基于光学全息的任意矢量光的生成方法

基于光学全息的角度复用特性, 根据空间光调制器对光场的相位和振幅调制原理, 通过加载产生任意矢量光所需要的相位分布, 设计了一种生成任意矢量光的方法. 该方法首先利用光学全息技术记录空间光调制器加载的相位, 从而制作一个全息光栅; 再现过程中, 两束具有相同入射角度的参考光照射全息光栅, 使得两束再现光相干叠加, 进而获得可调控的任意矢量光. 该方法能够避免复杂偏振态的出现, 并且具有生成光路简单、方便操作、生成矢量光的偏振纯度高等优势. 通过计算机模拟生成了任意矢量光, 获得了很好的效果.     

用于原子干涉仪的拉曼光的制备

原子干涉仪是利用原子物质波的特性而实现的干涉仪,广泛应用于精密测量领域.在原子干涉仪中,通过拉曼光对原子进行相干操作,拉曼光的质量直接影响着干涉仪的技术指标.基于注入锁定技术,采用普通半导体激光器、声光调制器,实现了功率、频率和位相稳定的拉曼光的制备,并对拉曼光的相位噪声技术指标进行了测试.     

Spatial correlation properties of apertured partially coherent beams propagating through atmospheric turbulence

The spatial correlation properties of apertured partially coherent beams propagating through atmospheric turbulence are studied in detail. By using the quadratic approximation of the Rytov’s phase structure function and the finite complex Gaussian expansion of the aperture function, the closed-form expression for the spectral degree of coherence of apertured partially coherent beams in turbulence is derived. It is shown that the larger the aperture width h is, and the smaller the spatial correlation length σ₀ of the source is, the less the spatial correlation is affected by turbulence. Specially, the influence of turbulence on the spatial correlation for unapertured partially coherent beams is less than that for apertured ones. The spectral degree of coherence is shown to possess phase singularities for apertured partially coherent beams, but the phase singularities behavior disappears when the turbulence is strong enough, which is very different from the behavior of unapertured partially coherent beams. In addition, a comparison between the width of the spectral degree of coherence and that of the spectral intensity of apertured partially coherent beams in turbulence is also given, and some interesting results are obtained. The results are interpreted physically. PACS  42.68.Bz; 42.79.Ag; 42.25.Fx     

相对论速调管放大器的相位特性研究

理论分析了影响相对论速调管放大器(RKA)输出微波相位的相关因素,同时采用粒子模拟程序分析了RKA输出微波相位随电压、束流、电子束尺寸、电子束前沿和延迟时间等电子束参数以及腔体和漂移管长度等几何参数的变化,另外还开展了RKA相位特性的初步实验研究. 研究结果表明,电压、束流和电子束尺寸的改变,会造成RKA相移的改变,引导磁场、电子束前沿和延迟时间以及注入微波功率在适当范围内改变不会造成明显的RKA相移改变. RKA的相位灵敏度为2.6°,相位抖动小于20°. 关键词： 相对论速调管放大器 相位特性 功率合成 高功率微波     

Rows of optical vortices from elliptically perturbing a high-order beam

An optical vortex (phase singularity) with a high topological strength resides on the axis of a high-order light beam. The breakup of this vortex under elliptic perturbation into a straight row of unit-strength vortices is described. This behavior is studied in helical Ince-Gauss beams and astigmatic, generalized Hermite-Laguerre-Gauss beams, which are perturbations of Laguerre-Gauss beams. Approximations of these beams are derived for small perturbations, in which a neighborhood of the axis can be approximated by a polynomial in the complex plane: a Chebyshev polynomial for Ince-Gauss beams, and a Hermite polynomial for astigmatic beams.     

半导体激光器远轴光束的准直特性研究

对半导体激光器光束准直场的研究具有重要的意义,半导体激光器的远轴模型能精确描述其发出的光束。根据瑞利索末菲衍射公式,利用稳相法得出了半导体激光器远轴光束经过透镜准直后的场分布解析表达式。根据该表达式可以得出如下结论:准直后光束在两个方向上的光斑大小与透镜焦距成正比,且与传输距离无关,沿轴光强与波导尺寸参量和准直透镜焦距有关,且与透镜焦距成平方反比关系,在传输距离较短的情况下,准直光场相位分布近似为球面,传输距离较长时,光场相位近似为平面.这些结论在工程应用中具有重要的价值。     

Generation of radially polarized beams using spatial light modulator

Radially polarized beams have attracted much attention and found many applications in many optical systems, recently. And generation of radially polarized beams is necessary for experimental research and applications. In this paper, a kind of generation method was proposed. Two beams are obtained by spatial light modulator and pi phase plate, and then interfere to form desirable radially polarized beams. Experimental results show that radially polarized beams are higher property, which shows this kind of interferential generation of radially polarized laser beams work effectively.     

Lateral shift of X-ray beams and determination of phase in reflectometry of multilayer periodic structures

Lateral shift of X-ray beams during Bragg’s reflection from a multilayer periodic structure (MS) is studied analytically and numerically. The field distribution in the MS, as well as the displacement of reflected and transmitted beams are determined. Analytic expressions for the shifts are derived in the approximation of spectrally narrow beams. Since the shift is controlled by the phase of the reflectance (transmittance), it is possible in principle to extract information concerning the phase of reflection (transmission) by measuring the spatial shift.     

External-cavity birefringence feedback effects of microchip Nd:YAG laser and its application in angle measurement

External-cavity birefringence feedback effects of the microchip Nd:YAG laser are presented. When a birefringence element is placed in the external feedback cavity of the laser, two orthogonally polarized laser beams with a phase difference are output. The phase difference is twice as large as the phase retardation in the external cavity along the two orthogonal directions. The variable extra-cavity birefringence, caused by rotation of the external-cavity birefringence element, results in tunable phase difference between the two orthogonally polarized beams. This means that the roll angle information has been translated to phase difference of two output laser beams. A theoretical analysis based on the Fabry--Perot cavity equivalent model and refractive index ellipsoid is presented, which is in good agreement with the experimental results. This phenomenon has potential applications for roll angle measurement.     

STED microscopy based on axially symmetric polarized vortex beams

A stimulated emission depletion(STED) microscopy scheme using axially symmetric polarized vortex beams is proposed based on unique focusing properties of such kinds of beams. The concept of axially symmetric polarized vortex beams is first introduced, and the basic principle about the scheme is described. Simulation results for several typical beams are then shown, including radially polarized vortex beams, azimuthally polarized vortex beams, and high-order axially symmetric polarized vortex beams. The results indicate that sharper doughnut spots and thus higher resolutions can be achieved, showing more flexibility than previous schemes based on flexible modulation of both phase and polarization for incident beams.     

用四台阶相位板产生涡旋光束

涡旋光束的产生与应用是当前光学领域的研究热点. 利用傅里叶级数展开法分析了四台阶相位板的相位结构, 发现四台阶相位板可看作是由一系列不同拓扑荷数的螺旋相位板所组成, 用线偏振光直接照射相位板时, 将产生多级衍射光波, 各级衍射光均为不同拓扑荷数的涡旋光波, 由于多级衍射光波间的干涉导致光强分布偏离轴对称分布, 因而与涡旋光波有一定差距. 在此基础上, 提出了用四台阶相位板产生涡旋光束的新方案, 借助于Mach-Zehnder 干涉仪光路, 两块四台阶相位板产生的衍射光干涉叠加, 通过调节干涉仪光路的相位差, 使一部分衍射级干涉相消, 另一部分衍射级干涉相长, 相互加强, 从而把线偏振光转换为涡旋光束. 数值模拟计算了几种周期数不同的四台阶相位板衍射光强和角动量分布, 并与螺旋相位板进行比较, 证明用简单的四台阶相位板不仅能够获得与用螺旋相位板相同的涡旋光束, 而且可以用周期数较小的四台阶相位板产生具有大拓扑荷数的涡旋光束, 降低了制作相位板的难度.     

Phase singularity annihilation of focused partially coherent beams

Expressions for focused Gaussian Schell-model (GSM) beams are derived and used to study the annihilation and subwavelength structures of phase singularities in the focal region, and to compare with the case of fully coherent Gaussian beams. It is found that the truncation parameter δ and normalized coherence length ε both affect the presence and spatial distribution of phase singularities in the focal plane. Additionally, during the creation and annihilation process the saddle point near the phase singularity does not disappear in the focal plane for GSM beams.     

Propagation properties of apertured laser beams with amplitude modulations and phase fluctuations through atmospheric turbulence

The propagation properties of apertured laser beams with amplitude modulations (AMs) and phase fluctuations (PFs) through atmospheric turbulence are studied in detail both analytically and numerically. The analytical expressions for the average intensity, power in the bucket (PIB) and Strehl ratio (S _R ) of apertured laser beams with AMs and PFs propagating through atmospheric turbulence are derived. It is found that the worse the phase fluctuation and the higher the amplitude modulation are, the less laser beams are affected by turbulence. Furthermore, apertured Gaussian beams are more sensitive to turbulence than apertured laser beams with AMs and PFs. The average intensity of apertured laser beams with AMs and PFs may be even larger than that of apertured Gaussian beams due to turbulence. In particular, the influence of turbulence on the average maximum intensity of apertured laser beams with PFs and AMs may become serious if an unsuitable truncated parameter is chosen, which should be avoided in practice.     

Generation of hollow beams by using a binary spatial light modulator

We demonstrate the generation of hollow laser beams by using a binary spatial light modulator and compare the results with those for a continuous modulator. The binary phase modulator produces beams that have continuous, azimuthally varying phase profiles and can be dynamically changed with kilohertz refresh rates. The intensity and phase profiles are recorded through the focus of an imaging lens and are compared with scalar diffraction theory. We highlight properties of the beams relevant to optical dipole traps.     

高阶涡旋光束生成技术研究

应用液晶空间光调制器加载螺旋相位片的方法可以高效地生成涡旋光束,但由于液晶空间光调制器分辨率有限,在加载高阶螺旋相位片时其中心会出现相位失真,造成涡旋光束质量不高。通过在螺线相位片中心区域引入闪耀光栅的方法,得到了光束质量较高的高阶单模涡旋光束和多模涡旋光束,为生成高阶涡旋光束提供了一种很好的方法。     

Propagations of Airy Beams and Nonlinear Accelerating Optical Beams in Photorefractive Crystals with Asymmetric Nonlocality

The impact of the asymmetric nonlocal diffusion nonlinearity of Airy beams and nonlinear accelerating beams supported by photorefractive crystals is addressed. It is revealed how the asymmetric nonlocal response alters the evolution of these optical beams. It is found that the evolution of these beams presents a bending action under the influence of the diffusion nonlinearity. It is also shown that nonlinear accelerating beams can exist in photorefractive crystals with asymmetric nonlocality. These accelerating solutions have the same Airy‐like tail, and accelerate along parabolic trajectories. Soliton states are formed in the interaction of both in‐phase and out‐of‐phase Airy beams and nonlinear accelerating beams and also present a bending action because of the action of diffusion nonlinearity.     

Vortex–edge dislocation interaction in second-order nonlinear media

Experimental and theoretical results on second harmonic generation with fundamental beams containing both a vortex and an edge phase dislocations are reported. The 3D trajectories in the fundamental and second harmonic beams are calculated for different distances between the dislocations in the input beam. It is shown that each phase dislocation in the second harmonic beam appears as a result of the joint actions of all phase dislocations in the fundamental beam.     

大气湍流对部分相干电磁平顶光束传输的影响

基于相干性和偏振性统一理论,采用Rytov相位结构函数平方近似推导出了部分相干电磁平顶光束在湍流大气中传输的偏振度、相干度和光谱强度公式,并研究了湍流对其传输特性的影响.研究表明,偏振度和相干度与源光谱的带宽无关.大气湍流使得不同阶数的部分相干电磁平顶光束的偏振度经长程传输后均趋于其初始值.大气湍流使得部分相干电磁平顶光束与电磁高斯-谢尔模型光束相干度的差别减小,并导致相干度的振荡和相位奇异现象消失.大气湍流使得相干性较好的部分相干电磁平顶光束的光谱跃变现象消失.     

大气风速对大气传输光束相位特性的影响

采用功率谱反演法构建湍流相位屏,通过横向平移相位屏的方法模拟大气风速引起的湍流时间变化,进而模拟分析了包括时间进程的激光大气传输特性,从波前相位功率谱密度的角度,定量分析了大气风速引起的激光束在大气湍流中传输时的相位特性变化。在此基础上,采用影响函数模拟变形镜对畸变波前的校正作用,对激光束经大气湍流传输后的自适应校正效果进行了预估,分析了大气风速对校正效果的影响。结果表明,大气风速对边界层湍流中光束相位特性的影响很小,然而,对于自由大气湍流中的传输光束,大气风速越大,波前相位畸变程度越大,畸变波前中高频相位比例也越大;环状光束的校正效果受大气风速的影响比平顶光束更小,并且,随着环状光束阶数的增大,校正效果所受影响逐渐减小;在一定相位畸变范围内,畸变程度越大的环状光束的相位校正效果受大气风速的影响越小。     

Focusing properties of Gaussian beam with mixed screw and conical phase fronts

Vector diffraction theory is employed to investigate the focusing properties of the Gaussian beams with mixed screw and conical phase fronts. Numerical simulations show that the Gaussian beams with screw-conical phase fronts are different from both the ordinary Laguerre-Gaussian beams and the higher-order Bessel beams. Rather than forming the ring-shaped intensity distributions characteristic of optical vortices, focusing the Gaussian beams with screw-conical phase fronts produce non-symmetric spiral intensity distributions at the focal plane. The intensity distribution forms a counter-clockwise non-symmetric screw path around the focus. The rotation of intensity distributions was observed in the focal plane. The gradient force patterns of these beams focused with high NA are also investigated. The results show that the gradient force pattern shape depends principally on parameter topological charge n of the phase distribution. The gradient force pattern expands with increase in the parameter m of the phase distribution. Therefore, one can change the topological charge n or the parameter m of the phase mask to construct the tunable optical trap to meet different requirements. Its potential application might include rotational positioning of particles and accumulation of smaller non-symmetric particles towards the focus.