高斯涡旋光束在自由空间传输中电场和磁场的偏振奇点

利用矢量菲涅尔衍射积分公式, 以高斯涡旋光束为例, 推导出傍轴高斯涡旋光束在自由空间传输过程中电场分量和磁场分量的解析表达式, 详细研究了自由空间中电场和磁场的偏振奇点变化规律. 结果表明, 高斯涡旋光束在自由空间传输中, 存在二维和三维电场和磁场的偏振奇点, 其位置一般不重合. 改变光束束腰宽度比、 振幅比以及传输距离, 偏振奇点出现移动. 在二维电场和磁场中, 当满足一定条件时, 会有V点产生.     

部分相干圆偏振贝塞耳-高斯光束经高数值孔径透镜的聚焦

研究了部分相干圆偏振贝塞耳一高斯光束经高数值孑L径透镜的聚焦特性.基于德拜矢量积分理论,分别推导出了部分相十圆偏振涡旋光束经过高数值孔径透镜聚焦以后的光强和偏振度表达式.根据数值模拟的结果,比较了左旋和右旋圆偏振涡旋光束的不同深聚焦特性以及相关参量对涡旋光束深聚焦特性的影响.研究表明,入射光束的相关参数和聚焦透镜的数值孔径大小都会影响光束的聚焦特性.此外,还得出一个重要结论,部分相于圆偏振涡旋光束经高数值孔径透镜聚焦以后.光束本身带有的白旋角动晕会转化成轨道角动量,这一研究成果对于利用涡旋光束进行微粒操控等方面应用具有十分重要的意义.     

离轴高斯涡旋光束的深聚焦特性

基于德拜矢量衍射积分理论,对离轴高斯涡旋光束经过大数值孔径透镜后聚焦场的特性进行了研究,获得了离轴高斯涡旋光束深聚焦后复振幅分布函数,在此基础上对离轴高斯涡旋光束深聚焦场的光强和相位分别进行了分析.数值模拟结果表明:离轴距离的改变对高斯涡旋光束在焦平面上的光强分布和相位分布会产生影响,离轴距离的增加会加剧聚焦场光强在y轴方向上分布的差异,而离轴距离的符号决定了光强集中区域的方向.另一方面,与一阶离轴涡旋光束不同,高阶离轴涡旋光束经过深聚焦后会发生暗核分裂现象,出现多个相位奇点,奇点个数等于原始光束对应的拓扑荷数,且分裂后的奇点具有明显的对称性.研究表明,这种暗核分裂现象由大数值孔径透镜深聚焦引起.     

基于圆偏振涡旋光束强聚焦的平顶光束的构成

由于圆偏振涡旋光束可以表征为柱坐标的径向矢量光束和角向矢量光束的线性叠加,因而在研究其聚焦特性时,必须考虑具有拓扑核的径向矢量光束聚焦后有角向分量和角向矢量光束聚焦后有径向分量。在修正关于圆偏振涡旋光束强聚焦公式的基础上,重新模拟计算了不同拓扑核的圆偏振涡旋光束的强聚焦特性。结果显示不仅单自旋手性的圆偏振涡旋光束聚焦能形成平顶光束,而且两束不同的自旋手性的涡旋光束的叠加聚焦也可以实现平顶光束。通过调节光束的振幅、束腰半径以及遮挡通光孔径可以有效地改变平顶光束的半宽。     

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.     

随机电磁光束经像散透镜后磁场的光谱Stokes奇点

利用交叉谱密度函数的传输公式,以部分相干刃型位错光束为例,推导出随机电磁光束磁场通过像散透镜传输后的解析表达式.使用光谱Stokes参数,详细讨论了光谱Stokes场的奇点变化规律.结果表明,随机电磁光束磁场通过透镜后的传输过程中,存在光谱s12,s23和s31奇点.改变刃型位错的离轴量、斜率、空间相关长度等光束参数以及随着传输距离的变化,会有磁场光谱Stokes奇点的移动、产生和湮没,也会有V点的产生和C点旋向性的反转.此外,还与电场的光谱Stokes奇点做了比较.     

双曲余弦高斯涡旋光束的远场特性研究

运用电磁光束的角谱法和稳相法, 推导出双曲余弦高斯(ChG) 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, 用以研究了ChG涡旋光束在远场中的位相奇点和能流密度分布特性. 结果表明, 改变ChG 涡旋光束中的离心参数或束腰宽度, 位相奇点的密度、位置会发生变化. 涡旋离轴量的变化会导致能流密度分布的不对称性. 当离心参数增大时, 原点周围黑核会向原点中心移动. 关键词： 双曲余弦高斯涡旋光束 位相奇点 能流密度     

高次方涡旋光束经大数值孔径透镜的聚焦特性

为了获得多种类型的波长量级聚焦光斑,研究了一种新型涡旋光束,高次方涡旋光束经过大数值孔径透镜的聚焦。基于矢量德拜积分公式,理论上研究了线偏振的高次方涡旋光束经过大数值孔径透镜的聚焦特性。研究了涡旋光束的拓扑荷数和幂次方数对聚焦平面光强和电场x分量的相位分布的影响。研究结果表明,通过控制涡旋光束的拓扑荷数和幂次方数可以产生不同类型的聚焦光强分布,例如尺寸约为2个波长大小的实心和空心型聚焦光斑。此外,与普通的涡旋光束聚焦不同,高次方涡旋光束聚焦后的奇点并不在焦点处。这些特殊的聚焦光斑有望在微粒的操控等领域中得到应用。     

聚焦部分相干涡旋光束的传输和相干特性

根据部分相干光的传输理论,研究了部分相干高斯-贝塞尔涡旋光束通过光阑透镜聚焦后的传输和空间相关性质.数值计算结果表明,涡旋暗核的大小和焦平面上的光谱相干度都取决于入射光的拓扑电荷n、截断参量δ、相对相干长度σg和参量α.当选择适当的参量,在几何焦点附近会出现局域空心光束.研究还发现在焦面上光谱相干度会产生一个或多个的相位奇点(相干涡旋),而且拓扑电荷和相对相干长度会对相干涡旋的位置和个数产生影响.在相干极限下,相干涡旋可逐渐演变为光学涡旋.     

基于高次谐波产生的极紫外偏振涡旋光

突破传统涡旋光场束缚,发展短波极紫外涡旋光场是实现阿秒脉冲偏振控制的有效途径.本研究利用自制的平场光栅光谱仪和超快时间保持的单色仪,以800 nm,35 fs高斯或具有偏振奇点的涡旋光脉冲驱动诱导氩原子产生高次谐波,分别获得相应的高次谐波光谱以及谐波谱单阶光源的分布.实验结果表明,基于高次谐波产生实现近红外波段的涡旋光束特性转移到极紫外波段,优化后的极紫外涡旋可以实现每秒108光子数输出.同时发现极紫外波段的涡旋场和高斯场高次谐波产生具有相似相位匹配机制.基于高次谐波产生的极紫外波段的偏振涡旋光为探究和操控原子分子量子态的含时演化动力学以及形成阿秒矢量光束提供了重要的方法和技术手段.     

The effect of spherical aberration on the phase singularities of focused dark-hollow Gaussian beams

The phase singularities of focused dark-hollow Gaussian beams in the presence of spherical aberration are studied. It is shown that the evolution behavior of phase singularities of focused dark-hollow Gaussian beams in the focal region depends not only on the truncation parameter and beam order, but also on the spherical aberration. The spherical aberration leads to an asymmetric spatial distribution of singularities outside the focal plane and to a shift of singularities near the focal plane. The reorganization process of singularities and spatial distribution of singularities are additionally dependent on the sign of the spherical aberration. The results are illustrated by numerical examples.     

随机电磁涡旋光束的深聚焦特性

基于德拜矢量积分理论,研究了随机电磁涡旋光束经过大数值孔径透镜之后的聚焦特性及透镜的数值孔径、入射光束的偏振度、拓扑荷以及横向相干长度对焦平面附近聚焦光束的光强分布和相干度的影响.结果表明:适当地选择相关参量,可在焦平面上得到椭圆形光斑的光强分布以及平顶光强分布.随机电磁涡旋光束在焦平面上同一点处两个相互垂直分量之间的相干度,不同两点处两个相同分量之间的相干度以及不同两点处两个相互垂直分量之间的相干度研究表明,入射光束的拓扑荷和横向相干长度对聚焦光束的相干性有着十分明显的影响.     

Propagation of Gaussian background vortex beams diffracted at a half-plane screen

Taking the Gaussian background vortex beam with topological charge +2 as a typical example, a closed-form expression for vortex Gaussian beams passing through a half-plane screen is derived and used to study the propagation dynamics of on-axis and off-axis vortex diffracted beams, and to compare with the case of the free-space propagation. It is shown that there may exist many phase singularities or no phase singularity of vortex diffracted Gaussian beams in the diffraction field. Number and position of phase singularities are dependent on the vortex position at the source plane and propagation distance. The creation, motion and annihilation of phase singularities in the diffraction field may appear by varying the vortex position and propagation distance.     

Phase singularity annihilation of focused partially coherent beams

Expressions for focused Gaussian Schell-model (GSM) beams are derived and used to study the annihilation and subwavelength structures of phase singularities in the focal region, and to compare with the case of fully coherent Gaussian beams. It is found that the truncation parameter δ and normalized coherence length ε both affect the presence and spatial distribution of phase singularities in the focal plane. Additionally, during the creation and annihilation process the saddle point near the phase singularity does not disappear in the focal plane for GSM beams.     

The Effect of the Spin Angular Momentum on the Tight-Focusing Vortex Hollow Gaussian Beams

The propagation properties of a hollow Gaussian beam (HGB) carrying on-axis and off-axis vortices through a high numerical aperture lens are investigated. The intensity of the focused beam in the focal plane can be controlled by choosing the different topological charges, the beam order, and the semi-aperture angle. As intrinsic properties, vortex beams possess both spin and orbital angular momenta. The spin angular momenta (SAM) density can be treated as a vector in 3D since it exists in arbitrary orientation during the beam propagation. The vectors of SAM density orientation of the focused beam in 3D rotate around the central axis whose locations mainly rely on the vortices. The magnitude of the SAM density near the focus plane abruptly varies by altering the focal length of the lens. Under tightly focusing condition, two new pairs of vortices generate alternately on x and y axes in the vectorial electric fields, while the topological charges increase by one.     

Tight focusing of spirally polarized vortex beams

The tight focusing of spirally polarized focused vortex beams is analyzed numerically based on the vectorial Debye theory. The expressions for the electric field and the orbital angular momentum of focused beams are derived. It is shown that the intensity distribution in the focal plane is dependent on the specific spirally polarized state and the coefficient of the spiral polarization function. By presenting the phase contours of the component polarized in the radial direction, it is found that the radii of dislocation lines will increase with the increase of the power of the spirally polarization function. It is reveled that the same orbital angular momentum can be obtained for different spirally polarized state at certain distance along the propagation direction in the focal region. Besides, the orbital angular momentum distributions for different polarized states have fewer crossover points with each other for higher topological charge. The influence of the spirally polarized state on the orbital angular momentum in the focal plane is also studied.     

完美涡旋光中微米级粒子的受力与力矩特性分析

基于紧聚焦方法在几何焦平面处获得了完美涡旋光场,理论分析了该光场中微米级尺寸微粒受到的光学力与轨道矩。结果表明,该完美涡旋光可以在横平面上捕获微粒并驱动其绕光轴做轨道旋转运动,微粒受到的轨道矩随着拓扑荷的增大先增大后趋近于稳定。此外,分析了圆偏振、径向偏振和方位角偏振完美涡旋光对微粒施加的光学力和轨道矩。结果表明完美涡旋光的偏振态在一定程度上会影响微粒的轨道运动,圆偏振完美涡旋光更适合用于诱导微粒轨道旋转。     

Phase and polarization singularities of nonparaxial Gaussian vortex beams

The analytical expression for nonparaxial Gaussian vortex beams propagating in free space is derived, which enables us to study phase and polarization singularities in nonparaxial vector wavefields. Differing from the polarization singularities formed by two transverse electric-field components in the paraxial regime, the polarization singularities can be formed by the transverse and longitudinal electric-field components of nonparaxial beams, and there exist C-points and L-lines. The variation of the beam parameters and propagation distance will result in a shift of phase and polarization singularities, but their position relation remains unchanged and the topological relationship holds true.