拉盖尔高斯光的衍射和轨道角动量的弥散

根据菲涅耳衍射积分和拉盖尔高斯光束场强分布,对拉盖高斯光束中的圆孔衍射、单缝衍射和方孔衍射进行了研究,并分析了拉盖高斯光束的相位结构对光束衍射后场分布的影响。拉盖高斯光束的相位奇点落在衍射孔中心时,由螺旋谱计算出拉盖高斯光束通过单缝和方孔衍射后的轨道角动量的弥散程度,从理论上证明了拉盖尔高斯光束通过圆孔衍射后,轨道角动量不发生弥散。     

涡旋光束与相位全息光栅不对准时的衍射特性研究

研究了涡旋光束与相位全息光栅不对准时衍射光束的解析特性.利用理论推导的方法得出涡旋光束经相位全息光栅接收后一阶衍射光束的解析表达式.然后通过仿真分析分别得出在发生正常对准、横向偏移、角向倾斜及横向偏移和角向倾斜两者同时出现时衍射光束的质心偏移特性和中心强度变化特性.研究表明: 拉盖尔-高斯光束经相位全息光栅衍射后得到的光场表达式为合流超几何函数形式.光束与相位全息光栅间的不对准会引起衍射光束质心的偏移,而且光束质心的偏移量随入射光束偏移距离和偏离角的增加而增加,与入射光束的偏移方向和方位角无关.角向倾斜时 关键词： 拉盖尔-高斯光束 相位全息光栅 横向偏移 角向倾斜     

大气湍流信道中聚焦涡旋光束轨道角动量串扰特性

携带轨道角动量的涡旋光束作为传输信息的载体能有效提高信息传输效率,然而在传输过程中受大气湍流影响轨道角动量会发生串扰.基于螺旋谱分析理论,推导得到了聚焦拉盖尔高斯光束在各向异性大气湍流中传输时的螺旋谱解析表达式,并对比分析不同湍流和光束参数对聚焦与非聚焦拉盖尔高斯光束接收功率的影响,最后利用多相位屏法进行模拟验证.结果表明:随着传输距离、湍流强度、拓扑荷数的增大以及湍流内尺度、光束波长的减小,接收功率减小,轨道角动量串扰增大;接收孔径到达一定值时对轨道角动量串扰的影响非常小;聚焦光束比非聚焦光束的轨道角动量串扰要小.这些结果将对提高自由空间光通信的质量有一定意义.     

在大气湍流斜程传输中拉盖高斯光束的轨道角动量的研究

大气湍流引起大气折射率随机变化,导致空间不均匀性.拉盖高斯光束在大气湍流中传输时,空间不均匀性会使光子波函数改变,引起轨道角动量的变化.本文讨论了拉盖尔高斯光束在大气斜程传输时,湍流介质改变光子轨道角动量而形成不同的光子态.计算了螺旋谐波各分量所占光束总能量的权重,分析了拉盖高斯光束的轨道角动量的变化规律.     

拉盖尔-高斯光束在湍流大气中的螺旋谱特性

研究了拉盖尔-高斯光束在湍流大气中的传输特性.在利托夫近似下,得到接收孔径处光束的螺旋谱的积分表达式.通过数值仿真得出大气湍流对光束螺旋谱的影响以及光束螺旋谱随各参数值的变化特性.仿真发现大气湍流会使螺旋谱发生弥散.而且随着拓扑荷,接收孔径半径,折射率结构函数及距离的增加,螺旋谱弥散加剧.经拟合得到描述螺旋谱弥散程度的无量纲方差V随距离成6次函数关系;与接收孔径半径及折射率结构函数成二项式关系;而与拓扑荷呈11次多项式关系.最后得出径向指数,束腰半径对螺旋谱的影响非常小,并且根据此结论推出光 关键词： 拉盖尔-高斯光束 大气湍流 螺旋谱 无量纲方差     

汉克-贝塞尔光束在海洋湍流信道中的螺旋相位谱分析

携带轨道角动量的汉克-贝塞尔(Hankel-Bessel,HB)光束具有无衍射和自聚焦特性,用来作为信息传输的载体有望增大信息传输容量.基于Rytov近似理论,推导得到了HB涡旋光束经过海洋水平弱湍流信道后的螺旋相位谱的解析表达式,并利用数值仿真方法研究了海洋湍流参数对轨道角动量模式探测概率的影响.结果表明,海洋湍流导致发射轨道角动量模式的探测概率下降,出现模式串扰和螺旋相位谱扩展.海洋湍流对HB涡旋光束的负面影响随着轨道角动量模式数、传输距离、温度方差耗散率的增加而增强,随湍流动能耗散率的增加而减弱.HB涡旋光束受以盐度波动驱动的海洋湍流的负面影响更大.另外,在弱湍流及几十米传输距离条件下,HB涡旋光束的传输性能要差于最佳束腰大小设置的拉盖尔-高斯涡旋光束.这些结果有望为海洋环境水下光通信链路的实现提供一定的参考价值.     

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     

光学涡旋横向线动量密度的传输演化特性

对于光学涡旋特别是具有复杂拓扑结构的光学涡旋,可以通过数值计算的方法获得实验上难以准确测量的角动量分布及其传输演化特性。在略去线偏振光场线动量密度中的轴向分量的情况下可获得涡旋光场的横向线动量密度,其在光束截面上的角向分量表征了涡旋角动量的分布。通过数值模拟,研究了单束拉盖尔-高斯光束和拓扑荷不同的两束拉盖尔-高斯光束同轴叠加后在自由空间中的传播过程,获得了强度分布、相位分布和横向线动量密度在瑞利长度内的分布特征。通过分析光束横截面上强度分布和线动量密度的演化特性表明,在远离束腰处光束的衍射效应不仅降低了横向线动量密度,还会增加径向分量,因而增强了径向力学特性,减弱了角向力学特性,因此在具体实施微操控时不宜在距离束腰面较远的横截面内进行。     

高阶椭圆厄密–高斯光束的轨道角动量研究

从傍轴条件下光束轨道角动量的基本理论出发,根据高阶椭圆厄密–高斯光束的光场分布,运用张量方法,对高阶椭圆厄密-高斯光束轨道角动量的密度分布进行了理论分析,得到了求解该密度分布的计算公式,并在给定参量条件下作了数值模拟.进一步对光束中每个光子携带的平均轨道角动量进行了计算,发现其值随着椭圆厄密-高斯光束阶次的增大而增大,表明高阶椭圆厄密-高斯光束能够比椭圆高斯光束或拉盖尔-高斯光束提供高得多的轨道角动量.     

螺旋轴棱锥的光束传输特性

 分析了螺旋轴棱锥的结构和光传输特性,基于衍射积分理论研究了发散球面波和拉盖尔-高斯光束经螺旋轴棱锥后的传输过程。研究表明,发散球面波经过螺旋轴棱锥后产生贝塞尔光束,其阶数与拓扑电荷数相同,但中心光斑（空心光斑）半径随传输距离的增加而变大;拉盖尔-高斯光束入射后同样产生贝塞尔光束,但其阶数变为拉盖尔-高斯光束和螺旋轴棱锥的拓扑电荷数之和,出射光束的拓扑电荷数与阶数相等。     

Propagation of a Lorentz-Gauss beam through a misaligned optical system

Based on the generalized integral formula and the convolution theorem of the Fourier transform, an analytical propagation formula of a Lorentz-Gauss beam passing through a misaligned paraxial optical system is derived. As numerical examples, the propagation properties of a Lorentz-Gauss beam through a misaligned thin lens with the lateral displacement and the angle displacement are graphically illustrated, respectively. The influences of the lateral displacement and the angle displacement of the misaligned thin lens on the normalized light intensity and the phase distributions are also examined, respectively.     

分划板失调时猫眼系统的反射特性

为降低光电装备猫眼效应,减小光学窗口被激光主动侦察系统探测到的概率,对分划板失调情况下猫眼系统的反射特性进行了研究。基于几何光学与2维平面波角谱衍射理论,推导并仿真了平面波通过分划板失调猫眼系统在出射面上的衍射光场分布特性,实验验证了猫眼目标的反射特性。研究结果表明:分划板失调会导致猫眼系统出射面的回波光斑发生椭圆形变,而斜入射探测激光会使这一现象更加明显。利用这一特性对猫眼系统进行改进,会大大增加激光主动侦察系统区分形变猫眼目标和漫反射背景干扰的难度。     

Misalignment measurement of optical vortex beam in free space

The misalignment of optical vortex(OV) beams, including transversal displacement and tilt, occurs in many situations, including on reflection or refraction at an interface between two different media and in propagation and tracking systems for optical communications. We propose a reliable method to determine and subsequently eliminate tilt and transversal displacement in an OV beam. An experimental setup was established to verify the proposed method, and the experimental results showed good agreement with those of the numerical simulations.Using the measured misalignments, the initial orbital angular momentum spectrum can be recovered in free space.     

Propagation analysis of flattened circular Gaussian beams with a misaligned circular aperture in turbulent atmosphere

The propagation properties of flattened Gaussian beam with a misaligned circular aperture in turbulent atmosphere have been studied by using the extended Huygens-Fresnel formula. From the study and numerical calculation, the effects of aperture parameters on the propagation properties of flattened Gaussian beams in turbulent atmosphere have been illuminated. The results show that angle misalignments and lateral displacements of aperture create unsymmetrical average intensity distribution at any cross section. The intensity distributions are much more sensitive to the lateral displacement than to the angle misalignments. And the propagation properties of different flattened Gaussian beams in turbulent atmosphere are also compared.     

轴锥镜光强分布的角谱衍射数值分析法

针对理论上推导轴锥镜的衍射光场分布解析式较为困难,且用菲涅耳衍射理论分析时存在近轴近似及不能适用于近场衍射光场分析的问题,采用了严格遵从标量衍射亥姆霍兹方程的角谱衍射波前重建方法,对轴锥镜在单色和准单色高斯光波照射下的横向和轴向衍射光强分布特性,以及在单色均匀平面光波照射下的轴向衍射光强分布进行了数值计算和分析。结果表明,轴锥镜后单色光衍射光强分布在几何光束重叠的菱形区域内为近似无衍射贝塞尔光强分布,轴上光强沿光轴方向呈振荡变化,轴上光强分布规律与入射光波的垂轴横向光强分布有关;入射光的准单色性使得贝塞尔衍射条纹对比度略下降、轴上光强沿光轴方向振荡程度减小,但分布规律与单色光一致。     

Study on holographic grating diffraction for Laguerre--Gaussian beam generation

Laguerre-Gaussian beams, as a special model with spiral phase structure, have been intensively investigated. Holographic grating method is a convenient method of generating Laguerre-Gaussian beams and measuring their orbital angular momenta. But due to some inevitable adverse factors such as lateral displacement, angular deflection and elliptical incident profile of incident beam, the practical effectiveness should be reevaluated. This paper is devoted to the study on the influences of the abovementioned three adverse factors on the holographic grating method. The characteristics of the mode decomposition of diffractive order and the relative powers of the orbital angular momentum eigen-states are also given.     

Angular Dependence of Lateral and Levitation Forces in Asymmetric Small Magnet/Superconducting Systems

The dipole-dipole interaction model is used to calculate the angular dependence of lateral and levitation forces on a small permanent magnet and a cylindrical superconductor in the Meissner state lying laterally off the symmetric axis of the cylinder. Under the assumption that the lateral displacement of the magnet is small compared with the physical dimensions of the system, we obtain analytical expressions for the lateral and levitation forces as functions of geometrical parameters of the superconductor as well as the height, the lateral displacement and the orientation of magnetic moment of the magnet. The effect of thickness and radius of the superconductor on the levitation force is similar to that for a symmetric magnet/superconducting cylinder system, but within the range of lateral displacement. The splitting in the levitation force increases with the increasing angle of orientation of the magnetic moment of the magnet. For a given lateral displacement of the magnet, the lateral force vanishes when the magnetic moment is perpendicular to the surface of the superconductor and has a maximum value when the moment is parallel to the surface. For a given orientation of the magnetic moment, the lateral force has a linear relationship with the lateral displacement. The stability of the magnet above the superconducting cylinder is discussed in detail.     

Modeling of Coulomb coupling and acoustic wave propagation in LiNbO3

The angular spectrum propagation technique is applied to modeling of wave propagation through piezoelectric media. The calculations of the angular spectrum propagator are based on the relevant equation for the slowness surface resulting from the solution of the Christoffel equation with piezoelectrically stiffened elastic constants. A two-dimensional FFT algorithm is applied in the final field superposition. We concentrate on the case of Coulomb coupling through local electrical point contacts on both the excitation and detection side. To model that case we superpose solutions for acoustic Green's functions of different propagation modes convoluted with equivalent distributed effective sources. Calculated results are in good agreement with the measured ones.