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A special issue of Applied Sciences (ISSN 2076-3417). This special issue belongs to the section "Optics and Lasers".

Deadline for manuscript submissions: closed (30 April 2020) | Viewed by 52445

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Prof. Dr. Kiyoshi Ueda

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Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, Sendai 980-8577, Japan
Interests: electron dynamics; molecular dynamics; atoms, molecules and clusters; ultrafast phenomena; photoionization; molecular imaging; electron spectroscopy; many particle spectroscopy; coherent control; free electron lasers
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Dear Colleagues,

X-ray Free Electron Lasers (FELs) deliver coherent x-ray pulses, combining unprecedented power densities of up to 10²⁰W/cm² and extremely short pulse durations down to hundreds of attoseconds. Such intense XFEL pulses make single-shot diffraction of nanometer-size objects, tiny protein crystals, and non-crystalized biomolecules a tangible reality. Such ultrashort XFEL pulses allow us to visualize femtosecond-scale temporal variations of charge and structure that may occur upon photoexcitation in any form of matter. Also, since the X-ray FEL pulses give access to a new regime of x-ray intensities, they open new venues in studying the interaction between intense X-rays and various forms of matter. Understanding the ultrafast reactions induced by the X-ray FEL pulses is of fundamental interest, as well as of crucial importance, for X-ray FEL applications.

Currently, there are six X-ray FEL facilities in operation in the world. The first FEL facility FLASH (the Free Electron LASer in Hamburg) in Germany started operation for users in 2005. It provides FEL pulses in the range of extreme ultraviolet to soft X-rays. The first hard X-ray FEL facility LCLS (the Linac Coherent Light Source) in the United States started user operation in 2009. In 2012, the second hard X-ray FEL SACLA (the Spring-8 Angstrom Compact free electron LAser) in Japan and the first fully coherent seeded FEL FERMI (the Free Electron laser Radiation for Multidisciplinary Investigations) in Italy started user operation. In 2016, another hard X-ray XFEL, PAL-XFEL (the Pohang Accelerator Laboratory X-ray Free Electron Laser) in Korea, started operation. Last year, European XFEL (European X-ray Free Electron Laser) and SwissFEL (Swiss X-ray Free Electron Laser) started operations. One can find status reports and future plans for these facilities, as well as on-going science, in the Special Issue of the journal Applied Sciences “X-ray free electron laser” (https://www.mdpi.com/journal/applsci/special_issues/x_ray_fel).

Following the success of the first Special Issue “X-ray free electron laser”, we will launch the second Special Issue “Science at X-ray free electron lasers”. This Special Issue aims to cover recent developments in science at all XFELs, as well as relevant theoretical studies.

Prof. Dr. Kiyoshi Ueda
Guest Editor

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Published Papers (13 papers)

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Editorial

Jump to: Research, Review

3 pages, 156 KiB

Open AccessEditorial

Science at X-ray Free Electron Lasers

by Kiyoshi Ueda

Appl. Sci. 2021, 11(22), 10622; https://doi.org/10.3390/app112210622 - 11 Nov 2021

Viewed by 1306

Abstract

X-ray Free Electron Lasers (FELs) deliver coherent X-ray pulses, combining unprecedented power densities of up to 1020 W/cm² and extremely short pulse durations down to hundreds of attoseconds [...] Full article

(This article belongs to the Special Issue Science at X-ray Free Electron Lasers)

Research

Jump to: Editorial, Review

20 pages, 5957 KiB

Open AccessArticle

Opportunities for Two-Color Experiments in the Soft X-ray Regime at the European XFEL

by Svitozar Serkez, Winfried Decking, Lars Froehlich, Natalia Gerasimova, Jan Grünert, Marc Guetg, Marko Huttula, Suren Karabekyan, Andreas Koch, Vitali Kocharyan, Yauhen Kot, Edwin Kukk, Joakim Laksman, Pavel Lytaev, Theophilos Maltezopoulos, Tommaso Mazza, Michael Meyer, Evgeni Saldin, Evgeny Schneidmiller, Matthias Scholz, Sergey Tomin, Maurizio Vannoni, Torsten Wohlenberg, Mikhail Yurkov, Igor Zagorodnov and Gianluca Geloni Show full author list Hide full author list

Appl. Sci. 2020, 10(8), 2728; https://doi.org/10.3390/app10082728 - 15 Apr 2020

Cited by 33 | Viewed by 4829

Abstract

X-ray pump/X-ray probe applications are made possible at X-ray Free Electron Laser (XFEL) facilities by generating two X-ray pulses with different wavelengths and controllable temporal delay. In order to enable this capability at the European XFEL, an upgrade project to equip the soft X-ray SASE3 beamline with a magnetic chicane is underway. In the present paper we describe the status of the project, its scientific focus and expected performance, including start-to-end simulations of the photon beam transport up to the sample, as well as recent experimental results demonstrating two-color lasing at photon energies of 805 eV + 835 eV and 910 eV + 950 eV. Additionally, we discuss methods to analyze the spectral properties and the intensity of the generated radiation to provide on-line diagnostics for future user experiments. Full article

(This article belongs to the Special Issue Science at X-ray Free Electron Lasers)

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8 pages, 1185 KiB

Open AccessArticle

Nanofocusing Optics for an X-Ray Free-Electron Laser Generating an Extreme Intensity of 100 EW/cm² Using Total Reflection Mirrors

by Hirokatsu Yumoto, Yuichi Inubushi, Taito Osaka, Ichiro Inoue, Takahisa Koyama, Kensuke Tono, Makina Yabashi and Haruhiko Ohashi

Appl. Sci. 2020, 10(7), 2611; https://doi.org/10.3390/app10072611 - 10 Apr 2020

Cited by 18 | Viewed by 3149

Abstract

A nanofocusing optical system—referred to as 100 exa—for an X-ray free-electron laser (XFEL) was developed to generate an extremely high intensity of 100 EW/cm² (10²⁰ W/cm²) using total reflection mirrors. The system is based on Kirkpatrick-Baez geometry, with 250-mm-long elliptically figured mirrors optimized for the SPring-8 Angstrom Compact Free-Electron Laser (SACLA) XFEL facility. The nano-precision surface employed is coated with rhodium and offers a high reflectivity of 80%, with a photon energy of up to 12 keV, under total reflection conditions. Incident X-rays on the optics are reflected with a large spatial acceptance of over 900 μm. The focused beam is 210 nm × 120 nm (full width at half maximum) and was evaluated at a photon energy of 10 keV. The optics developed for 100 exa efficiently achieved an intensity of 1 × 10²⁰ W/cm² with a pulse duration of 7 fs and a pulse energy of 150 μJ (25% of the pulse energy generated at the light source). The experimental chamber, which can provide different stage arrangements and sample conditions, including vacuum environments and atmospheric-pressure helium, was set up with the focusing optics to meet the experimental requirements. Full article

(This article belongs to the Special Issue Science at X-ray Free Electron Lasers)

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18 pages, 6238 KiB

Open AccessArticle

Applications and Limits of Time-to-Energy Mapping of Protein Crystal Diffraction Using Energy-Chirped Polychromatic XFEL Pulses

by Alisia Fadini, Sven Reiche, Karol Nass and Jasper J. van Thor

Appl. Sci. 2020, 10(7), 2599; https://doi.org/10.3390/app10072599 - 9 Apr 2020

Cited by 5 | Viewed by 3193

Abstract

A broadband energy-chirped hard X-ray pulse has been demonstrated at the SwissFEL (free electron laser) with up to 4% bandwidth. We consider the characteristic parameters for analyzing the time dependence of stationary protein diffraction with energy-chirped pulses. Depending on crystal mosaic spread, convergence, and recordable resolution, individual reflections are expected to spend at least ≈ 50 attoseconds and up to ≈ 8 femtoseconds in reflecting condition. Using parameters for a chirped XFEL pulse obtained from simulations of 4% bandwidth conditions, ray-tracing simulations have been carried out to demonstrate the temporal streaking across individual reflections and resolution ranges for protein crystal diffraction. Simulations performed at a higher chirp (10%) emphasize the importance of chirp magnitude that would allow increased observation statistics for the temporal separation of individual reflections for merging and structure determination. Finally, we consider the fundamental limitation for obtaining time-dependent observations using chirped pulse diffraction. We consider the maximum theoretical time resolution achievable to be on the order of 50–200 as from the instantaneous bandwidth of the chirped SASE pulse. We then assess the ability to propagate ultrafast optical pulses for pump-probe cross-correlation under characteristic conditions of material dispersion; in this regard, the limiting factors for time resolution scale with crystal thickness. Crystals that are below a few microns in size will be necessary for subfemtosecond time resolution. Full article

(This article belongs to the Special Issue Science at X-ray Free Electron Lasers)

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8 pages, 1890 KiB

Open AccessArticle

Development of an Experimental Platform for Combinative Use of an XFEL and a High-Power Nanosecond Laser

by Yuichi Inubushi, Toshinori Yabuuchi, Tadashi Togashi, Keiichi Sueda, Kohei Miyanishi, Yoshinori Tange, Norimasa Ozaki, Takeshi Matsuoka, Ryosuke Kodama, Taito Osaka, Satoshi Matsuyama, Kazuto Yamauchi, Hirokatsu Yumoto, Takahisa Koyama, Haruhiko Ohashi, Kensuke Tono and Makina Yabashi

Appl. Sci. 2020, 10(7), 2224; https://doi.org/10.3390/app10072224 - 25 Mar 2020

Cited by 21 | Viewed by 4238

Abstract

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 diffraction measurement. An in-situ single-shot X-ray diffraction pattern expands to a large angle side, which shows a corundum was compressed by laser irradiation. Full article

(This article belongs to the Special Issue Science at X-ray Free Electron Lasers)

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18 pages, 2053 KiB

Open AccessArticle

The Magnitude and Waveform of Shock Waves Induced by X-ray Lasers in Water

by Claudiu Andrei Stan, Koji Motomura, Gabriel Blaj, Yoshiaki Kumagai, Yiwen Li, Daehyun You, Taishi Ono, Armin Kalita, Tadashi Togashi, Shigeki Owada, Kensuke Tono, Makina Yabashi, Tetsuo Katayama and Kiyoshi Ueda

Appl. Sci. 2020, 10(4), 1497; https://doi.org/10.3390/app10041497 - 22 Feb 2020

Cited by 7 | Viewed by 5046

Abstract

The high energy densities deposited in materials by focused X-ray laser pulses generate shock waves which travel away from the irradiated region, and can generate complex wave patterns or induce phase changes. We determined the time-pressure histories of shocks induced by X-ray laser pulses in liquid water microdrops, by measuring the surface velocity of the microdrops from images recorded during the reflection of the shock at the surface. Measurements were made with ~30 µm diameter droplets using 10 keV X-rays, for X-ray pulse energies that deposited linear energy densities from 3.5 to 120 mJ/m; measurements were also made with ~60 µm diameter drops for a narrower energy range. At a distance of 15 µm from the X-ray beam, the peak shock pressures ranged from 44 to 472 MPa, and the corresponding time-pressure histories of the shocks had a fast quasi-exponential decay with positive pressure durations estimated to range from 2 to 5 ns. Knowledge of the amplitude and waveform of the shock waves enables accurate modeling of shock propagation and experiment designs that either maximize or minimize the effect of shocks. Full article

(This article belongs to the Special Issue Science at X-ray Free Electron Lasers)

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15 pages, 3110 KiB

Open AccessArticle

Ultrafast X-ray Photochemistry at European XFEL: Capabilities of the Femtosecond X-ray Experiments (FXE) Instrument

by Dmitry Khakhulin, Florian Otte, Mykola Biednov, Christina Bömer, Tae-Kyu Choi, Michael Diez, Andreas Galler, Yifeng Jiang, Katharina Kubicek, Frederico Alves Lima, Angel Rodriguez-Fernandez, Peter Zalden, Wojciech Gawelda and Christian Bressler

Appl. Sci. 2020, 10(3), 995; https://doi.org/10.3390/app10030995 - 3 Feb 2020

Cited by 44 | Viewed by 6955

Abstract

Time-resolved X-ray methods are widely used for monitoring transient intermediates over the course of photochemical reactions. Ultrafast X-ray absorption and emission spectroscopies as well as elastic X-ray scattering deliver detailed electronic and structural information on chemical dynamics in the solution phase. In this work, we describe the opportunities at the Femtosecond X-ray Experiments (FXE) instrument of European XFEL. Guided by the idea of combining spectroscopic and scattering techniques in one experiment, the FXE instrument has completed the initial commissioning phase for most of its components and performed first successful experiments within the baseline capabilities. This is demonstrated by its currently 115 fs (FWHM) temporal resolution to acquire ultrafast X-ray emission spectra by simultaneously recording iron Kα and Kβ lines, next to wide angle X-ray scattering patterns on a photoexcited aqueous solution of [Fe(bpy)₃]²⁺, a transition metal model compound. Full article

(This article belongs to the Special Issue Science at X-ray Free Electron Lasers)

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10 pages, 2680 KiB

Open AccessFeature PaperArticle

Multispectroscopic Study of Single Xe Clusters Using XFEL Pulses

by Toshiyuki Nishiyama, Christoph Bostedt, Ken R. Ferguson, Christopher Hutchison, Kiyonobu Nagaya, Hironobu Fukuzawa, Koji Motomura, Shin-ichi Wada, Tsukasa Sakai, Kenji Matsunami, Kazuhiro Matsuda, Tetsuya Tachibana, Yuta Ito, Weiqing Xu, Subhendu Mondal, Takayuki Umemoto, Catalin Miron, Christophe Nicolas, Takashi Kameshima, Yasumasa Joti, Kensuke Tono, Takaki Hatsui, Makina Yabashi and Kiyoshi Ueda Show full author list Hide full author list

Appl. Sci. 2019, 9(22), 4932; https://doi.org/10.3390/app9224932 - 16 Nov 2019

Cited by 2 | Viewed by 3237

Abstract

X-ray free-electron lasers (XFELs) deliver ultrashort coherent laser pulses in the X-ray spectral regime, enabling novel investigations into the structure of individual nanoscale samples. In this work, we demonstrate how single-shot small-angle X-ray scattering (SAXS) measurements combined with fluorescence and ion time-of-flight (TOF) spectroscopy can be used to obtain size- and structure-selective evaluation of the light-matter interaction processes on the nanoscale. We recorded the SAXS images of single xenon clusters using XFEL pulses provided by the SPring-8 Angstrom compact free-electron laser (SACLA). The XFEL fluences and the radii of the clusters at the reaction point were evaluated and the ion TOF spectra and fluorescence spectra were sorted accordingly. We found that the XFEL fluence and cluster size extracted from the diffraction patterns showed a clear correlation with the fluorescence and ion TOF spectra. Our results demonstrate the effectiveness of the multispectroscopic approach for exploring laser–matter interaction in the X-ray regime without the influence of the size distribution of samples and the fluence distribution of the incident XFEL pulses. Full article

(This article belongs to the Special Issue Science at X-ray Free Electron Lasers)

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13 pages, 1544 KiB

Open AccessArticle

Probing Attosecond Electron Coherence in Molecular Charge Migration by Ultrafast X-Ray Photoelectron Imaging

by Kai-Jun Yuan and André D Bandrauk

Appl. Sci. 2019, 9(9), 1941; https://doi.org/10.3390/app9091941 - 11 May 2019

Cited by 9 | Viewed by 3990

Abstract

Electron coherence is a fundamental quantum phenomenon in today’s ultrafast physics and chemistry research. Based on attosecond pump–probe schemes, ultrafast X-ray photoelectron imaging of molecules was used to monitor the coherent electron dynamics which is created by an XUV pulse. We performed simulations [...] Read more.

_{2}^{+}

by numerically solving time-dependent Schrödinger equations. It was found that the X-ray photoelectron angular and momentum distributions depend on the time delay between the XUV pump and soft X-ray probe pulses. Varying the polarization and helicity of the soft X-ray probe pulse gave rise to a modulation of the time-resolved photoelectron distributions. The present results provide a new approach for exploring ultrafast coherent electron dynamics and charge migration in reactions of molecules on the attosecond time scale. Full article

(This article belongs to the Special Issue Science at X-ray Free Electron Lasers)

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Review

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19 pages, 4298 KiB

Open AccessFeature PaperReview

First Experiments in Structural Biology at the European X-ray Free-Electron Laser

by Grant Mills, Richard Bean and Adrian P. Mancuso

Appl. Sci. 2020, 10(10), 3642; https://doi.org/10.3390/app10103642 - 25 May 2020

Cited by 12 | Viewed by 3760

Abstract

Ultrabright pulses produced in X-ray free-electron lasers (XFELs) offer new possibilities for industry and research, particularly for biochemistry and pharmaceuticals. The unprecedented brilliance of these next-generation sources enables structure determination from sub-micron crystals as well as radiation-sensitive proteins. The European X-Ray Free-Electron Laser (EuXFEL), with its first light in 2017, ushered in a new era for ultrabright X-ray sources by providing an unparalleled megahertz-pulse repetition rate, with orders of magnitude more pulses per second than previous XFEL sources. This rapid pulse frequency has significant implications for structure determination; not only will data collection be faster (resulting in more structures per unit time), but experiments requiring large quantities of data, such as time-resolved structures, become feasible in a reasonable amount of experimental time. Early experiments at the SPB/SFX instrument of the EuXFEL demonstrate how such closely-spaced pulses can be successfully implemented in otherwise challenging experiments, such as time-resolved studies. Full article

(This article belongs to the Special Issue Science at X-ray Free Electron Lasers)

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11 pages, 2146 KiB

Open AccessReview

Atomic, Molecular and Cluster Science with the Reaction Microscope Endstation at FLASH2

by Severin Meister, Hannes Lindenblatt, Florian Trost, Kirsten Schnorr, Sven Augustin, Markus Braune, Rolf Treusch, Thomas Pfeifer and Robert Moshammer

Appl. Sci. 2020, 10(8), 2953; https://doi.org/10.3390/app10082953 - 24 Apr 2020

Cited by 9 | Viewed by 3228

Abstract

The reaction microscope (REMI) endstation for atomic and molecular science at the free-electron laser FLASH2 at DESY in Hamburg is presented together with a brief overview of results recently obtained. The REMI allows coincident detection of electrons and ions that emerge from atomic or molecular fragmentation reactions in the focus of the extreme-ultraviolet (XUV) free-electron laser (FEL) beam. A large variety of target species ranging from atoms and molecules to small clusters can be injected with a supersonic gas-jet into the FEL focus. Their ionization and fragmentation dynamics can be studied either under single pulse conditions, or for double pulses as a function of their time delay by means of FEL-pump–FEL-probe schemes and also in combination with a femtosecond infrared (IR) laser. In a recent upgrade, the endstation was further extended by a light source based on high harmonic generation (HHG), which is now available for upcoming FEL/HHG pump–probe experiments. Full article

(This article belongs to the Special Issue Science at X-ray Free Electron Lasers)

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11 pages, 1702 KiB

Open AccessFeature PaperReview

Pump-Probe Time-Resolved Serial Femtosecond Crystallography at SACLA: Current Status and Data Collection Strategies

by Eriko Nango, Minoru Kubo, Kensuke Tono and So Iwata

Appl. Sci. 2019, 9(24), 5505; https://doi.org/10.3390/app9245505 - 14 Dec 2019

Cited by 10 | Viewed by 4555

Abstract

Structural information on protein dynamics is a critical factor in fully understanding the protein functions. Pump-probe time-resolved serial femtosecond crystallography (TR-SFX) is a recently established technique for visualizing the structural changes or reactions in proteins that are at work with high spatial and temporal resolution. In the pump-probe method, protein microcrystals are continuously delivered from an injector and exposed to an X-ray free-electron laser (XFEL) pulse after a trigger to initiate a reaction, such as light, chemicals, temperature, and electric field, which affords the structural snapshots of intermediates that occur in the protein. We are in the process of developing the device and techniques for pump-probe TR-SFX while using XFEL produced at SPring-8 Angstrom Compact Free-Electron Laser (SACLA). In this paper, we described our current development details and data collection strategies for the optical pump X-ray probe TR-SFX experiment at SACLA and then reported the techniques of in crystallo TR spectroscopy, which is useful in clarifying the nature of reaction that takes place in crystals in advance. Full article

(This article belongs to the Special Issue Science at X-ray Free Electron Lasers)

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12 pages, 1537 KiB

Open AccessReview

X-ray Spectroscopies of High Energy Density Matter Created with X-ray Free Electron Lasers

by Byoung Ick Cho

Appl. Sci. 2019, 9(22), 4812; https://doi.org/10.3390/app9224812 - 10 Nov 2019

Cited by 6 | Viewed by 3324

Abstract

The recent progress in the development of X-ray free electron lasers (XFELs) allows for the delivery of over 10¹¹ high-energy photons to solid-density samples in a femtosecond time scale. The corresponding peak brightness of XFEL induces a nonlinear response of matter in a short-wavelength regime. The absorption of an XFEL pulse in a solid also results in the creation of high energy density (HED) matter. The electronic structure and related fundamental properties of such HED matter can be investigated with the control of XFEL and various X-ray spectroscopic techniques. These experimental data provide unique opportunities to benchmark theories and models for extreme conditions and to guide further advances. In this article, the current progress in spectroscopic studies on intense XFEL–matter interactions and HED matter are reviewed, and future research opportunities are discussed. Full article

(This article belongs to the Special Issue Science at X-ray Free Electron Lasers)

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