG光束进行了理论分析,采用计算全息图的方法制作了振幅型叉状衍射光栅,实验上获得了角量子数为±1的LG光束,并对光束变换过程中影响光束特性的主要因素进行了讨论. 关键词： 信息光学 拉盖尔高斯光束 计算全息光栅 光束轨道角动量     

空心光束的产生及其在现代光学中的应用

近年来,随着激光应用技术的发展,各种中心强度为零的激光束被相继产生,并正在形成一个新颖的所谓空心光束(也称暗中空光束)的大家族。作为激光导管、光学镊子(光钳)和光学扳手,空心光束在微观粒子(如微米粒子、纳米粒子、自由电子、生物细胞和原子或分子等)的精确、无接触操纵和控制中有着广泛的应用。本文将首先给出空心光束的定义及其参数,并详细介绍各种空心光束产生的基本原理、方法及其实验结果。其次,就空心光束的分类及其应用场合进行了简单归纳与讨论。最后就空心光束在微观粒子(包括微米粒子、纳米粒子、生物细胞和自由电子等)的光学囚禁与操控中的应用进行简要综述,并就空心光束的产生与应用及其未来研究与应用前景进行了简短总结与展望。     

On the non-synchronous rotation of binary systems

During the evolution of the binary system,many physical processes occur,which can influence the orbital angular velocity and the spin angular velocities of the two components,and influence the non-synchronous or synchronous rotation of the system.These processes include the transfer of masses and angular momentums between the component stars,the loss of mass and angular momentum via stellar winds,and the deformation of the structure of component stars.A study of these processes indicates that they are closely related to the combined effects of tide and rotation.This means,to study the synchronous or non-synchronous rotation of binary systems,one has to consider the contributions of different physical processes simultaneously,instead of the tidal effect alone.A way to know whether the rotation of a binary system is synchronous or non-synchronous is to calculate the orbital angular velocity and the spin angular velocities of the component stars.If all of these angular velocities are equal,the rotation of the system is synchronous.If not,the rotation of the system is non-synchronous.For this aim,a series of equations are developed to calculate the orbital and spin angular velocities.The evolutionary calculation of a binary system with masses of 10M⊙+6M⊙shows that the transfer of masses and angular momentums between the two components,and the deformation of the components structure in the semidetached or in the contact phase can change the rotation of the system from synchronous into non-synchronous rotation.     

Angular momentum of a magnetically trapped atomic condensate

For an atomic condensate in an axially symmetric magnetic trap, the sum of the axial components of the orbital angular momentum and the hyperfine spin is conserved. Inside an Ioffe-Pritchard trap (IPT) whose magnetic field (B field) is not axially symmetric, the difference of the two becomes surprisingly conserved. In this Letter we investigate the relationship between the values of the sum or difference angular momentums for an atomic condensate inside a magnetic trap and the associated gauge potential induced by the adiabatic approximation. Our result provides significant new insight into the vorticity of magnetically trapped atomic quantum gases.     

Stresses and strains in a deformable fractal medium and in its fractal continuum model

The model of fractal continuum accounting the topological, metric, and dynamic properties of deformable physical fractal medium is suggested. The kinematics of fractal continuum deformation is developed. The corresponding geometric interpretations are provided. The concept of stresses in the fractal continuum is defined. The conservation of linear and angular momentums is established. The mapping of mechanical problems for physical fractal media into the corresponding problems for fractal continuum is discussed.     

The fine structure splitting of the level of lithium in Rydberg states

The Hamiltonian of the four-body problem for a lithium atom is expanded in series. The level shift and level formula of a lithium atom in Rydberg states are achieved by means of the calculation of polarization of the atomic core (including the contribution of dipole, quadrupole and octupole components). We also consider the effect of relativity theory, the orbital angular momentum L and the spin angular momentum S coupling scheme (LS coupling) and high-order correction of the effective potential to the level shift. The fine structure splitting (N=5-12, L=4-9, J=L±1/2) and level intervals in Rydberg states have been calculated by the above-mentioned formula and compared with recent experimental data.     

Transverse energy flows in vectorial fields of paraxial beams with singularities

A general study of transverse energy flows (TEF) as physically meaningful and informative characteristics of paraxial light beams’ spatial structure is presented. The total TEF can be decomposed into the spin and orbital contributions giving rise to the spin and orbital angular momentums, correspondingly. Definitions and properties of these constituents are discussed in relation with the optical field representation through linear and circular orthogonal polarization bases. With the help of model examples, the results are applied to investigation of TEF singularities in connection with the usual polarization morphology characteristics of paraxial optical fields. An analysis of TEFs near singular points has been carried out; in particular, the behavior of TEF and its partial contributions near polarization singularities (C-points) has demonstrated the special role of a boundary flow in the origin of the spin angular momentum. The analytical and experimental applicability of the introduced concepts are discussed.     

Yb的激光三步激发自电离谱

用激光三步共振激发研究Yb原子的自电离谱,测得能量在50443一57750cm^-1范围内的16个自电离能级。并用偏振光技术测定两个自电离态的J值。 关键词：     

Gravitational Corrections to Energy-Levels of a Hydrogen Atom

The first-order perturbations of the energy levels of a hydrogen atom in central internal gravitational field are investigated. The internal gravitational field is produced by the mass of the atomic nucleus. The energy shifts are calculated for the relativistic 1S, 2S, 2P, 3S, 3P, 3D, 4S, and 4P levels with Schwarzschild metric. The calculated results show that the gravitational corrections are sensitive to the total angular momentum quantum number.     

Calculation of the fine structure of the level in Rydberg state of lithium

The level shift and level formula of lithium atom in Rydberg states are achieved by means of the calculation of polarization of the atomic core (including the contribution of dipole moment, quadrupole moment and octupole moment);meanwhile, the effect of relativity theory, the orbital angular momentum L and the spin angular momentum S coupling (LS coupling), and high order correction of the effective potential are considered. The some fine structures (N=5～12,L=4～9,J=L±1/2) and the corresponding level intervals in Rydberg states can be calculated by the above-mentioned level formula and compared with correlated experimental data.     

Velocity map imaging study of OCS photodissociation followed by S(1S) autoionization at 157 nm

Atomic sulphur ions (S+) were observed directly by crossing a carbonyl sulphide (OCS) molecular beam with a F2 laser. In this study both S+ ion and electron images were measured using the velocity map imaging technique. The results imply that S+ is produced from the well-known photodissociation of OCS at 157 nm leading to the dominant S(1S) + CO(1Σ+) channel, and then the excited S(1S) atom is directly ionized by another 157 nm photon. Correlated vibrationally resolved angular distributions and internal energy distribution of the CO coproducts are reported here and compared with previous studies. This experiment yields strong and sharp S+ images which may be useful for calibrating any imaging or laser ionization apparatus when using a 157 nm laser. A number of technical aspects such as corrections for partial slicing and imperfect laser polarization are described. Abstraction of product angular distributions using both polarized and unpolarized photolysis lasers is also demonstrated using velocity map imaging.     

Angular correlation studies of heavy-particle impact excitation of atoms

A review is given of recent developments of angular correlation studies of heavy-particle impact excitation of atoms and molecules. After a brief discussion of the basic principles of experimental methods a theory of measurement of angular correlations from heavy-particle atom collisions is outlined in the following way. By applying angular correlation measurements a subensemble from the collision processes is selected which is described by state and scattering parameters. These parameters (scattering amplitudes and their phases, alignment and orientation, state multipoles and coherence parameters) can be connected with the experimental angular correlation data. Results from heavy-particle angular correlations have been discussed in separate sections with ions or atoms as projectiles; subsections are dealing with charge exchange excitation, excitation of autoionizing states, direct and simultaneous excitation of target and projectile particles. The angular correlation parameters are very sensitive to the detailed excitation mechanisms and quasi-molecular parameters in heavy-particle atom collisions. The majority of data available so far were obtained from simple projectile-target systems such as one-electron atom systems and are rare gas atoms. Attention is drawn to possible spin-orbit effects in the analysis of angular correlations from collisions between very heavy atomic particles.