Asymmetric-cut variable-incident-angle monochromator

A novel asymmetric-cut variable-incident-angle monochromator was constructed and tested in 1997 at the Advanced Photon Source of Argonne National Laboratory. The monochromator was originally designed as a high heat load monochromator capable of handling 5-10 kW beams from a wiggler source. This was accomplished by spreading the x-ray beam out on the surface an asymmetric-cut crystal and by using liquid metal cooling of the first crystal. The monochromator turned out to be a highly versatile monochromator that could perform many different types of experiments. The monochromator consisted of two 18° asymmetrically cut Si crystals that could be rotated about 3 independent axes. The first stage (Φ) rotates the crystal around an axis perpendicular to the diffraction plane. This rotation changes the angle of the incident beam with the surface of the crystal without changing the Bragg angle. The second rotation (Ψ) is perpendicular to the first and is used to control the shape of the beam footprint on the crystal. The third rotation (Θ) controls the Bragg angle. Besides the high heat load application, the use of asymmetrically cut crystals allows one to increase or decrease the acceptance angle for crystal diffraction of a monochromatic x-ray beam and allows one to increase or decrease the wavelength bandwidth of the diffraction of a continuum source like a bending-magnet beam or a normal x-ray-tube source. When the monochromator is used in the doubly expanding mode, it is possible to expand the vertical size of the double-diffracted beam by a factor of 10-15. When this was combined with a bending magnet source, it was possible to generate an 8 keV area beam, 16 mm wide by 26 mm high with a uniform intensity and parallel to 1.2 arc sec that could be applied in imaging experiments.     

Tunable laboratory extended x-ray absorption fine structure system

A new sensitive x-ray monochromator and detector system for performing extended x-ray absorption fine structure (EXAFS) measurements in the laboratory is described. The monochromator combines x-ray focusing optics with rapid elemental tunability. The detection system effectively removes glitches from the data stream, regardless of whether they are due to impurity lines from the x-ray source or if they are due to random instabilities in the incident beam. Used together with a high intensity rotating anode x-ray source, this system can provide synchrotronlike photon intensities, flexibility and resolution, with the easy access and control possible only in the laboratory.     

Hard x-ray monochromator with milli-electron volt bandwidth for high-resolution diffraction studies of diamond crystals

We report on design and performance of a high-resolution x-ray monochromator with a spectral bandwidth of ΔE(X) ? 1.5 meV, which operates at x-ray energies in the vicinity of the backscattering (Bragg) energy E(H) = 13.903 keV of the (008) reflection in diamond. The monochromator is utilized for high-energy-resolution diffraction characterization of diamond crystals as elements of advanced x-ray crystal optics for synchrotrons and x-ray free-electron lasers. The monochromator and the related controls are made portable such that they can be installed and operated at any appropriate synchrotron beamline equipped with a pre-monochromator.     

KMC-1: a high resolution and high flux soft x-ray beamline at BESSY

The crystal monochromator beamline KMC-1 at a BESSY II bending magnet covers the energy range from soft (1.7 keV) to hard x-rays (12 keV) employing the (n,-n) double crystal arrangement with constant beam offset. The monochromator is equipped with three sets of crystals, InSb, Si (111), and Si (422) which are exchangeable in situ within a few minutes. Beamline and monochromator have been optimized for high flux and high resolution. This could be achieved by (1) a windowless setup under ultrahigh-vacuum conditions up to the experiment, (2) by the use of only three optical elements to minimize reflection losses, (3) by collecting an unusually large horizontal radiation fan (6 mrad) with the toroidal premirror, and (4) the optimization of the crystal optics to the soft x-ray range necessitating quasibackscattering crystal geometry (theta(Bragg,max)=82 degrees) delivering crystal limited resolution. The multipurpose beamline is in use for a variety of user facilities such as extended x-ray absorption fine structure, ((Bio-)EXAFS) near-edge x-ray absorption fine structure (NEXAFS), absorption and fluorescence spectroscopy. Due to the windowless UHV setup the k edges of the technologically and biologically important elements such as Si, P, and S are accessible. In addition to these experiments this beamline is now extensively used for photoelectron spectroscopy at high kinetic energies. Photon flux in the 10(11)-10(12) photons/s range and beamline resolving powers of more than E/DeltaE approximately 100.000 have been measured at selected energies employing Si (nnn) high order radiation in quasibackscattering geometry, thus photoelectron spectroscopy with a total instrumental resolution of about 150 meV is possible. This article describes the design features of the beamline and reports some experimental results in the above mentioned fields.     

大曲率弧矢弯曲复合晶体的研制

为提升国家同步辐射实验室X射线吸收精细结构(NSRL-XAFS)的光束线性能,提出将现有双平面晶单色器改造成弧矢聚焦双晶单色器的思想。采取将晶体与钛合金复合的工艺,实现了晶体的大曲率弹性弯曲,并将其用作弧矢聚焦晶体单色器中第二晶体的成像元件。鉴于NSRL-XAFS实验的光学要求,设计制作了复合晶体试验模型,通过有限元分析计算和长程面形仪实际测量得到了不同弯曲半径下晶体的面形精度,并用激光模拟其聚焦性能。结果表明,在缩放比为1/3时,样品上的成像束斑水平尺度(FWHM)由43mm(无聚焦)缩小到3mm,光子密度提高了近一个量级。这些结果满足NSRL在现有光源条件下提升XAFS数据采集质量的要求。     

Development of a laboratory EXAFS facility

The EXAFS technique is a powerful new structural tool, particularly useful for studies of disordered or otherwise complex materials for which x-ray diffraction techniques are difficult or unfeasible. At the present time, most EXAFS experiments are carried out at a synchrotron facility because of the larger fluxes available. We have developed an in-laboratory apparatus utilizing a focusing crystal technique which increases available fluxes two to three orders of magnitude over previous laboratory facilities, so that EXAFS measurements can be carried out quickly and accurately in the laboratory. We will discuss the principles of the focusing monochromator and we will also illustrate the experimental method with examples, including studies of chemical solutions, defect crystalline solids, and high-temperature superconductors.     

A high resolution and large solid angle x-ray Raman spectroscopy end-station at the Stanford Synchrotron Radiation Lightsource

We present a new x-ray Raman spectroscopy end-station recently developed, installed, and operated at the Stanford Synchrotron Radiation Lightsource. The end-station is located at wiggler beamline 6-2 equipped with two monochromators-Si(111) and Si(311) as well as collimating and focusing optics. It consists of two multi-crystal Johann type spectrometers arranged on intersecting Rowland circles of 1 m diameter. The first one, positioned at the forward scattering angles (low-q), consists of 40 spherically bent and diced Si(110) crystals with 100 mm diameters providing about 1.9% of 4π sr solid angle of detection. When operated in the (440) order in combination with the Si (311) monochromator, an overall energy resolution of 270 meV is obtained at 6462.20 eV. The second spectrometer, consisting of 14 spherically bent Si(110) crystal analyzers (not diced), is positioned at the backward scattering angles (high-q) enabling the study of non-dipole transitions. The solid angle of this spectrometer is about 0.9% of 4π sr, with a combined energy resolution of 600 meV using the Si (311) monochromator. These features exceed the specifications of currently existing relevant instrumentation, opening new opportunities for the routine application of this photon-in/photon-out hard x-ray technique to emerging research in multidisciplinary scientific fields, such as energy-related sciences, material sciences, physical chemistry, etc.     

同步辐射X射线双晶单色仪能量扫描

晶体单色仪是X射线光束线上的关键设备,它用晶体作为色散元件,衍射、分离具有连续光谱的同步辐射,向用户提供一定带宽的X射线单色光.在合肥同步辐射装置上的晶体单色仪,使用两块Si(111)晶体,按(⁺n,^-n)无色散排列,通过一台专门研制的L型联动装置,仅一维简单的Bragg角转动,便可保证在动态能量扫描过程中,两晶体衍射面始终平行,且输出的单色光束与入射光束的相对位置不变.本文重点讨论的是用于合肥晶体单色仪上的能量扫描装置.     

The soft x-ray instrument for materials studies at the linac coherent light source x-ray free-electron laser

The soft x-ray materials science instrument is the second operational beamline at the linac coherent light source x-ray free electron laser. The instrument operates with a photon energy range of 480-2000 eV and features a grating monochromator as well as bendable refocusing mirrors. A broad range of experimental stations may be installed to study diverse scientific topics such as: ultrafast chemistry, surface science, highly correlated electron systems, matter under extreme conditions, and laboratory astrophysics. Preliminary commissioning results are presented including the first soft x-ray single-shot energy spectrum from a free electron laser.     

A double-crystal monochromator for neutron stress diffractometry

The problem of developing a dedicated neutron diffractometer for placement on a horizontal reactor channel to measure internal stresses in bulk materials and components under conditions of a limited space is considered. It is shown that the use of a double-crystal monochromator composed of pyrolytic graphite and a focusing bent perfect silicon single crystal is the optimal solution to this problem. The diffractometer with such a monochromator that is installed at the IR-8 reactor of the National Research Center Kurchatov Institute is comparable in luminosity and resolution at a reactor power of 6 MW to modern stress diffractometers at more powerful reactors.     

Quick-scanning x-ray absorption spectroscopy system with a servo-motor-driven channel-cut monochromator with a temporal resolution of 10 ms

We have developed a quick-scanning x-ray absorption fine structure (QXAFS) system and installed it at the recently constructed synchrotron radiation beamline BL33XU at the SPring-8. Rapid acquisition of high-quality QXAFS data was realized by combining a servo-motor-driven Si channel-cut monochromator with a tapered undulator. Two tandemly aligned monochromators with channel-cut Si(111) and Si(220) crystals covered energy ranges of 4.0-28.2 keV and 6.6-46.0 keV, respectively. The system allows the users to adjust instantly the energy ranges of scans, the starting angles of oscillations, and the frequencies. The channel-cut crystals are cooled with liquid nitrogen to enable them to withstand the high heat load from the undulator radiation. Deformation of the reflecting planes is reduced by clamping each crystal with two cooling blocks. Performance tests at the Cu K-edge demonstrated sufficiently high data quality for x-ray absorption near-edge structure and extended x-ray absorption fine-structure analyses with temporal resolutions of up to 10 and 25 ms, respectively.     

X-ray filter assembly for fluorescence measurements of x-ray absorption fine structure

Fluorescence detection, in principle, permits the detection of the extended x-ray absorption fine structure (EXAFS) of more dilute atoms than can be obtained in absorption. To take advantage of this it is necessary, in practice, to eliminate the background that normally accompanies the fluorescence signal. We describe an x-ray filter assembly that accomplishes this purpose. The unique characteristic of the assembly is a slit system that minimizes the fluorescence background from the filter. The theory of the slit assembly is presented and is found to agree with measurements made on the Fe EXAFS of a dilute sample. The filter assembly has a better effective counting rate in this case than that of a crystal monochromator design.     

K-shell emission x-ray imaging of Z-pinch plasmas with a pinhole and a logarithmic spiral crystal

An in-chamber, mini x-ray imaging instrument employs a pinhole and a logarithmic spiral crystal has been developed for obtaining K-shell line images of the imploding aluminum wire array on the "Yang" accelerator. The logarithmic spiral crystal acts as a monochromator and a non-dispersive mirror that reflects the pinhole image to a x-ray film detector with a very narrow photon energy bandwidth (<1 eV, mainly determined by the width of rocking curve of the crystal). Two imaging configurations with the use of Quartz (10 ?10) crystal and Mica (002) crystal are designed, respectively, to image the Al Ly(α2) line (1727.7 eV) emission and Al He(α) intercombination line (1588.3 eV) emission. The primary experimental data corresponding to these two configurations are presented and discussed.     

One-shot spectrometer for several elements using an integrated conical crystal analyzer

Time-resolved x-ray spectrometry using an ultrastrong x-ray source such as an x-ray free electron laser is one of the new trends in the field of x-ray physics. To achieve such time-resolved measurement, the development of an one-shot spectrometer with a wide wavelength range, high efficiency, and good energy resolution is an essential prerequisite. Here we developed an integrated conical Ge crystal analyzer consisting of several conical rings, which were connected using spline surfaces to form a single body using our previously developed hot deformation technique, which can form a Si or Ge wafer into an arbitrary and accurate shape. We simultaneously focused several characteristic lines from an alloy sample onto different positions on a small x-ray charge-coupled device with very high image brightness (gain relative to planar analyzer: 100) and a good spatial resolution of 9-13 eV. The small radius of curvature of the crystal (28-50 mm) enabled us to realize a very short sample-detector distance of 214.4 mm. The present result shows the possibility of realizing a new focusing x-ray crystal spectrograph that can control the focal position as desired.     

A dual-channel, focusing x-ray spectrograph with uniform dispersion for Z pinch plasmas measurement

A dual-channel, focusing x-ray spectrograph with uniform dispersion (i.e., the linear dispersion of this spectrograph is a constant) is described for measuring the x-ray spectra emission from the hot, dense Al Z pinch plasmas. The spectrograph uses double uniform-dispersed crystals (e.g., a Quartz 1010 crystal and a Mica 002 crystal) as dispersion elements and a double-film box as detector to achieve the simultaneous recording of the time integrated spectrum covering a wide spectral range of ~5-9 A?. Since this spectrograph disperse the x-rays on the detector plane with uniform spacing for every wavelength, it needs not the calibration of the wavelength with spatial coordinate, thereby own the advantages of easiness and veracity for spectra identification. The design of this spectrograph and the example of experiment on the "Yang" accelerator are presented.     

中子衍射应力谱仪的垂直聚焦单色器的优化设计

本文应用蒙特卡罗模拟程序MCSTAS对中子衍射应力谱仪的垂直聚焦单色器利用单晶Ge（511）进行聚焦的情况进行了优化计算,得到垂直聚焦单色器的高度和单晶片间的倾角等参数的最佳值;同时对比分析了垂直聚焦单色器与平板单色器两种情况下样品处的中子注量率。最后讨论了单色器起飞角对谱仪分辨率产生的影响。     

Construction and characterization of the fringe field monochromator for a field emission gun

Although some microscopes have shown stabilities sufficient to attain below 0.1 eV spectral resolution in high-resolution electron energy loss spectroscopy, the intrinsic energy width of the high brightness source (0.3-0.6 eV) has been limiting the resolution. To lower the energy width of the source to 50 meV without unnecessary loss of brightness, a monochromator has been designed consisting of a short (4 mm) fringe field Wien filter and a 150 nm energy selection slit (nanoslit) both to be incorporated in the gun area of the microscope. A prototype has been built and tested in an ultra-high-vacuum setup (10(-9) mbar). The monochromator, operating on a Schottky field emission gun, showed stable and reproducible operation. The nanoslits did not contaminate and the structure remained stable. By measuring the current through the slit structure a direct image of the beam in the monochromator could be attained and the monochromator could be aligned without the use of a microscope. Good dispersed imaging conditions were found indicating an ultimate resolution of 55 meV. A Mark II fringe field monochromator (FFM) was designed and constructed compatible with the cold tungsten field emitter of the VG scanning transmission microscope. The monochromator was incorporated in the gun area of the microscope at IBM T.J. Watson research center, New York. The monochromator was aligned on 100 kV and the energy distribution measured using the monochromator displayed a below 50 meV filtering capability. The retarding Wien filter spectrometer was used to show a 61 meV EELS system resolution. The FFM is shown to be a monochromator which can be aligned without the use of the electron microscope. This makes it directly applicable for scanning transmission microscopy and low-voltage scanning electron microscopy, where it can lower the resolution loss which is caused by chromatic blur of the spot.     

Transmissive x-ray beam position monitors with submicron position- and submillisecond time resolution

We present the development of fast transmissive center-of-mass x-ray beam position monitors with a large active area, based on a thinned position sensitive detector in both a duo- and a tetra-lateral variant. The detectors were tested at BESSY beamlines BL14.1, KMC-1, and KMC-2 and yielded signal currents of up to 3 microA/100 mA ring current at 10 keV photon energy using the monochromatic focused beam of BL14.1. The active area sizes were 1 x 1 and 3 x 3 mm(2) for the duo-lateral and 5 x 5 mm(2) for the tetra-lateral devices, with the duo-lateral detectors currently being available in sizes from 1 x 1 to 10 x 10 mm(2) and thicknesses between 5 and 10 microm. The presented detectors' thicknesses were measured to be 5 and 8 microm with a corresponding transmission of up to 93% at 10 keV and 15% at 2.5 keV. Up to a detection bandwidth of 10 kHz, the monitors provide submicron position resolution. For lower detection bandwidths, the signal-to-noise reaches values of up to 6 x 10(4) at 10 Hz, corresponding to a position resolution of better than 50 nm for both detector sizes. As it stands, this monitor design approach promises to be a generic solution for automation of state-of-the-art crystal monochromator beamlines.     

Shape error measurement using ray-tracing and fringe scanning methods: projection of grating displayed on a liquid crystal panel

We present an improved Hartmann test, which has high spatial resolution with respect to the measuring points, for measuring projection mirrors. In the method, grid lines with a sinusoidal transmittance distribution are displayed on a liquid crystal panel and illuminated with a collimated laser beam. The beam transmitted through the liquid crystal panel reflects off the mirror surface being tested and reaches a screen. A charge-coupled device camera detects the projected images, which contain information about the inclination of the surface being tested. Any error in the shape of the mirror surface is identified by integrating the inclination. To increase the spatial resolution, the fringe scanning method is performed by shifting the grid lines on the liquid crystal panel. The grid lines are optimized for the shape of the mirror being tested. Because the grid lines are displayed by an electrical method, the shifting operation is easy and rapid, and furthermore, the displacement can be done precisely. The shape error of an off-axis parabolic mirror made of plastic is measured by the proposed method.     

Variable rowland radius laboratory vacuum surface-sensitive x-ray absorption fine structure spectrometer

A new laboratory x-ray spectrometer for surface-sensitive extended x-ray absorption fine structure [(S)EXAFS] and surface-sensitive x-ray absorption near-edge structure [(S)XANES] measurements is described. The spectrometer employs a 12 kV mA rotating anode generator. It has a monochromator equipped with a set of exchangeable curved crystals of Johann or Johansson type with different cell parameters, orientations, and Rowland radii. The computer controlled movement system based on nine stepping motors allows all the main elements of the spectrometer to be positioned freely relative to the x-ray source and gives an opportunity to use sophisticated scanning modes (for example, a mode with a focus spot position on a sample surface instead of an exit slit). The whole x-ray beam line is completely enclosed in a vacuum chamber that is directly connected to the x-ray generator, thereby preventing the absorption of x rays in the air. This layout allows a wide x-ray photon energy range from a few keV up to dozens of keV. A registration of x rays transmitted through the sample with proportional counter- and photoelectrons emitted from the sample with channeltron is used to carry out bulk- and surface-sensitive measurements, respectively. Using a 25 x 200 kV mA power regime of a rotating anode x-ray generator, a photon flux of 2.5 x 10(5) counts/s was registered at the Cu K edge, where the energy resolution was about 5 eV. High near surface sensitivity is demonstrated by the EXAFS spectra of Cu K and Hf LIII edges measured from 3 nm Cu and Hf oxide films.