Photon Sources at DESY

During the past 10 years, photon science activities at DESY in Hamburg, Germany, have expanded significantly and this development is expected to continue in the coming years. The soft X-ray free-electron laser (FEL) FLASH has been in user operation for over 10 years and the high-brilliance hard X-ray synchrotron radiation source PETRA III started serving the user community five years ago. Access to both light sources has since been highly demanded by scientists not only from Germany and Europe, but from all over the world. The request for beamtime far exceeded the capacity of available experimental infrastructure at both facilities and, for this reason, it was necessary to add further beamlines and also to broaden the portfolio of techniques. Therefore, new facilities have recently been built to almost double the existing capacity for user beamtime at both sources (Figure 1).     

The NIGMS structural biology facility at the NSLS

FLASH at DESY in Hamburg, the first and currently only free-electron laser for VUV and soft X-ray radiation, started user operation in the summer of 2005. Currently it covers a wavelength range from 13 nm to 50 nm with GW peak power and pulse durations between 10 fs and 50 fs. Approximately 20 weeks of beamtime are provided per year for scientific experiments that are not possible on any other radiation source.     

Workshop on high energy X-ray scattering at the APS

SPring-8 has been successfully increasing the use of its cutting-edge facilities by industrial researchers and continuously improving the system for supporting new users when carrying out experiments. The most important factor contributing to this success is the synchronicity of both the appointment of new staff and the implementation of new propulsion programs. As a result, nearly 300 research proposals were accepted in 2006 from industries in various fields, such as electronics, materials, life science, energy and the environment, and the beamtime assigned to industrial use was about 20% of the total user beamtime.     

Photoemission of spinpolarized electrons from strained GaAsP

Strained layer GaAs_.95P_.05 photo cathodes are presented, which emit electron beams spinpolarized to a degree of P = 75% typically. Quantum yields around QE = 0.4% are observed routinely. The figure of merit P² × QE = 2.3 × 10^–3 is comparable to that of the best strained layer cathodes reported in literature. The optimum wavelength of irradiating light around 830 nm is in convenient reach of Ti:sapphire lasers or diode lasers respectively. The cathodes are produced using MOCVD-techniques. A GaAs_.55P_.45-GaAs_.85P_.15 superlattice structure prevents the migration of dislocations from the substrate and bottom layers to the strained overlayer. The surface is protected by an arsenic layer so that no chemical cleaning is necessary before installation into vacuum. The source of polarized electrons attached to the Mainz race track microtron MAMI works with such cathodes now. More than 1000 hours beamtime have been performed successfully.     

Measurement of mobility and damping of floors

Point mobility and damping (loss factor) were measured for different types of wooden and concrete floors in occupied buildings. A vertically applied excitation force was used. Various types of woodworking machines and workshop equipment were present during the tests in order to give a practical measure of floor damping. For comparison, the characteristics of a free concrete slab with point supports at each corner, a newly constructed unfurnished office building, and an experimental floating floor were also measured. Measurements were made in three frequency bands in the range from 5 to 1600 Hz. For concrete floors maximum point mobility was typically in the region 10^?4–10^?7 m/N s, and for wooden floors, typically 10^?2–10^?4 m/N s. Loss factors were typically in the region 0.01–0.6, depending on floor construction and frequency.     

Single crystal diffraction under high pressure with synchrotron radiation and a diamond anvil cell

Abstract

A single crystal study on AlPO₄ was performed at 2.90 GPa with synchrotron radiation with a wavelength of only 0.54 ?. The diffracted intensity was high enough to measure even weak reflections with sufficient counting statistics. However, the search for the reflections needed to setup the orientation matrix required a lot of beamtime. A feasibility study was carried out using a proportional area counter to reduce this search time. The results demonstrate that such counters can considerably reduce the time needed for the orientation of the crystal and the data collection.

Presented at the IUCr Workshop on ‘Synchrotron Radiation Instrumentation for High Pressure Crystallography’. Daresbury Laboratory 20-21 July 1991     

A Cauchois-type X-ray spectrometer for momentum density studies on heavy-element materials

This article describes the new spectrometer setup for high-resolution Compton scattering experiments at BL08W, SPring-8. It employs an X-ray image intensifier (X-II) system as a position sensitive detector (PSD). The installation of the X-II system has improved the data-acquisition efficiency by 20 times compared to the previous quasi-PSD system. Compton profiles of CeRh₃B₂ have been measured with sufficient statistical accuracy, which indicates that the new setup can measure Compton profiles of virtually all materials within a reasonable beamtime.     

Die Störung der Resonanzstreuung von γ-Strahlung einer Kr79-Quelle an Br79 durch gaskinetische Stöße in der Quelle

γ-quanta emitted by gaseous Kr⁷⁹-sources were scattered resonantly from Br⁷⁹-nuclei. By increasing the density in the source the effective cross section for resonance scattering was influenced due to gaskinetic collisions of the recoiling Br⁷⁹-nuclei with atoms before emission of theγ-quantum. The cross section for gaskinetic collisions was determined to beσ _st=(12.0±1.8) 10^?16 cm² in agreement with the theoretical value obtained from a hard sphere model. This technique, similar to the usual “Doppler shift technique”, yields, if combined with the measurement of the absolute cross section for resonance scattering, spin and lifetime of the levels at 398 and 606 keV. The resonance scattering from the 834 keV level shows an unexpected behaviour in complete contradiction to the hard sphere model, indicating that the velocity of the recoiling nuclei is increased in a dense source atmosphere.     

The beauty of non-resonant X-ray magnetic scattering

The Canadian Light Source's 11^th Annual Users' Meeting (AUM), held June 9 and 10 in Saskatoon, marked several firsts for the regular gathering of the Canadian synchrotron community. It was the first time the meeting was held in conjunction with an international meeting hosted by the CLS, sharing joint workshops with the Fifth International MEDSI workshop and 15^th Pan-American SRI conference. In addition, for the first time all of the papers presented at the AUM described results obtained with data from the CLS.     

Mercury in archeological hair samples from Xiongnu burials (Noin‐Ula,Mongolia): SR XRF and CXRM analysis

A technique has been developed for determining mercury content in the concentration range of 1–1000 μg/g in hair samples by X‐ray fluorescence analysis using synchrotron radiation (synchrotron radiation X‐ray fluorescence, Siberian Synchrotron and Terahertz Radiation Center, Budker Institute of Nuclear Physics SB RAS). The mercury content was identified in archeological hair samples from an ancient burial of Xiongnu nobility (Mongolia, mound 22, 1^st century BC–1^st century AD); the content values were elevated (up to 1100 μg/g) in all the samples (n = 41). An X‐ray microanalysis using polycapillary lenses in a confocal scheme (confocal X‐ray microscopy station) was developed at the Synchrotron radiation X‐ray fluorescence to establish mercury distribution in a cross section of hair shaft with a spatial resolution of 5 μm. The findings of the study make it possible to assume exogenous income of mercury (from the burial environment) to the hair.     

Rapid and sensitive trace gas detection with continuous wave Optical Parametric Oscillator-based Wavelength Modulation Spectroscopy

A fiber-amplified Distributed Bragg Reflector diode laser is used to pump a continuous wave, singly resonant Optical Parametric Oscillator (OPO). The output radiation covers the 3–4 μm with ability of rapid (100 THz/s) and broad mode-hop-free tuning (5 cm⁻¹). Wavelength Modulation Spectroscopy is combined with the OPO to take optimal advantage of the spectral scan speed. The sensitivity of the system was determined as 0.8 ppbv (parts-per-billion by volume) for ethane (C₂H₆) for the absorption peak at 2996.9 cm⁻¹ recorded in 1.3 seconds, corresponding to a noise equivalent absorption sensitivity (NEAS) of 1.2×10⁻⁹ cm⁻¹/Hz^1/2. A comparison between results using the 1^st, 2^nd and 4^th harmonic derivative signal from wavelength modulation was performed. The broad continuous tunability was demonstrated by covering 35 cm⁻¹ while recording absorption features of ethane, methane and water.     

Scaling properties of fluctuations in stationary turbulence

Turbulent fluctuations are treated using a stationary distribution functionw _st for an order parameter field representing a fluid. Naive scale invariance ofw _st yields thek ^–5/3 spectral law in three dimensions andk ^–3 in two dimensions. The noise parameter of the stationary distribution is connected with energy flow or enstrophy conservation, respectively. In order to include fluctuations of the local energy dissipation a grand distribution function is introduced.     

Three-dimensional simulation of laser–plasma-based electron acceleration

A sequential three-dimensional (3D) particle-in-cell simulation code PICPSI-3D with a user friendly graphical user interface (GUI) has been developed and used to study the interaction of plasma with ultrahigh intensity laser radiation. A case study of laser–plasma-based electron acceleration has been carried out to assess the performance of this code. Simulations have been performed for a Gaussian laser beam of peak intensity 5 × 10¹⁹ W/cm² propagating through an underdense plasma of uniform density 1 × 10¹⁹ cm^− 3, and for a Gaussian laser beam of peak intensity 1.5 × 10¹⁹ W/cm² propagating through an underdense plasma of uniform density 3.5 × 10¹⁹ cm^− 3. The electron energy spectrum has been evaluated at different time-steps during the propagation of the laser beam. When the plasma density is 1 × 10¹⁹ cm^− 3, simulations show that the electron energy spectrum forms a monoenergetic peak at ~14 MeV, with an energy spread of ±7 MeV. On the other hand, when the plasma density is 3.5 × 10¹⁹ cm^− 3, simulations show that the electron energy spectrum forms a monoenergetic peak at ~23 MeV, with an energy spread of ±7.5 MeV.     

Self-Supported Graphite/Graphene/NiFe-LDH Electrodes for High Performance Oxygen Evolution Reaction

Reducing energy consumption and improving energy utilization efficiency has become the focus of research in the 21^st century. Electrocatalytic water splitting is one of the promising strategies for producing hydrogen energy. In this study, the non-noble nickel-iron layered double hydroxide (NiFe-LDH) catalyst is deposited on the electrochemically intercalated graphite/graphene (G/GE) substrate and directly used as the self-supported and binder-free electrode for electrocatalytic water oxidation. The Ni₂Fe₁-LDH@G/GE catalyst shows a low overpotential of 194 mV at a current density of 10 mA cm^–2, which is better than the noble metal catalyst IrO₂ (314 mV) and RuO₂ (330 mV) and many other related works. This research provides a facile way to directly prepare the catalyst electrode with high performance and low cost.     

The temperature dependences of electromechanical properties of PLZT ceramics

The mechanical and electrical properties in lanthanum modified lead zirconate-titanate ceramics of 5/50/50 and 10/50/50 were studied by mechanical loss Q ^{- 1}, Young's modulus E, electric permittivity ε and tangent of dielectric loss of angle tgδ measurements. The internal friction Q ^{- 1} and Young modulus E measured from 290 K to 600 K shows that Curie temperature T_C is located at 574 K and 435 K (1^st cycle of heating) respectively for ceramic samples 5/50/50 and 10/50/50. The movement of T_C in second cycle of heating to lower temperature (561 K for 5/50/50 and 420 K for 10/50/50) has been observed. Together with Q ^{- 1} and E measurements, temperature dependences of ε=f(T) and tgδ=f(T) were determinated in temperature range from 300 K to 730 K. The values of T_C obtained during ε and tgδ measurements were respectively: 560 K for 5/50/50 and 419 K for 10/50/50. These temperatures are almost as high as the temperatures obtained by internal friction Q ^{- 1} measurements in second cycle of heating. In ceramic sample 10/50/50 the additional maximum on internal friction Q ^{- 1} curve at the temperature 316 K was observed.     

NMR-on of182Ta and183Ta in Fe

Nuclear magnetic resonance has been observed on radioactive¹⁸²Ta and¹⁸³Ta oriented at low temperature in an Fe host, by detection of the change in spatial anisotropy of γ-rays emitted during nuclear decay. By measuring the resonant frequencies of¹⁸³Ta in four different applied magnetic fields the nuclear magnetic moment and hyperfine field have been deduced. These are: $$|\mu \left( {{}^{183}Ta; I = \tfrac{\user2{7}}{\user2{2}}} \right)| = 2.28(3)\mu _{\rm N} and B_{hf} \left( {Ta\underline {Fe} at 0 K} \right) = - 67.2(1.3)T$$ . The spin of the ground state of¹⁸²Ta has been determined asI=3 by comparing resonance results with those obtained in a thermal equilibrium nuclear orientation study. The ratio of the resonant frequencies observed for¹⁸²Ta and¹⁸³Ta at one applied field value yields a magnetic moment for the former of $$|\mu \left( {{}^{182}Ta; I = \user2{3}} \right)| = 2.91(3)\mu _{\rm N} $$ . The spin lattice relaxation time for¹⁸³TaFe (0.12 at% Ta) at 18 mK in an applied field of 0.5 T has been found to be 40(10) s.     

Software package for modeling spin–orbit motion in storage rings

A software package providing a graphical user interface for computer experiments on the motion of charged particle beams in accelerators, as well as analysis of obtained data, is presented. The software package was tested in the framework of the international project on electric dipole moment measurement JEDI (Jülich Electric Dipole moment Investigations). The specific features of particle spin motion imply the requirement to use a cyclic accelerator (storage ring) consisting of electrostatic elements, which makes it possible to preserve horizontal polarization for a long time. Computer experiments study the dynamics of 10⁶–10⁹ particles in a beam during 10⁹ turns in an accelerator (about 10¹²–10¹⁵ integration steps for the equations of motion). For designing an optimal accelerator structure, a large number of computer experiments on polarized beam dynamics are required. The numerical core of the package is COSY Infinity, a program for modeling spin–orbit dynamics.     

Excited states of97Pd

The⁹⁷Pd nucleus has been studied from the reaction⁹⁶Ru(³He, 2n)⁹⁷Pd. From in and out beam directγ-spectra andγ-γ coincidences a partial level scheme is proposed. The observed high spin states can be explained by the coupling of the even proton core with the d_5/2 51^st neutron.     

Optical absorption and linear/nonlinear parameters of polyvinyl alcohol films doped by fullerene

New polymeric films were developed for optoelectronic devices by an interaction between Fullerene (C60) and polyvinyl alcohol (PVALC) via the casting method. The structure analysis was studied by Gaussian fitting of XRD patterns and SAED (Selected area electron diffraction). Using HRTEM and SEM, the particle shape and the nanocomposite surface on PVALC are investigated. The change in the functional group of the composites was observed via FT-IR and Raman spectroscopy. In this work, we calculated the bandgap and localized state's width, in the forbidden band, via the absorption coefficient obtained from the Beer-Lambert relation. The bandgap of nanocomposite films was reduced to 4.05 eV. Moreover, due to the surface plasmon absorption in nanocomposite films, k (Extinction index) increases with the doping concentration. The bandgap and refractive index (n) relations were studied via various empirical formulas to calculate the average value of n. The linear optical parameters, such as 1^st-order susceptibility (χ⁽¹⁾), high-frequency dielectric (e_∞), and static dielectric (e_o) constants, were calculated. The nonlinear susceptibility χ⁽³⁾ raised from 0.928 × 10⁻¹² esu to 1.779 × 10⁻¹² esu. Also, the refractive index (n₂) enhanced from 1.665 × 10⁻¹¹ esu to 2.993 × 10⁻¹¹ esu. The optical limiting performance and the ability of nanocomposite to absorb laser beams were tested. The result suggests that C60 has a considerable effect on the PVALC matrix, and the samples have the necessary guidance for laser CUT-OFF and photonic applications.     

单级衍射量子点阵光栅的聚焦离子束直写法制备及光学性能检测

采用聚焦离子束直写技术,成功制作了面积为200μm×200μm,线密度500 mm 1,圆孔直径800 nm,金吸收体厚度为500 nm的单级衍射量子点阵光栅.研究了该光栅在波长442 nm激光下不同传输距离的衍射特性以及相对衍射效率.实验结果表明,量子点阵光栅不存在高级衍射,只保留了±1级和0级衍射,具有良好的单级衍射特性.1级衍射与0级衍射间距随传输距离的增大而增大,实测值与理论计算值相符.