上海光源真空紫外角分辨光电子能谱束线设计

在上海光源上设计了一条光子能量覆盖5~140 eV的高通量、高分辨的真空紫外角分辨光电子能谱束线。本光束线采用准周期椭圆偏振波荡器光源,其周期长度为0.32 m,周期数为14。单色仪采用Dragon型,分为覆盖5~32 eV的低能分支和25~140 eV的高能分支。计算表明,当入射/出射狭缝开启宽度为5/5 μm时,在整个能量扫描范围内,单色仪分辨率可以高达15 000~100 000,光学元件的面型误差对分辨率的影响最大。通量计算显示,样品处s偏振光子通量高达~10¹² phs/s。Shadow追迹模拟结果表明,设计的光束线具有很好的聚焦特性。     

Five-element Johann-type x-ray emission spectrometer with a single-photon-counting pixel detector

A Johann-type spectrometer with five spherically bent crystals and a pixel detector was constructed for a range of hard x-ray photon-in photon-out synchrotron techniques, covering a Bragg-angle range of 60°-88°. The spectrometer provides a sub emission line width energy resolution from sub-eV to a few eV and precise energy calibration, better than 1.5 eV for the full range of Bragg angles. The use of a pixel detector allows fast and easy optimization of the signal-to-background ratio. A concentration detection limit below 0.4 wt% was reached at the Cu Kα(1) line. The spectrometer is designed as a modular mobile device for easy integration in a multi-purpose hard x-ray synchrotron beamline, such as the SuperXAS beamline at the Swiss Light Source.     

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 synchrotron beamline for delivering high purity vacuum ultraviolet photons

We report on the current status and performance of the toroidal grating monochromator beamline at the Brazilian Synchrotron Light Laboratory (Laboratorio Nacional de Luz Sincrotron). This beamline provides photons in the vacuum ultraviolet and soft x-ray regions from 12 to 330 eV with three interchangeable gratings. We report on the improvement, which allows the possibility of choosing the light polarization degree from linear to almost circular. Here, we also describe the development of a new apparatus, namely, the mirror-inserted harmonic attenuator and calibrating-device with a long length (MIRHACLLE). All beamlines based on diffraction gratings suffer from the problem of high harmonics contaminations to some extent. The MIRHACLLE provides a way to efficiently suppress high harmonics from 25% to 1 ppm in a grazing incidence bending magnet beamline. Its principle of operation relays on the absorption of the high energy photons in a gas phase region. It allows negligible high harmonics contamination for photon energies ranging from 12 eV to the gas first ionization threshold, 21.6 eV, in the case of neon. We also demonstrate the possibility to use this device for energy calibration and resolution evaluation together with any experiment needing its filtering capabilities. The device is also very cost effective compared to other filters presented previously in the literature.     

A diffraction-compensating 0-25 ns free space terahertz delay line for coherent quantum control

Free space delay lines provide pulses of variable time spacing for optical experiments such as pump-probe spectroscopy and coherent quantum control, including spin and photon echo techniques. However, in the terahertz region of the spectrum, beam divergence due to diffraction limits the useful length of traditional free space delay lines. We present a novel double-folded variable delay line for light in the frequency range 0.24-1.2 THz, which incorporates a symmetric arrangement of lenses whose spacing can be adjusted to compensate for diffraction at each delay. Scalable for use in other wavelength regimes, the design relays an input Gaussian beam waist to the output with up to 25 ns ( approximately 8 m) total delay and is enclosed in a desiccated volume of <0.5 m3. The delay line can deliver two or three pulses with relative amplitudes controlled via variable spacing silicon etalon beam splitters. Profiles of a 0.24 THz beam show good agreement with calculations at long delays, with insertion loss per delay stage of approximately 3 dB.     

The electron spectro-microscopy beamline at National Synchrotron Light Source II: a wide photon energy range, micro-focusing beamline for photoelectron spectro-microscopies

A comprehensive optical design for a high-resolution, high-flux, wide-energy range, micro-focused beamline working in the vacuum ultraviolet and soft x-ray photon energy range is proposed. The beamline is to provide monochromatic radiation to three photoelectron microscopes: a full-field x-ray photoelectron emission microscope and two scanning instruments, one dedicated to angle resolved photoemission spectroscopy (μ-ARPES) and one for ambient pressure x-ray photoelectron spectroscopy and scanning photoelectron microscopy (AP-XPS/SPEM). Microfocusing is achieved with state of the art elliptical cylinders, obtaining a spot size of 1 μm for ARPES and 0.5 μm for AP-XPS/SPEM. A detailed ray tracing analysis quantitatively evaluates the overall beamline performances.     

Femtosecond time-resolved photoelectron spectroscopy with a vacuum-ultraviolet photon source based on laser high-order harmonic generation

A laser-based tabletop approach to femtosecond time-resolved photoelectron spectroscopy with photons in the vacuum-ultraviolet (VUV) energy range is described. The femtosecond VUV pulses are produced by high-order harmonic generation (HHG) of an amplified femtosecond Ti:sapphire laser system. Two generations of the same setup and results from photoelectron spectroscopy in the gas phase are discussed. In both generations, a toroidal grating monochromator was used to select one harmonic in the photon energy range of 20-30 eV. The first generation of the setup was used to perform photoelectron spectroscopy in the gas phase to determine the bandwidth of the source. We find that our HHG source has a bandwidth of 140 ± 40 meV. The second and current generation is optimized for femtosecond pump-probe photoelectron spectroscopy with high flux and a small spot size at the sample of the femtosecond probe pulses. The VUV radiation is focused into the interaction region with a toroidal mirror to a spot smaller than 100 × 100 μm(2) and the flux amounts to 10(10) photons/s at the sample at a repetition rate of 1 kHz. The duration of the monochromatized VUV pulses is determined to be 120 fs resulting in an overall pump-probe time resolution of 135 ± 5 fs. We show how this setup can be used to map the transient valence electronic structure in molecular dissociation.     

Design and performance of a versatile curved-crystal spectrometer for high-resolution spectroscopy in the tender x-ray range

A complete in-vacuum curved-crystal x-ray emission spectrometer in Johansson geometry has been constructed for a 2-6 keV energy range with sub natural line-width energy resolution. The spectrometer is designed to measure x-ray emission induced by photon and charged particle impact on solid and gaseous targets. It works with a relatively large x-ray source placed inside the Rowland circle and employs position sensitive detection of diffracted x-rays. Its compact modular design enables fast and easy installation at a synchrotron or particle accelerator beamline. The paper presents main characteristics of the spectrometer and illustrates its capabilities by showing few selected experimental examples.     

Ultrahigh resolution soft x-ray emission spectrometer at BL07LSU in SPring-8

An extremely high resolution flat field type slit less soft x-ray emission spectrometer has been designed and constructed for the long undulator beamline BL07LSU in SPring-8. By optimizing the ruling parameters of two cylindrical gratings, a high energy resolution ΔE < 100 meV and/or an E∕ΔE ~ 10 000 are expected for the energy range of 350 eV - 750 eV taking into account the broadening by the spatial resolution (25 μm) of a CCD detector. A coma-free operation mode proposed by Strocov et al., is also applied to eliminate both defocus and coma aberrations. The spectrometer demonstrated experimentally that E/ΔE = 10 050 and 8046 for N 1s (402.1 eV) and Mn 2p (641.8 eV) edges, respectively.     

High energy resolution five-crystal spectrometer for high quality fluorescence and absorption measurements on an x-ray absorption spectroscopy beamline

Fluorescence detection is classically achieved with a solid state detector (SSD) on x-ray absorption spectroscopy (XAS) beamlines. This kind of detection however presents some limitations related to the limited energy resolution and saturation. Crystal analyzer spectrometers (CAS) based on a Johann-type geometry have been developed to overcome these limitations. We have tested and installed such a system on the BM30B/CRG-FAME XAS beamline at the ESRF dedicated to the structural investigation of very dilute systems in environmental, material and biological sciences. The spectrometer has been designed to be a mobile device for easy integration in multi-purpose hard x-ray synchrotron beamlines or even with a laboratory x-ray source. The CAS allows to collect x-ray photons from a large solid angle with five spherically bent crystals. It will cover a large energy range allowing to probe fluorescence lines characteristic of all the elements from Ca (Z = 20) to U (Z = 92). It provides an energy resolution of 1-2 eV. XAS spectroscopy is the main application of this device even if other spectroscopic techniques (RIXS, XES, XRS, etc.) can be also achieved with it. The performances of the CAS are illustrated by two experiments that are difficult or impossible to perform with SSD and the complementarity of the CAS vs SSD detectors is discussed.     

High-intensity xenon plasma discharge lamp for bulk-sensitive high-resolution photoemission spectroscopy

We have developed a highly brilliant xenon (Xe) discharge lamp operated by microwave-induced electron cyclotron resonance (ECR) for ultrahigh-resolution bulk-sensitive photoemission spectroscopy (PES). We observed at least eight strong radiation lines from neutral or singly ionized Xe atoms in the energy region of 8.4-10.7 eV. The photon flux of the strongest Xe I resonance line at 8.437 eV is comparable to that of the He Ialpha line (21.218 eV) from the He-ECR discharge lamp. Stable operation for more than 300 h is achieved by efficient air-cooling of a ceramic tube in the resonance cavity. The high bulk sensitivity and high-energy resolution of PES using the Xe lines are demonstrated for some typical materials.     

An experimental setup for high resolution 10.5 eV laser-based angle-resolved photoelectron spectroscopy using a time-of-flight electron analyzer

We present an experimental setup for laser-based angle-resolved time-of-flight photoemission. Using a picosecond pulsed laser, photons of energy 10.5 eV are generated through higher harmonic generation in xenon. The high repetition rate of the light source, variable between 0.2 and 8 MHz, enables high photoelectron count rates and short acquisition times. By using a time-of-flight analyzer with angle-resolving capabilities, electrons emitted from the sample within a circular cone of up to ±15° can be collected. Hence, simultaneous acquisition of photoemission data for a complete area of the Brillouin zone is possible. The current photon energy enables bulk sensitive measurements, high angular resolution, and the resulting covered momentum space is large enough to enclose the entire Brillouin zone in cuprate high-T(c) superconductors. Fermi edge measurements on polycrystalline Au shows an energy resolution better than 5 meV. Data from a test measurement of the Au(111) surface state are presented along with measurements of the Fermi surface of the high-T(c) superconductor Bi(2)Sr(2)CaCu(2)O(8 + δ) (Bi2212).     

同步辐射高分辨率衍射光束线的设计

介绍了第三代同步辐射高分辨率X射线衍射光束线的总体设计。给出了高分辨率衍射的基本原理并描述了获得确定光子能量的近平行高强度X射线光束线所必需的光学元件。特别是用X射线动力学理论,解释了双晶及四次反射晶体单色器。作为一个实例,介绍了将于2009年开始在德国汉堡运行的一个新的同步辐射源PETRAⅢ的高分辨率衍射(HighRes)光束线的设置情况。通过优化光学部件,对微米尺寸光束,q空间的分辨减小到Δq=10^-5 nm^-1,光通量大于10¹¹ cts/s。     

Full characterization and optimization of a femtosecond ultraviolet laser source for time and angle-resolved photoemission on solid surfaces

A novel experimental apparatus for time and angle-resolved photoemission on solid surfaces is presented. A 6.28 eV laser source operating at 250 kHz repetition rate is obtained by frequency mixing in nonlinear beta barium borate crystals. This UV light source has a high photon flux of 10(13) photons/s with relatively low number of photons/pulse so that Fermi surface mapping over a wide region of the Brillouin zone is possible while mitigating space charge effects. The UV source has been fully characterized spatially, spectrally, and temporally. Its potential for time and angle-resolved photoemission is demonstrated through Fermi surface mapping and photoexcited electron dynamics in Bismuth. True femtosecond time resolution <65 fs is obtained while the energy resolution of 70 meV appears to be mainly limited by the laser bandwidth.     

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.     

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.     

Design and performance of a curved-crystal x-ray emission spectrometer

A curved-crystal x-ray emission spectrometer has been designed and built to measure 2-5 keV x-ray fluorescence resulting from a core-level excitation of gas phase species. The spectrometer can rotate 180 degrees, allowing detection of emitted x rays with variable polarization angles, and is capable of collecting spectra over a wide energy range (20 eV wide with 0.5 eV resolution at the Cl K edge) simultaneously. In addition, the entire experimental chamber can be rotated about the incident-radiation axis by nearly 360 degrees while maintaining vacuum, permitting measurements of angular distributions of emitted x rays.     

An in-vacuum diffractometer for resonant elastic soft x-ray scattering

We describe the design, construction, and performance of a 4-circle in-vacuum diffractometer for resonant elastic soft x-ray scattering. The diffractometer, installed on the resonant elastic and inelastic x-ray scattering beamline at the Canadian Light Source, includes 9 in-vacuum motions driven by in-vacuum stepper motors and operates in ultra-high vacuum at base pressure of 2 × 10(-10) Torr. Cooling to a base temperature of 18 K is provided with a closed-cycle cryostat. The diffractometer includes a choice of 3 photon detectors: a photodiode, a channeltron, and a 2D sensitive channelplate detector. Along with variable slit and filter options, these detectors are suitable for studying a wide range of phenomena having both weak and strong diffraction signals. Example measurements of diffraction and reflectivity in Nd-doped (La,Sr)(2)CuO(4) and thin film (Ga,Mn)As are shown.     

多种材料软X光平面镜反射率标定

利用北京同步辐射装置(BSRF) 3W1B束线及反射率计靶室,在束流强度40～120mA、贮存环电子能量2GeV专用光运行模式下,做了不同材料掠入射平面镜反射率标定实验。标定过程用高灵敏度无死层的硅光二极管代替X射线二极管(XRD)作探测器,使输出信号提高2～3个量级,可标定能区从150～270eV拓展为50～1500eV能区,对C,Si和Ni材料平面镜给出完整的反射率标定曲线,最终把实验数据与理论计算比对并分析。     

Visualizing soft tissue in the mammalian cochlea with coherent hard X-rays

This paper concerns an important aspect of current developments in medical and biological imaging: the possibility for imaging soft tissue at relatively high resolution in the micrometer range or better, without tedious and/or entirely destructive sample preparation. Structures with low absorption contrast have been visualized using in-line phase contrast imaging. The experiments have been performed at the Advanced Photon Source, a third generation source of synchrotron radiation. The source provides highly coherent X-ray radiation with high photon flux (>10(14) photons/s) at high photon energies (5-70 keV). Thick gerbil cochlear slices have been imaged and were compared with those obtained by light microscopy. Furthermore, intact gerbil cochleae have been imaged to identify the soft tissue structures involved in the hearing process. The present experimental approach was essential for visualizing the inner ear structures involved in the hearing process in an intact cochlea.