The LCLS-II Project represents over a billion dollars investment from the US Department of Energy to provide a new, superconducting accelerator in the first kilometer of the SLAC linac tunnel, feeding a pair of new variable gap undulators. This facility will deliver X-rays from 0.25 to 5 keV at up to 1 million pulses per second in a continuous stream. This leap in repetition rate from the current level of 120 Hz, and the corresponding increase in average brightness, will transform the scientific breadth and impact of the LCLS facility. A suite of new instruments, pump/probe laser systems, detectors, data systems and integrated controls is being deployed in parallel to take full advantage of this new source. LCLS-II will be a transformative tool for energy science, qualitatively changing the way that X-ray imaging, scattering and spectroscopy can be used to study how natural and artificial systems function, revealing dynamics on timescales down to the attosecond regime, and mapping spatial response down to sub-atomic levels. It will enable new ways to capture rare chemical events, characterize fluctuating heterogeneous complexes, and reveal quantum phenomena in matter, using nonlinear, multidimensional and coherent X-ray techniques that are possible only with a high repetition-rate X-ray laser. This facility will provide access to the “tender X-ray” regime (2 to 5 keV), and will use seeding technologies to provide fully coherent X-rays in a uniformly spaced series of pulses with programmable repetition rate and rapidly tunable photon energies. LCLS-II is anticipated to start generating x-rays in February 2023, with initial operating ramping from 1 kHz to 33 kHz in readiness for the first science experiments in mid 2023. This talk will present the early performance of the new facility, and describe the capabilities being made available to the international community.

PAL-XFEL started supporting regular user experiments in mid-2017, and we have supported more than 250 user experiments. In the meantime, the PAL-XFEL has progressed much in both FEL operation and beamline experiments. It includes generating intense self-seeding FEL, two-color FELs operation, and a simultaneous operation between HX and SX. Concurrently, the beamline has tried to apply those improvements in the accelerator to actual beamline experiments. In this presentation, I will report the latest status of the PAL-XFEL.

The Shanghai soft X-ray Free-Electron Laser facility (SXFEL) is the first X-ray FEL facility in China. The construction of the SXFEL facility was finished recently. The output photon energy of the SXFEL can cover the whole water window range. Except for the self-amplified spontaneous emission, various seeding technques have also been adopted for improving the performances of the SXFEL. Here we presents an overview of the SXFEL facility, including the layout and design, construction status, commissioning progress and future plans.

X-ray free-electron laser (XFEL) facilities have been excellent light sources to explore ultrafast phenomena in the fields of physics, chemistry, biology and material science by supplying intense femtosecond X-ray pulses with a few tens of gigawatt power. However, shorter pulse lengths have been desired to trace the electron dynamics in atomic and molecular systems, theoretical and experimental studies also have been devoted to how to generate attosecond X-ray pulses from XFEL facilities. In this talk, I will discuss the following issues to generate isolated terawatt attosecond pulses from a free-electron laser with simulation results: (1) the generation of the current spike in the electron beam with optimal width and peak current; (2) the amplification of a photon pulse to the terawatt-level in the attosecond time domain with variable-spaced current spikes; (3) the enhancement of the signal-to-noise ratio of the attosecond pulse with optimized undulator layout. Also, the ongoing project to demonstrate the generation of attosecond pulse at Pohang Accelerator Laboratory X-ray Free Electron Laser (PAL-XFEL) will be briefly introduced.

In Self-Amplified Spontaneous Emission Free Electron Laser (SASE FEL) based short-pulse schemes, pulse duration is limited by FEL coherence time. A laser-based scheme overcoming this barrier was developed in [1] and proposed for realization at the soft X-ray FEL user facility FLASH. It allows to generate attosecond pulses in the wavelength range 2 - 10 nm. The installation of the laser system requires time and ressources, but a significant reduction of FEL pulse duraton below coherence time limit is possible even without a laser. The method is described in this presentation and is illustrated by numerical simulations. [1] E.A. Schneidmiller, Phys. Rev. AB 25(2022)010701

Despite tremendous progress in X-ray free-electron laser (FEL) science over the last decade, future applications still demand fully coherent, stable X-rays that have not been demonstrated in existing X-ray FEL facilities. In this talk, we describe an active Q-switched X-ray regenerative amplifier FEL (XRAFEL) to produce fully coherent, high-brightness, hard X-rays. By using simple electron beam phase space manipulation, we show this scheme is very flexible in controlling the X-ray cavity quality factor Q and hence the output radiation. We report both theoretical and numerical studies on this scheme with a wide range of accelerator, X-ray cavity, and undulator parameters. We also report an experimental demonstration of a large-scale, low-loss, stable Bragg cavity.

Ptychography is a scanning coherent diffraction imaging technique capable of simultaneous imaging of extended samples and beam characterization with diffraction-limited resolution. However, the scanning mode of data acquisition nature makes ptychography time-consuming and prevents its application for imaging of dynamical processes or single-shot beam characterization required at free-electron lasers. It is possible to perform ptychography in the single-shot mode by collecting the diffraction patterns of multiple overlapping beams in one shot, thus measuring the whole dataset at once and removing the need for scanning. A setup realizing this principle was proposed for visible light[1] however, it cannot be straightforwardly applied to X-ray due to the use of refractive optics. We present a novel single-shot ptychography setup based on a combination of X-ray focusing optics and beam-splitting grating, and a corresponding forward model that facilitates single-shot imaging of extended samples at soft X-ray wavelengths. The setup was tested during the proof of concept experiment at the free-electron laser FLASH at DESY and allowed us to obtain a reconstruction of a test sample and probe wavefield from the data measured with a single pulse of FLASH. This technique, further improved and adapted for harder X-ray, will allow the high-resolution single-shot imaging of extended dynamical samples as well as the single-shot beam characterization at X-ray free-electron lasers. [1] Sidorenko, Pavel, and Oren Cohen. "Single-shot ptychography." Optica 3.1 (2016): 9-14.

Fundamental electron dynamics at the attosecond frontier and their direct coupling to structural dynamics of matter yield novel insights into the energy-distribution and protection mechanisms of Nature. The angular-streaking technique has exclusively demonstrated its capability of obtaining the full time-energy structure of XFEL pulses with attosecond resolution directly in the time-domain, thus enabling XFELs to study electron dynamics from element-specific vistas and their importance as onset of subsequent structural dynamics. We will present latest advances of this technique together with first results from the 2022 EuXFEL atto-campaign and the complementary prospects of the FLASH 2020+ innovation project at DESY.

Free Electron Laser (FELs) as well as storage-ring-based photon sources have seen an enormous improvement over the past decade regarding stability, brilliance and availability of coherence. To give today`s photon science a benefit from these unique source properties the availability of optical elements of utmost quality is essential. However, their supply is very limited because due to the lack of sufficient manufacturing capacity at companies as well as at laboratories world-wide. Only a few companies are technological skilled to supply mirror or grating substrates of sub-nm quality regarding figure- and finish-error on a sufficient length of aperture. Even more critical is the situation for diffractive optical elements such as gratings or reflection zone plates. Especially gratings of blazed groove-profile are provided by very few manufacturers only with extremely long delivery time and high risk of failure during manufacturing. In this presentation we will report on the current state of quality achieved for different type of X-ray-optical elements like mirrors of different size and geometry as well as gratings, of laminar or blazed groove profile. Further consideration will be given to new developments on the production of blazed gratings like new ruling machines to provide gratings of significant larger aperture size as well as the option to obtain blazed gratings by means of e-beam lithography. In addition we report on the methods to verify their quality by means of ex-situ and at-wave-length metrology during manufacturing and for final acceptance test at facility side.

FLASH, the soft X-ray free-electron laser (FEL) in Hamburg provides high-brilliance ultrashort femtosecond pulses at MHz repetition rate for user experiments. For many spectroscopic and dynamical studies in various research fields a small FEL energy bandwidth and ultrashort pulses are a prerequisite. In order to preserve a short pulse duration and still monochromatize the FEL radiation, the new pulse-length preserving monochromator beamline FL23 at FLASH2 uses a double-grating design. While the first grating disperses the radiation and an intermediate slit reduces the spectral bandwidth, the second grating compensates the introduced pulse front tilt, thereby preserving the ultrashort photon pulses. The beamline is designed to work in the soft X-ray regime covering the spectral range between 1.3 nm and 20 nm with a spectral resolving power of approximately 2000 [1]. To maximize the transmission at the high energy end where the pulse elongation is not so critical the beamline can also be operated in a single grating configuration. A flexible microfocusing is provided at the experiment by a bendable Kirkpatrick-Baez mirror system – similar to the one used at the FL24 beamline at FLASH. A femtosecond optical laser synchronized to the FEL will be provided for pupm-probe experiments. The beamline concept and design has been developed using ray tracing simulations and confirmed by wavefront propagation simulations [2]. In the presentation, the pulse-length preserving double monochromator beamline concept will be introduced, the different operation modes and the expected photon parameters at the experimental station will be discussed and the first commissioning results will also be shown. [1] L. Poletto, F. Frassetto, G. Brenner, M. Kuhlmann and E. Plönjes, Double-grating monochromatic beamline with ultrafast response for FLASH2 at DESY, Special Issue (PhotonDiag2017), J. Synchrotron Rad. 25, 131-137 (2018); https://doi.org/10.1107/S1600577517013777 [2] M. Ruiz-Lopez, L. Samoylova, G. Brenner, M. Mehrjoo, B. Faatz, M. Kuhlmann, L. Poletto and E. Plönjes, Wavefront-propagation simulations supporting the design of a time-delay compensating monochromator beamline at FLASH2, J. Synchrotron Rad. 26, 899-905 (2019); https://doi.org/10.1107/S160057751900345X

The recent development of X-ray free electron lasers (XFELs) has made a breakthrough extending resonant X-ray scattering techniques into the ultrafast time domain via ultrashort femtosecond X-ray pulses with high brightness. In this talk, I will discuss the time-resolved resonant X-ray scattering instruments available for the user’s beamtime experiment at PAL-XFEL. They utilize the self-seeded hard X-ray beam, of which monochromatic characteristics are brighter flux and narrower bandwidth than those of the monochromatic beam filtered from the SASE beam. The advanced experimental platform established at PAL-XFEL may contribute to the emerging research paradigm to understand ultrafast non-equilibrium dynamics of material states.

The scope of the proposed talk is to present the available tools at the EuXFEL facility, developed by the SEC group, to standardize liquid jet support in order to allow less experienced user groups to perform experiments as well as to reduce the effort of the support team in the long run. This streamlining consists of standardizing both the sample delivery instrumentation and the experimental configuration(s) as much as possible. For the first experiments, many small user groups depended strongly on collaborations with expert user groups for liquid jet sample delivery. With the SEC standardization approach, this issue is overcome. The standardized tools offered by SEC in liquid jet delivery simplify quality control and allow faster learning by gradually optimizing the design with feedback from each experiment. Furthermore, they streamline the liquid jet support. A detailed summary of the nozzles developed by the SEC group, a presentation of the different liquid jets test chambers, and the sample environment sections available at the different EuXFEL instruments will be presented at this conference. The improvement of the described resources together with reinforced communication among the collaborators, and the higher proximity with the users lead to proven better outcomes.

Large area detectors with high dynamic range, low noise and fast pulse-to-pulse readout have been developed to accommodate the unique requirements and pulse structure of XFEL facilities. In the case of hard x-ray solution scattering the detectors need to capture intense diffuse scattering patterns covering a large area and dynamic range. Furthermore, time-resolved solution scattering needs the performance, stability, linearity and noise profile to extract percent to permille level changes in such scattering patterns reliably. The ePix10k2M (2019) is the second hard x-ray large area detector developed for the LCLS, it offers a number of advantages over the previous CSPAD detector. The ePix10k2M has 3 different fixed gain-modes as well as two auto-ranging/auto-switching modes. The combination of gains allows for the coverage of a large hard x-ray dynamic range from single photon counting to ~10k photons/pixel/pulse. Here, the performance is evaluated for the detection of hard x-ray solution scattering and compares the different configurations in which it can be run. Finally, some perspectives are presented on the future use and development of such detectors at the higher energies and higher repetition rates that are becoming available.

Recording images of individual molecules with ultrashort “exposure times” has been a long-standing dream in molecular physics, chemistry, and biology, because this would allow one to follow the motion of atoms on their inherent timescale. While X-ray and electron diffraction have been successfully used for larger molecules, both are challenging to apply to small gas-phase molecules. We could recently demonstrate that snapshot images of the complete structure of a molecule with eleven atoms, including all hydrogens, can be recorded by Coulomb explosion imaging (CEI) using intense, femtosecond soft X-ray pulses [Nature Physics 18, 423 (2022)]. While it was possible to record up to six-fold ion coincidences, even three-fold ion coincidences can be sufficient to image the full structure of a molecule. The X-ray intensity is high enough to produce extreme charge states (e.g. up to 42+ in xenon atoms), and to Coulomb-explode molecules into individual atoms very quickly, such that the initial molecular structure is well preserved in the recorded momenta of all ions. The intriguingly clear momentum images allow us to identify each atom’s position in the molecule unambiguously. The sensitivity of CEI to the molecular structure at the instant of ionization allows studying processes such as molecular charge-up, the influence of transient molecular resonances, intramolecular charge rearrangement and fragmentation dynamics. The femtosecond pulse duration opens the door to monitoring the temporal evolution of the molecular structure. Furthermore, combining CEI with coincident electron detection provides access to molecular-frame photoelectron diffraction – a powerful tool for accessing molecular dynamics.

Modern techniques for the investigation of correlated materials in the time domain combine selective excitation in the THz frequency range with selective probing of coupled structural, electronic and magnetic degrees of freedom using x-ray scattering techniques. Cryogenic sample temperatures are commonly required to prevent thermal occupation of the low energy modes and to access relevant material ground states. Here, we present a chamber optimized for high-field THz excitation and (resonant) x-ray diffraction at sample temperatures between 5 and 500 K. Directly connected to the beamline vacuum and featuring both a Beryllium window and an in-vacuum detector, the chamber covers the full (2–12.7) keV energy range of the femtosecond x-ray pulses available at the Bernina endstation of the SwissFEL free electron laser. Successful commissioning experiments made use of the energy tunability to selectively track the dynamics of the structural, magnetic and orbital order of Ca2RuO4 and Tb2Ti2O7 at the Ru (2.96 keV) and Tb (7.55 keV) L-edges, respectively. The chamber has been employed extensively in user operation since 2021, during which THz field amplitudes up to 1.12 MV cm−1 peak field were demonstrated and used to excite the samples at temperatures as low as 5 K. New developments, which allow the chamber to be used in optical pump, x-ray probe experiments in grazing incidenc geometry down to 5 K sample temperature have been commissioned recently. For more details, see https://iopscience.iop.org/article/10.1088/1361-648X/ac08b5

This conference presentation was prepared for SPIE Optics + Optoelectronics, 2023.