- 标题
- 摘要
- 关键词
- 实验方案
- 产品
-
AIP Conference Proceedings [Author(s) PROCEEDINGS OF THE 12TH INTERNATIONAL CONFERENCE ON SYNCHROTRON RADIATION INSTRUMENTATION – SRI2015 - New York, NY USA (6–10 July 2015)] - Physical optics simulations with Phase for SwissFEL beamlines
摘要： PHASE is a software tool for physical optics simulation based on the stationary phase approximation method. The code is under continuous development since about 20 years and has been used for instance for fundamental studies and ray tracing of various beamlines at the Swiss Light Source. Along with the planning for SwissFEL a new hard X-ray free electron laser under construction, new features have been added to permit practical performance predictions including diffraction effects which emerge with the fully coherent source. We present the application of the package on the example of the ARAMIS 1 beamline at SwissFEL. The X-ray pulse calculated with GENESIS and given as an electrical field distribution has been propagated through the beamline to the sample position. We demonstrate the new features of PHASE like the treatment of measured figure errors, apertures and coatings of the mirrors and the application of Fourier optics propagators for free space propagation.
关键词： beamline optics,X-rays,XFEL,synchrotron radiation
更新于2025-09-23 15:23:52
-
Improving signal strength in serial crystallography with <i>DIALS</i> geometry refinement
摘要： The DIALS diffraction-modeling software package has been applied to serial crystallography data. Diffraction modeling is an exercise in determining the experimental parameters, such as incident beam wavelength, crystal unit cell and orientation, and detector geometry, that are most consistent with the observed positions of Bragg spots. These parameters can be re?ned by nonlinear least-squares ?tting. In previous work, it has been challenging to re?ne both the positions of the sensors (metrology) on multipanel imaging detectors such as the CSPAD and the orientations of all of the crystals studied. Since the optimal models for metrology and crystal orientation are interdependent, alternate cycles of panel re?nement and crystal re?nement have been required. To simplify the process, a sparse linear algebra technique for solving the normal equations was implemented, allowing the detector panels to be re?ned simultaneously against the diffraction from thousands of crystals with excellent computational performance. Separately, it is shown how to re?ne the metrology of a second CSPAD detector, positioned at a distance of 2.5 m from the crystal, used for recording low-angle re?ections. With the ability to jointly re?ne the detector position against the ensemble of all crystals used for structure determination, it is shown that ensemble re?nement greatly reduces the apparent nonisomorphism that is often observed in the unit-cell distributions from still-shot serial crystallography. In addition, it is shown that batching the images by timestamp and re-re?ning the detector position can realistically model small, time-dependent variations in detector position relative to the sample, and thereby improve the integrated structure-factor intensity signal and heavy-atom anomalous peak heights.
关键词： sparse algebra,refinement,DIALS,metrology,XFEL
更新于2025-09-23 15:21:21
-
Development of an Experimental Platform for Combinative Use of an XFEL and a High-Power Nanosecond Laser
摘要： We developed an experimental platform for combinative use of an X-ray free electron laser (XFEL) and a high-power nanosecond laser. The main target of the platform is an investigation of matter under high-pressure states produced by a laser-shock compression. In this paper, we show details of the experimental platform, including XFEL parameters and the focusing optics, the laser irradiation system and X-ray diagnostics. As a demonstration of the high-power laser-pump XFEL-probe experiment, we performed an X-ray di?raction measurement. An in-situ single-shot X-ray di?raction pattern expands to a large angle side, which shows a corundum was compressed by laser irradiation.
关键词： X-ray di?raction,high-pressure science,laser shock,XFEL
更新于2025-09-23 15:21:01
-
Virus Structures by X-Ray Free-Electron Lasers
摘要： Until recently X-ray crystallography has been the standard technique for virus structure determinations. Available X-ray sources have continuously improved over the decades, leading to the realization of X-ray free-electron lasers (XFELs). They provide high-intensity femtosecond X-ray pulses, which allow for new kinds of experiments by making use of the diffraction-before-destruction principle. By overcoming classical dose constraints, they at least in principle allow researchers to perform X-ray virus structure determination for single particles at room temperature. Simultaneously, the availability of XFELs led to the development of the method of serial femtosecond crystallography, where a crystal structure is determined from the measurement of hundreds to thousands of microcrystals. In the case of virus crystallography this method does not require freezing of the crystals and allows researchers to perform experiments under non-equilibrium conditions (e.g., by laser-induced temperature jumps or rapid chemical mixing), which is currently not possible with electron microscopy.
关键词： structure determination,serial crystallography,XFEL,single particle imaging,virus crystallography,X-ray free-electron laser
更新于2025-09-16 10:30:52
-
A host dTMP-bound structure of T4 phage dCMP hydroxymethylase mutant using an X-ray free electron laser
摘要： The hydroxymethylation of cytosine bases plays a vital role in the phage DNA protection system inside the host Escherichia coli. This modification is known to be catalyzed by the dCMP hydroxymethylase from bacteriophage T4 (T4dCH); structural information on the complexes with the substrate, dCMP and the co-factor, tetrahydrofolate is currently available. However, the detailed mechanism has not been understood clearly owing to a lack of structure in the complex with a reaction intermediate. We have applied the X-ray free electron laser (XFEL) technique to determine a high-resolution structure of a T4dCH D179N active site mutant. The XFEL structure was determined at room temperature and exhibited several unique features in comparison with previously determined structures. Unexpectedly, we observed a bulky electron density at the active site of the mutant that originated from the physiological host (i.e., E. coli). Mass-spectrometric analysis and a cautious interpretation of an electron density map indicated that it was a dTMP molecule. The bound dTMP mimicked the methylene intermediate from dCMP to 5′-hydroxymethy-dCMP, and a critical water molecule for the final hydroxylation was convincingly identified. Therefore, this study provides information that contributes to the understanding of hydroxymethylation.
关键词： hydroxymethylation,XFEL,dCMP hydroxymethylase,X-ray free electron laser,T4dCH,hydroxylation,cytosine bases,phage DNA protection,dTMP,Escherichia coli,bacteriophage T4,methylene intermediate
更新于2025-09-12 10:27:22
-
X-ray-assisted nuclear excitation by electron capture in optical laser-generated plasmas
摘要： X-ray-assisted nuclear excitation by electron capture (NEEC) into inner-shell atomic holes in a plasma environment generated by strong optical lasers is investigated theoretically. The considered scenario involves the interaction of a strong optical laser with a solid-state nuclear target leading to the generation of a plasma. In addition, intense x-ray radiation from the X-ray Free Electron Laser (XFEL) produces inner-shell holes in the plasma ions, into which NEEC may occur. As a case study, we consider the 4.85-keV transition starting from the 2.4-MeV long-lived 93mMo isomer that can be used to release the energy stored in this metastable nuclear state. We ?nd that the recombination into 2p1/2 inner-shell holes is most ef?cient in driving the nuclear transition. The generation of inner-shell holes while the plasma is at a temperature of a few hundred eV can allow optimal conditions for NEEC, which are otherwise reached for steady-state plasma conditions in thermodynamical equilibrium only at few keV. The combination of x-ray and optical lasers presents two advantages: First, NEEC rates can be maximized at plasma temperatures where the photoexcitation rate remains low. Second, with mJ-class optical lasers and an XFEL repetition rate of 10 kHz, the NEEC excitation number can reach ≈1 depleted isomer per second and is competitive with scenarios recently envisaged at petawatt-class lasers.
关键词： XFEL,optical laser-generated plasmas,X-ray-assisted nuclear excitation,NEEC,electron capture
更新于2025-09-12 10:27:22
-
Stripline beam position monitor for X-ray free electron laser of Pohang Accelerator Laboratory
摘要： Beam position monitors (BPMs) are important instruments even in the case of an X-ray free-electron laser (XFEL). Pohang Accelerator Laboratory (PAL) finished the construction of an XFEL (PAL-XFEL) in 2015, and new stripline BPMs were installed in PAL-XFEL. New BPMs were designed to have a strong signal and a high resolution. In addition, the impedance matching was considered to reduce a signal reflection. These features of the BPM design were confirmed with a simulation study as well. Fabricated BPMs were tested by using a wire test stand. Two-dimensional position errors and offsets were measured to select best BPMs for PAL-XFEL. Finally, a real beam test was tried to check the BPM performance and a better resolution than the requirement was obtained.
关键词： stripline BPM,X-ray free-electron laser,Beam position monitors,impedance matching,PAL-XFEL
更新于2025-09-11 14:15:04
-
Stochastic stimulated electronic x-ray Raman spectroscopy
摘要： Resonant inelastic x-ray scattering (RIXS) is a well-established tool for studying electronic, nuclear, and collective dynamics of excited atoms, molecules, and solids. An extension of this powerful method to a time-resolved probe technique at x-ray free electron lasers (XFELs) to ultimately unravel ultrafast chemical and structural changes on a femtosecond time scale is often challenging, due to the small signal rate in conventional implementations at XFELs that rely on the usage of a monochromator setup to select a small frequency band of the broadband, spectrally incoherent XFEL radiation. Here, we suggest an alternative approach, based on stochastic spectroscopy, which uses the full bandwidth of the incoming XFEL pulses. Our proposed method is relying on stimulated resonant inelastic x-ray scattering, where in addition to a pump pulse that resonantly excites the system a probe pulse on a specific electronic inelastic transition is provided, which serves as a seed in the stimulated scattering process. The limited spectral coherence of the XFEL radiation defines the energy resolution in this process and stimulated RIXS spectra of high resolution can be obtained by covariance analysis of the transmitted spectra. We present a detailed feasibility study and predict signal strengths for realistic XFEL parameters for the CO molecule resonantly pumped at the O1s ! p(cid:2) transition. Our theoretical model describes the evolution of the spectral and temporal characteristics of the transmitted x-ray radiation, by solving the equation of motion for the electronic and vibrational degrees of freedom of the system self consistently with the propagation by Maxwell equations.
关键词： CO molecule,covariance analysis,Stochastic stimulated electronic x-ray Raman spectroscopy,resonant inelastic x-ray scattering,XFEL
更新于2025-09-04 15:30:14