相干性对X光全息图分辨率的影响

分析计算了Ｘ光束的相干性对Ｘ光全息图分辨率的影响，结论是Ｘ光无透镜傅里叶变换全息术所要求的相干长度和分辨率与样品尺雨戌二次线型关系；Ｘ光同轴全息术所要求的相干长度和分辨率的平方以及样品到全息图的距离成正比。     

激光空间相干性对照明均匀性的影响

 研究了激光相干性对照明均匀性的影响，为照明激光器的选择提供了理论参考。其中，部分相干高斯光束分解为模式间相互独立的厄米-高斯光束的迭加。采用相位屏的近似处理方法对激光通过大气湍流的传输进行计算模拟。数值模拟的结果表明：当照明光束的空间相干性降低时，其照明均匀度逐步提高。因此对于照明激光器而言，选择空间相干性较差的激光器对其照明均匀度更加有益。     

基于光束的相干特性拓展双缝实验教学实验内容

对部分相干光束的双缝实验干涉条纹进行了研究。利用转动的毛玻璃以及两个透镜构成了一个简单的产生部分相干光束的光学系统,通过调整毛玻璃与两个透镜的共焦点之间的距离,可以定量地控制光束的相干性。对不同相干性的光束经过双缝干涉之后的光强进行了实验观测,发现光束的相干性会对双缝干涉条纹的衬比度产生影响,光束的相干性越低,条纹衬比度也越小。并对实验结果进行了理论模拟,理论数值模拟的结果与实验观测结果基本一致。     

宽频带径向偏振光束的产生及传输特性

从理论和实验两方面研究宽频带径向偏振光束的产生及其传输特性。分析光束时间相干性和空间相干性对径向偏振光束的产生和传输的影响。数值模拟了宽频带径向偏振光束的传播。实验上,通过径向偏振转换器,得到径向偏振光束。通过调整入射光束的传输距离来改变光束空间相干性,研究了不同空间相干度下宽频带径向偏振的传输特性。同时还考察了光束偏振度的变化,给出了偏振度发生变化的条件,理论和实验符合较好。     

部分相干光的轨道角动量及其谱的分析研究

针对光束轨道角动量的研究主要集中在相干光束的研究，而对于部分空间相干光束的轨道角动量研究较少，依据部分相干光的Wigner分布函数推导出部分相干光的轨道角动量表达式，分析了部分相干光的轨道角动量谱特性。采用Mercer展开法得到了轨道角动量谱，计算了给定部分相干光束的轨道角动量谱，讨论了部分相干性对轨道角动量谱的影响。研究结果表明：部分相干光和相干光具有相同的轨道角动量表达式，部分相干光的轨道角动量谱随着相干性的变差而愈发弥散，携带轨道角动量的部分相干光束的轨道角动量谱比不携带轨道角动量的部分相干光束的轨道角动量谱更容易受相干度的影响。     

各向异性的非相干矢量光束的传播特性

利用坡印亭矢量,研究了相干性为各向异性的非相干矢量光束在自由空间的传输特性,得到了光束横截面上能量分布及演化,导出了角偏振光束中心出现能量峰值的条件,详细分析了相干性对偶极子光束能量旁瓣的影响,并发现各向异性的偶极子光束具有三种不同的演化形式,得到了具体判据.     

多束部分相干光抑制光强闪烁效应的仿真实验研究

为了有效抑制激光大气传输过程中引起的闪烁效应,本文围绕照明光束相干性与闪烁指数关系展开研究。首先,明确闪烁效应产生机理,建立与光束相干性相关的数学模型。然后,采用偏振分光元件将出射激光分为4束,并破坏其相干性。在此基础上,以随机相位屏为核心元件构建大气湍流仿真实验装置,评估不同光束相干性条件下的远场光斑闪烁指数。实验结果表明,4束光照明的光斑闪烁指数比单光束照明降低了75%。理论分析及实验结果均证明了多束部分相干光在抑制光强闪烁效应方面的有效性。     

上海同步辐射装置波荡器光源空间相干性的研究

利用高斯-谢尔光源模型理论与交叉谱密度函数在自由空间传输的规律, 研究了上海同步辐射装置波荡器光源(BL15U)的空间相干性; 讨论了预聚焦镜、单色器对光束空间相干性的影响;实验测量了单色光狭缝S2处光束的横向相干长度(Z方向). 理论计算表明, S2处光束的横向相干长度为66.5 μm,但实验测量结果为27 μm. 理论与实验相差较大的原因是由于S2上游光学元件预聚焦镜或单色器周期性高频振动导致了光束空间相干性的退化.实验结果表明,上海同步辐射装置波荡器光源已有较强的空间相干性, 可以满足微米尺度的硬X射线相干性实验.     

部分相干平顶光束在梯度折射率介质中的传输特性

利用广义惠更斯-菲涅尔衍射积分方法,推导出部分相干平顶光束在梯度折射率介质中传输的交叉谱密度函数解析表达式,对部分相干平顶光束在梯度折射率介质中的传输特性进行了分析,并进一步讨论了介质梯度折射率系数、光束阶数以及光束相干性对传输特性的影响.结果表明,部分相干平顶光束在梯度折射率介质中传输时的轴上光强分布呈现周期性变化了,且周期由梯度折射率系数决定,而与光束相干性无关.光束阶数越高、相干性越好、介质梯度折射率系数越大,则在介质中的轴上峰值光强越大.并且,在光强峰值位置附近的光强分布随传输距离的变化非常剧烈.     

基于调制光束的空间相干性获得局域空心光束

 通过调制部分相干光的空间相干性,实现了局域空心光束的产生。理论上根据范西泰特-策尼克定理及标量衍射积分,构造出具有一定空间相干性的部分相干光,并研究其聚焦特性。实验上采用理论上要求的光学系统来构造具有特定空间相干性的部分相干光,并采用薄透镜聚焦部分相干光。研究表明,当构造出的部分相干光经透镜聚焦,可得到局域空心光束。研究了光学系统的参数及透镜焦距对产生局域空心光束的影响,结果显示：光阑的拦截比及透镜的焦距越大,获得的空心光束的尺寸就越大。     

同步辐射的相干模式

在分析了光源相干相体积的基础上，重点研讨了第三代同步辐射中波荡器（ｕｎｄｕｌａｔｏｒ）辐射的相干模式，能谱亮度，相干光子通量等，这对提高光束线相干能量的传输效率和软Ｘ光相干学束线的设计具有重要意义。     

X‐ray dynamical diffraction Fraunhofer holography

An X‐ray dynamical diffraction Fraunhofer holographic scheme is proposed. Theoretically it is shown that the reconstruction of the object image by visible light is possible. The spatial and temporal coherence requirements of the incident X‐ray beam are considered. As an example, the hologram recording as well as the reconstruction by visible light of an absolutely absorbing wire are discussed.     

Characterization of spatial coherence of synchrotron radiation with non‐redundant arrays of apertures

A method to characterize the spatial coherence of soft X‐ray radiation from a single diffraction pattern is presented. The technique is based on scattering from non‐redundant arrays (NRAs) of slits and records the degree of spatial coherence at several relative separations from 1 to 15 µm, simultaneously. Using NRAs the spatial coherence of the X‐ray beam at the XUV X‐ray beamline P04 of the PETRA III synchrotron storage ring was measured as a function of different beam parameters. To verify the results obtained with the NRAs, additional Young's double‐pinhole experiments were conducted and showed good agreement.     

The coherent radiation fraction of low‐emittance synchrotrons

In this work the coherence properties of the synchrotron radiation beam from an X‐ray undulator in a fourth‐generation storage ring are analyzed. A slightly focused X‐ray beam is simulated using a wavefront propagation through a non‐redundant array of slits and the mutual coherence function is directly obtained and compared with the Gaussian–Schell approximation. The numerical wave propagation and the approximate analytical approaches are shown to agree qualitatively, and it is also shown that, when the coherent fraction is selected by a finite aperture before the focusing element, even achromatic focusing systems like total reflection mirrors become slightly chromatic. This effect is also well accounted for in the Gaussian–Schell model. The wavefront propagation simulation through the non‐redundant array was repeated with an imperfect mirror demonstrating that, although the wavefront is distorted, its coherent length is practically unchanged.     

A monolithic Fresnel bimirror for hard X‐rays and its application for coherence measurements

Experiments using a simple X‐ray interferometer to measure the degree of spatial coherence of hard X‐rays are reported. A monolithic Fresnel bimirror is used at small incidence angles to investigate synchrotron radiation in the energy interval 5–50 keV with monochromatic and white beam. The experimental set‐up was equivalent to a Young's double‐slit experiment for hard X‐rays with slit dimensions in the micrometre range. From the high‐contrast interference pattern the degree of coherence was determined.     

High‐efficiency coherence‐preserving harmonic rejection with crystal optics

This work reports a harmonic‐rejection scheme based on the combination of Si(111) monochromator and Si(220) harmonic‐rejection crystal optics. This approach is of importance to a wide range of X‐ray applications in all three major branches of modern X‐ray science (scattering, spectroscopy, imaging) based at major facilities, and especially relevant to the capabilities offered by the new diffraction‐limited storage rings. It was demonstrated both theoretically and experimentally that, when used with a synchrotron undulator source over a broad range of X‐ray energies of interest, the harmonic‐rejection crystals transmit the incident harmonic X‐rays on the order of 10^?6. Considering the flux ratio of fundamental and harmonic X‐rays in the incident beam, this scheme achieves a total flux ratio of harmonic radiation to fundamental radiation on the order of 10^?10. The spatial coherence of the undulator beam is preserved in the transmitted fundamental radiation while the harmonic radiation is suppressed, making this scheme suitable not only for current third‐generation synchrotron sources but also for the new diffraction‐limited storage rings where coherence preservation is an even higher priority. Compared with conventional harmonic‐rejection mirrors, where coherence is poorly preserved and harmonic rejection is less effective, this scheme has the added advantage of lower cost and footprint. This approach has been successfully utilized at the ultra‐small‐angle X‐ray scattering instrument at the Advanced Photon Source for scattering, imaging and coherent X‐ray photon correlation spectroscopy experiments. With minor modification, the harmonic rejection can be improved by a further five orders of magnitude, enabling even more performance capabilities.     

光学元件表面粗糙度对第三代同步辐射光源空间相干性的影响

以单丝的同轴全息干涉花样为判别标准,通过计算机数值模拟,研究了Ｂｅ窗的表面粗糙度对硬Ｘ射线相干特性的影响。提出了Ｘ射线在粗糙表面反射的一个简单模型,以此为基础模拟研究了反射镜表面粗糙度的对硬Ｘ射线及软Ｘ射线空间相干特性的影响,模拟结果与实验结果相符。     

Versatility of a hard X‐ray Kirkpatrick–Baez focus characterized by ptychography

In the past decade Kirkpatrick–Baez (KB) mirrors have been established as powerful focusing systems in hard X‐ray microscopy applications. Here a ptychographic characterization of the KB focus in the dedicated nano‐imaging setup GINIX (Göttingen Instrument for Nano‐Imaging with X‐rays) at the P10 coherence beamline of the PETRA III synchrotron at HASLYLAB/DESY, Germany, is reported. More specifically, it is shown how aberrations in the KB beam, caused by imperfections in the height profile of the focusing mirrors, can be eliminated using a pinhole as a spatial filter near the focal plane. A combination of different pinhole sizes and illumination conditions of the KB setup makes the prepared optical setup well suited not only for high‐resolution ptychographic coherent X‐ray diffractive imaging but also for moderate‐resolution/large‐field‐of‐view propagation imaging in the divergent KB beam.     

Development of dispersive XAFS system for analysis of time‐resolved spatial distribution of electrode reaction

Apparatus for a technique based on the dispersive optics of X‐ray absorption fine structure (XAFS) has been developed at beamline BL‐5 of the Synchrotron Radiation Center of Ritsumeikan University. The vertical axis of the cross section of the synchrotron light is used to disperse the X‐ray energy using a cylindrical polychromator and the horizontal axis is used for the spatially resolved analysis with a pixel array detector. The vertically dispersive XAFS (VDXAFS) instrument was designed to analyze the dynamic changeover of the inhomogeneous electrode reaction of secondary batteries. The line‐shaped X‐ray beam is transmitted through the electrode sample, and then the dispersed transmitted X‐rays are detected by a two‐dimensional detector. An array of XAFS spectra in the linear footprint of the transmitted X‐ray on the sample is obtained with the time resolution of the repetition frequency of the detector. Sequential measurements of the space‐resolved XAFS data are possible with the VDXAFS instrument. The time and spatial resolutions of the VDXAFS instrument depend on the flux density of the available X‐ray beam and the size of the light source, and they were estimated as 1 s and 100 µm, respectively. The electrode reaction of the LiFePO₄ lithium ion battery was analyzed during the constant current charging process and during the charging process after potential jumping.     

Multimodal hard X‐ray imaging of a mammography phantom at a compact synchrotron light source

The Compact Light Source is a miniature synchrotron producing X‐rays at the interaction point of a counter‐propagating laser pulse and electron bunch through the process of inverse Compton scattering. The small transverse size of the luminous region yields a highly coherent beam with an angular divergence of a few milliradians. The intrinsic monochromaticity and coherence of the produced X‐rays can be exploited in high‐sensitivity differential phase‐contrast imaging with a grating‐based interferometer. Here, the first multimodal X‐ray imaging experiments at the Compact Light Source at a clinically compatible X‐ray energy of 21 keV are reported. Dose‐compatible measurements of a mammography phantom clearly demonstrate an increase in contrast attainable through differential phase and dark‐field imaging over conventional attenuation‐based projections.