Proposal for generating brilliant x-ray beams carrying orbital angular momentum

We consider use of a variable polarizing undulator for generating brilliant x-ray beams carrying orbital angular momentum. We find that higher harmonics of the radiation correspond to Laguerre-Gaussian modes with azimuthal mode indices l equal to one less than the harmonic number when the undulator is operated to produce circularly polarized light. Beams with nonzero l carry orbital angular momentum quantized in units of lvariant Planck's over 2pi per photon. When operated to produce linear polarization, the harmonics correspond to Hermite-Gaussian modes. Selection of these modes with conventional monochromator optics opens the door for new research with x-ray synchrotron and free-electron laser sources.     

Breakup of ring beams carrying orbital angular momentum in sodium vapor

We have observed filamentation due to azimuthal modulational instabilities in spinning ring solitons with orbital angular momentum m variant Planck's over 2pi in sodium vapor. We show experimentally that vortex beams with m values of 1, 2, and 3 tend to break into two, four, and six filaments, respectively. Treating the sodium vapor as a Doppler broadened two-level atomic system, we find that we can accurately model the propagation and breakup of these beams with numerical simulations.     

Up-conversion detection of mid-infrared light carrying orbital angular momentum

Frequency up-conversion is an effective method of mid-infrared (MIR) detection by converting long-wavelength photons to the visible domain, where efficient detectors are readily available. Here, we generate MIR light carrying orbital angular momentum (OAM) from a difference frequency generation process and perform up-conversion on it via sum frequency conversion in a bulk quasi-phase-matching crystal. The maximum quantum conversion efficiencies from MIR to visible are 34.0%, 10.4%, and 3.5% for light with topological charges of 0, 1, and 2, respectively, achieved by utilizing an optimized strong pump light. We also verify the OAM conservation with a specially designed interferometer, and the results agree well with the numerical simulations. Our study opens up the possibilities for generating, manipulating, and detecting MIR light that carries OAM, and will have great potential for optical communications and remote sensing in the MIR regime.     

Microobject manipulations using laser beams with nonzero orbital angular momentum

Microobject manipulation with a laser is investigated. The functional capabilities of the laser manipulators can be significantly enhanced using beams with predetermined distributions of intensity and angular momentum. Beams with nonzero angular momentum are generated using phase and amplitude-phase masks. Such beams make it possible to rotate weakly absorbing particles and to move them along a given trajectory. Experimental results on the microobject motion along various trajectories (circle, triangle contour, self-intersecting curve, and Archimedes spiral) are presented.     

Delocalized correlations in twin light beams with orbital angular momentum

We generate intensity-difference-squeezed Laguerre-Gauss twin beams of light carrying orbital angular momentum by using four-wave mixing in a hot atomic vapor. The conservation of orbital angular momentum in the four-wave mixing process is studied as well as the spatial distribution of the quantum correlations obtained with different configurations of orbital angular momentum. Intensity-difference squeezing of up to -6.7 dB is demonstrated with beams carrying orbital angular momentum. Delocalized spatial correlations between the twin beams are observed.     

Utilization of photon orbital angular momentum in the low-frequency radio domain

We show numerically that vector antenna arrays can generate radio beams that exhibit spin and orbital angular momentum characteristics similar to those of helical Laguerre-Gauss laser beams in paraxial optics. For low frequencies (< or = 1 GHz), digital techniques can be used to coherently measure the instantaneous, local field vectors and to manipulate them in software. This enables new types of experiments that go beyond what is possible in optics. It allows information-rich radio astronomy and paves the way for novel wireless communication concepts.     

海洋湍流对光子轨道角动量量子通信的影响

本文研究了基于光子轨道角动量的量子通信在水下量子信道中受海洋湍流运动的影响.基于Elamassie等提出的海洋湍流功率谱模型,本文建立了不同海洋湍流参数与光子轨道角动量量子通信的单光子探测概率、信道容量、密钥产生率以及双光子共生纠缠度的定量关系,并利用纠缠光子对的共生纠缠度在海洋湍流中的普适衰减特性进一步研究了轨道角动量纠缠光子对在海洋湍流中的最大纠缠距离.研究结果表明:水下量子通信性能和纠缠光子对的共生纠缠度都随海洋湍流的湍流动能耗散率的增大或温度方差耗散率的减小而降低;温度和盐度因素对海洋湍流贡献的比值对水下量子通信的影响在海水是否稳定分层的条件下具有显著的区别;在通过海洋湍流进行量子通信时,增加信号光子的初始轨道角动量量子数可以提高量子密钥分发的密钥产生率和纠缠光子的纠缠衰减抵抗性.     

Whispering gallery resonators for studying orbital angular momentum of a photon

We propose a simple method for generation and detection of photons with nonzero angular momentum. The method utilizes high-quality factor ring resonators that transform a plane electromagnetic wave into a wave with nonzero angular momentum, and vice versa. We show that the method is especially promising for studying high-order Bessel beams, unreachable by other techniques.     

Rotation of laser beams with zero of the orbital angular momentum

We show that among the multitude of rotating light beams whose complex amplitude can be represented as a linear superposition of the Laguerre-Gaussian (LG) modes with definite numbers there are light beams with zero orbital angular momentum (OAM) and vice versa, multi-mode LG beams that show no rotation and are lacking the radially symmetric intensity distribution can possess the non-zero OAM. Also, we give examples of the rotating light beams with zero OAM, represented as a superposition of the Bessel and new hypergeometric modes. Using an SLM, we generate a rotating Bessel beam with zero OAM for the first time.     

Vortex-bearing array of singular beams with very high orbital angular momentum

We consider theoretically and experimentally an array of singular beams whose axes lie on the surface of a hyperboloid of revolution. We show that such a singular array can carry a very high orbital angular momentum. Experimental results demonstrate a way of generating such singular arrays.     

Nonparaxial TE and TM vector beams with well-defined orbital angular momentum

A new formalism is developed for diffraction-free vector beams in free space. The solutions of Maxwell's equations are separated into two polarization modes, TE and TM. We discuss the validity of the method by applying it to a particular solution, the vectorial Bessel beam of order m.     

Concentration of higher dimensional entanglement: qutrits of photon orbital angular momentum

Enhancement of entanglement is necessary for most quantum communication protocols many of which are defined in Hilbert spaces larger than 2. In this work we present the experimental realization of entanglement concentration of orbital angular momentum entangled photons. We investigate the specific case of three dimensions and the possibility of generating different entangled states out of an initial state. The results presented here are of importance for pure states as well as for mixed states.     

Influence of atmospheric turbulence on states of light carrying orbital angular momentum

We have experimentally studied the degradation of mode purity for light beams carrying orbital angular momentum (OAM) propagating through simulated atmospheric turbulence. The turbulence is modeled as a randomly varying phase aberration, which obeys statistics postulated by Kolmogorov turbulence theory. We introduce this simulated turbulence through the use of a phase-only spatial light modulator. Once the turbulence is introduced, the degradation in mode quality results in crosstalk between OAM modes. We study this crosstalk in OAM for 11 modes, showing that turbulence uniformly degrades the purity of all the modes within this range, irrespective of mode number.     

Path and phase determination for an interfering photon with orbital angular momentum

A polarized photon with well-defined orbital angular momentum that emerges from a Mach-Zehnder interferometer (MZI) is shown to seemingly circumvent wave-particle duality constraints. For certain phase differences between the MZI arms, this pattern yields both reliable which-path information and high phase sensitivity.     

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     

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     

Measuring the orbital angular momentum of elliptical vortex beams by using a slit hexagon aperture

The far-field diffraction pattern of an elliptical vortex beam by a slit hexagon aperture is investigated theoretically and experimentally. It is found that the number of the dark spots or stripes in the Fraunhofer diffraction intensity distribution is just equal to the topological charge value of the measured optical vortex, and that the centre of each dark spot or stripe is just a phase singularity point. Based on this property, it provides us a simple way to detect the orbital angular momentum (OAM) of an optical vortex beam.     

Acoustic beams with angular momentum

A family of exact solutions of the Helmholtz equation is used to represent transversely bounded helicoidal sound beams. Simple results are obtained for the energy content per unit length, the momentum content per unit length, and the angular momentum content per unit length. The analysis is restricted to lossless media; scattering and viscous damping are neglected. The energy, momentum, and angular momentum are calculated to second order in the velocity potential. The angular momentum content is always equal to m/omega times the energy content, where m (an integer) is the topological charge and omega is the angular frequency.