水下轨道角动量态传输特性的实验研究

通过实验方法研究轨道角动量(OAM)态水下传输特性。首先搭建OAM态水下光通信系统,然后通过OAM态展开谱和接收到的初始及其相邻OAM态概率变化曲线来研究其水下传输能力。实验结果表明:随着盐度的增加,初始OAM态的概率明显降低;相邻OAM态的传输概率随着拓扑荷间隔的增加而减少。     

角动量算符与轨道波函数

稀土元素、锕系元素的价电子都处于f态,研究价电子轨道角动量问题是量子力学中重要的课题.在量子力学教科书中只给出了氢原子L_2、L_z算符共同本征矢的递推公式,没有计算出L_x、L_y的本征矢;只给出了氢原子的s、p和d电子L_2、L_z算符共同本征矢,没有给出f电子L_2、L_z算符共同本征矢.本文运用表象理论和氢原子L_2、L_z本征矢的递推公式不仅求出了氢原子f电子L_2、L_z算符的共同本征矢,而且还计算出氢原子f电子L_x、L_y的本征矢,并讨论了它们的有关性质.这对于全面了解氢原子电子轨道运动的细节是有好处的,完善了教科书中的不足.     

声子角动量与手性声子

在经典的物理学理论中,声子广泛地被认为是线极化的、不具有角动量的.最近的理论研究发现,在具有自旋声子相互作用的磁性体系(时间反演对称性破缺)中,声子可以携带非零的角动量,在零温时声子除了具有零点能以外还带有零点角动量;非零的声子角动量将会修正通过爱因斯坦-德哈斯效应测量的回磁比.在非磁性材料中,总的声子角动量为零,但是在空间反演对称性破缺的六角晶格体系中,其倒格子空间的高对称点上声子具有角动量,并具有确定的手性;三重旋转对称操作给予声子量子化的赝角动量,赝角动量的守恒将决定电子谷间散射的选择定则;此外还理论预测了谷声子霍尔效应.     

轨道角动量模式识别方法综述

光子轨道角动量具有涡旋和高维特性,在经典和量子领域有巨大应用潜力,目前在光学系统中有多种轨道角动量识别方法,常见的方法有以下8种:干涉仪法、镜像干涉法、平面波干涉法、角双缝干涉法、三角孔衍射法、计算全息光栅法、光学几何变换法和旋转多普勒效应法.本文详细介绍了8种方法的实验原理、实验装置、实验结果及现阶段的研究成果.     

轨道角动量光的区分

载有轨道角动量(OAM)的光可用于提高光通信网络的带宽,而对不同轨道角动量态的区分是有效利用轨道角动量光的核心。利用空间光调制器设置合适的传递函数以实现傅里叶平面间的光学坐标变换。变换后,轨道角动量光随方位角的相位变化变成横向相位变化。相位修正后将不同轨道角动量的光聚焦到不同的横向位置,实现了对轨道角动量光的有效区分。     

复杂像散椭圆光束的轨道角动量的实验研究

提出一种直接测量光束的轨道角动量的方法，其原理是把具有轨道角动量的光束照射到一个金属靶上，使其在光束的角动量作用下发生转动. 通过测量靶转动的角度来计算光束的角动量值. 对几种不同参数的光束的轨道角动量进行了测量，获得了轨道角动量与光束参数之间的关系，实验结果与理论分析较好地符合. 关键词： 复杂像散椭圆光束 轨道角动量 测量     

螺旋相位光束轨道角动量态测量的实验研究

对螺旋光束的轨道角动量态的测量技术进行了实验研究.建立了一套利用Mach-Zehnder干涉仪测量光束轨道角动量态的系统,对利用空间光调制器生成的携带不同轨道角动量的光束进行了测量,通过Mach-Zehnder干涉仪分离出了具有不同角量子数的螺旋光束. 关键词： 轨道角动量 空间光调制器 Mach-Zehnder干涉仪     

对经典力学中的轨道角动量和自转角动量的探讨

角动量是力学中的重要概念.本文建立了经典力学中质点系的轨道角动量和自转角动量的概念,使经典力学的理论体系更加完备,并通过几个例子阐述其应用意义.在经典力学中引入轨道角动量和自转角动量的概念,能够使学生加深对角动量的理解.     

磁单极场中的空间转动对称性与轨道角动量

对于带电粒子在磁单极场中运动的问题,推广了量子力学中关于空间转动对称性的分析,得到了推广的轨道角动量,结果与其他方法所得一致.波函数在空间转动下的变换比没有磁单极场的情况多了一个相因子.解出了该相因子的显式.要求其在转角为2π的转动下为±1,可以得出熟知的电荷量子化条件.     

电子自旋不是轨道角动量的相对论效应

根据氢原子的相对论性环电流密度jψ的表示式，指出由该jψ给出的氢原子磁矩公式必然涉及电子自旋磁矩，电子自旋不是轨道角动量的相对论效应。     

Emission of underwater acoustic orbital angular momentum and data transmission

Emission of underwater acoustic orbital angular momentum(OAM) is studied as well as underwater acoustic communications with OAM multiplexing. Theoretical acoustic properties for circular phased array are analyzed based on point source theory. We optimize and design an array prototype based on cymbal transducer. The diameter of array prototype is 180 mm, the number of array elements is 10, and the working frequency is 25 k Hz. It emits acoustic OAM with topological charges-3 to 3. The favorable results provide the theoretical basis for emitting acoustic OAM with different topological charges. We encode on-off states of acoustic OAM with different topological charges according to ASCII code to realize underwater acoustic communications. The transmission results suggest that acoustic OAM with various topological charges have intrinsically orthogonal properties. This research will offer potential applications in underwater acoustic communications.     

Emission of underwater acoustic orbital angular momentum and data transmission

Emission of underwater acoustic orbital angular momentum(OAM) is studied as well as underwater acoustic communications with OAM multiplexing. Theoretical acoustic properties for circular phased array are analyzed based on point source theory. We optimize and design an array prototype based on cymbal transducer. The diameter of array prototype is 180 mm, the number of array elements is 10, and the working frequency is 25 k Hz. It emits acoustic OAM with topological charges-3 to 3. The favorable r...     

单光子轨道角动量的传输特性研究

描述了高阶椭圆厄米-高斯光束及其单光子平均轨道角动量,并分析了一些与其单光子轨道角动量变化的有关情况,通过计算机仿真简要进行了说明.最后分析了单光子轨道角动量在空间某范围的概率分布及其变化情况.研究结果表明,高阶椭圆厄米-高斯光束与物质相互作用时,其单光子平均轨道角动量的变化幅度随接触物质材料的不同而异.     

Generation of orbital angular momentum hologram using a modified U-net

Orbital angular momentum(OAM) holography has become a promising technique in information encryption, data storage and opto-electronic computing, owing to the infinite topological charge of one single OAM mode and the orthogonality of different OAM modes. In this paper, we propose a novel OAM hologram generation method based on a densely connected U-net(DCU), where the densely connected convolution blocks(DCB) replace the convolution blocks of the U-net. Importantly, the reconstruction process of...     

Generation and application of the twisted beam with orbital angular momentum

The twisted Laguerre-Gaussian beam was generated by transforming of Hermite-Gaussian beams through an optical system consisting of three rotated cylindrical lenses. The intensity distribution and phase structure of the twisted hollow beam were theoretically analyzed by using Collins diffraction integral. By utilizing the method of mode decomposition, the theory of transformation was analyzed. In the experiment,micro particles were trapped and rotated by this twisted beam.     

Generation of high-energy photons with large orbital angular momentum by compton backscattering

Usually, photons are described by plane waves with a definite 4-momentum. In addition to plane-wave photons, "twisted photons" have recently entered the field of modern laser optics; these are coherent superpositions of plane waves with a defined projection hm of the orbital angular momentum onto the propagation axis, where m is an integer. In this Letter, we show that it is possible to produce high-energy twisted photons by Compton backscattering of twisted laser photons off ultrarelativistic electrons. Such photons may be of interest for experiments related to the excitation and disintegration of atoms and nuclei, and for studying the photoeffect and pair production off nuclei in previously unexplored experimental regimes.     

Linear up-conversion of orbital angular momentum

We experimentally demonstrated that infrared light imprinted with orbital angular momentum (OAM) was linearly converted into visible light using four-wave mixing (FWM) via a ladder-type configuration in Rb85 atoms. Simultaneously, we theoretically simulated this linear conversion process, and the theoretical analysis was in reasonable agreement with the experimental results. A large single-photon detuning process was used to reduce the absorption of the atoms to the up-converted light and to avoid pattern formation in the FWM process. The multi-mode image linear conversion process is important for applications including image communications, astrophysics, and quantum information.     

Observation of orbital angular momentum transfer between acoustic and optical vortices in optical fiber

Acousto-optic interaction in optical fiber is examined from the perspective of copropagating optical and acoustic vortex modes. Calculation of the acousto-optic coupling coefficient between different optical modes leads to independent conservation of spin and orbital angular momentum of the interacting photons and phonons. We show that the orbital angular momentum of the acoustic vortex can be transferred to a circularly polarized fundamental optical mode to form a stable optical vortex in the fiber carrying orbital angular momentum. The technique provides a useful way of generating stable optical vortices in the fiber medium.     

Controlling acoustic orbital angular momentum with artificial structures: From physics to application

Acoustic orbital angular momentum (OAM) associated with helicoidal wavefront recently attracts rapidly-growing attentions, offering a new degree of freedom for acoustic manipulation. Due to the unique dynamical behavior and inherent mode orthogonality of acoustic OAM, its harnessing is of fundamental interests for wave physics, with great potential in a plethora of applications. The recent advance in materials physics further boosts efforts into controlling OAM-carrying acoustic vortices, especially acoustic metasurfaces with planar profile and subwavelength thickness. Thanks to their unconventional acoustic properties beyond attainable in the nature, acoustic artificial structures provide a powerful platform for new research paradigm for efficient generation and diverse manipulation of OAM in ways not possible before, enabling novel applications in diverse scenarios ranging from underwater communication to object manipulation. In this article, we present a comprehensive view of this emerging field by delineating the fundamental physics of OAM-metasurface interaction and recent advances in the generation, manipulation, and application of acoustic OAM based on artificial structures, followed by an outlook for promising future directions and potential practical applications.     

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