Intensity distribution properties of Gaussian vortex beam propagation in atmospheric turbulence

By using wave optics numerical simulation, the intensity-hole effect, beam spreading and wandering properties of Gaussian vortex beam propagation in atmospheric turbulence are investigated quantitatively. It is found that an intensity hole in the center of the beam pattern appears gradually as a Gaussian vortex beam propagates. The size of the intensity hole increases with the increase of the topological charge of the vortex phase. However, the intensity hole could to some extent be filled with optical energy by atmospheric turbulence, especially in strong turbulence. The radius of the intensity hole first decreases and then increases with the growth of turbulence strength. The effective radius of vortex beam with larger topological charge is greater than with a smaller topological charge. But the topological charge has no evident influence on beam wandering.

Propagation of Airy Gaussian vortex beams in uniaxial crystals

The propagation dynamics of the Airy Gaussian vortex beams in uniaxial crystals orthogonal to the optical axis has been investigated analytically and numerically. The propagation expression of the beams has been obtained. The propagation features of the Airy Gaussian vortex beams are shown with changes of the distribution factor and the ratio of the extraordinary refractive index to the ordinary refractive index. The correlations between the ratio and the maximum intensity value during the propagation, and its appearing distance have been investigated.

Nonparaxial propagation properties of the chirped Airy Gaussian vortex beams in uniaxial crystals orthogonal to the optical axis

In this article, we investigate the nonparaxial propagation properties of the chirped Airy Gaussian vortex（CAiGV）beams in uniaxial crystals orthogonal to the optical axis analytically and numerically. We discuss how the linear chirp parameters, the quadratic chirp parameters, and the Gaussian factors influence the nonparaxial propagation dynamics of the CAiGV beams. The intensity, the energy flow, the beam center, and the angular momentum of the CAiGV beams are deeply investigated. It is shown that the Gaussian factors have a great effect on the intensity and the centroid positions of the CAiGV beams. With the Gaussian factors increasing, the intensity of CAiGV beams decreases rapidly. The main lobes of the transverse intensity distribution of the CAiGV beams are similar to triangles.

Polarization singularities in near-field of Gaussian vortex beam diffracted by a circular aperture

Polarization singularities in the near-field of Gaussian vortex beams diffracted by a circular aperture are studied by a rigorous electromagnetic theory. It is shown that there exist C-points and L-lines, which depend on off-axis displacement parameters along the x and y directions, waist width, wavelength, and topological charge of the diffracted Gaussian vortex beam, as well as on propagation distance. The results are illustrated by numerical calculations.

Angular momentum density of a Gaussian vortex beam

The Gaussian vortex beam is assumed to be linearly polarized.The analytical expression of the electric field of a linearly polarized Gaussian vortex beam propagating in free space is derived by using the vectorial Rayleigh-Sommerfeld integral formulae.The propagating magnetic field of the linearly polarized Gaussian vortex beam is presented by taking the curl of the electric field.By employing the electromagnetic field of the linearly polarized Gaussian vortex beam beyond the paraxial approximation,the analytical expression of the angular momentum density of the linearly polarized Gaussian vortex beam is derived.The three components of the angular momentum density of a linearly polarized Gaussian vortex beam are demonstrated in the reference plane.The effects of the linearly polarized angle and the topological charge on the three components of the angular momentum density are investigated.To acquire the more longitudinal angular momentum density requires such an optimal choice that the linearly polarized angle is set to be zero and the topological charge increases.This research is useful to the optical trapping,the optical guiding,and the optical manipulation.

Collapse arrest in a two-dimensional Airy Gaussian beam and Airy Gaussian vortex beam in nonlocal nonlinear media

Propagation dynamics of a two-dimensional Airy Gaussian beam and Airy Gaussian vortex beam are investigated numerically in local and nonlocal nonlinear media.The self-healing and collapse of the beam crucially depend on the distribution factor b and the topological charge m.With the aid of nonlocality,a stable Airy Gaussian beam and an Airy Gaussian vortex beam with larger amplitude can be obtained,which always collapse in local nonlinear media.When the distribution factor b is large enough,the Airy Gaussian vortex beam will transfer into quasivortex solitons in nonlocal nonlinear media.

Gaussian beam with non-spiral optical vortex

Optical vortex has attracted much interest re-cently due to its novel properties and applica-tions. In this paper, the focusing properties of Gaussian beam containing one non-spiral opti-cal vortex are investigated by means of scalar diffraction theory. Simulation results show that topological charge of non-spiral optical vortex affects optical intensity distribution in focal re-gion considerably, and non-spiral focal pattern may also occur. Multiple intensity peaks may appear companying with center main focal spot under condition of higher topological charge. In addition, the number of weak intensity peak outside of the center main intensity peak is re-lated to the value of topological charge.

Composite optical vortices in noncollinear Laguerre–Gaussian beams and their propagation in free space

Taking two Laguerre-Gaussian beams with topological charge 1 = ±1 as an example, this paper studies the composite optical vortices formed by two noncollinear Laguerre-Gaussian beams with different phases, amplitudes, waist widths, off-axis distances, and their propagation in free space. It is shown by detailed numerical illustrative examples that the number and location of composite vortices at the waist plane are variable by varying the relative phase β, amplitude ratio η, waist width ratio ξ, or off-axis distance ratio μ. The net topological charge lnet is not always equal to the sum lsum of charges of the two component beams. The motion, creation and annihilation of composite vortices take place in the free-space propagation, and the net charge during the propagation remains unchanged and equals to the net charge at the waist plane.

Cosh-Pearcey-Gaussian涡旋光束在单轴晶体中的坡印廷矢量和角动量密度

为了分析和研究Cosh-Pearcey-Gaussian涡旋(CPeGV)光束的传播特性,通过皮尔斯积分式得到了CPeGV光束传播的一般表达式,推导出CPeGV光束在单轴晶体中传播的解析式。详细研究了CPeGV光束在单轴晶体中传播时的纵向和横向坡印廷矢量和角动量密度(AMD)。探讨了双曲余弦参数、拓扑电荷和传播距离对CPeGV光束传播特性的影响。研究结果表明:与PeG光束相比,CPeGV光束的调制自由度更高。较大的双曲余弦调制参数可以控制能量沿横向坡印廷矢量方向传递,从而不仅可以改变能量分布也可以使AMD峰值变大。在远场,CPeGV光束的纵向坡印廷矢量随着双曲余弦参数的增大会从抛物线形状分离为四个波瓣的分布形状。而拓扑电荷会影响远场抛物线形状中暗区的数量。本文研究将有助于更好地理解CPeGV光束在单轴晶体中的传播特性,并有助于信息传输和存储的应用。

海洋湍流下双拉盖尔-高斯涡旋光束的闪烁指数与误码率研究

采用功率谱反演法模拟了同轴叠加产生的双拉盖尔-高斯涡旋光束(Double Laguerre-Gaussian Vortex Beam,DLGVB)在海洋湍流中传输时的光强和相位分布,仿真分析了DLGVB光束在不同海洋湍流参数下的闪烁指数以及在基于开关键控调制的水下光通信系统中的通信误码率。结果表明,随着湍流动能耗散率的减小,盐度温度波动平衡参数、温度方差耗散率及传输距离的增加,闪烁指数逐渐增加;随着湍流动能耗散率以及拓扑电荷差值的增加,误码率减小。在海洋湍流环境下,使用DLGVB光束进行传输可以抑制海洋湍流带来的干扰,选择最佳的拓扑电荷差值,可以有效提高传输通信质量及通信系统容量。本文研究结果对涡旋光束及其叠加态在海洋湍流下传输特性研究及水下光通信系统持续扩容的发展需求方面具有重要的参考价值。

一维阵列涡旋光束在海面大气中的传输特性

相较于单涡旋光束,涡旋阵列光束能够扩充信息的传输容量,研究其传输特性对其光通信应用具有重要意义。本文选取阶数为n的螺旋因斯-高斯(HIG_(n,n))模式,采用海上大气折射率变换的功率谱,模拟海面大气湍流。基于相位屏法研究了一维阵列涡旋光束在海面大气湍流中光强、相位、闪烁因子和质心漂移的变化情况。结果表明:(1)HIG_(n,n)模式的闪烁因子和质心漂移标准差随湍流强度以及大气湍流内尺度的增加而增加;(2)n为奇数的HIG_(n,n)模式的闪烁因子随着阶数的增大而减小,且高于n为偶数的HIG_(n,n)模式;(3)阶数n>1的HIG_(n,n)模式比LG_(0,1)模式具有更好的稳定性;(4)阶数越高,HIG_(n,n)模式的质心漂移标准差越小。其次,选取线性阵列涡旋光束(LAVBs)进行对比,研究得出虽然LAVBs比HIG光束具有更好的传输性能,但由于HIG光束具有独特的结构,故可适用于不同的应用场景。最后,分析了椭圆参量和椭圆环数对HIG模式传输的影响,结果表明适当地增大椭圆参量或椭圆环数有助于提高HIG模式的抗湍流能力。本文研究结果对涡旋光束的海上应用具有指导意义。

圆偏振涡旋激光脉冲驱动等离子体产生飞秒磁脉冲的研究

飞秒磁场脉冲对研究超快磁化、超快退磁、超快磁存储和自旋超快动力学等过程具有重要意义。传统的脉冲磁场受限于脉冲电源性能无法获得毫秒量级以下的超短脉冲磁场,无法研究飞秒尺度的磁动力学过程。利用超短脉冲激光驱动等离子体产生旋转电流是目前产生飞秒磁场脉冲的有效方法。本文利用质点网格法模拟圆偏振拉盖尔高斯光束驱动等离子体中的电子运动从而产生光电流以及飞秒磁脉冲的过程,模拟产生了特斯拉量级的飞秒超短磁脉冲,并系统讨论了驱动激光强度与等离子体密度对磁脉冲的影响。结果表明,脉冲磁场的脉宽与驱动光一致,其强度随着激光场强度、等离子体密度增加而增加。通过本文研究寻找产生飞秒磁脉冲的优化实验参数,有望将超快磁动力学研究推进到飞秒时间尺度。

Hollow vortex Gaussian beams

A kind of hollow vortex Gaussian beam is introduced. Based on the Collins integral, an analytical propagation formula of a hollow vortex Gaussian beam through a paraxial ABCD optical system is derived. Due to the special distribution of the optical field, which is caused by the initial vortex phase, the dark region of a hollow vortex Gaussian beam will not disappear upon propagation. The analytical expressions for the beam propagation factor, the kurtosis parameter, and the orbital angular mo- mentum density of a hollow vortex Gaussian beam passing through a paraxial ABCD optical system are also derived, respec- tively. The beam propagation factor is determined by the beam order and the topological charge. The kurtosis parameter and the orbital angular momentum density depend on beam order n, topological charge m, parameter y, and transfer matrix ele- ments A and D. As a numerical example, the propagation properties of a hollow vortex Gaussian beam in free space are demonstrated. The hollow vortex Gaussian beam has eminent propagation stability and has crucial application prospects in op- tical micromanipulation.

相对论涡旋高次谐波的产生与调控理论研究

目前,具有螺旋相位波前和环状光强分布的涡旋光束已在光学领域获得了广泛应用,其产生与调控自然成了研究的热点。利用三维粒子模拟程序对双色拉盖尔高斯激光驱动固体等离子激发同时携带自旋角动量与轨道角动量的高次谐波的物理过程进行了研究,根据高次谐波产生过程中的光子能量与角动量守恒定律对其内在物理机制进行了理论分析,并讨论了对谐波阶次、偏振态(自旋角动量)以及拓扑荷数(轨道角动量)进行调控的方法。研究结果为开发高亮度、超短超快、短波长、自旋与轨道角动量可调控的涡旋光束辐射源提供了理论依据,在光学微操控、超分辨成像、光通信以及离子加速等领域具有较大的实际应用前景。

高斯涡旋光束在大气湍流传输中的特性研究

为了研究大气湍流对高斯涡旋光束传递信息的影响,理论分析了经过大气湍流的高斯涡旋光束轨道角动量(OAM)模式的径向平均功率和归一化平均功率分布、固有模式指数、初始光束半径和湍流强度;采用纯相位扰动逼近的有效性,数值模拟高斯涡旋光束在传输中的OAM模式径向平均功率分布的变化。建立传输模型并进行外场激光大气传输实验,对比分析了模拟和实测的OAM归一化平均功率分布,结果表明在弱湍流条件下,OAM模式的径向平均功率随着接收器孔径尺寸的增加而变化,逐渐趋于稳定值。对于一般常用的接收孔径,在强湍流或较小的初始光束半径条件下对OAM模式干扰十分严重。验证了用数值方法模拟OAM在湍流介质中的模式变化过程的可靠性。

正弦高斯涡旋光束的远场传输特性

根据角谱法和稳相法,推导了正弦高斯涡旋光束TE波和TM波在远场传输和能流密度的解析表达式,研究了正弦高斯涡旋光束在远场中的相位奇点和能流密度分布.结果表明:正弦高斯涡旋光束的远场特性与高斯光束的束腰宽度、涡旋离轴量、坐标位置以及与正弦项相关的参量有关.在一定条件下,远场中会出现相位奇点和能流密度黑核;当控制参量改变时,相位奇点和黑核的位置会发生移动,但原点处不受影响.相位奇点和能流密度的对称性主要受涡旋离轴量影响,当涡旋离轴量为0时,相位奇点和能流密度分布关于原点对称;当涡旋离轴量改变时,相位奇点和能流密度分布呈现出非对称性.

空心高斯涡旋光束的远场特性

基于角谱法和稳相法,推导出了空心高斯涡旋光束的TE波和TM波在自由空间远场传输和能流密度的解析表达式,研究了其相位奇点和能流密度分布。结果表明,空心高斯涡旋光束的远场特性主要跟控制参数有关。改变光束中的涡旋离轴量,光涡旋和能流密度黑核会发生移动。圆刃型位错线的半径和能流密度暗环位置跟束腰宽度有关,而能流密度的对称性主要受涡旋离轴量的影响。

高阶贝塞尔-高斯脉冲光束相位奇点的演化

推导出被光阑衍射高阶贝塞尔-高斯脉冲光束的场和光强分布的解析公式,对其相位奇点的演化特性做了计算和分析。结果表明,高阶贝塞尔-高斯脉冲光束经光阑衍射后,中心光涡旋始终存在,拓扑电荷守恒。随脉冲频率和脉冲宽度增加,等相位线均沿逆时针方向旋转,涡旋核随脉冲频率增加而减小,而脉冲宽度对涡旋核大小几乎无影响。等相位线随截断参数和传输距离的增加分别沿逆时针和顺时针方向旋转,涡旋核大小随截断参数增加而变化,随传输距离和光束阶数的增加而增大。

球差对圆偏涡旋贝塞耳-高斯光束聚焦场的影响

利用理查德-沃耳夫矢量衍射积分,分析了初级球差对圆偏振涡旋贝塞耳-高斯光束聚焦光场的影响,获得不同球差系数下的光强分布.结果表明,当初级球差系数增加,会聚光点偏离系统焦平面,纵向光场发生改变;焦点光强逐渐减小,焦平面光场发生变化;光轴上光强峰值逐渐减小,峰值两侧的旁瓣变化趋势相反,光强由对称分布变成非对称分布;初级球差对贝塞耳-高斯光束聚焦光场的影响不依赖其偏振态;离焦无法完全补偿初级球差对聚焦光场的影响.

涡旋光束通过非高斯随机粗糙面的场分布特性

基于角谱衍射理论,利用Johnson传递系统数值模拟非高斯粗糙面,研究了拉盖尔-高斯涡旋光束通过随机非高斯粗糙表面的场分布特性。在分析了非高斯粗糙面方向自相关长度、峰度、偏斜以及均方根粗糙度对涡旋光束场分布影响的基础上,研究了涡旋光束通过随机粗糙表面后光束光强分布变化时的均方根粗糙度取值范围,并通过实验,将实验数据与仿真结果进行了对比分析。结果表明:当非高斯粗糙面方向相关长度为20 mm,偏斜为0.001,峰度为6,均方根粗糙度大于0.12 mm时,拉盖尔-高斯光束透过随机表面的光强分布不再保持空心分布,对应的相位奇点消失。