相位屏法模拟高斯阵列光束海洋湍流传输特性

基于功率谱反演法产生海洋湍流相位屏,对多次传输过程进行统计平均,仿真分析不同海洋湍流参量下不同高斯阵列光束(矩形分布、径向分布及单束)长曝光光斑半径、光斑质心漂移特性及光强闪烁特性。结果表明:光束长曝光光斑半径、光斑质心漂移标准差及轴上闪烁系数均随湍流效应(湍流强度或传输距离)的增强而增大;同时,阵列光束与单束高斯光的光斑半径趋于一致,当传输距离继续增大时,单束高斯光束长曝光光斑半径略大。相对于单束高斯光,阵列光束在相同湍流条件下具有更小的漂移标准差,但轴上闪烁系数较大。相对于大气湍流而言,海洋湍流具有较强的闪烁效应。     

超短脉冲径向偏振光束的解析解及时空耦合效应

从超短脉冲光束的傍轴传输方程出发, 运用傅里叶变换和相关数学算符的对易性, 得到了超短脉冲径向偏振光束的解析表达式.该解可适用于任意脉冲驱动的径向偏振光束. 基于该解析表达式并结合具体例子,讨论了超短脉冲径向偏振光束在自由空间中的传输性质. 结果表明, 在传输过程中时空耦合主要体现在光束边沿的脉冲延迟. 这一效应导致了脉冲不同时间位置处横向光强分布随传输的变化, 以及脉冲前后沿关于束腰的不对称性. 本文的方法同样适用于得到超短脉冲方位角偏振光束的解析解和传输性质.     

超短脉冲径向偏振光束的解析解及时空耦合效应

从超短脉冲光束的傍轴传输方程出发,运用傅里叶变换和相关数学算符的对易性,得到了超短脉冲径向偏振光束的解析表达式,该解可适用于任意脉冲驱动的径向偏振光束.基于该解析表达式并结合具体例子,讨论了超短脉冲径向偏振光束在自由空间中的传输性质.结果表明,在传输过程中时空耦合主要体现在光束边沿的脉冲延迟.这一效应导致了脉冲不同时间位置处横向光强分布随传输的变化,以及脉冲前后沿关于束腰的不对称性.本文的方法同样适用于得到超短脉冲方位角偏振光束的解析解和传输性质.     

一维线阵离轴高斯光束通过湍流大气的传输特性

研究了一维(1D)线阵离轴高斯光束通过湍流大气的传输特性，推导出了其光强传输方程. 研究表明，1D线阵离轴高斯光束通过湍流大气传输经历了三个阶段，即在近场其光强分布为类似于入射光的锯齿状分布，随着传输距离的增加逐渐变为平顶分布，最后在远场成为类高斯分布. 湍流的增强会使光束传输经历三阶段的进程加快. 并且，湍流使得不同子光束数的1D线阵离轴高斯光束的归一化光强分布相接近. 此外，子光束数越多的1D线阵离轴高斯光束受到湍流的影响越小；1D线阵离轴高斯光束较高斯光束受到湍流的影响要小. 关键词： 一维(1D)线阵离轴高斯光束 湍流大气 传输特性     

离轴椭圆矢量光场传输中的光斑演变

对离轴椭圆矢量光场的传输特性进行了研究. 推导出离轴椭圆矢量光场在自由空间传输电场和光强的解析表达式. 数值分析结果表明, 离轴高阶圆柱矢量光场具有非对称的光强分布, 传输后的光强分布由传输距离、错位位移、椭圆率决定. 在传输过程中除了光斑会展宽外, 光场中的暗斑会逐渐消失, 最终趋于一种稳态光强分布; 相对于初入射平面的椭圆光斑, 稳态椭圆光斑长短轴互换了. 研究结果有助于深入理解离轴情况下椭圆矢量光场的动态传输特性, 同时可以指导实际椭圆矢量光场的校准.     

部分相干离轴涡旋光束在大气湍流中的光强分布

根据广义惠更斯-菲涅耳原理以及交叉谱密度函数,利用Kolmogorov湍流谱推导得到部分相干离轴涡旋光束在大气湍流中传输时光束的光强分布表达式,讨论了离轴距离、拓扑荷数、束腰宽度、相干长度、传输距离、湍流强度参数对光强分布的影响。仿真结果表明,拓扑荷数的大小不会改变暗核的位置;离轴距离的正负号决定了暗核移动的方向和光强集中区域的方向;暗核向上移动的距离随相干长度、束腰宽度的增大而减小,随传输距离、湍流强度的增大而增大;光斑展宽随相干长度、束腰宽度、传输距离、湍流强度的增大而增大。     

聚焦径向调制Bessel-Gaussian光束实现亚波长尺寸纵向偏振光束

亚波长尺寸纵向偏振光束在粒子加速,单个分子偶极矩测量,二次谐波成像和纵向偏振共焦显微镜等方面有非常广泛的应用.本文提出径向调制的Bessel-Gaussian光束模型,经高数值孔径显微物镜聚焦可以获得高纯度的纵向偏振光束.利用矢量衍射理论数值模拟了焦点附近光强分布、磁场分布和能流密度空间分布.结果表明光斑半高全宽度可以达到0.4λ.该方法无需环形孔径或环形相位滤波器,光能利用率高,分辨率好,达到改进各种应用的效果. 关键词： Bessel-Gaussian光束 纵向偏振光束 聚焦 亚波长     

初级球差对矢量柱状贝塞耳-高斯光束聚焦场的影响

通过柱坐标下的的分析方法,获得径向偏振和方位角偏振贝塞耳-高斯光束经具有球差的高数值孔径系统聚焦后的三维光场分布函数,根据光场分布函数模拟了不同球差系数下贝塞耳-高斯光束在焦平面和通过焦点的纵向切面上的光场分布.结果表明,在球差系数增加时,方位角偏振贝塞耳-高斯光束在焦平面上的圆环状光斑内半径逐渐变小到趋于恒定,而外环半径先减小后增大;而衍射焦点偏离高斯焦点的距离越来越大,纵向光强不再对衍射焦平面呈对称分布,调整离焦距离无法完全消除球差的影响;径向偏振贝塞耳-高斯光束会聚场的光强随初级球差的变化规律与方位角偏振贝塞耳-高斯光束的一致.     

离轴拉盖尔-高斯涡旋光束传输中的光斑演变

在产生涡旋光束过程中, 固体激光器所输出的光束中心 很难与螺旋相位板的中心完全对准, 实际出射的光束为离轴涡旋光束. 在衍射理论的基础上, 对离轴涡旋光束的传输进行了研究, 推导了离轴涡旋光束传输一段距离后电场和光强的解析表达式.研究表明, 与理想的涡旋光束不同, 离轴涡旋光束具有非对称性的光强分布, 在传输过程中光斑除了展宽外, 涡旋暗核还会发生移动. 拓扑电荷数的大小只影响到光束的展宽, 拓扑电荷数为正时, 暗核沿着逆时针切线方向移动; 拓扑电荷数为负时, 暗核沿着顺时针的切线方向移动, 该结果对长距离探测涡旋光束的对准问题起到指导作用.     

径向偏振高阶贝塞尔-高斯涡旋光束的传输及其偏振特性

理论和实验研究了径向偏振高阶贝塞尔-高斯涡旋光束在自由空间传输的光强分布和偏振特性.数值计算表明,在无衍射区域,随着传输距离的增加,光强分布基本保持不变;对于零阶光束,其偏振态一直保持径向偏振不变;对于高阶光束,其偏振态发生变化,由初始的径向偏振逐渐变为椭圆偏振和线偏振的杂化状态.实验上,利用径向偏振转换器、螺旋相位板和轴棱锥元件产生了径向偏振高阶贝塞尔-高斯涡旋光束,探测了其通过不同偏振片后的光强分布.实验结果与理论结果基本相符合.该研究也提供了一种产生杂化偏振矢量光束的方法.     

Effect of annular apodization and pupil beam parameter in the focal region of high NA lens

Focusing properties of the radially polarized axisymmetric Bessel-modulated Gaussian beam with quadratic radial dependence (QBG beam) and annular aperture are investigated theoretically by vector diffraction theory. Simulation results show that the intensity distribution in the focal region of the radially polarized axisymmetric QBG beam can be adjusted considerably by small beam parameter (μ) and annular aperture (δ). When μ increases, the focal spot may change to focal hole and changes focal pattern remarkably. On introducing annular aperture, focus can split or extends along the optical axis for different μ. In this paper, we have shown the generation of the focal spot, dark focal spot, focal split and increase in focal depth in the axial direction of the incident beam propagating through the aligned optical system.     

Efficient extracavity generation of radially and azimuthally polarized beams

We demonstrate an efficient transformation of a linearly polarized Gaussian beam to a radially or an azimuthally polarized doughnut (0,1)* Laguerre-Gaussian beam of high purity. We use a spatially variable retardation plate, composed of eight sectors of a lambda/2 retardation plate, to transform a linear polarization distribution to radial/azimuthal distribution. We transformed an Nd:YAG Gaussian beam with M(2)=1.3 to a radially and azimuthally polarized (0,1)* Laguerre-Gaussian beams with M(2)=2.5 and degree of radial/azimuthal polarization of 96-98%.     

Experimental Research on Focusing Property of Radially Polarized Beam Based on Solid Immersion Lens

Realization of a near-field optical virtual probe based on an evanescent Bessel beam is strongly dependent on a radially polarized beam; this makes it essential to study the focusing property of the beam. In this paper, two experimental setups based on a fiber device and a liquid crystal device, respectively, are built to generate a radially polarized beam. This beam and an annular radially polarized beam are focused by means of a high numerical aperture objective and a solid immersion lens (SIL). Near-field distribution of the focus spot, the evanescent Bessel field, is experimentally measured with a scanning near-field optical microscope (SNOM). The full width at half maximum (FWHM) of the central peak of the evanescent Bessel field is about 200 nm in the close vicinity of the bottom surface of SIL. This has potential for use as a near-field optical virtual probe.     

大数值孔径光子筛偏振特性研究

根据角谱理论建立不同偏振照明条件下的光子筛矢量衍射模型。在此基础上,对入射光分别为线偏振光、径向偏振光、切向偏振光三种特殊偏振状态下的光子筛聚焦光强分布进行了模拟分析。研究结果表明,对于大数值孔径光子筛,入射光的偏振特性将对光子筛聚焦光强分布产生巨大影响。线偏振光将使聚焦光斑沿偏振方向拉伸,切向偏振光产生的聚焦光斑具有"中空"结构,而径向偏振光所产生的聚焦光斑呈较为规则的圆形,且其焦深优于线偏照明情况。在激光直写及高分辨成像等光子筛典型应用中采用径向偏振照明将进一步提高系统分辨力。     

Investigation of Near-Field Imaging Characteristics of Radial Polarization for Application to Optical Data Storage

Radially polarized incident light can generate a more confined longitudinal electric field on a focal plane in near-field (NF) optics than focusing circularly polarized light. Using this phenomenon, it is feasible to reduce beam spot size on storage media to increase the areal density of optical data storage. A radially polarized beam generates a beam spot which is 20% more confined on the 1st surface of medium than that of circularly polarized light. However, the peak intensity of total electric field sharply decreases and its transverse component is much more dominant inside the media stack. This confirms that radially polarized optics can be a candidate not for an NF recording system but for an NF read-only memory (ROM) system. Potentially, the results could be useful to understand the effect of radial and circular polarizations inside and outside medium for various applications of NF optics.     

Realization of a subwavelength focused spot without a longitudinal field component in a solid immersion lens-based system

In a solid immersion lens (SIL)-based system, we predict theoretically that, by using the illumination of an azimuthally polarized beam with helical phase (APH), the subwavelength focusing can be simultaneously realized both in SIL and the third medium in spite of the presence of an air gap between the SIL and the third medium, which is not easily achieved in the case of the illumination of linearly, circularly, and radially polarized beams. For the APH illumination, the field in the focal region of the multilayered medium has no longitudinal component, and the on-axis intensity of the focused spot is nonzero. The APH illumination extends the capacity of SIL in realizing a supersmall focused spot, which is useful in microscopy, near-field optics, recording optics, and lithographic optics.     

Calculation of optical trapping forces on a dielectric sphere in the ray optics regime produced by a radially polarized laser beam

We calculated the optical trapping forces on a microscopic particle in the ray optics regime for the case where a radially polarized laser beam is applied. A higher axial trapping efficiency than for a circularly polarized doughnut beam was predicted due to the large p polarization component. Three-dimensional optical trapping was expected for particles with a larger index of refraction and for objectives with a smaller numerical aperture.     

Generation of multiple sub wavelength focal spot segments using radially polarized Bessel Gaussian beam with complex phase filter

We propose a new approach for generating multiple focal spot segment of sub wavelength size, by tight focusing of phase modulated radially polarized Bessel Gaussian beam. The focusing properties are investigated theoretically by vector diffraction theory. We observed that focal segment with multiple focal spots structure separated with different axial distance can be generated by properly tuning the phase of the incident radially polarized Bessel Gaussian (BG) beam. Potential applications of this focal shaping technique are also discussed.     

Tight focusing of phase modulated radially polarized hollow Gaussian beam using complex phase filter

We propose a new approach for generating multiple focal spot segment of sub wavelength size, by tight focusing of phase modulated radially polarized hollow Gaussian beam. The focusing properties are investigated theoretically by vector diffraction theory. We observed that focal segment with multiple focal spots structure separated with different axial distance can be generated by properly tuning the phase of the incident radially polarized hollow Gaussian (HGB) beam. Potential applications of this focal shaping technique are also discussed.