X-ray laser beam with diffraction-limited divergence generated with two gain media

We demonstrate an x-ray laser at a wavelength of 13.9 nm with a beam divergence of 0.2 mrad, which is 1.8 times the diffraction limit. The x-ray laser is generated with two gain media; the seed x-ray pulse from the first medium is amplified in the second medium. The effect of refraction on x-ray propagation is reduced by spatially and temporally controlling the injection of the seed x-ray to the second medium.     

High-resolution study of x-ray resonant Raman scattering at the K edge of silicon

We report on the first high-resolution measurements of the K x-ray resonant Raman scattering (RRS) in Si. The measured x-ray RRS spectra, interpreted using the Kramers-Heisenberg approach, revealed spectral features corresponding to electronic excitations to the conduction and valence bands in silicon. The total cross sections for the x-ray RRS at the 1s absorption edge and the 1s-3p excitation were derived. The Kramers-Heisenberg formalism was found to reproduce quite well the x-ray RRS spectra, which is of prime importance for applications of the total-reflection x-ray fluorescence technique.     

X-ray spatial harmonic imaging of phase objects

Refractive index gradients in materials or at material interfaces lead to x-ray diffraction. Interference of this radiation with adjacent x-ray waves causes phase contrast that can be used for imaging purposes if an x-ray source with sufficient spatial coherence is used. The imaging modality presented here uses hard x radiation diffracted at interfaces, but requires only little spatial coherence. We report experiments showing, first, that image contrast is not diminished by motional blurring, and second, that contrast can be increased by orders of magnitude relative to in-line x-ray phase-contrast imaging. These properties substantially broaden the applicability of phase-sensitive imaging to moving samples and very weak density gradients.     

Unveiling and driving hidden resonances with high-fluence, high-intensity x-ray pulses

We show that high fluence, high-intensity x-ray pulses from the world's first hard x-ray free-electron laser produce nonlinear phenomena that differ dramatically from the linear x-ray-matter interaction processes that are encountered at synchrotron x-ray sources. We use intense x-ray pulses of sub-10-fs duration to first reveal and subsequently drive the 1s?2p resonance in singly ionized neon. This photon-driven cycling of an inner-shell electron modifies the Auger decay process, as evidenced by line shape modification. Our work demonstrates the propensity of high-fluence, femtosecond x-ray pulses to alter the target within a single pulse, i.e., to unveil hidden resonances, by cracking open inner shells energetically inaccessible via single-photon absorption, and to consequently trigger damaging electron cascades at unexpectedly low photon energies.     

Time resolved spectroscopy with femtosecond soft-x-ray pulses

The most challenging application of time resolved spectroscopy is to directly observe the structural and electronic dynamics. Here we present the combination of x-ray absorption spectroscopy with laser driven x-ray sources, offering atomic spatial and temporal resolution. Our new approaches for optimization of laser driven x-ray sources resulted in the demonstration of spatially coherent sub-20 fs x-ray pulses in a range up to several keV. We excited polycrystalline silicon with an ultrashort laser pulse and characterized the collective motion of atoms with time resolved x-ray absorption spectroscopy at a temporal resolution of less than 20 fs. Finally, we have shown the feasibility of probing the dynamics of the electronic structure of silicon and carbon with near edge x-ray absorption spectroscopy.     

连续脉冲X光摄影

单次脉冲X光摄影,已有四十多年的发展历史,较为广泛地应用于各种瞬态过程的分析。但连续脉冲X光摄影,仍是一项尚未完全成熟的技术。特别是单X光管,单发生器的连续摄影装置,更是方兴未艾。本文介绍了脉冲X光高速连续摄影的国内外研制现状,对几种摄影机结构形式作了比较。以作者几年来的科研实践为基础,重点介绍其中一种-单X光管单发生器的连续脉冲X光机,包括它的原理结构、用途和技术特点,以及存在问题和发展动向。     

X-ray diffraction microscopy of magnetic structures

We report the first proof-of-principle experiment of iterative phase retrieval from magnetic x-ray diffraction. By using the resonant x-ray excitation process and coherent x-ray scattering, we show that linearly polarized soft x rays can be used to image both the amplitude and the phase of magnetic domain structures. We recovered the magnetic structure of an amorphous terbium-cobalt thin film with a spatial resolution of about 75 nm at the Co L3 edge at 778 eV. In comparison with soft x-ray microscopy images recorded with Fresnel zone plate optics at better than 25 nm spatial resolution, we find qualitative agreement in the observed magnetic structure.     

Refractive microlens array for wave-front analysis in the medium to hard x-ray range

We report an alternative approach to x-ray wave-front analysis that uses a refractive microlens array as a Shack-Hartmann sensor. The sensor was manufactured by self-assembly and electroplating techniques and is suitable for high-resolution wave-front analysis of medium to hard x rays. We demonstrate its effectiveness at an x-ray energy of 3 keV for analysis of x-ray wave-front perturbations caused by microscopic objects. The sensor has potential advantages over other methods for x-ray phase imaging and will also be useful for the characterization of x-ray beams and optics.     

1 kHz tabletop ultrashort hard x-ray source for time-resolved x-ray protein crystallography

We describe a compact, reliable, and high-average-power femtosecond x-ray source and its first application to diffraction on protein crystal. The setup relies on a homemade Ti: sapphire system delivering 12 mJ at a 1 kHz repetition rate, associated with a small vacuum chamber especially designed for laser-plasma interaction and x-ray applications. This device allows the generation of 5 x 10(9) photons/s/sr at 8 keV and optimized x-ray irradiation of the studied sample, which can be placed close to the source. We present the diffraction pattern of a protein crystal in a divergent beam geometry, which is a first step to a subpicosecond x-ray diffraction experiment.     

强光1号装置上钨丝阵列的Z箍缩实验研究

本文报道了2003年在强光一号装置上进行的钨丝阵列的Z箍缩实验研究的主要结果。为了研究钨丝阵列的内爆过程和x光辐射特性，使用了x光功率谱仪和一维时空分辨x光成像系统等诊断设备。实验中由32根5微米钨丝组成的直径8mm长20mm的优化负载获得了最高能量为36.6kJ的x光产额，一维时空分辨x光成像系统的数据显示x光辐射区域以6.4×10⁶cm/s的速度减小，同时x光峰值时刻出现在等离子体被压缩到近轴区域之前。     

Simulation of x-ray transmission through an ellipsoidal capillary

This paper develops a simulation program for x-ray transmission in an ellipsoidal capillary based on a ray-tracing method.The influence of the parameters of ellipsoidal capillary and x-ray energy on transmission efficiency,full width at half maximum and power density gain of x-ray beams through an ellipsoidal capillary was analysed by this program.It shows that the particular rules of the ellipsoidal capillary x-ray lens are different from the polycapillary lens.Furthermore,this analysis method can be applied to the optimized design of ellipsoidal capillary.     

Energy dispersive x-ray diffraction of micro-crystals at ultrahigh pressures

Abstract

Ultrahigh pressures and temperatures in diamond-anvil cells are achieved at the expense of reducing sample volume. The capability of x-ray diffraction with high spatial resolution is most fundamental for probing microscopic samples at the maximum P-T and for minimizing the effect of gradients. Polychromatic synchrotron radiation with energy dispersive x-ray diffraction is ideal for the development of new classes of structural microprobes. Primary x-ray beams down to 3 microns can be produced with microbeam slit systems and microfocusing optical devices. The microprobe can be routinely used for a variety of high-pressure experiments, including single-crystal x-ray diffraction above 50 GPa, polycrystal-line diffraction above 300 GPa, deviatoric strain measurements, and diffraction at simultaneous high pressure and temperature.     

Multiwavelength anomalous diffraction at high x-ray intensity

The multiwavelength anomalous diffraction (MAD) method is used to determine phase information in x-ray crystallography by employing anomalous scattering from heavy atoms. X-ray free-electron lasers (FELs) show promise for revealing the structure of single molecules or nanocrystals, but the phase problem remains largely unsolved. Because of the ultrabrightness of x-ray FEL, samples experience severe electronic radiation damage, especially to heavy atoms, which hinders direct implementation of MAD with x-ray FELs. Here, we propose a generalized version of MAD phasing at high x-ray intensity. We demonstrate the existence of a Karle-Hendrickson-type equation in the high-intensity regime and calculate relevant coefficients with detailed electronic damage dynamics of heavy atoms. The present method offers a potential for ab initio structural determination in femtosecond x-ray nanocrystallography.     

Laser-ablation rates measured using x-ray laser transmission

The rate of laser ablation at irradiances of approximately 2 x 10{14} W cm{-2} of solid iron has been measured using the transmission of a neonlike zinc x-ray laser at 21.2 nm through thin iron targets. Ablated iron becomes transparent to the x-ray laser flux, enabling the thickness of unablated material and hence the rate of ablation to be measured from time resolved x-ray laser transmission.     

The microcalorimeter X-ray detector: A true paradigm shift in X-ray spectroscopy

The microcalorimeter x-ray detector registers the heat deposited in an absorber from individual x-ray photons by means of a sensitive thermometer. It combines advantages of wavelength-dispersive and energy-dispersive detectors: relatively high energy resolution over a broad energy spectrum. Operating at very low temperatures reduces the noise, making the high energy resolution possible. The absorber can be tailored to any energy range, from soft x-rays to gamma rays. After many years of development, several designs have reached a level of performance and reliability that makes them competitive x-ray detectors for many kinds of experiment. We survey current microcalorimeter detectors using several different thermometers. Their applications already run from chemical analysis to plasma physics and x-ray astronomy. We describe two examples of how the microcalorimeter detector can enable novel determinations in x-ray physics.     

Double-sided laser heating system at HPCAT for in situ x-ray diffraction at high pressures and high temperatures

An overview of a YLF:Nd laser heating system at the undulator x-ray diffraction station (16ID-B) of the high-pressure collaborative access team (HPCAT) of the Advanced Photon Source is presented. Based on the double-sided laser heating technique, the system is designed with considerable effort on the mechanical and optical stabilities, features for user-friendly operation, and the capability of accommodating diamond anvil cells of various heights up to 68?mm. This system has been used for x-ray diffraction studies of a wide range of materials to over 150?GPa and above 3000?K. Applying the laser heating technique to radial x-ray diffraction studies at simultaneous high-pressure and high-temperature (PT) conditions requires heating to be conducted at variable angles relative to the x-ray direction. A rotation laser heating design is discussed.     

4f delocalization in Gd: inelastic x-ray scattering at ultrahigh pressure

We present resonant inelastic x-ray scattering and x-ray emission spectroscopy results on Gd metal to 113 GPa which suggest Kondo-like aspects in the delocalization of 4f electrons. Analysis of the resonant inelastic x-ray scattering data reveals a prolonged and continuous delocalization with volume throughout the entire pressure range, so that the volume-collapse transition at 59 GPa is only part of the phenomenon. Moreover, the Lgamma1 x-ray emission spectroscopy spectra indicate no apparent change in the bare 4f moment across the collapse, suggesting that Kondo screening is responsible for the expected Pauli-like behavior in magnetic susceptibility.     

Generation of suprathermal electrons during magnetic reconnection at the sawtooth crash and disruption instability in the T-10 tokamak

Evidence for excitation of suprathermal electrons ( E(gamma) approximately 20-100 keV) during magnetic reconnection in the T-10 tokamak is presented through analysis of the x-ray measurements with enhanced spatial and time resolution. A toroidally viewing x-ray imaging system and a fast hard x-ray detector placed inside the tokamak vessel allow identification of bursts of the nonthermal x-ray radiation around X points of the m = 1 and m = 2 magnetic islands during the sawtooth crash and prior to the energy quench at the density limit disruption.     

K<Subscript><Emphasis Type="Italic">α</Emphasis></Subscript> x-ray emission characterization of 100 Hz, 15 mJ femtosecond laser system with high contrast ratio

We report K _α x-ray production with a high energy (110 mJ per pulse at 800 nm before compression/15 mJ at 400 nm after compression), high repetition rate (100 Hz), and high pulse contrast (better than 10⁻⁹ at 400 nm) laser system. To develop laser-based x-ray sources for biomedical imaging requires to use high-energy and high-power ultrafast laser system where compression is achieved under vacuum. Using this type of laser system, we demonstrate long-term stability of the x-ray yield, conversion efficiency higher than 1.5×10⁻⁵ with a Mo target, and the x-ray spot size close to the optical focal spot. This high-repetition K _α x-ray source can be very useful for x-ray phase-contrast imaging. S. Fourmaux and C. Serbanescu contributed equally to this work.     

Mo:Y multilayer mirror technology utilized to image the near-field output of a Ni-like Sn laser at 11.9 nm

Although bright x-ray sources exist at shorter wavelengths, the development of sophisticated diagnostics with x-ray laser sources has been restricted to wavelengths longer than 12.5 nm because of the limitations of the widely used Mo:Si multilayer mirrors. With the novel Mo:Y multilayer mirrors that we present, many x-ray laser applications can be extended to the 7-12-nm range. We demonstrate this new capability by imaging the near-field output of the Ni-like Sn laser at 11.9 nm.