基于L型线阵的二维分布源参数估计方法

针对二维分布源信号波达方向估计问题,提出了一个新的二维分布源模型及其参数估计方法。将基于角度信号密度函数的一维相干分布源模型扩展至二维,推导了二维分布源的广义阵列方向向量。在L型线阵下,利用广义MUSIC算法,首先估计出俯仰角及其扩散参数,然后利用估计出来的俯仰角及扩散参数对方位角及扩散参数进行估计。仿真实验表明,所提出的二维相干分布源参数估计算法具有良好的定向精度。     

Thue-Morse 光子晶体的格点形状对衍射特性的影响

根据傅里叶光学原理,研究了二维Thue-Morse准周期光子晶体结构的格点形状对其远场衍射特性的影响.通过对二维Thue-Morse准周期光子晶体远场衍射图案的分析表明,格点形状对低阶结构的衍射光场有明显影响,但不改变高阶结构的衍射光场分布,仅衍射精细结构的光强度有细微差别.为了证实数值模拟的结果,采用电子束刻蚀技术在...     

X射线多晶面探测器衍射系统及其应用

介绍了目前世界上先进的粉末衍射系统——X射线多晶面探测嚣衍射系统的主要配置、工作原理、二维衍射几何关系以及X射线多晶面探测器衍射系统在材料学研究中的典型应用，重点讨论了在金属的晶体学织构和应力研究中的应用。     

基于可调谐二极管激光吸收光谱技术的炉内燃烧场参数在线监测系统设计

基于可调谐二极管激光吸收光谱(tunable diode laser absorption spectroscopy,TDLAS)技术,设计了炉内多燃烧场参数(温度,CO、CO₂和NO浓度等)同时在线监测技术方案,包括一维燃烧参数监测系统和多维燃烧参数监测系统。在一维燃烧参数监测系统中,引入光开关技术实现多个燃烧参数的同时测量。在二维燃烧参数监测系统中,引入分光器技术和代数迭代算法(algebraic reconstruction technique,ART)实现平面内二维燃烧参数的反演和测量。在此基础上,设计了三维燃烧参数监测系统,三维燃烧参数测量步骤为：先将炉内燃烧区域划分为多层二维切片;再基于ART法重建二维燃烧参数;最后基于多层二维燃烧参数数据重构三维燃烧参数。本文所设计的炉内燃烧场参数监测系统有利于未来锅炉精细化调整。     

一种新型近似无衍射栅型结构光及其实现方法

本文提出一种新型的近似无衍射栅型结构光的概念与实现方法.该结构光具有焦深长、线宽细、在一定范围内光场分布稳定,光场光强不变等特点.文中采用精密三角截面棱镜组成的光学系统生成近似无衍射栅型线结构光,用惠更斯一菲涅尔原理及基尔霍夫衍射理论对该系统进行了理论分析和计算,并在无衍射范围内对近似无衍射栅型结构光的光场分布进行了数值仿真.文中对系统进行了实验对比及验证,结果表明,实验数据与理论计算及仿真结果基本一致.应用文中的系统参数,获得了条纹宽度为18 μm,焦深范围为570 cm的近似无衍射栅型结构光,其条纹宽度及光场强度分布不随距离而变化.与传统的光源相比,近似无衍射栅型结构光在三维轮廓测量等应用中具有分辨率高、精度高等优势.     

NiTi非晶薄膜的径向分布函数及结构分析

径向分布函数（RDF）是描述非晶态材料结构的重要工具,一般是通过对衍射强度的解析计算得到的。RAD程序是根据非晶材料X射线衍射数据计算其径向分布函数的集成程序。介绍了该程序的结构和应用方法,并采用RAD程序计算了采用磁控溅射法制备不同成分NiTi合金的径向分布函数,利用径向分布函数计算了非晶微结构参数。结果表明非晶薄膜中钛含量不同影响了非晶微结构参数。     

基于衍射光栅的二维纳米位移测量技术

提出了一种基于正交衍射光栅作为测量基准元件的二维激光干涉测量系统.利用正交光栅的空间对称级的衍射光进行干涉,基于多普勒效应,采用偏振检测的方法获得相位相差90°的干涉信号.通过光电检测把获得的正弦和余弦信号进行相位细分,系统可在平面二维方向上实现纳米级的分辨率.该系统相比其他干涉测量系统,测量结构紧凑,环境因素对其影响较小,可应用于较大行程的平面微位移精密检测.     

柔性板的多变量频域辨识及其主动控制

从控制系统的角度出发，利用压电陶瓷作为传感器和作动器，研究了二维柔性板的多变量频域建模问题。对一个柔性板物理实验系统．采用最小二乘法在频率域中建立了二输入二输出传递矩阵描述，设计了基于辨识模型的多变量最优调节控制器，并在上述柔性板物理实验系统上针对初始扰动、持续正弦扰动、窄带随机扰动等典型形式的扰动进行了实验验证。结果显示，控制对象的弯曲和扭转振动模态都得到了有效抑制。由此证明了辨识模型的有效性，同时也表明采用集中参数模型在一定的范围内是可以描述本质上是无穷维分布参数系统的。     

用计算机模拟光栅光谱次级明纹相对强度的分布

根据惠更斯-菲涅耳原理,应用MATLAB软件编程,模拟光栅光谱次级明纹光强的分布图形,通过改变光栅缝数、光栅常数和缝宽等参数,观察到光栅衍射次级明纹强度的相应变化,得出缝数越多,次级明纹的相对强度越小,而光栅常数和缝宽的变化只能改变次级明纹的分布。用计算机模拟光栅衍射,尤其对于课堂教学具有很直观效果。     

微构件拉伸测试辅助引导对中测量系统设计

设计了一套微构件拉伸测试辅助引导对中测量系统,该系统以激光准直特性为基础并结合折反射定律,采用正交二维相机获得包含平移和角偏移的激光光点图像信息,建立了二维位移和二维角偏移与激光器成像点变化的数学模型。搭建了实验平台,依据该模型,利用MATLAB对获取图像进行处理获得需要调整的二维平移和角偏移参数变量。实验结果表明,该测量系统的二维角偏移分辨率可达到0.001°,重复性优于0.02°;二维位移分辨率可达到亚微米,重复性优于10μm。可为微构件拉伸测试中辅助引导对中提供调整参数并提高拉伸测试数据的准确性。     

厄米双曲余弦高斯光束的焦开关

对双曲余弦高斯光束通过光阑透镜分离系统的轴上光强分布做了详细的数值分析。研究发现,在一定条件下轴上存在两个光强极大值点,并且在这两个极大值点相互竞争中会出现焦点位置的有效置换,即出现焦开关。厄米双曲余弦高斯光束产生焦开关的条件是:光阑与透镜相对间距为1,光束阶数为偶数,光束参数小于其相应的临界值,截断参数在它的两个临界值之间。进一步研究表明,焦点位置相对跃迁量和轴上相对光强下凹量随光束参数的减小而增大,但是随着截断参数的增大焦点位置相对跃迁量和轴上相对光强下凹量将分别出现一个极大值。在大范围调焦的应用中,可利用焦开关实现调焦之目的;在精密聚焦的激光应用中,应控制焦开关的产生。     

Measurement of the three-dimensional intensity distribution in the neighborhood of a paraxial focus

We describe a technique for measuring the three-dimensional(3D) intensity distribution of a paraxial focus, based on scanning a CCD image sensor along the optical axis and on subsequently analyzing the data. We demonstrate the possibility of measuring high-resolution 3D intensity maps of the focal field, down to intensities of more than 5 orders of magnitude below that in the focal point, and show the excellent agreement with scalar diffraction theory. Further applications of the technique are indicated.     

X-ray diffraction investigation of cation distribution in CdχCu1-χFe2O4 ferrite system

Assuming the distribution of copper ions on tetrahedral (A) and octahedral (B) sites in the polycrystalline Cd_χCu_1-χFe₂O₄ (χ=0.2, 0.4, 0.6, 0.8 and 1.0) ferrite system, the theoretical intensities are calculated. Structural refinement of the diffraction pattern converges the R factor to between 0.0103 and 0.0315. Theoretical intensity ratios of (220) to (222) planes are considered, as these reflections are sensitive to cations on the A and B sites. Close agreement of the theoretical intensity ratio with the intensity ratio observed from X-ray diffraction pattern supports the occupancy of cadmium on the tetrahedral site. The cation distribution is predicted employing a new method wherein a graph of theoretical intensity is plotted against the inversion parameter for the (220) plane. The experimentally observed intensity of the same plane is then used to get an exact inversion parameter with the help of this plot. The cation distribution estimated by this method supports the cation distribution predicted by the magnetization method.     

经穴磁刺激线圈优化设计与仿真

经穴磁刺激与传统针灸、电刺激相比具有无创伤、无不适感、易重复和进行深部刺激等独特优点.磁刺激系统中载流线圈设计对磁场强度和磁场分布具有重要作用.在理论分析载流线圈磁场分布基础上,设计了不同8字形和碗状结构磁刺激线圈,并采用Ansys有限元分析软件对线圈沿径向和轴向产生的磁场分布进行仿真,研究8字形和碗状结构线圈的磁场聚焦性和刺激深度.结果表明,碗状线圈具有较好的磁场聚焦性且有一定的刺激深度,在皮层下1.5～2 cm左右仍有3～10 mT的磁场强度.同时获得了适合于经穴磁刺激系统的最佳线圈形状和参数,为穴位磁刺激技术应用于临床治疗奠定了良好基础.     

High-aspect-ratio line focus for an x-ray laser by a deformable mirror

A high-aspect-ratio line focus is required on a plane target in x-ray laser experiments for obtaining a high gain-length product. Inherent wave-front aberrations in line-focusing optics, which consist of a cylindrical lens and a spherical lens, are discussed with respect to beam diameter. The nonuniformity of the linewidth that is due to the aberrations is also calculated by the ABCD matrix method. A deformable mirror of a continuous plate type with a diameter of 185 mm provides an adequate wave-front distribution for compensating for the wave-front aberration. The wave-front control by the deformable mirror realizes a fine linewidth of 25 mum and 18.2 mm long, corresponding to the aspect ratio of 728. The linewidth is three times the diffraction limit. The intensity distribution along the line focus is also improved.     

标准硅球直径精密测量系统的设计

基于多光束干涉的基本原理，导出了使用斐索干涉仪测量硅球直径多光束干涉光强分布的精确公式。针对目前的硅球直径测量系统忽略了多次反射对干涉信号造成的影响和系统中固有的条纹清晰度低的问题，研究了多次反射对干涉信号造成的误差，结果表明其最大光强误差可达到8％。通过对光学干涉系统结构设计和元件参数选择，最大限度地优化了干涉条纹的可见度，并设计出零背景光强标准硅球直径精密测量系统。数值模拟结果表明，该系统不仅极大地提高了干涉条纹对比度、消除了背景噪声，而且可通过改变透镜焦距调节干涉条纹的强度以达到CCD的最佳工作范围，从而提高了光强信号的测量准确度。     

Experimental observation of truncated fractional Fourier transform for a partially coherent Gaussian Schell-model beam

The truncated fractional Fourier transform (FRT) is applied to a partially coherent Gaussian Schell-model (GSM) beam. The analytical propagation formula for a partially coherent GSM beam propagating through a truncated FRT optical system is derived by using a tensor method. Furthermore, we report the experimental observation of the truncated FRT for a partially coherent GSM beam. The experimental results are consistent with the theoretical results. Our results show that initial source coherence, fractional order, and aperture width (i.e., truncation parameter) have strong influences on the intensity and coherence properties of the partially coherent beam in the FRT plane. When the aperture width is large, both the intensity and the spectral degree of coherence in the FRT plane are of Gaussian distribution. As the aperture width decreases, the diffraction pattern gradually appears in the FRT plane, and the spectral degree of coherence becomes of non-Gaussian distribution. As the coherence of the initial GSM beam decreases, the diffraction pattern for the case of small aperture widths gradually disappears.     

Non-paraxial analytical solution for the generation of focal curves

Abstract

A solution for the transmittance of elements forming planar and nonplanar focal curves in the non-paraxial case is proposed in this paper. The treatment is based on the scalar diffraction theory and makes use of the stationary phase method in evaluation of the diffraction integral. The equation of a stationary point enables one to establish mapping relations between the geometrical regions of the element and the corresponding points of the focal curve. These regions turn out to be described by conical curves. The mapping relations can be manipulated by a phase function imposed onto the focal curve. The amplitude factors of the derived transmittances can be omitted and the desired intensity distribution along the focal curve can then be obtained by an appropriate change in the aperture of pure phase elements. The approach is illustrated by examples of elliptical, hyperbolic, conical and circular zone plates. The focus generations for both non-paraxial and paraxial cases of these elements are compared using numerical simulations.     

On the spherical X-ray wave focusing upon backscattering from a biaxially bent crystal

It is shown that a spherical X-ray wave incident at the Bragg angle θ_B≈π/2 onto a biaxially bent crystal exhibits independent diffraction in two mutually perpendicular planes. An analytical formula for the size of the diffraction reflection region in the backscattering mode is derived and the analytical expression for the wave intensity distribution at the two-dimensional focus is refined.     

Droplet profiles obtained from the intensity distribution of refraction patterns

A noninterferometric method for obtaining profiles of axially symmetric transparent liquid droplets is described. The drops are illuminated along the symmetry axis by a uniform parallel beam whose intensity distribution is recorded at the focal plane of a lens placed behind the drop. In some conditions and within the geometrical optics approach, it is possible to reconstruct the profile of the drop from this intensity distribution except for the length scale factor, which, if necessary, may be provided by an additional simple measurement. Because of CCD cameras and digital image processing, this method is an interesting alternative technique for measuring drop profile shapes with considerable accuracy when interferometry is unwieldy. We also analyze the diffraction features of the intensity distribution to clarify the extent that they affect the approach that we used and to establish additional information that they may provide.