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Special Issue "XUV and X-ray Free-Electron Lasers and Applications"

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

Deadline for manuscript submissions: closed (30 April 2023) | Viewed by 11723

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Special Issue Editors

Dr. Luca Poletto

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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

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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

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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 (12 papers)

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Research

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Open AccessArticle

Focusing and Wavefront Splitting of an Extreme Ultraviolet Laser with a Tubular Optical Element

and

Photonics 2023, 10(6), 629; https://doi.org/10.3390/photonics10060629 - 29 May 2023

Viewed by 178

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 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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Open AccessArticle

Sample Delivery Systems for Serial Femtosecond Crystallography at the PAL-XFEL

Jaehyun Park

and

Ki Hyun Nam

Photonics 2023, 10(5), 557; https://doi.org/10.3390/photonics10050557 - 10 May 2023

Viewed by 438

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 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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Open AccessCommunication

Ultrashort X-ray Free Electron Laser Pulse Manipulation by Optical Matrix

and

Photonics 2023, 10(5), 491; https://doi.org/10.3390/photonics10050491 - 24 Apr 2023

Viewed by 404

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 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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Open AccessArticle

Dispersion Caused by the Penetration Effect in X-ray Compressors

and

Photonics 2023, 10(5), 484; https://doi.org/10.3390/photonics10050484 - 23 Apr 2023

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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 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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Open AccessArticle

Generating High-Power, Frequency Tunable Coherent THz Pulse in an X-ray Free-Electron Laser for THz Pump and X-ray Probe Experiments

and

Photonics 2023, 10(2), 133; https://doi.org/10.3390/photonics10020133 - 28 Jan 2023

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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 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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Open AccessArticle

Generation of Uniform X-ray Illumination and Its Application to X-ray Diffraction Microscopy

Katarzyna Kunio

Shirly Espinoza

and

Krishna P. Khakurel

Photonics 2022, 9(12), 934; https://doi.org/10.3390/photonics9120934 - 03 Dec 2022

Viewed by 973

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 (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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Open AccessArticle

Control Scheme of Phase-Shifter for Photon Energy Scan

and

Photonics 2022, 9(6), 418; https://doi.org/10.3390/photonics9060418 - 15 Jun 2022

Viewed by 871

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 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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Open AccessFeature PaperArticle

A Tunable Resolution Grating Monochromator and the Quest for Transform Limited Pulses

Josep Nicolas

and

Daniele Cocco

Photonics 2022, 9(6), 367; https://doi.org/10.3390/photonics9060367 - 24 May 2022

Viewed by 1164

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 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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Open AccessArticle

Numerical Simulation of Heat Load for Multilayer Laue Lens under Exposure to XFEL Pulse Trains

and

Photonics 2022, 9(5), 362; https://doi.org/10.3390/photonics9050362 - 22 May 2022

Cited by 1 | Viewed by 1144

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 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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Open AccessArticle

AC/DC: The FERMI FEL Split and Delay Optical Device for Ultrafast X-ray Science

and

Photonics 2022, 9(5), 314; https://doi.org/10.3390/photonics9050314 - 05 May 2022

Viewed by 1253

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 (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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Open AccessCommunication

Broadband Time-Delay and Chirp Compensator for X-ray Pulses

Christoph Braig

and

Alexei Erko

Photonics 2022, 9(5), 302; https://doi.org/10.3390/photonics9050302 - 28 Apr 2022

Viewed by 1478

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.

410 eV

. Assuming a source size of

50 μ m

and an angular acceptance of 1 mrad, the spectral resolving power may reach

6 \times 10^{2}

, at a pulse length as short as

4.3 femtoseconds (fs)

. In the case of

μ m

-sized sources, the resolution can be better than

0.1 eV

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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Open AccessFeature PaperReview

Early Days of SACLA XFEL

Tetsuya Ishikawa

Photonics 2022, 9(5), 357; https://doi.org/10.3390/photonics9050357 - 18 May 2022

Viewed by 1215

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 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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