The well-established theory of synchrotron light sources (SyncLs) and X-ray free electron lasers (FELs) allows the determination of parameters, such as the wavelength of the emitted radiation, Pierce ...parameter, and the gain length, when variables such as energy spread parameter and undulator's peak magnetic field (<inline-formula> <tex-math notation="LaTeX">B_{u} </tex-math></inline-formula>) and period (<inline-formula> <tex-math notation="LaTeX">\lambda _{u} </tex-math></inline-formula>) are known. However, the opposite is not true. For example, there is not a formula providing the value of the undulator's period when the wavelength of the emitted radiation is known in advance. In this direction, the present work uses the Lambert-Tsallis <inline-formula> <tex-math notation="LaTeX">W_{q} </tex-math></inline-formula> function to invert some formulas of the synchrotron and self-amplified spontaneous emission (SASE) free-electron laser theory, aiming to provide new formulas to calculate the undulator's period, the energy dispersion parameter of a transverse gradient undulator (TGU), and the Pierce parameter in the absence of inhomogeneous broadening when the Pierce parameter value in the presence of inhomogeneous broadening is known in advance.
•Molecular structure determinations by Coulomb explosion imaging are reviewed.•Intact multiply charged molecular cation productions are summarized.•Contribution of electrostatic interactions behind ...the ablation of solid materials is introduced.
Intense femtosecond lasers as well as X-ray free electron lasers provide new means to produce multiply charged molecular cations. The fragmentation processes that these high energy species undergo, termed Coulomb explosion, are utilized to determine the static molecular structures as well as to trace the molecular dynamics of ultrafast chemical reactions. This review focuses on recent advances made in studies of Coulomb explosion imaging, highlighting the use of this process to determine the static structures of complex molecules, geometric isomers, chiral molecules and molecular complexes. Briefly, we summarize the recent time-resolved studies of surface electric fields and the controversy pertaining to the contribution of Coulomb explosion to the mechanism for ablation of solid surfaces.
A study is made of the saturation mechanism of a single superradiant ‘spike’ of radiation in a Free Electron Laser. A one-dimensional (1D) computer model is developed using the Puffin, un-averaged ...FEL simulation code, which allows sub-radiation wavelength evolution of both the spike radiation field and the electron dynamics to be modelled until the highly non-linear saturation process of the spike is observed. Animations of the process from the start to the end of the interaction are available. The resultant saturated spike duration is at the sub-wavelength scale and has a broad spectrum. The electrons passing through the spike can both lose and gain energy many times greater than that of the ‘normal’ non-pulsed FEL interaction. A saturation mechanism is proposed and tested via a simple analysis of the 1D FEL equations. The scaling results of the analysis are seen to be in good agreement with the numerical results. A simple model of three dimensional diffraction effects of the radiation is applied to the results of the 1D simulations. This greatly reduces longer wavelengths of the power spectrum, which are seen to be emitted mainly after the electrons have propagated through the spike, and is seen to be in qualitative agreement with recent experimental results.
•First computer simulation of superradiant pulse saturation in a Free Electron Laser.•Saturated superradiant pulses are shorter than one radiation wavelength.•Saturated superradiant pulses are very high powers.•Results are in agreement with simple scaled theory.•Three dimensional estimates are given.
Large‐bandwidth pulses produced by cutting‐edge X‐ray free‐electron lasers (FELs) are of great importance in research fields like material science and biology. In this paper, a new method to generate ...high‐power ultrashort FEL pulses with tunable spectral bandwidth with spectral coherence using a dielectric‐lined waveguide without interfering operation of linacs is proposed. By exploiting the passive and dephasingless wakefield at terahertz frequency excited by the beam, stable energy modulation can be achieved in the electron beam and large‐bandwidth high‐intensity soft X‐ray radiation can be generated. Three‐dimensional start‐to‐end simulations have been carried out and the results show that coherent radiation pulses with duration of a few femtoseconds and bandwidths ranging from 1.01% to 2.16% can be achieved by changing the undulator taper profile.
Ultrashort large‐bandwidth X‐ray free‐electron laser generation is proposed using a dielectric‐lined waveguide. With this modulation scheme through strong terahertz wakefield self‐excited, a cheap and flexible large‐bandwidth operation mode is researched for free‐electron‐laser complexes.
The Pohang Accelerator Laboratory X‐ray Free‐Electron Laser (PAL‐XFEL) is a recently commissioned X‐ray free‐electron laser (XFEL) facility that provides intense ultrashort X‐ray pulses based on the ...self‐amplified spontaneous emission process. The nano‐crystallography and coherent imaging (NCI) hutch with forward‐scattering geometry is located at the hard X‐ray beamline of the PAL‐XFEL and provides opportunities to perform serial femtosecond crystallography and coherent X‐ray diffraction imaging. To produce intense high‐density XFEL pulses at the interaction positions between the X‐rays and various samples, a microfocusing Kirkpatrick–Baez (KB) mirror system that includes an ultra‐precision manipulator has been developed. In this paper, the design of a KB mirror system that focuses the hard XFEL beam onto a fixed sample point of the NCI hutch, which is positioned along the hard XFEL beamline, is described. The focusing system produces a two‐dimensional focusing beam at approximately 2 µm scale across the 2–11 keV photon energy range. XFEL pulses of 9.7 keV energy were successfully focused onto an area of size 1.94 µm × 2.08 µm FWHM.
Microfocusing of hard X‐ray free‐electron laser pulses using Kirkpatrick–Baez mirrors at the nano‐crystallography and coherent imaging hutch of the Pohang Accelerator Laboratory X‐ray Free‐Electron Laser facility is reported.
In this paper, we propose for first time practical parameters to construct a compact sub-Angstrom Free Electron Laser (FEL) based on Compton backscattering. Our recipe is based on using picocoulomb ...electron bunch, enabling very low emittance and ultracold electron beam. We assume the FEL is operating in a quantum regime of Self Amplified Spontaneous Emission (SASE). The fundamental quantum feature is a significantly narrower spectrum of the emitted radiation relative to classical SASE. The quantum regime of the SASE FEL is reached when the momentum spread of the electron beam is smaller than the photon recoil momentum. Following the formulae describing SASE FEL operation, realistic designs for quantum FEL experiments are proposed. We discuss the practical constraints that influence the experimental parameters. Numerical simulations of power spectra and intensities are presented and attractive radiation characteristics such as high flux, narrow linewidth, and short pulse structure are demonstrated.
•We propose practical parameters for a compact sub-Angstrom FEL based on Compton backscattering.•We discuss the practical constraints that influence the experimental parameters.•We numerically demonstrate that the QFEL has a number of potentially attractive spectral features.
Understanding molecular femtosecond dynamics under intense X-ray exposure is critical to progress in biomolecular imaging and matter under extreme conditions. Imaging viruses and proteins at an ...atomic spatial scale and on the time scale of atomic motion requires rigorous, quantitative understanding of dynamical effects of intense X-ray exposure. Here we present an experimental and theoretical study of C-60 molecules interacting with intense X-ray pulses from a free-electron laser, revealing the influence of processes not previously reported. Our work illustrates the successful use of classical mechanics to describe all moving particles in C-60, an approach that scales well to larger systems, for example, biomolecules. Comparisons of the model with experimental data on C-60 ion fragmentation show excellent agreement under a variety of laser conditions. The results indicate that this modelling is applicable for X-ray interactions with any extended system, even at higher X-ray dose rates expected with future light sources.
The photoinduced relaxation dynamics of nucleobases and their thionated analogs have been investigated extensively over the past decades motivated by their crucial role in organisms and their ...application in medical and biochemical research and treatment. Most of these studies focused on the spectroscopy of valence electrons and fragmentation. The advent of ultrashort x‐ray laser sources such as free‐electron lasers, however, opens new opportunities for studying the ultrafast molecular relaxation dynamics utilizing the site‐ and element‐selectivity of x‐rays. In this review, we want to summarize ultrafast experiments on thymine and 2‐thiouracil performed at free‐electron lasers. We performed time‐resolved x‐ray absorption spectroscopy at the oxygen K‐edge after UV excitation of thymine. In addition, we investigated the excited state dynamics of 2‐tUra via x‐ray photoelectron spectroscopy at sulfur. For these methods, we show a strong sensitivity to the electronic state or charge distribution, respectively. We also performed time‐resolved Auger–Meitner spectroscopy, which shows spectral shifts associated with internuclear distances close to the probed site. We discuss the complementary aspects of time‐resolved x‐ray spectroscopy techniques compared to optical and UV spectroscopy for the investigation of ultrafast relaxation processes.
Nucleobases are very efficient ultraviolet absorbers. Light excitation triggers a change in the valence‐charge distribution, which leads to bond‐elongation changes and in turn couples back to the electronic occupation via non‐Born‐Oppenheimer effects. The review presents, how element and site‐selective ultrafast x‐ray spectroscopy can be used to unravel the different processes.
In oxygenic photosynthesis, light-driven oxidation of water to molecular oxygen is carried out by the oxygen-evolving complex (OEC) in photosystem II (PS II). Recently, we reported the ...room-temperature structures of PS II in the four (semi)stable S-states, S
, S
, S
, and S
, showing that a water molecule is inserted during the S
→ S
transition, as a new bridging O(H)-ligand between Mn1 and Ca. To understand the sequence of events leading to the formation of this last stable intermediate state before O
formation, we recorded diffraction and Mn X-ray emission spectroscopy (XES) data at several time points during the S
→ S
transition. At the electron acceptor site, changes due to the two-electron redox chemistry at the quinones, Q
and Q
, are observed. At the donor site, tyrosine Y
and His190 H-bonded to it move by 50 µs after the second flash, and Glu189 moves away from Ca. This is followed by Mn1 and Mn4 moving apart, and the insertion of O
(H) at the open coordination site of Mn1. This water, possibly a ligand of Ca, could be supplied via a "water wheel"-like arrangement of five waters next to the OEC that is connected by a large channel to the bulk solvent. XES spectra show that Mn oxidation (τ of ∼350 µs) during the S
→ S
transition mirrors the appearance of O
electron density. This indicates that the oxidation state change and the insertion of water as a bridging atom between Mn1 and Ca are highly correlated.
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