Phase‐space analysis and experimental results for secondary focusing at X‐ray beamlines

Micro‐focusing optical devices at synchrotron beamlines usually have a limited acceptance, but more flux can be intercepted if such optics are used to focus secondary sources created by the primary optics. Flux throughput can be maximized by placing the secondary focusing optics close to or exactly at the secondary source position. However, standard methods of beamline optics analysis, such as the lens equation or matching the mirror surface to an ellipse, work poorly when the source‐to‐optics distance is very short. In this paper the general characteristics of the focusing of beams with Gaussian profiles by a `thin lens' are analysed under the paraxial approximation in phase space, concluding that the focusing of a beam with a short source‐to‐optics distance is distinct from imaging the source; slope errors are successfully included in all the formulas so that they can be used to calculate beamline focusing with good accuracy. A method is also introduced to use the thin‐lens result to analyse the micro‐focusing produced by an elliptically bent trapezoid‐shaped Kirkpatrick–Baez mirror. The results of this analysis are in good agreement with ray‐tracing simulations and are confirmed by the experimental results of the secondary focusing at the 18‐ID Bio‐CAT beamline (at the APS). The result of secondary focusing carried out at 18‐ID using a single‐bounce capillary can also be explained using this phase‐space analysis. A discussion of the secondary focusing results is presented at the end of this paper.     

Optimizing X‐ray mirror thermal performance using matched profile cooling

To cover a large photon energy range, the length of an X‐ray mirror is often longer than the beam footprint length for much of the applicable energy range. To limit thermal deformation of such a water‐cooled X‐ray mirror, a technique using side cooling with a cooled length shorter than the beam footprint length is proposed. This cooling length can be optimized by using finite‐element analysis. For the Kirkpatrick–Baez (KB) mirrors at LCLS‐II, the thermal deformation can be reduced by a factor of up to 30, compared with full‐length cooling. Furthermore, a second, alternative technique, based on a similar principle is presented: using a long, single‐length cooling block on each side of the mirror and adding electric heaters between the cooling blocks and the mirror substrate. The electric heaters consist of a number of cells, located along the mirror length. The total effective length of the electric heater can then be adjusted by choosing which cells to energize, using electric power supplies. The residual height error can be minimized to 0.02 nm RMS by using optimal heater parameters (length and power density). Compared with a case without heaters, this residual height error is reduced by a factor of up to 45. The residual height error in the LCLS‐II KB mirrors, due to free‐electron laser beam heat load, can be reduced by a factor of ～11 below the requirement. The proposed techniques are also effective in reducing thermal slope errors and are, therefore, applicable to white beam mirrors in synchrotron radiation beamlines.     

Tests and characterization of a laterally graded multilayer Montel mirror

Multilayers are becoming an increasingly important tool in X‐ray optics. The essential parameters to design a pair of laterally graded multilayer mirrors arranged in a Montel‐type configuration for use as an X‐ray collimating device are provided. The results of X‐ray reflectometry tests carried out on the optics in addition to metrology characterization are also shown. Finally, using experimental data and combined with X‐ray tracing simulations it is demonstrated that the mirror meets all stringent specifications as required for a novel ultra‐high‐resolution inelastic X‐ray scattering spectrometer at the Advanced Photon Source.     

Microfocusing options for the inelastic X‐ray scattering beamline at sector 3 of the Advanced Photon Source

Synchrotron radiation from third‐generation high‐brilliance storage rings is an ideal source for X‐ray microbeams. The aim of this paper is to describe a microfocusing scheme that combines both a toroidal mirror and Kirkpatrick–Baez (KB) mirrors for upgrading the existing optical system for inelastic X‐ray scattering experiments at sector 3 of the Advanced Photon Source. SHADOW ray‐tracing simulations without considering slope errors of both the toroidal mirror and KB mirrors show that this combination can provide a beam size of 4.5 µm (H) × 0.6 µm (V) (FWHM) at the end of the existing D‐station (66 m from the source) with use of full beam transmission of up to 59%, and a beam size of 3.7 µm (H) × 0.46 µm (V) (FWHM) at the front‐end of the proposed E‐station (68 m from the source) with a transmission of up to 52%. A beam size of about 5 µm (H) × 1 µm (V) can be obtained, which is close to the ideal case, by using high‐quality mirrors (with slope errors of less than 0.5 µrad r.m.s.). Considering the slope errors of the existing toroidal and KB mirrors (5 and 2.9 µrad r.m.s., respectively), the beam size grows to about 13.5 µm (H) × 6.3 µm (V) at the end of the D‐station and to 12.0 µm (H) × 6.0 µm (V) at the front‐end of the proposed E‐station. The simulations presented here are compared with the experimental measurements that are significantly larger than the theoretical values even when slope error is included in the simulations. This is because of the experimental set‐up that could not yet be optimized.     

X射线Kirkpatrick-Baez显微镜用超反射镜的研制

 介绍了一种可应用于X射线Kirkpatrick-Baez（KB）显微镜的光学元件—X射线超反射镜。选用的W和B₄C作为镀膜材料，膜对数为20，采用单纯型调优的方法实现了X射线超反射镜设计，用磁控溅射的方法在Si基片上完成了W/B₄C X射线超反射镜的制备。采用高分辨率X射线衍射仪（8 keV）测量了X射线超反射镜的反射特性。制备的X射线超反射镜在掠入射角分别为1.052°和1.143°处，反射角度带宽为0.3°，反射率达到20%，可满足KB型显微镜的要求。     

辐射驱动内爆流线实验测量

内爆速度的测量是惯性约束聚变研究中的核心问题, 是判断聚变点火反应的关键物理量. 在神光II激光装置上, 利用KB显微镜配合时间分辨为10 ps的条纹相机, 对1600 J激光能量注入, 3倍频, 脉宽为1 ns黑腔辐射驱动CH靶球, 获得了清晰的辐射驱动内爆流线轨迹X射线图像. 通过流线轨迹图像给出了最大内爆速度为160 km/s. 利用Multi1D程序对内爆压缩流线和壳层速度变化进行了模拟, 实验数据和理论模拟较符合.     

单色化X射线显微成像实验研究

围绕激光惯性约束聚变(ICF)内爆压缩阶段高空间分辨、高能谱分辨的诊断需求,提出了一种将KB显微镜和衍射晶体组合的大视场、单色化成像系统。在实验室条件下,利用Fe靶X射线光管,采用KB显微镜结合高定向热解石墨(HOPG)对网格进行背光成像,晶体选能后的成像结果表明,系统的视场能达到800μm,其中高分辨区域成像的分辨率为37μm。采用能谱探测器测试成像能谱,结果表明,系统的能量分辨率为28,验证了系统的单色性能。该系统兼顾了大视场、空间分辨和能量分辨,对内爆压缩阶段实验中热斑结构及混合效应的研究具有重要应用。     

基于非周期多层膜的X射线成像研究

设计了惯性约束聚变（ICF）诊断实验用X射线Kirkpatrick-Baez（KB）显微镜，给出了系统的结构参量.使用ZEMAX光学软件对KB型显微镜进行了性能模拟，结果表明：在8 keV能点，放大率为8倍时，轴上点的最佳空间分辨率小于2 μm，200微米视场的空间分辨率优于10μm.采用磁控溅射方法制备了W/B4C非周期多层膜，经X射线衍射仪（XRD，工作能量8 keV）测量，其反射率为20％，带宽为0.3°，达到了KB型显微镜成像系统的要求.使用Cu靶X射线管进行了成像实验，得到了放大倍数分别为1倍和2倍的一维X射线像.     

用于几keV能点动态成像诊断的KB-KBA混合型光学系统设计

围绕激光ICF研究中几keV能点的动态成像诊断需求,提出了具有大视场、高空间分辨、高集光效率和谱分辨特性的新型KB-KBA混合型光学结构。该结构以子午方向上两块单层膜球面镜校正像差,实现大视场内的高空间分辨;在弧矢方向上用一块多层膜球面镜聚焦,以保证较高的集光效率和谱分辨能力。该结构克服了传统单层膜和周期膜KBA结构在几keV能点动态成像诊断中存在的集光效率低,强度不均匀和有效视场受限等不足。针对2.5 keV和4.3 keV两个能点,给出了光学初始结构和膜系的设计,建立了考虑膜系反射性质的光线追迹模型。模拟结果表明,该KB-KBA混合型结构在子午方向1.4 mm视场内空间分辨均优于5μm,有效集光效率优于2×10~(-7)sr,可以满足动态成像诊断的需求。     

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提出了一种以多目标参数优化确定热斑的温度和密度径向分布的方法。用热斑中心位置和燃料界面位置对应的电子温度、靶剩余烧蚀层峰值密度、剩余烧蚀层质量与初始烧蚀层质量的比值以及燃料与烧蚀层分界面位置构成五维变量空间参数空间的每个点描述一组温度和密度分布。将实验测量的X射线图像的归一化强度分布与理论模型计算的强度分布的方差作为两个目标函数;另一个目标函数是实验测量的热斑的平均温度与理论模型计算的平均温度的方差。通过多目标遗传算法搜索五维参数空间获得最优参数,从而获得最优的温度和密度分布。对KB显微镜配合X射线胶片测量的实验结果进行了计算,给出了热斑的最佳温度和密度的径向分布。由测试算例发现,温度分布对目标函数的依赖较强。     

Radiation-induced processes and defects in alkali and alkaline-earth borate crystals

The paper presents the results of a study of the radiation-induced processes and defects in nonlinear optical crystals Li₂B₄O₇ (LTB), LiB₃O₅ (LBO), CsLiB₆O₁₀, KB₅O₈·4H₂O, β-BaB₂O₄. It was revealed that a pulsed electron beam irradiation at 290 K forms the radiation-induced pairs of the ‘vacancy—interstitial atom’ defects in the cation sublattice of these crystals. This gives rise to a creation of metastable electronic (interstitial atom) and hole (small-radius polaron near the cation vacancy) centers in high concentrations. Optical hole-transitions from the local level of the trapped hole centers to the valence band states are responsible for the transient optical absorptions (TOA) of borates in the visible and UV spectral ranges. A sublattice of the weakly bound mobile lithium cations in LTB and LBO favors a spatial separation of the radiation-induced pair defects ‘hole polaron near Li-vacancy—mobile interstitial Li⁰ atom’. Their decay rated by the electron–hole nonradiative tunnel recombination determines a peculiar feature of the TOA decay kinetics in LTB and LBO.     

Generating a Squeezed‐Coherent‐Cat State in a Double‐Cavity Optomechanical System

A squeezed‐coherent‐cat state (SCCS) in a mechanical system not only plays an important role for macroscopic quantum coherence, but also can be a carrier for quantum information. A scheme to generate a SCCS in a two‐mode optomechanical system is proposed, in which the modulated hopping interaction of two cavities is introduced. The two cavity modes couple with the same mechanical mode with linear and quadratic interaction, respectively. The SCCS is analytically deduced under an appropriate initial state, and the average phonon number and the parameter of squeeze are numerically calculated. Wigner function shown the properties of superposition and squeezing is plotted. Including the dissipation of the environment, the results show that a high quality mechanical resonator and a low noise environment are required to obtain high fidelity.     

Landau-Zener-Stckelberg interference in a multi-anticrossing system

We propose a universal analytical method of studying the dynamics of a multi-anticrossing system subjected to driving by a single large-amplitude triangle pulse,within a time scale smaller than the dephasing time.Our approach can explain the main features of the Landau-Zener-Stuckelberg interference patterns recently observed in a tripartite system [Nature Communications 1 51 (2010)].In particular,we focus on the effect of the size of the anticrossing on interference and compare the calculated interference patterns with numerical simulations.In addition,a Fourier transform of the patterns can extract the information about the energy level spectrum.     

Casimir friction force between a SiO<Subscript>2</Subscript> probe and a graphene-coated SiO<Subscript>2</Subscript> substrate

The possibility of mechanical detection of Casimir friction with the use of a noncontact atomic force microscope is discussed. A SiO₂ probe tip located above a graphene-coated SiO₂ substrate is subjected to the frictional force caused by a fluctuating electromagnetic field produced by a current in graphene. This frictional force will create the bend of a cantilever, which can be measured by a modern noncontact atomic force microscope. Both the quantum and thermal contributions to the Casimir frictional force can be measured using this experimental setup. This result can also be used to mechanically detect Casimir friction in micro- and nanoelectromechanical systems.     

Formation of a √3 × √3 surface on Si/Ge(1 1 1) studied by STM and LEED

We have performed a detailed study of the formation and the atomic structure of a √3 × √3 surface on Si/Ge(1 1 1) using both scanning tunneling microscopy (STM) and low energy electron diffraction (LEED). Both experimental methods confirm the presence of a √3 × √3 periodicity but unlike the Sn/Ge(1 1 1) and the Sn/Si(1 1 1) surfaces, the Si/Ge(1 1 1) surface is not well ordered. There is no long range order on the surface and the √3 × √3 reconstruction is made up of double rows of silicon atoms separated by disordered areas composed of germanium atoms.     

Development of a Liver‐Targeting Gold–PEG–Galactose Nanoparticle Platform and a Structure–Function Study

For the specific liver parenchymal cell delivery, a series of short heterobifunctional poly(ethylene glycol) (PEG) derivatives containing dimercapto and galactose (Gal) terminals is synthesized for the preparation of gold conjugates. The Gal density on the surface of all gold conjugates can be well controlled and the prepared gold conjugates are stable in various media, even in the presence of serum. For the liver targeting and reflectance imaging applications, the structure–function relationships of this platform, including the influence of the PEG molecular weight and the Gal ligand coverage of hybrid particles on the cytotoxicity and cellular recognition of tumor cells in vitro and on their liver‐targeting ability in small animals, are studied. Biocompatibility results show that HepG2 cells are more sensitive than HeLa cells to gold conjugates. Cellular uptake studies demonstrate that a lower PEG molecular weight, a higher Gal density, or a higher gold concentration can increase the cellular uptake efficiency of these hybrid particles in HepG2 cells when the other parameters are constant. The results reveal the importance of parameter modulation for the design and control of nanoprobes and the gold conjugates with short PEG chains and a high Gal density are a potential vector for active‐targeting therapy.     

Photonic‐on‐a‐chip: a thermal actuated Mach‐Zehnder interferometer and a molecular thermometer based on a single di‐ureasil organic‐inorganic hybrid

An integrated photonic‐on‐a‐chip device based on a single organic‐inorganic di‐ureasil hybrid was fabricated for optical waveguide and temperature sensing. The device is composed by a thermal actuated Mach‐Zehnder (MZ) interferometer operating with a switching power of 0.011 W and a maximum temperature difference between branches of 0.89 ºC. The MZ interferometer is covered by a Eu³⁺/Tb³⁺ co‐doped di‐ureasil luminescent molecular thermometer with a temperature uncertainty of 0.1ºC and a spatial resolution of 13 µm. This is an uncommon example in which the same material (an organic‐inorganic hybrid) that is used to fabricate a particular device (a thermal‐actuated MZ interferometer) is also used to measure one of the device intrinsic properties (the operating temperature). The photonic‐on‐a‐chip example discussed here can be applied to sense temperature gradients with high resolution (10⁻³ ºC·µm⁻¹) in chip‐scale heat engines or refrigerators, magnetic nanocontacts and energy‐harvesting machines.     

How to catch a ‘fat’ proton

We argue that high-multiplicity events in proton–proton or proton–nucleus collisions originate from large-size fluctuations of the nucleon shape. We discuss a pair of simple models of such proton shape fluctuations. A “fat” proton with a size of 3 fm occurs with observable frequency. In light of this result, collective flow behavior in the ensuing nuclear interaction seems feasible. We discuss the influence of these models on the parton structure of the proton.     

Spectroscopic analysis of a dye–mineral composite–a Raman and FT‐IR study

In this investigation, we address the question of how organic thioindigo binds to inorganic palygorskite to form a pigment similar to Maya Blue. We also address how such binding, if it occurs, might be affected by varying the proportion of dye relative to that of the mineral, and by varying the length of heating time used in preparation of the pigment. In addition to samples of palygorskite and thioindigo both alone, four synthetic pigment samples were prepared; two samples of 8 wt.% dye, one heated at 170 °C for 3 h and one at 170 °C for 9 h, and two samples of 16 wt.% dye, one heated at 170 °C for 3 h and one at 170 °C for 9 h. All samples were examined using Fourier transform‐infrared (FT‐IR) and FT‐Raman spectroscopy. For the pigment samples, FT‐IR peaks at 1627 cm⁻¹ are attributed to a downshifted CO stretching mode of thioindigo due to dye–clay interaction. This interpretation is corroborated by FT‐Raman CO peaks with 14 cm⁻¹ shifts to lower wavenumber for the pigment relative to thioindigo alone. Additional Raman scattering between 550 cm⁻¹ and 650 cm⁻¹ also suggests dye–clay interaction through metal–oxygen bonding. We are thus led to the possibility of mostly hydrogen bonding between silanol and carbonyl at lower dye concentration, with a predominance of metal–oxygen bonding at higher dye concentration. Copyright © 2008 John Wiley & Sons, Ltd.     

Charge ordering modulations in a Bi_0.4Ca_0.6MnO₃ film with a thickness of 110 nm

The low temperature sample stage in a transmission electron microscope is used to investigate the charge ordering behaviours in a Bi 0.4 Ca 0.6 MnO 3 film with a thickness of 110 nm at 103 K.Six different types of superlattice structures are observed using the selected-area electron diffraction(SAED) technique,while three of them match well with the modulation stripes in high-resolution transmission electron microscopy(HRTEM) images.It is found that the modulation periodicity and direction are completely different in the region close to the Bi 0.4 Ca 0.6 MnO 3 /SrTiO 3 interface from those in the region a little further from the Bi 0.4 Ca 0.6 MnO 3 /SrTiO 3 interface,and the possible reasons for this are discussed.Based on the experimental results,structural models are proposed for these localized modulated structures.