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Photonics
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XUV and X-ray Free-Electron Lasers and Applications
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XUV and X-ray Free-Electron Lasers and Applications

A special issue of Photonics (ISSN 2304-6732).

Deadline for manuscript submissions: closed (30 April 2023) | Viewed by 25077

Special Issue Editors

Dr. Luca Poletto

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Guest Editor
Senior Research Scientist, National Council for Research of Italy - Institute of Photonics and Nanotechnologies (CNR-IFN), Via Trasea 7, 35131 Padova, Italy
Interests: high-order laser harmonics; free-electron lasers; attosecond pulses; extreme-ultraviolet optics; ultrafast beamlines
Dr. Fabio Frassetto

E-Mail Website
Guest Editor
Institute for Photonics and Nanotechnologies (IFN), Italian National Research Council (CNR), Padova, Italy
Interests: XUV ultrafast spectroscopy; XUV ultrafast optics; Generation of femto- and attosecond pulses; Ultrafast pulse conditioning Space optics

Special Issue Information

Dear Colleagues,

Nowadays, free-electron laser (FEL) technology is rapidly developing and opens new perspectives for sources of extreme peak brightness in the X-ray spectral region with ultrashort pulse duration and full transverse coherence. Since the operation of FLASH as the first user-dedicated facility for soft-X rays in 2005, the capability of FEL facilities to operate towards higher X-ray energies opens up a new realm for experiments dedicated to coherent X-ray imaging, structure determination of molecules in biology, medical diagnosis, nondestructive testing, and the study ultrafast electron dynamics in matter. Nowadays, seven FEL facilities are in operation worldwide (FLASH, LCLS, SACLA, FERMI, PAL-XFEL, European XFEL, Swiss XFEL) and others are in an advanced stage of development.

This Special Issue aims to explore the current state-of-the-art of FEL sources in delivering ultrashort pulses in the femtosecond or sub-femtosecond regime with high photon energy, which enable the use of X-ray-based techniques for coherent control and state-selective spectroscopy. Contributions related to measurement of the spectral phase of FEL pulses and the realization of coherent control are welcome.

One research field where X-ray FELs play a central role is coherent imaging, as they enable atomic-resolution imaging of biological molecules with single-pulse imaging techniques. Contributions related coherent time-resolved imaging techniques involving FELs are welcome.

On the technological side, the development of a new generation of detectors has been one of the keys for the successful operation of FEL facilities. Contributions related to the development of FEL detectors particularly suited for emerging FELs with higher repetition rates are also welcome.

In addition, optics play a crucial role in handling ultrashort and ultraintense FEL pulses at high energies. Contributions related to the development of optical components to manage, handle, and condition FEL beams are also welcome.

Dr. Luca Poletto
Dr. Fabio Frassetto
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Photonics is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2400 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • free-electron lasers
  • coherent control
  • coherent X-ray imaging
  • diffractive imaging
  • X-ray diffraction techniques
  • X-ray ultrafast detectors
  • X-ray microfocusing and nanofocusing

Published Papers (15 papers)

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Research

Jump to: Review

9 pages, 1880 KiB  
Article
Application of Micro-Tubing Reeling System to Serial Femtosecond Crystallography
by Jihan Kim, Sehan Park, Yunje Cho and Jaehyun Park
Photonics 2024, 11(1), 95; https://doi.org/10.3390/photonics11010095 - 22 Jan 2024
Viewed by 769
Abstract
Microcrystal delivery instruments are pivotal to performing serial femtosecond crystallography experiments at the XFEL facilities. We present a novel sample delivery technique based on a micro-tubing reeling system (MRS). Despite the tiny size of the micro-tubing, the MRS device has the advantage of [...] Read more.
Microcrystal delivery instruments are pivotal to performing serial femtosecond crystallography experiments at the XFEL facilities. We present a novel sample delivery technique based on a micro-tubing reeling system (MRS). Despite the tiny size of the micro-tubing, the MRS device has the advantage of operating without real-time position adjustment of the tube to match with the XFEL pulses. Moreover, the applicable repetition rate is more flexible than the previously reported chip-based one-dimensional fixed target system. Full article
(This article belongs to the Special Issue XUV and X-ray Free-Electron Lasers and Applications)
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8 pages, 1481 KiB  
Communication
The Role of Stepwise Photoionization in Measurements of the Ionization Potentials in Dense Plasma
by Igor Yu. Skobelev, Sergey N. Ryazantsev, Roman K. Kulikov, Maksim V. Sedov and Sergey A. Pikuz
Photonics 2023, 10(8), 939; https://doi.org/10.3390/photonics10080939 - 17 Aug 2023
Viewed by 771
Abstract
The interaction of high-contrast high-intensity laser radiation with solids allows us to create hot or warm plasma of solid or even over-solid density, such as in the case of inertial fusion particularly. The multicharged ions contained in it can no longer be considered [...] Read more.
The interaction of high-contrast high-intensity laser radiation with solids allows us to create hot or warm plasma of solid or even over-solid density, such as in the case of inertial fusion particularly. The multicharged ions contained in it can no longer be considered isolated. As a result, this leads to a decrease in the ionization potentials and to the disappearance of a number of bound ionic states. To describe the ionization potential depression, two major approaches are now used predominantly, where the key parameter is either average interelectronic or interionic distance. Since neither of the approaches can be substantiated purely theoretically, their applicability can only be established by comparison with experimental results. In recent experiments with X-ray free-electron lasers, it was concluded that the ionization potential depression rather depends on the interelectronic distance. However, when measuring ionization potentials, it was assumed that the main role in ionization processes is played by the direct photoionization of the ion ground state. In the present paper, we show that stepwise photoionization processes should play a significant role in dense plasma, disrupting a straight correspondence between the threshold in direct photoionization by X-ray laser photons and the actual ionization potential of multicharged ions. It means that the measurement results mentioned above are not correct, and the main conclusion about the importance of the interelectronic distance for depression of the ionization potential is not correct. Full article
(This article belongs to the Special Issue XUV and X-ray Free-Electron Lasers and Applications)
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9 pages, 676 KiB  
Communication
Generation of Ultrashort Pulses in XUV and X-ray FELs via an Excessive Reverse Undulator Taper
by Evgeny Schneidmiller, Matthias Dreimann, Marion Kuhlmann, Juliane Rönsch-Schulenburg and Helmut Zacharias
Photonics 2023, 10(6), 653; https://doi.org/10.3390/photonics10060653 - 05 Jun 2023
Cited by 2 | Viewed by 1472
Abstract
The pulse duration in short-pulse schemes for Self-Amplified Spontaneous Emission Free Electron Lasers (SASE FELs) is limited by the FEL coherence time. A recently proposed concept allows to overcome the coherence time barrier and to obtain much shorter pulses. When the lasing part [...] Read more.
The pulse duration in short-pulse schemes for Self-Amplified Spontaneous Emission Free Electron Lasers (SASE FELs) is limited by the FEL coherence time. A recently proposed concept allows to overcome the coherence time barrier and to obtain much shorter pulses. When the lasing part of an electron bunch is much shorter than the coherence time, one can suppress the radiation in the long main undulator while preserving microbunching within that short lasing slice. Then, a short radiation pulse is produced in a relatively short radiator. A possible suppression method, an excessive reverse undulator taper, is discussed and illustrated numerically in this paper. We also performed the first experimental tests of this method at the soft X-ray FEL user facility FLASH. The measured pulse duration approaches 1 fs (FWHM) at the wavelength of 5 nm. Full article
(This article belongs to the Special Issue XUV and X-ray Free-Electron Lasers and Applications)
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9 pages, 3399 KiB  
Article
Focusing and Wavefront Splitting of an Extreme Ultraviolet Laser with a Tubular Optical Element
by Huaiyu Cui, Zhiyuan Wang, Shan Wu, Haojie An, Jinshi Wang and Yongpeng Zhao
Photonics 2023, 10(6), 629; https://doi.org/10.3390/photonics10060629 - 29 May 2023
Viewed by 927
Abstract
A capillary discharge extreme ultraviolet laser is focused and wavefront split at 46.9 nm by a tubular optical element. The reflectivity at 46.9 nm is both simulated and measured to be higher than 90% with a slight optical aberration. The operating principle of [...] Read more.
A capillary discharge extreme ultraviolet laser is focused and wavefront split at 46.9 nm by a tubular optical element. The reflectivity at 46.9 nm is both simulated and measured to be higher than 90% with a slight optical aberration. The operating principle of the tubular element for focusing and wavefront splitting is discussed. Dense and intense grating-like fringes with a period of ~150 nm are achieved. The method used in this work allows nano-scale processing with extreme ultraviolet laser at single-shot exposure mode. Full article
(This article belongs to the Special Issue XUV and X-ray Free-Electron Lasers and Applications)
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13 pages, 3382 KiB  
Article
Sample Delivery Systems for Serial Femtosecond Crystallography at the PAL-XFEL
by Jaehyun Park and Ki Hyun Nam
Photonics 2023, 10(5), 557; https://doi.org/10.3390/photonics10050557 - 10 May 2023
Cited by 2 | Viewed by 1332
Abstract
Serial femtosecond crystallography (SFX) using an X-ray free electron laser (XFEL) enables the determination of room-temperature structures without causing radiation damage. Using an optical pump-probe or mix-and-injection, SFX enables the intermediate state visualization of a molecular reaction. In SFX experiments, serial and stable [...] Read more.
Serial femtosecond crystallography (SFX) using an X-ray free electron laser (XFEL) enables the determination of room-temperature structures without causing radiation damage. Using an optical pump-probe or mix-and-injection, SFX enables the intermediate state visualization of a molecular reaction. In SFX experiments, serial and stable microcrystal delivery to the X-ray interaction point is vital for reasonable data collection and efficient beam time. The Pohang Accelerator Laboratory X-ray Free Electron Laser (PAL-XFEL) facility established SFX instruments at a nanocrystallography and coherent imaging (NCI) experimental station. Various sample delivery methods, including injection, fixed-target scanning, and hybrid methods, have been developed and applied to collect XFEL diffraction data. Herein, we report the currently available sample delivery methods for SFX at the NCI experimental station at the PAL-XFEL. This article will help PAL-XFEL users access the SFX system for their experiments. Full article
(This article belongs to the Special Issue XUV and X-ray Free-Electron Lasers and Applications)
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14 pages, 2192 KiB  
Communication
Ultrashort X-ray Free Electron Laser Pulse Manipulation by Optical Matrix
by Kai Hu, Ye Zhu, Zhongmin Xu, Qiuping Wang, Weiqing Zhang and Chuan Yang
Photonics 2023, 10(5), 491; https://doi.org/10.3390/photonics10050491 - 24 Apr 2023
Cited by 2 | Viewed by 1112
Abstract
Free electron laser (FEL) is capable of producing ultra-short X-ray pulses. The estimation of X-ray pulse propagation is the key process of X-ray FEL beamline design. By using the Kostenbauder matrix approach, the evolution of an ultra-short pulse in a beamline system can [...] Read more.
Free electron laser (FEL) is capable of producing ultra-short X-ray pulses. The estimation of X-ray pulse propagation is the key process of X-ray FEL beamline design. By using the Kostenbauder matrix approach, the evolution of an ultra-short pulse in a beamline system can be calculated. Therefore, it is of significant importance to investigate the Kostenbauder matrices of different kinds of X-ray optics. In this work, we derive a unified 6 × 6 optical matrix to describe various kinds of X-ray optical elements, including varied-line-spacing (VLS) toroidal grating, VLS spherical grating, VLS cylindrical grating, VLS plane grating, toroidal grating, spherical grating, cylindrical grating, plane grating, toroidal mirror, spherical mirror, cylindrical mirror, and plane mirror. These optics are usually adopted in soft X-ray regime. We apply this method to describe the transverse focusing, pulse front tilt, and pulse stretching after an X-ray pulse going through a VLS plane grating monochromator (VLS-PGM). We also use this approach to simulate a grating compressor which can be used to compress chirped soft X-ray pulse. This work is helpful in the design and optimization of X-ray beamline systems. Full article
(This article belongs to the Special Issue XUV and X-ray Free-Electron Lasers and Applications)
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15 pages, 5235 KiB  
Article
Dispersion Caused by the Penetration Effect in X-ray Compressors
by Chuan Yang, Kai Hu, Ye Zhu, Xiaofan Wang, Qinming Li, Zhongmin Xu, Juhao Wu and Weiqing Zhang
Photonics 2023, 10(5), 484; https://doi.org/10.3390/photonics10050484 - 23 Apr 2023
Cited by 2 | Viewed by 1391
Abstract
Chirped X-ray pulse compression is a promising approach for generating ultra-short X-ray free electron laser (XFEL) pulses. The design of X-ray pulse compressors requires the careful control of group delay dispersion (GDD), which plays a critical role in achieving optimal compression. However, the [...] Read more.
Chirped X-ray pulse compression is a promising approach for generating ultra-short X-ray free electron laser (XFEL) pulses. The design of X-ray pulse compressors requires the careful control of group delay dispersion (GDD), which plays a critical role in achieving optimal compression. However, the penetration dispersion of crystals and multilayers can induce an extra GDD, which may result in over-compression or under-compression. In this study, we investigate the penetration dispersion of crystals and multilayers theoretically and numerically. Our results indicate that the extra GDD induced by the penetration effect increases as the bandwidth of the rocking curve decreases. Moreover, the extra GDD is nonlinear and can be mitigated by optimizing the configuration of X-ray pulse compressors. This work provides insights into the dispersion compensation and configuration optimization of X-ray pulse compressors, which are essential for generating ultra-short XFEL pulses. Full article
(This article belongs to the Special Issue XUV and X-ray Free-Electron Lasers and Applications)
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12 pages, 10218 KiB  
Article
Generating High-Power, Frequency Tunable Coherent THz Pulse in an X-ray Free-Electron Laser for THz Pump and X-ray Probe Experiments
by Yin Kang, Zhen Wang, Kaiqing Zhang and Chao Feng
Photonics 2023, 10(2), 133; https://doi.org/10.3390/photonics10020133 - 28 Jan 2023
Cited by 3 | Viewed by 1860
Abstract
Precisely synchronized X-ray and strong-field coherent terahertz (THz) enable the coherent THz excitation of many fundamental modes (THz pump) and the capturing of X-ray dynamic images of matter (X-ray probe), while the generation of such a light source is still a challenge for [...] Read more.
Precisely synchronized X-ray and strong-field coherent terahertz (THz) enable the coherent THz excitation of many fundamental modes (THz pump) and the capturing of X-ray dynamic images of matter (X-ray probe), while the generation of such a light source is still a challenge for most existing techniques. In this paper, a novel X-ray free-electron laser based light source is proposed to produce a synchronized high-powered X-ray pulse and strong field, widely frequency tunable coherent THz pulse simultaneously. The technique adopts a frequency beating laser modulated electron bunch with a Giga-electron-volt beam energy to generate an X-ray pulse and a THz pulse sequentially by passing two individual undulator sections with different magnetic periods. Theoretical analysis and numerical simulations are carried out using the beam parameters of the Shanghai soft X-ray free-electron laser facility. The results show that the technique can generate synchronized 4 nm X-ray radiation with a peak power of 1.89 GW, and narrow-band THz radiation with a pulse energy of 1.62 mJ, and the frequency of THz radiation can be continuously tuned from 0.1 to 40 THz. The proposed technique can be used for THz pump and X-ray probe experiments for dynamic research on the interaction between THz pulse and matter at a femtosecond time scale. Full article
(This article belongs to the Special Issue XUV and X-ray Free-Electron Lasers and Applications)
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10 pages, 3187 KiB  
Article
Generation of Uniform X-ray Illumination and Its Application to X-ray Diffraction Microscopy
by Katarzyna Kunio, Shirly Espinoza and Krishna P. Khakurel
Photonics 2022, 9(12), 934; https://doi.org/10.3390/photonics9120934 - 03 Dec 2022
Viewed by 1609
Abstract
X-ray diffraction microscopy (XDM) is an established lens-less imaging method extensively practiced at synchrotrons and X-ray free-electron lasers (XFELs). XDM is broadly operated in two different modes: scanning and non-scanning. The non-scanning mode of operation in XDM is commonly called coherent diffraction imaging [...] Read more.
X-ray diffraction microscopy (XDM) is an established lens-less imaging method extensively practiced at synchrotrons and X-ray free-electron lasers (XFELs). XDM is broadly operated in two different modes: scanning and non-scanning. The non-scanning mode of operation in XDM is commonly called coherent diffraction imaging (CDI) and has been the key research direction of many XFEL facilities. This method typically images objects smaller than the size of the illumination, which precludes the imaging of a large group of samples physically larger than the illumination. Furthermore, satisfying this requirement at X-ray free-electron lasers tremendously reduces the volume of practically useful data, leading the experimental scheme to be less efficient. Such a limitation can be circumvented by using a uniform illumination probe rather than the traditional Gaussian-focused probe from the X-ray focusing optics. Here in this article, we report a numerical study on the design of an optical element to generate uniform X-ray illumination and its application to the CDI. We demonstrate the benefits of such illumination in imaging objects that are larger than the illumination size and in improving the efficiency of the experimental scheme overall. Full article
(This article belongs to the Special Issue XUV and X-ray Free-Electron Lasers and Applications)
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12 pages, 3524 KiB  
Article
Control Scheme of Phase-Shifter for Photon Energy Scan
by Gyujin Kim, Haeryong Yang, Chi Hyun Shim, Inhyuk Nam, Myung Hoon Cho, Hoon Heo, Changbum Kim, Chang-Ki Min and Heung-Sik Kang
Photonics 2022, 9(6), 418; https://doi.org/10.3390/photonics9060418 - 15 Jun 2022
Viewed by 1314
Abstract
Variable gap undulator widely used in X-ray free-electron laser (XFEL) enables the photon energy scan by changing its gap. A phase-shifter should be incorporated to compensate for the phase mismatch between the electron bunches and X-ray pulses arising while those traverse the drift [...] Read more.
Variable gap undulator widely used in X-ray free-electron laser (XFEL) enables the photon energy scan by changing its gap. A phase-shifter should be incorporated to compensate for the phase mismatch between the electron bunches and X-ray pulses arising while those traverse the drift space between undulator segments. The uncertainties in both the undulator parameter and the drift space distance introduce an error in calculating the optimum gap distance of the phase-shifter for the different undulator K. The phase-shifter gap needs to be set where the error is within the tolerable range. The control scheme we propose can maintain full FEL intensity over the scanned photon energies. Full article
(This article belongs to the Special Issue XUV and X-ray Free-Electron Lasers and Applications)
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12 pages, 1240 KiB  
Article
A Tunable Resolution Grating Monochromator and the Quest for Transform Limited Pulses
by Josep Nicolas and Daniele Cocco
Photonics 2022, 9(6), 367; https://doi.org/10.3390/photonics9060367 - 24 May 2022
Cited by 1 | Viewed by 3094
Abstract
A variable resolution, transform limited monochromator is designed for the Free Electron Laser (FEL) source of LCLS. It provides monochromatic beam in the 250–1500 eV range, delivering the beam on the second floor of the LCLS experimental Hall. One major requirement for this [...] Read more.
A variable resolution, transform limited monochromator is designed for the Free Electron Laser (FEL) source of LCLS. It provides monochromatic beam in the 250–1500 eV range, delivering the beam on the second floor of the LCLS experimental Hall. One major requirement for this monochromator is to provide, as close as possible, monochromatic transform limited pulses for time-resolved experiments. The theory and the limit of using classical diffraction scheme to monochromatize Soft X-ray beam, while preserving the pulse length, will be presented, together with the optical scheme of this versatile monochromator design. Full article
(This article belongs to the Special Issue XUV and X-ray Free-Electron Lasers and Applications)
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18 pages, 5586 KiB  
Article
Numerical Simulation of Heat Load for Multilayer Laue Lens under Exposure to XFEL Pulse Trains
by Zlatko Rek, Henry N. Chapman, Božidar Šarler and Saša Bajt
Photonics 2022, 9(5), 362; https://doi.org/10.3390/photonics9050362 - 22 May 2022
Cited by 1 | Viewed by 1809
Abstract
Multilayer Laue lenses (MLLs) made from WC and SiC were previously used to focus megahertz X-ray pulse trains of the European XFEL free-electron laser, but suffered damage with trains of 30 pulses or longer at an incident fluence of about 0.13 J/cm2 [...] Read more.
Multilayer Laue lenses (MLLs) made from WC and SiC were previously used to focus megahertz X-ray pulse trains of the European XFEL free-electron laser, but suffered damage with trains of 30 pulses or longer at an incident fluence of about 0.13 J/cm2 per pulse. Here, we present numerical simulations of the heating of MLLs of various designs, geometry and material properties, that are exposed to such pulse trains. We find that it should be possible to focus the full beam of about 10 J/cm2 fluence of XFEL using materials of a low atomic number. To achieve high diffraction efficiency, lenses made from such materials should be considerably thicker than those used in the experiments. In addition to the lower absorption, this leads to the deposition of energy over a larger volume of the multilayer structure and hence to a lower dose, a lower temperature increase, and an improved dissipation of heat. Full article
(This article belongs to the Special Issue XUV and X-ray Free-Electron Lasers and Applications)
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12 pages, 3549 KiB  
Article
AC/DC: The FERMI FEL Split and Delay Optical Device for Ultrafast X-ray Science
by Alberto Simoncig, Michele Manfredda, Giulio Gaio, Nicola Mahne, Lorenzo Raimondi, Claudio Fava, Simone Gerusina, Riccardo Gobessi, Alessandro Abrami, Flavio Capotondi, Dario De Angelis, Ralf Hendrik Menk, Matteo Pancaldi, Emanuele Pedersoli and Marco Zangrando
Photonics 2022, 9(5), 314; https://doi.org/10.3390/photonics9050314 - 05 May 2022
Cited by 1 | Viewed by 1879
Abstract
Free-electron lasers (FELs) are the most advanced class of light-sources, by virtue of their unique capability to lase high-brightness pulses characterized by wavelengths spanning the extreme-ultraviolet, the soft and hard X-ray spectral domains, as well as by temporal lengths lying in the femtosecond [...] Read more.
Free-electron lasers (FELs) are the most advanced class of light-sources, by virtue of their unique capability to lase high-brightness pulses characterized by wavelengths spanning the extreme-ultraviolet, the soft and hard X-ray spectral domains, as well as by temporal lengths lying in the femtosecond (fs) timescale. The next step to push the current standards in ultrafast X-ray science is strongly linked to the possibility of engineering and exploiting time-resolved experiments exclusively for FELs pulses, ideally having different colors tunable at specific electronic resonance of the chemical elements. At the seeded FERMI FEL (Trieste, Italy) this goal is committed to the optical device known as AC/DC, which stands for the auto correlator/delay creator. AC/DC is designed to double the incoming FEL pulse splitting the photon beam by inserting a grazing incidence flat mirror, thus preserving the spectral and temporal properties, and further delaying one of these two pulses in time. It can independently tune the FEL pulses fluence on the two optical paths by means of solid-state filters, too. Here, we present a detailed description about this optical device. Strong emphasis is dedicated to the AC/DC opto-mechanical design and to the laser-based feedback systems implemented to compensate for any mismatch affecting the FEL optical trajectory, ascribable to both mechanical imperfections and paraxial errors rising during a temporal delay scan. Full article
(This article belongs to the Special Issue XUV and X-ray Free-Electron Lasers and Applications)
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13 pages, 18310 KiB  
Communication
Broadband Time-Delay and Chirp Compensator for X-ray Pulses
by Christoph Braig and Alexei Erko
Photonics 2022, 9(5), 302; https://doi.org/10.3390/photonics9050302 - 28 Apr 2022
Viewed by 2109
Abstract
A new type of aberration-corrected time-delay compensating monochromator (TDCM) for soft X-rays is presented. Composed of two identical reflection zone plates (RZPs) on spherical substrates and an intermediate flat mirror for band-pass selection, the TDCM can operate in a wide energy range of [...] Read more.
A new type of aberration-corrected time-delay compensating monochromator (TDCM) for soft X-rays is presented. Composed of two identical reflection zone plates (RZPs) on spherical substrates and an intermediate flat mirror for band-pass selection, the TDCM can operate in a wide energy range of about ±20% around the design energy of 410eV. Assuming a source size of 50μm and an angular acceptance of 1 mrad, the spectral resolving power may reach 6×102, at a pulse length as short as 4.3femtoseconds(fs). In the case of μm-sized sources, the resolution can be better than 0.1eV and the sub-fs regime could become accessible. The overall transmission efficiency varies within (4.2–6.0)% across the energy range (310–510) eV. In the complementary mode, chirped-pulse compression works as well. Depending on the properties of the source, simulations predict an up to 9-fold reduction in pulse duration, whereas ≤50% of the peak intensity is maintained. Full article
(This article belongs to the Special Issue XUV and X-ray Free-Electron Lasers and Applications)
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Review

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19 pages, 2377 KiB  
Review
Early Days of SACLA XFEL
by Tetsuya Ishikawa
Photonics 2022, 9(5), 357; https://doi.org/10.3390/photonics9050357 - 18 May 2022
Viewed by 2057
Abstract
The SACLA (SPring-8 Angstrom compact laser) was designed to significantly downsize the SASE (self-amplified spontaneous emission) type XFEL (X-ray free-electron laser), in order to generate coherent light in the wavelength region of 0.1 nm by adopting an in-vacuum undulator that can shorten the [...] Read more.
The SACLA (SPring-8 Angstrom compact laser) was designed to significantly downsize the SASE (self-amplified spontaneous emission) type XFEL (X-ray free-electron laser), in order to generate coherent light in the wavelength region of 0.1 nm by adopting an in-vacuum undulator that can shorten the magnetic field period length. In addition, a SASE XFEL facility with a total length of 700 m has become a reality by using a C-band RF accelerating tube that enables a high acceleration gradient. Although progress was initially slow, the small-scale, low-cost SACLA was smoothly constructed, and it became the second light source to lase in the 0.1 nm wavelength region, following the LCLS (linac coherent light source) in the United States. In this paper, we look back on the history leading up to SACLA. and describe the SCSS (SPring-8 compact SASE source) project as a preparatory stage and a part of the construction/commissioning of SACLA. Since March 2012, SACLA has been operating as a shared user facility. Just a few of the upgrade activities of the facility and advanced research conducted are introduced. Finally, we will discuss the future development of the SPring-8 site, which has co-located the third-generation synchrotron radiation facility SPring-8 and the X-ray free-electron laser facility SACLA. Full article
(This article belongs to the Special Issue XUV and X-ray Free-Electron Lasers and Applications)
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