Radially polarized hollow Gaussian beam with on-axis spiral optical vortex

The focusing properties of radially polarized hollow Gaussian beam (HGB) with on-axis spiral optical vortex are investigated theoretically by vector diffraction theory. The phase wavefront of HGB is the function of radial coordinate. Calculation results show that the focusing properties can be altered considerably by beam order of HGB, topological charge of the on-axis optical vortex, and phase parameter that characterizes the radial phase wavefront distribution. Higher topological charge induces focal evolution from one focal spot to annular focal pattern in transverse direction, while phase parameter can lead to focal shift along optical axis remarkably. In addition, focal shift direction can also be adjusted by changing varying direction of phase parameter.     

线偏振相位涡旋光束的像散特性

提出采用像散系数表征涡旋光束的像散特性。利用螺旋相位板产生了线偏振相位涡旋光束,并对其光束质量及像散特性进行了实际测量。数值模拟了不同拓扑荷数的涡旋光束的传输特性及光束质量,分析了像散系数随拓扑荷数变化的规律,结果表明：当拓扑荷数为整数时,光束无像散,像散系数为零;当拓扑荷数为半奇数时,光束的像散特性明显,像散系数达到极大值;随着拓扑荷数整数部分的增加,像散系数的极大值减小。     

Focus evolution of Gaussian beam induced by phase plate

In this article, vector diffraction theory is employed to investigate the focusing properties of the Gaussian beam through a phase plate. The phase plate may alter the wavefront phase of an incoming beam by topological charge. Both the circular phase distribution and the annular phase distribution plates are investigated. Numerical simulations show that the focal intensity distribution depends on topological charge. With changing topological charge, focal intensity distribution may evolve into ring shape, and some novel focal spots may occur. Focal intensity distribution evolving process with integer topological charge differs considerably from that with fraction topological charge. When the concentric annular phase plate is placed in the laser path, the focal intensity distribution depends on both the inner radius and topological charge. For small inner radius of the phase plate, doughnut-shape focal pattern occurs. With increasing inner radius, the diameter of the doughnut focal pattern decreases, and doughnut shape disappears slowly in some cases.     

Focusing of hyperbolic-cosine-Gaussian beam with a non-spiral vortex

The focusing properties of the hyperbolic-cosine-Gaussian beam, which contains an optical vortex induced by a non-spiral phase plate, are investigated numerically. The phase plate alters phase distribution linearly in a half-section part of the hyperbolic-cosine-Gaussian beam, which results in one non-spiral optical vortex. Results show that the phase variation rate of the non-spiral phase plate influences focal intensity distribution considerably, and some novel focal patterns, such as line focal spot, “H”-shape focal spot, and intensity peaks array, may occur. Focal shift, focal split, and focal switch appear in focal evolution with increasing phase variation rate. The focal evolution differs for different parameters in cosh parts of the hyperbolic-cosine-Gaussian beam. For big parameters in cosh parts, the value of local intensity peaks is comparable to that of maximum intensity peaks.     

Switchable vector vortex beam generation using an optical fiber

We present our experimental results on directly transforming a circular-polarized Gaussian beam into linear-polarized vector vortex beams using a two-mode fiber and demonstrate switching between the different 0th-order vector vortex modes excited and guided in the fiber. Depending on the handiness of circular-polarization of the input Gaussian light beam, its launch angle with respect to the fiber axis and by changing them appropriately it is possible to excite and switch between the different vector vortex modes and its coherent linear superposition supported by the two-mode fiber. The output optical beams due to the selectively excited vector modes in the fiber are characterized by using a rotating analyzer and a two-beam interferometer setup to study the polarization and the phase behavior of the vector vortex beam.     

Focusing of radially polarized beam with radial cosine phase wavefront

Radially polarized beam has gained much interest recently due to its properties and applications. In this article, the focusing properties of radially polarized beam with radial cosine phase wavefront are investigated theoretically. Results show that when the radially polarized beam with radial cosine wavefront phase is focused, the focal pattern differs considerably with frequency parameter in the cosine function term. In the high numerical aperture focusing system, focal shift occurs, and novel focal patterns evolve considerably, for instance, from only one peak to two or multiple overlapping peaks. In addition, peak intensity ratio of radially polarized component to longitudinal polarized component in the focal region fluctuates smoothly for low-frequency parameter, then drops sharply, and comes back remarkably with increasing frequency parameter. Simultaneously focal shift increases slowly, and then decreases, suddenly, focal shift sign changes that results from focal switch phenomenon, and then fluctuates.     

Concentric piecewise azimuthally polarized beam by a pure phase plate

Focusing properties of the azimuthally polarized beam induced by a pure phase plate are investigated theoretically. The pure phase plate consists of two concentric portions, one center circle portion and one outer annular portion, through which the azimuthally polarized beam passed evolves into concentric piecewise azimuthally polarized beam. When the phase shift of the center portion is π, one ring focus may evolve into novel focal patterns with increasing radius of the center circle portion, such as cylindrical crust focus, two-ring focus, and three-ring focus. And if the geometrical parameters are unchanged, focal patterns also changes considerably with tunable phase of the center portion. Ring focus shifts along the optical axis on the increasing phase. Some optical gradient force distributions and dependence of focal shift on phase shift are also illustrated. This kind of concentric piecewise azimuthally polarized beam can be used in optical manipulation technology.     

洛伦兹光束经光阑失调傍轴光学系统的传输

基于广义衍射积分公式和光阑函数的复高斯展开,导出了一洛伦兹光束经一个带圆形光阑失调傍轴光学系统的近似解析传输公式.作为一般公式的特例,还给出了洛伦兹光束经一无光阑失调傍轴光学系统的解析传输式.作为数值计算的例子,运用所得到的公式分析了洛伦兹光束经带光阑失调薄透镜的传输特性.结果表明：不同强度的衍射即圆形光阑半径的大小明显影响衍射光束的归一化强度分布及其传输变化规律. 关键词： 洛伦兹光束 失调傍轴光学系统 光束传输     

Polarization vortex spatial optical solitons in Bessel optical lattices

We investigate the formation of polarization vortex spatial optical solitons in optical lattice induced by a non-diffracting Bessel beam. The properties of these solitons in zeroth-order and first-order Bessel lattices with focusing and defocusing Kerr nonlinearity are discussed. It is found that these solitons have some analogies with phase vortex solitons carrying single positive or negative topological charge in these lattices. Besides, these polarization vortex solitons have complicated dynamical characteristic and can be stabilized in some parameter region.     

Resistance of nondiffracting vortex beam against amplitude and phase perturbations

The revival of the nondiffracting vortex beam after its interaction with the 2D on axis obstacle is examined. We show that the phase topology and the spatial distribution of the orbital angular momentum of the beam transmitted through the obstacle regenerate to the initial form during further free propagation. We verify that the healing effect appears even if the interaction is accompanied by the exchange of the orbital angular momentum.     

双环径向偏振涡旋光束经介质界面的深聚焦

基于矢量德拜理论,研究了双环径向偏振涡旋光束经介质分界面的深聚焦特性。当选取适当的入射光束拦截比时（即透镜孔径半径与入射光束的束腰半径的比）,在聚焦场中可以得到一个极小的局域空心光束。局域空心光束的大小不仅与透镜的数值孔径有关,还与聚焦场介质的折射率有关。另外,还研究了透镜的数值孔径、入射光束的拦截比以及探测深度对聚焦光束实际焦点位置的影响。通过对聚焦光束的实际焦点位置的计算发现：当选取一定的光束拦截比时,聚焦光束存在一个焦点开关。     

Focal depth and focal splitting of truncated hyperbolic-cosine-Gaussian beam induced by phase plate

Focal depth and focal splitting of hyperbolic-cosine-Gaussian beams induced by a phase plate were investigated. The pure phase plate consists of three concentric zones: a center circle zone, an inner annular zone and an outer annular zone. The phase variance of the inner annular zone is adjustable. Simulation results show that the focal depth can be adjusted by changing the radii of zones. With the increase of the inner radius of the outer annular zone, the focal spot broadens along the optical axis and splits into two peaks. Then the two peaks combine back into one peak. There are two critical values for the inner radius of the outer annular zone, at which focal spot changes sharply. The tunable range of the focal depth varies considerably. The phase variance of the inner annular zone affects focal depth also; when the phase variance is π, the effect attains maximum. The parameters of cosh parts of the beam affect both focal splitting and focal depth evidently; focal splitting disappears with increasing parameters of cosh parts, and focal depth increases with increasing the parameters of cosh parts in both the low and the high numerical-aperture optical systems.     

拉盖尔高斯涡旋光束的传输

针对拉盖尔高斯涡旋光束,推导了其传输后目标平面上光电场的解析表达式,理论研究表明,传输一段距离后, 对于拉盖尔高斯光束的光斑大小的描述,高斯光斑尺寸已经不再适用.如果采用光强最亮处的半径来表示目标平面上的光斑大小则比较方便. 除了传输中的衍射导致光束展宽以外, 横截面上光束的相位分布也发生了独特的变化. 等相位线由原来的射线转化为弧线,拓扑电荷数为正时,弧线朝顺时针方向弯曲,拓扑电荷数为负时,弧线朝逆时针方向弯曲. 关键词： 涡旋光束 传输 光斑尺寸 相位分布     

环形分布激光束引起光学窗口镜热变形理论分析

 用有限Hankel变换就常见的环形分布激光束情形，推导得到了激光束辐照透过窗口镜引起热传导温度场和热变形分布的理论解，以此计算结果与实验值相比较，分析了白宝石、石英两种窗口镜在激光辐照下的热变形情况。分析结果表明，在激光束辐照的4s时段内，温升场主要集中在激光束辐照的环形区内，在镜面内远未拉平，由此引起的厚度方向热膨胀变形也很不均匀。材料对激光的吸收系数和热膨胀系数以及热扩散率分别是决定热变形量值大小和空间分布的最主要的物性参数。     

弱场中光抽运极化Eu原子束的制备

自五十年代首次实现光抽运技术以来,人们用它已对多种原子进行了极化原子束制备的研究[1～5],但所有这些工作只是以相对简单的碱金属原子为对象,而对价电子数大于1的复杂原子的极化原子束的制备目前尚未见报道.描述了用一台连续波染料激光器对复杂原子Eu进行了弱场制备极化原子束的实验研究,得到了较满意的结果.     

Focusing of a vortex carrying beam with Gaussian background by an apertured system in presence of coma

In this paper, diffraction pattern of a vortex carrying beam with a Gaussian background has been studied by using Fresnel-Kirchhoff diffraction integral, in the presence of third-order coma. Results of intensity distribution and encircled energy at the Gaussian plane have been presented for two values of the topological charge. Positional shift and splitting of the dark core have been investigated in detail. It is noticed that the diffraction pattern of a beam with double topological charge is affected more by comatic aberration in comparison to the beam with single topological charge. We have also verified our results by using the optical transfer function approach. Propagation of an apertured Gaussian background vortex beam through a π-phase shifter has also been studied for two values of the topological charge.     

Phase modulation of acoustic vortex beam with metasurfaces

We present a new acoustic metasurface structure to generate the stable acoustic vortex beams with controllable topological charge in the broadening of operating frequency. The proposed acoustic metasurface can dynamically achieve a full span of 360° phase modulation by three simple solutions. Acoustic plane beam and acoustic vortex beam can convert each other based on multi-metasurfaces combination. Potential applications of such phase modulation schemes can be anticipated.     

Tightly focusing of linearly polarized vortex beams through a dielectric interface

Based on vectorial Debye theory, the tightly focusing properties of linearly polarized vortex beams through a dielectric interface are studied. Then the intensity distribution in the focal region is investigated in detail by numerical calculations. The focal shifts induced by the mismatch of the refractive indices across the interface has been found. And the dependence of focal shifts and spot size of the focused field on the probe depth and numerical aperture of the objective are presented. Furthermore, the characteristic of intensity pattern of the cross section of the focused field is illustrated, finding that the intensity pattern rotates with the propagation of beams.     

贝塞尔-高斯涡旋光束相干合成研究

基于相干合成技术,提出了对特定离散空间分布的高斯光束阵列加载离散涡旋相位生成二阶贝塞尔-高斯(Bessel-Gaussian,BG)涡旋光束的方案.利用干涉法、桶中功率和相关系数对合成BG涡旋光束的拓扑荷、光束质量进行了定量评价及参数优化.结果表明:基于相干合成技术能够产生特定的目标BG涡旋光束,阵列子光束紧密排布时合成BG光束的光束质量更高.该方法的提出对于其他涡旋光束的产生或者涡旋光束功率的提高具有一定的参考意义.     

Gradient force evolution of Gaussian beam induced by a phase plate

The evolution of gradient force pattern induced by an annular phase distribution plate is numerically investigated in this paper. The phase plate, which may alter the wavefront phase of incident Gaussian beam with tunable topological charge, consists of two concentric portions, one center circle portion and one annular portion. Numerical simulations show that the proposed plate can induce the tunable gradient force on the particles in the focal region. By adjusting the geometrical parameters or changing the topological charge of the phase-shifting plate, some novel trap patterns may occur, such as triangle shape trap, quadrangle shape trap, pentagon shape trap, hexagon shape trap, and the shapes of optical traps change very considerably. Therefore, the phase plate may be very advantageous for constructing tunable optical traps. The method is more versatile in that it allows precise control of the parameters and has the possibility of generating specific patterns of optical vortices. The gradient force pattern focal of intensity distribution depends on both the annular width and the topological charge.