Hard X-ray Free Electron Laser Research Articles

Single-shot experiments at the soft X-FEL FERMI using a back-side-illuminated scientific CMOS detector.

The latest Complementary Metal Oxide Semiconductor (CMOS) 2D sensors now rival the performance of state-of-the-art photon detectors for optical application, combining a high-frame-rate speed with a wide dynamic range. While the advent of high-repetition-rate hard X-ray free-electron lasers (FELs) has boosted the development of complex large-area fast CCD detectors in the extreme ultraviolet (EUV) and soft X-ray domains, scientists lacked such high-performance 2D detectors, principally due to the very poor efficiency limited by the sensor processing. Recently, a new generation of large back-side-illuminated scientific CMOS sensors (CMOS-BSI) has been developed and commercialized. One of these cost-efficient and competitive sensors, the GSENSE400BSI, has been implemented and characterized, and the proof of concept has been carried out at a synchrotron or laser-based X-ray source. In this article, we explore the feasibility of single-shot ultra-fast experiments at FEL sources operating in theEUV/soft X-ray regime with an AXIS-SXR camera equipped with the GSENSE400BSI-TVISB sensor. We illustrate the detector capabilities by performing a soft X-ray magnetic scattering experiment at the DiProi end-station of the FERMI FEL. These measurements show the possibility of integrating this camera for collecting single-shot images at the 50 Hz operation mode of FERMI with a cropped image size of 700× 700 pixels. The efficiency of the sensor at a working photon energy of 58 eV and the linearity over the large FEL intensity have been verified. Moreover, on-the-fly time-resolved single-shot X-ray resonant magnetic scattering imaging from prototype Co/Pt multilayer films has been carried out with a time collection gain of 30 compared to the classical start-and-stop acquisition method performed with the conventional CCD-BSI detector available at the end-station.

Simulation of wire scanner for high repetition free electron laser facilities

The high-gain Free Electron Lasers (FEL) have promised scientists for new scientific discoveries in many frontier research areas. For that purpose, this kind of facilities have been installed or will be installed worldwide. As to FELs, high repetition is the future development trend. Herein, wire scanner provides a measurement of beam profile which realizes real-time and non-intercepting for the FELs. The simulation of key parameters of wire scanner for the FELs is discussed in this paper. Since wire scanner for FELs mainly use tungsten wires, then empirical formula for optimum installation position of Beam Loss Monitor (BLM) and empirical formula for the maximum temperature of tungsten wires are given based on theoretical analysis and numerical simulation. These formulas can provide a reference for high repetition and high-gain FELs that will be installed with wire scanners in the future. In recent years, the Shanghai HIgh repetition rate XFEL aNd Extreme light facility (SHINE), a quasi-continuous wave hard X-ray free electron laser facility, is under construction in China. Upon its completion, the linear accelerator will accelerate electrons with bunch charge of 10–300 pC to 8 GeV, at a maximum repetition frequency of 1 MHz. We calculate key parameters of the wire scanner for SHINE with these empirical formulas.

Experimental demonstration of two-color x-ray free-electron-laser pulses via wakefield excitation

Several beam manipulation methods have been studied and experimentally demonstrated to generate x-ray multipulses in free-electron-laser (FEL) facilities, advancing the fields of material science, molecular physics, and photochemistry by enabling x-ray pump/x-ray probe experiments. We have demonstrated a novel method to generate hard x-ray multipulses using a hybrid compression scheme. Compared to other methods, this approach minimizes the time jitter among the FEL subpulses, produces large power FEL subpulses, is suitable for high repetition rate machines, since it does not imply the generation of losses, and it works at short and hard x-ray FEL wavelengths as well. All of these aspects make this approach attractive for the novel FEL facilities aiming to explore the hard x-ray region and to work at high repetition rate.

The cryogenic control system of SHINE

The Shanghai High repetition rate XFEL and Extreme Light Facility (SHINE), an advanced XFEL project, is now being built at Shanghai Advanced Research Institute (SARI), Chinese Academy of Sciences. It includes a hard X-ray free electron laser and a 100 pW intense laser facilities with overall length of 3.1 km. The XFEL part including an 8 GeV LINAC and 3 undulator lines is cooled with forced superfluid and supercritical helium at 2 K/4 K. The cryogenic system of SHINE consists of test facility cryogenic system (TFCS), accelerator cryogenic system (ACCS), and undulator cryogenic system (UNCS). A dedicated control system based on Experimental Physics and Industrial Control System (EPICS) will be built to automate the cryogenic system with process control, PID control loops, real-time data acquisition and storage, alarm handler and human machine interface. It is capable of automatic recovery as well. This paper describes details of control system structure, interfaces, controllers and the integration under EPICS framework.

New frontiers in extreme conditions science at synchrotrons and free electron lasers

Synchrotrons and free electron lasers are unique facilities to probe the atomic structure and electronic properties of matter at extreme thermodynamical conditions. In this context, ‘matter at extreme pressures and temperatures’ was one of the science drivers for the construction of low emittance 4th generation synchrotron sources such as the Extremely Brilliant Source of the European Synchrotron Radiation Facility and hard x-ray free electron lasers, such as the European x-ray free electron laser. These new user facilities combine static high pressure and dynamic shock compression experiments to outstanding high brilliance and submicron beams. This combination not only increases the data-quality but also enlarges tremendously the accessible pressure, temperature and density space. At the same time, the large spectrum of available complementary x-ray diagnostics for static and shock compression studies opens unprecedented insights into the state of matter at extremes. The article aims at highlighting a new horizon of scientific opportunities based on the synergy between extremely brilliant synchrotrons and hard x-ray free electron lasers.

Resolution of a bent-crystal spectrometer for X-ray free-electron laser pulses: diamond versus silicon.

The resolution function of a spectrometer based on a strongly bent single crystal (bending radius of 10 cm or less) is evaluated. It is shown that the resolution is controlled by two parameters: (i) the ratio of the lattice spacing of the chosen reflection to the crystal thickness and (ii) a single parameter comprising crystal thickness, its bending radius, distance to a detector, and anisotropic elastic constants of the chosen crystal. The results allow the optimization of the parameters of bent-crystal spectrometers for the hard X-ray free-electron laser sources.

Optimization and Design of Cutting-Edge-Technology Tools for Natural Sciences Research in the Twenty-First Century: X-Ray Free Electron Lasers

Regarding the chronologic evolution of accelerator-based light sources, optimization and design issues of cutting-edge-technology insertion devices (i.e., undulators, wigglers, etc.) have been a big competitive concern since the beginning of the twenty-first century. Although these sources are strongly restricted by technological limitations in terms of radiation wavelength, leading X-ray free-electron laser (FEL) facilities are spending considerable efforts to survive in this scientific competition by modifying/updating their insertion devices. In other words, even though they all generate almost identical free-electron laser pulses, advertising a “superconducting undulator based light source” in comparison with a “conventional undulator based light source” may sound more attractive for some scientists. However, in contrast to superconducting undulators, conventional undulators do not require cryogenic cooling systems resulting in a cost-effective operation as a matter of course. Under the circumstances, it is shown that generation of hard X-ray FEL pulses is feasible via unique PPM undulators driven by an electron linear accelerator (linac) within the energy range of 5–10 GeV. The results reveal good consistency with the operating X-ray FEL sources worldwide.

The data storage system for SHINE

Shanghai HIgh repetition rate XFEL aNd Extreme light facility (SHINE) is a quasi-continuous wave hard X-ray free electron laser facility, which is currently under construction. The data storage system holds large volumes of data generated instantaneously during the operation. A combination architecture of relational database, non-relational database and the distributed file system is designed as the centralized data storage system serving to multiple application demands for SHINE. The storage of high-speed stream data such as waveform and image data is studied and relevant storage schemas are tested and compared. The optimized schema is identified finally.

Materials Imaging and Dynamics (MID) instrument at the European X-ray Free-Electron Laser Facility.

The Materials Imaging and Dynamics (MID) instrument at the European X-ray Free-Electron Laser (EuXFEL) facility is described. EuXFEL is the first hard X-ray free-electron laser operating in the MHz repetition range which provides novel science opportunities. The aim of MID is to enable studies of nano-structured materials, liquids, and soft- and hard-condensed matter using the bright X-ray beams generated by EuXFEL. Particular emphasis is on studies of structure and dynamics in materials by coherent scattering and imaging using hard X-rays. Commission of MID started at the end of 2018 and first experiments were performed in 2019.

Overview of SwissFEL dual-photocathode laser capabilities and perspectives for exotic FEL modes

Abstract SwissFEL is a compact, high-brilliance, soft and hard X-ray free electron laser (FEL) facility that started user operation in 2019. The facility is composed of two parallel beam lines seeded by a common linear accelerator (LINAC), and a two-bunch photo-injector. For the injector, an innovative dual-photocathode laser scheme has been developed based on state-of-the-art ytterbium femtosecond laser systems. In this paper, we describe the performance of the SwissFEL photocathode drive lasers (PCDLs), the pulse-shaping capabilities as well as the versatility of the systems, which allow many different modes of operation of SwissFEL. The full control over the SwissFEL electron bunch properties via the unique architecture of the PCDLs will enable in the future the advent of more-advanced FEL modes; these modes include, but are not restricted to, the generation of single or trains of sub-femtosecond FEL pulses, multi-color FEL and finally, the generation of fully coherent X-ray pulses via laser-based seeding.

Conceptual design for an hard X-ray Free Electron Laser based on CLIC X-band structure

In this paper, a conceptual design of a hard X-ray Free-Electron Laser (FEL) facility based on CLIC-like X-band accelerating structure has been presented. The injector, based on an X-band rf gun, the main accelerating sections, using high-gradient CLIC-like structures including rf power distribution, and the two bunch compressors have been discussed. Simulations of the rf gun, of the injector, and of the linac have been performed, successfully meeting the stringent requirements in terms of minimum projected emittance, sliced emittance, and minimum bunch length. Full 6-D start-to-end linac simulations have been performed taking into account wakefield effects, misalignment of accelerator components, Coherent Synchrotron Radiation (CSR), and small dynamic variations of phase, voltage, and injection time. The performance of FEL at λ=1 Angstrom (Å) has also been evaluated for self-amplified spontaneous emission (SASE) FEL mode. A radiation power of about 10 GW has been achieved with a photon pulse length of 30 fs. The main advantage of the proposed design is that it achieved the required beam parameters in very short length, rendering the facility quite compact.

A compact and cost-effective hard X-ray free-electron laser driven by a high-brightness and low-energy electron beam

We present the first lasing results of SwissFEL, a hard X-ray free-electron laser (FEL) that recently came into operation at the Paul Scherrer Institute in Switzerland. SwissFEL is a very stable, compact and cost-effective X-ray FEL facility driven by a low-energy and ultra-low-emittance electron beam travelling through short-period undulators. It delivers stable hard X-ray FEL radiation at 1-A wavelength with pulse energies of more than 500 μJ, pulse durations of ~30 fs (root mean square) and spectral bandwidth below the per-mil level. Using special configurations, we have produced pulses shorter than 1 fs and, in a different set-up, broadband radiation with an unprecedented bandwidth of ~2%. The extremely small emittance demonstrated at SwissFEL paves the way for even more compact and affordable hard X-ray FELs, potentially boosting the number of facilities worldwide and thereby expanding the population of the scientific community that has access to X-ray FEL radiation. The first lasing results at SwissFEL, an X-ray free-electron laser, are presented, highlighting the facility’s unique capabilities. A general comparison to other major facilities is also provided.

Single- and two-color attosecond hard x-ray free-electron laser pulses with nonlinear compression

This work describes a method for the generation of one and two-color ultra-short X-ray free-electron-laser pulses, based on tailoring the Coulomb interaction between the electrons of a highly compressed beam in the nonlinear regime.

Femtosecond electronic structure response to high intensity XFEL pulses probed by iron X-ray emission spectroscopy

We report the time-resolved femtosecond evolution of the K-shell X-ray emission spectra of iron during high intensity illumination of X-rays in a micron-sized focused hard X-ray free electron laser (XFEL) beam. Detailed pulse length dependent measurements revealed that rapid spectral energy shift and broadening started within the first 10 fs of the X-ray illumination at intensity levels between 1017 and 1018 W cm-2. We attribute these spectral changes to the rapid evolution of high-density photoelectron mediated secondary collisional ionization processes upon the absorption of the incident XFEL radiation. These fast electronic processes, occurring at timescales well within the typical XFEL pulse durations (i.e., tens of fs), set the boundary conditions of the pulse intensity and sample parameters where the widely-accepted ‘probe-before-destroy’ measurement strategy can be adopted for electronic-structure related XFEL experiments.

Proof-of-concept Talbot-Lau x-ray interferometry with a high-intensity, high-repetition-rate, laser-driven K-alpha source.

Talbot-Lau x-ray interferometry is a grating-based phase-contrast technique, which enables measurement of refractive index changes in matter with micrometric spatial resolution. The technique has been established using a variety of hard x-ray sources, including synchrotron, free-electron lasers, and x-ray tubes, and could be used in the optical range for low-density plasmas. The tremendous development of table-top high-power lasers makes the use of high-intensity, laser-driven K-alpha sources appealing for Talbot-Lau interferometer applications in both high-energy-density plasma experiments and biological imaging. To this end, we present the first, to the best of our knowledge, feasibility study of Talbot-Lau phase-contrast imaging using a high-repetition-rate laser of moderate energy (100 mJ at a repetition rate of 10 Hz) to irradiate a copper backlighter foil. The results from up to 900 laser pulses were integrated to form interferometric images. A constant fringe contrast of 20% is demonstrated over 100 accumulations, while the signal-to-noise ratio continued to increase with the number of shots. Phase retrieval is demonstrated without prior ex-situ phase stepping. Instead, correlation matrices are used to compensate for the displacement between reference acquisition and the probing of a PMMA target rod. The steps for improved measurements with more energetic laser systems are discussed. The final results are in good agreement with the theoretically predicted outcomes, demonstrating the applicability of this diagnostic to a range of laser facilities for use across several disciplines.

Emergence of anomalous dynamics in soft matter probed at the European XFEL

Dynamics and kinetics in soft matter physics, biology, and nanoscience frequently occur on fast (sub)microsecond but not ultrafast timescales which are difficult to probe experimentally. The European X-ray Free-Electron Laser (European XFEL), a megahertz hard X-ray Free-Electron Laser source, enables such experiments via taking series of diffraction patterns at repetition rates of up to 4.5 MHz. Here, we demonstrate X-ray photon correlation spectroscopy (XPCS) with submicrosecond time resolution of soft matter samples at the European XFEL. We show that the XFEL driven by a superconducting accelerator provides unprecedented beam stability within a pulse train. We performed microsecond sequential XPCS experiments probing equilibrium and nonequilibrium diffusion dynamics in water. We find nonlinear heating on microsecond timescales with dynamics beyond hot Brownian motion and superheated water states persisting up to 100 μs at high fluences. At short times up to 20 μs we observe that the dynamics do not obey the Stokes-Einstein predictions.

Author Correction: A MHz-repetition-rate hard X-ray free-electron laser driven by a superconducting linear accelerator

Author Correction: A MHz-repetition-rate hard X-ray free-electron laser driven by a superconducting linear accelerator

Perspectives on single particle imaging with x rays at the advent of high repetition rate x-ray free electron laser sources.

X-ray free electron lasers (XFELs) now routinely produce millijoule level pulses of x-ray photons with tens of femtoseconds duration. Such x-ray intensities gave rise to the idea that weakly scattering particles—perhaps single biomolecules or viruses—could be investigated free of radiation damage. Here, we examine elements from the past decade of so-called single particle imaging with hard XFELs. We look at the progress made to date and identify some future possible directions for the field. In particular, we summarize the presently achieved resolutions as well as identifying the bottlenecks and enabling technologies to future resolution improvement, which in turn enables application to samples of scientific interest.

A method of bunch by bunch measurement at nanoseconds interval by using cavity beam position monitors

The application of RF cavity beam position monitors (CBPM) is essential for precise beam position measurements in X-ray Free-Electron Lasers (XFEL) and linear colliders. This paper addresses the solution to the inter-bunch signal interference when the bunch separation is as short as nanoseconds. The signals can overlap from bunch to bunch, which can induce appreciable error in evaluating beam position. We propose a conceptual method to eliminate the dominant signal overlap under a quadrature phase offset condition. Using this method, the elimination automatically occurs in the process of signal digitalization. The dominant interference that is contributed by the last bunch can be reduced over an order of magnitude in a conventional CBPM system. In addition, the required bandwidth can be effectively reduced by a factor of 2, and the design challenge for a wideband CBPM is relaxed. The method was demonstrated in an analytic approach by simulating the signal evolution in the RF front end of electronics built in MATLAB code. In the practical concern of applying this method, the factors that perturb the elimination have been examined as well. Based on the numerical result, the CBPM prototype has been designed for the pre-research plan of future high repetition rate hard XFEL at Chinese Academy of Engineering Physics. The combined simulations in CST and MATLAB on the CBPM prototype indicate agreement with the result obtained in the analytic approach.

A MHz-repetition-rate hard X-ray free-electron laser driven by a superconducting linear accelerator

The European XFEL is a hard X-ray free-electron laser (FEL) based on a high-electron-energy superconducting linear accelerator. The superconducting technology allows for the acceleration of many electron bunches within one radio-frequency pulse of the accelerating voltage and, in turn, for the generation of a large number of hard X-ray pulses. We report on the performance of the European XFEL accelerator with up to 5,000 electron bunches per second and demonstrating a full energy of 17.5 GeV. Feedback mechanisms enable stabilization of the electron beam delivery at the FEL undulator in space and time. The measured FEL gain curve at 9.3 keV is in good agreement with predictions for saturated FEL radiation. Hard X-ray lasing was achieved between 7 keV and 14 keV with pulse energies of up to 2.0 mJ. Using the high repetition rate, an FEL beam with 6 W average power was created.