X射线全息术

本文介绍了Ｘ射线全息术的工作原理和进展状况，详细地论述了与Ｘ射线全息术有关的Ｘ射线光学、Ｘ射线光学元件和Ｘ射线源的特性，并讨论了Ｘ射线全息实验的要求和记录方式，最后着重探讨了包括记录过程和重现过程中影响Ｘ射线全息术分辨率的各种因素。     

X射线全息术

本文介绍了Ｘ射线全息术的工作原理和进展状况,详细地论述了与Ｘ射线全息术有关的Ｘ射线光学、Ｘ射线光学元件和Ｘ射线源的特性,并讨论了Ｘ射线全息实验的要求和记录方式,最后着重探讨了包括记录过程和重现过程中影响Ｘ射线全息术分辨率的各种因素。     

X射线透明

通常气体原子吸收一定频率的光，这种频率对应于气体原子中两个量子能级之间的能量差。但是如果存在第三个能级，则可能产生所谓电磁诱发透明的量子现象。为产生这种现象，用一束激光作为抽运束，造成第二个与第三个能级的相干叠加，成为所谓的“缀饰态”。如果调谐得适当，由第一态到两个缀饰态的跃迁发生相消干涉。     

X射线物理学

X射线自1895年被发现以来,为科学研究提供了丰富多样的探测和分析手段。随着以同步辐射为代表的先进X射线光源的出现,X射线实验方法不断发展,已经成为推动前沿基础和应用科学研究突破的重要实验手段。文章从X射线与物质的相互作用出发,简要阐述X射线实验方法如何探测不同的物理研究对象,如局域结构、晶体结构、纳米尺度结构、表面界面结构、电子结构、自旋结构等。最后展望更先进的X射线光源为科学研究带来的机遇。     

X射线纳米诊断器

近百年来 ,在牙科与其他医学诊治中 ,Ｘ射线源是作为一种不变的诊断工具 .它是在一个真空管中将阴极加热到 15 0 0℃后就会发射一系列电子 ,当电子飞越过真空管后冲击靶极 ,最终发射出足够数量的Ｘ射线 .现在美国北卡罗米纳大学的ＯｔｔｏＺｈｏｕ博士与北卡罗来纳洲的纳米技术应用研究所合作第一次制造出了一种新颖的Ｘ射线纳米诊断器 .它是由一组碳纳米管所组成 ,在室温下能产生出电子束并释放出充足的Ｘ射线通量 ,以保证满足医学图像的需求 .这种新式的诊断器要比老式的仪器小巧适用 ,具有较快的响应速度 ,同时它还具有控制Ｘ射线脉冲的…     

X射线的发现

 著名物理学家丁肇中在瑞典为他举行的诺贝尔奖发奖宴会上说过:“自然科学理论不能离开实验的基础,特别是物理学是从实验产生的.”自从伦琴1901年获得首届诺贝尔奖以来,已经有94人因杰出的实验工作而获奖,占九十年获奖总数的67.1%.这充分说明实验在现代物理学发展中具有特殊的作用.鉴于此,本刊新辟《荣获诺贝尔奖的著名实验》栏目,除了介绍诺贝尔物理奖得主的生平事迹与科学贡献外,还将分析这些实验的物理思想。发展渊源和深远影响,并刊发一些有历史意义的图片资料.希望广大读者能从中温故知新,获得启迪,增进对物理实验的认识与喜爱.     

X射线相衬成像

本文介绍了近年来X射线位相衬度成像技术的发展状况，详细论述了X射线干涉相衬、衍射增强相衬，类同轴相衬和数字位相重构等几种典型的成像原理，讨论了影响成像衬度与分辨率的若干因素，并对位相成像的发展趋势作了展望。     

X射线荧光谱分析

XRF分析标准方法的进展K. Norrish 澳大利亚联邦科学与工业研究组织,土壤部.PB2,Glen Osmend,南澳大利亚.5064 XRF分析技术已得到广泛应用,特别是在采矿工业中更是如此。最初,这些方法用来控制流程并在室内分析,但是由于该方法所具备的长处带来了改进准确度的希望,而成为限     

X射线相衬成像

本文介绍了近年来X射线位相衬度成像技术的发展状况,详细论述了X射线干涉相衬、衍射增强相衬,类同轴相衬和数字位相重构等几种典型的成像原理,讨论了影响成像衬度与分辨率的若干因素,并对位相成像的发展趋势作了展望。     

磁性X射线散射

当一束X射线射入晶体时,它被构成晶体的原子周围的电子电荷所散射.由这种电荷散射所产生的X射线衍射,是研究凝聚态物质结构的有力工具.然而,由于X射线是电磁波谱的一部分,它不仅受到电荷的散射,也与电子磁矩发生相互作用,产生磁散射.早在1929年,Klein和Nishian在研究Compton 散     

一种激光驱动的超短X射线光源

介绍一种可产生超短脉冲的新型Ｘ射线光源。它由多碱光电阴极、金靶及铍输出窗组成，当该射线管的阴极受到强光照射时，产生光电子发射，并经电场加速后轰击金靶，产生连续谱的Ｘ射线轫致辐射，经铍窗输出。用超短的可见光脉冲驱动该光源，并借助Ｘ射线扫描相机测量了该管的Ｘ射线输出，获得了５ｐｓ的Ｘ射线脉冲，这种光源可方便地用来标定Ｘ射线扫描相机的时间分辨率，此种产生超短电子脉冲的方法可在其他方面获得应用。     

X‐ray focusing by the system of refractive lens(es) placed inside asymmetric channel‐cut crystals

An X‐ray one‐dimensionally focusing system, a refracting–diffracting lens (RDL), composed of Bragg double‐asymmetric‐reflecting two‐crystal plane parallel plates and a double‐concave cylindrical parabolic lens placed in the gap between the plates is described. It is shown that the focal length of the RDL is equal to the focal distance of the separate lens multiplied by the square of the asymmetry factor. One can obtain RDLs with different focal lengths for certain applications. Using the point‐source function of dynamic diffraction, as well as the Green function in a vacuum with parabolic approximation, an expression for the double‐diffracted beam amplitude for an arbitrary incident wave is presented. Focusing of the plane incident wave and imaging of a point source are studied. The cases of non‐absorptive and absorptive lenses are discussed. The intensity distribution in the focusing plane and on the focusing line, and its dependence on wavelength, deviation from the Bragg angle and magnification is studied. Geometrical optical considerations are also given. RDLs can be applied to focus radiation from both laboratory and synchrotron X‐ray sources, for X‐ray imaging of objects, and for obtaining high‐intensity beams. RDLs can also be applied in X‐ray astronomy.     

Analysis of tapered front‐coupling X‐ray waveguides

The coupling and propagation of electromagnetic waves through planar X‐ray waveguides (WG) with vacuum gap and Si claddings are analyzed in detail, starting from the source and ending at the detector. The general case of linearly tapered WGs (i.e. with the entrance aperture different from the exit one) is considered. Different kinds of sources, i.e. synchrotron radiation and laboratory desk‐top sources, have been considered, with the former providing a fully coherent incoming beam and the latter partially coherent beams. It is demonstrated that useful information about the parameters of the WG can be derived, comparing experimental results with computer simulation based on analytical solutions of the Helmholtz equation which take into account the amplitude and phase matching between the standing waves created in front of the WG, and the resonance modes propagating into the WG.     

Comparative study of multilayers used in monochromators for synchrotron‐based coherent hard X‐ray imaging

A systematic study is presented in which multilayers of different composition (W/Si, Mo/Si, Pd/B₄C), periodicity (from 2.5 to 5.5 nm) and number of layers have been characterized. In particular, the intrinsic quality (roughness and reflectivity) as well as the performance (homogeneity and coherence of the outgoing beam) as a monochromator for synchrotron radiation hard X‐ray micro‐imaging are investigated. The results indicate that the material composition is the dominating factor for the performance. By helping scientists and engineers specify the design parameters of multilayer monochromators, these results can contribute to a better exploitation of the advantages of multilayer monochromators over crystal‐based devices; i.e. larger spectral bandwidth and high photon flux density, which are particularly useful for synchrotron‐based micro‐radiography and ‐tomography.     

Diffractive–refractive optics: X‐ray splitter

The possibility of splitting a thin (e.g. undulator) X‐ray beam based on diffraction–refraction effects is discussed. The beam is diffracted from a crystal whose diffracting surface has the shape of a roof with the ridge lying in the plane of diffraction. The crystal is cut asymmetrically. One half of the beam impinges on the left‐hand part of the roof and the other half impinges on the right‐hand side of the roof. Owing to refraction the left part of the beam is deviated to the left whereas the right part is deviated to the right. The device proposed consists of two channel‐cut crystals with roof‐like diffraction surfaces; the crystals are set in a dispersive position. The separation of the beams after splitting is calculated at a distance of 10 m from the crystals for various asymmetry and inclination angles. It is shown that such a splitting may be utilized for long beamlines. Advantages and disadvantages of this method are discussed.     

Efficiency and coherence preservation studies of Be refractive lenses for XFELO application

Performance tests of parabolic beryllium refractive lenses, considered as X‐ray focusing elements in the future X‐ray free‐electron laser oscillator (XFELO), are reported. Single and double refractive lenses were subject to X‐ray tests, which included: surface profile, transmissivity measurements, imaging capabilities and wavefront distortion with grating interferometry. Optical metrology revealed that surface profiles were close to the design specification in terms of the figure and roughness. The transmissivity of the lenses is >94% at 8 keV and >98% at 14.4 and 18 keV. These values are close to the theoretical values of ideal lenses. Images of the bending‐magnet source obtained with the lenses were close to the expected ones and did not show any significant distortion. Grating interferometry revealed that the possible wavefront distortions produced by surface and bulk lens imperfections were on the level of ～λ/60 for 8 keV photons. Thus the Be lenses can be succesfully used as focusing and beam collimating elements in the XFELO.     

Status of the hard X‐ray microprobe beamline ID22 of the European Synchrotron Radiation Facility

The ESRF synchrotron beamline ID22, dedicated to hard X‐ray microanalysis and consisting of the combination of X‐ray fluorescence, X‐ray absorption spectroscopy, diffraction and 2D/3D X‐ray imaging techniques, is one of the most versatile instruments in hard X‐ray microscopy science. This paper describes the present beamline characteristics, recent technical developments, as well as a few scientific examples from recent years of the beamline operation. The upgrade plans to adapt the beamline to the growing needs of the user community are briefly discussed.     

Synchrotron‐based spectroscopy of X‐ray channeling through hollow capillary microchannels inside glass plates

Here, soft X‐ray synchrotron radiation transmitted through microchannel plates is studied experimentally. Fine structures of reflection and XANES Si L‐edge spectra detected on the exit of silicon glass microcapillary structures under conditions of total X‐ray reflection are presented and analyzed. The phenomenon of the interaction of channeling radiation with unoccupied electronic states and propagation of X‐ray fluorescence excited in the microchannels is revealed. Investigations of the interaction of monochromatic radiation with the inner‐shell capillary surface and propagation of fluorescence radiation through hollow glass capillary waveguides contribute to the development of novel X‐ray focusing devices in the future.     

A microfocus X‐ray fluorescence beamline at Indus‐2 synchrotron radiation facility

A microfocus X‐ray fluorescence spectroscopy beamline (BL‐16) at the Indian synchrotron radiation facility Indus‐2 has been constructed with an experimental emphasis on environmental, archaeological, biomedical and material science applications involving heavy metal speciation and their localization. The beamline offers a combination of different analytical probes, e.g. X‐ray fluorescence mapping, X‐ray microspectroscopy and total‐external‐reflection fluorescence characterization. The beamline is installed on a bending‐magnet source with a working X‐ray energy range of 4–20 keV, enabling it to excite K‐edges of all elements from S to Nb and L‐edges from Ag to U. The optics of the beamline comprises of a double‐crystal monochromator with Si(111) symmetric and asymmetric crystals and a pair of Kirkpatrick–Baez focusing mirrors. This paper describes the performance of the beamline and its capabilities with examples of measured results.     

XDS: a flexible beamline for X‐ray diffraction and spectroscopy at the Brazilian synchrotron

The majority of the beamlines at the Brazilian Synchrotron Light Source Laboratory (LNLS) use radiation produced in the storage‐ring bending magnets and are therefore currently limited in the flux that can be used in the harder part of the X‐ray spectrum (above ～10 keV). A 4 T superconducting multipolar wiggler (SCW) was recently installed at LNLS in order to improve the photon flux above 10 keV and fulfill the demands set by the materials science community. A new multi‐purpose beamline was then installed at the LNLS using the SCW as a photon source. The XDS is a flexible beamline operating in the energy range between 5 and 30 keV, designed to perform experiments using absorption, diffraction and scattering techniques. Most of the work performed at the XDS beamline concentrates on X‐ray absorption spectroscopy at energies above 18 keV and high‐resolution diffraction experiments. More recently, new setups and photon‐hungry experiments such as total X‐ray scattering, X‐ray diffraction under high pressures, resonant X‐ray emission spectroscopy, among others, have started to become routine at XDS. Here, the XDS beamline characteristics, performance and a few new experimental possibilities are described.