Free Electron Laser Technology Research Articles

Cryostat Design for an FEL SCU Demonstrator

A design for a 4.2 K cryostat to support superconducting undulator (SCU) magnets is being developed as part of an SCU free electron laser (FEL) technology demonstrator. An array of several cryostats will be installed as an afterburner at the end of the existing hard x-ray beam line of the LCLS-II facility at the SLAC National Accelerator Laboratory (SLAC). Cryostat requirements include high operational availability, precision positioning and measurement capability to support beam-based alignment, high undulator magnet packing fraction, operational transparency to the electron beam, and compatibility with the existing LCLS hardware and space constraints. A cryocooler-based refrigeration system is appropriate given the scale and operational profile of the demonstration. The design is being developed as part of a collaboration between SLAC and Argonne National Laboratory (ANL) and draws on ANL’s experience with SCUs at the Advanced Photon Source.

Harmonic generation and modulation based on intense x-ray interaction with crystal-like structures

The rapid advancement of x-ray free-electron laser technology facilitates the attainment of relativistic attosecond x-ray laser pulses in the future. It could serve as an ideal source to explore x-ray-driven high-energy density physics, such as particle acceleration and secondary radiation at solid densities. Here, utilizing particle-in-cell simulations, we systematically investigate high-order harmonic generation (HHG) based on intense x-ray lasers interacting with crystal-like structures. We find that the nonlinear interaction induces significant HHGs that are highly modulated due to the periodic target structure. By varying the spacing of the density spikes, the resonant conditions are tuned such that the efficiency of HHGs is drastically different. While each order of harmonic has multiple propagating directions, we find that the intensity can be enhanced significantly in the non-Bragg condition case than that in the Bragg case. The results indicate an approach to manipulate HHG emission driven by strong-field x-rays.

Principle of Free-electron Laser and Applications in Medical Research and Lithography

In recent years, as a breakthrough light source technology, free-electron laser (FEL) has the unique advantage of producing coherent radiation with high brightness, high energy, good directivity and excellent monochromaticity. With this in mind, this study will systematical discuss the historical development of FEL technology, from Einstein's laser theory to Dr. Maiman's first commercial laser, as well as the birth and evolution of FEL. To be specific, the basic principles and construction of FEL technology will be discussed in detail, including key components such as electron sources, electron accelerators, and oscillators. The application of free electron laser (FEL) technology in medicine and lithography will also be demonstrated in this paper. According to the analysis, the current limitations of the state-of-art facilities as well as the future development trends and improvements for FEL system will be clarified based on the evaluations. Overall, these results shed light on guiding further exploration of FEL techniques.

Discovering a corticotropin-releasing hormone receptor 1 antagonist through structure-based drug design with X-ray free-electron laser technology

Discovering a corticotropin-releasing hormone receptor 1 antagonist through structure-based drug design with X-ray free-electron laser technology

Isolated terawatt sub-attosecond high-energy x-ray pulse generated by an x-ray free-electron laser

The endless quest for dynamics in natural phenomena has resulted in the generation and application of attosecond pulses to trace electron dynamics in atomic and molecular systems. The next challenge is to generate powerful pulses on the zeptosecond time scale, which is currently inaccessible. Through a simulation study, a new type of x-ray source that can generate an isolated terawatt sub-attosecond pulse at high-energy x rays by combining attosecond pulse technology with free-electron laser technology is proposed. The successful generation of a sub-attosecond pulse necessitates the consideration of nanometer-wide current-spikes, the sub-attosecond pulse amplification, and pulse duration and background noise control. The underlying interaction mechanism between a sub-attosecond pulse and a current-spike is closely investigated using the simulation results. The proposed method is expected to produce an isolated ∼700 zs pulse with a peak output of 2.9 TW at a photon energy of 247.5 keV.

A custom high-stability pulse generator for the test of a novel in-situ magnetic sensor developed to detect radiation damage in undulators

High-performance analog-to-digital converters (ADC) have been widely applied in many areas of science. For instance, magnetic field measurements based on the Faraday’s induction law require high-precision voltmeters to measure induced voltages. In the context of free-electron lasers technology, the Magnetic Measurements Team at SLAC National Accelerator Laboratory proposed a novel in-situ radiation damage detection system (RDDS) for detecting small field variations in undulators. The system measures the flux change in a flexible printed-circuit coil attached to the magnet array during the undulator gap movement. The gap movement changes the magnetic field, which induces a voltage signal in the coil that is measured and integrated with an ADC. Although the system is capable of detecting relative flux changes better than 100ppm, drift in the ADC’s gain or offset can cause apparent changes in the relative flux. This paper describes the first attempt to developed a high-precision verification circuit to perform ADC testing in the framework of the novel RDDS. The circuit generates a reference voltage pulse with a voltage–time integral relative precision better than 50ppm for a few hundreds of mVs — the typical order of magnitude measured with the RDDS. The circuit’s design combines a fast and precise switch with a low-noise voltage reference. Long-term measurements allowed statistical analysis and showed that averaging the voltage–time integral of ten pulses gives the required 50ppm stability. Moreover, reproducibility tests confirmed that the circuit’s output is invariable under small power supply instabilities and equipment shutdown. Instruments and applications designed to quantify the magnetic field by integrating voltage signals may use the pulse generator proposed in this paper for verification purposes.

Development Strategy of Free Electron Laser Technology in China

Free electron laser (FEL) is a large-scale scientific research device based on electron linear accelerator and has been widely used in basic scientific research such as condensed matter physics, advanced materials and surface physics, atomic and molecular physics, chemistry, and biology. The advancement of FEL technology will promote the light sources to develop towards higher power and shorter wavelength to satisfy the increasing demands of users. This study introduces the necessity of development based on the characteristics of the FEL technology and summarizes the current development status of the technology in China and abroad. It also analyzes the existing problems in its development in China and proposes ideas and goals for the development of FEL technology in China. By 2035, China should focus on making breakthroughs in long-wave FEL, X-ray FEL, new FEL, and FEL-based extreme ultraviolet (EUV) lithography light source technologies. Based on the research and analysis, this study proposes some suggestions for the steady and healthy development of the FEL technology in China, including making scientific development strategies, raising investment in fundamental research to promote independent innovation, strengthening multi-party cooperation to promote the transformation of scientific and technological achievements, promoting market application, and strengthening personnel training.

Focusing of Microcrystals and Liquid Condensates in Acoustofluidics

Manipulation of high-density materials, such as crystals and liquid condensates, is of great importance for many applications, including serial crystallography, structural and molecular biology, chemistry, and medicine. In this work, we describe an acoustic technique to focus and harvest flowing crystals and liquid condensates. Moreover, we show, based on numerical simulations, that the acoustic waves can be used for size-based particle (crystals, droplets, etc.) separation. This is an essential technological step in biological research, medical applications, and industrial processes. The presented technology offers high precision, biocompatibility, ease of use and additionally, is non-invasive and inexpensive. With the recent advent of X-ray Free Electron Laser (XFEL) technology and the associated enormous importance of a thin jet of crystals, this technology might pave the way to a novel type of XFEL injector.

Theoretical investigation of atomic low-order harmonics under irradiation of two high frequency laser pulses

With the development of laser technology,the extreme ultraviolet and X-ray light sources can be obtained by utilizing the high-order harmonic radiation and the free electron laser.When an atom is irradiated by an intense highfrequency laser,many nonlinear phenomena can be observed,such as high-order harmonic emission,threshold ionization and ionization stability of atom,etc. The emission spectra with some new features appear when the atom is irradiated by a high-frequency laser pulse. The harmonic spectra with a clear cut-off plateau do not appear,and the three-step model is no longer valid for explaining the results.In addition to the odd-order harmonic radiation observed in the emission spectra,many super-Raman lines can be seen clearly.These radiations are generated from the transition between the dressed eigenstates of the atom. When the incident high-frequency laser pulse is strong enough,the peak of the harmonic splits into many sub-peaks. The generation of the sub-peaks of harmonic is due to the contributions from the rising and falling parts in the pulse. With the development of free electron laser technology,one can obtain a combined pulse with different frequencies. Many new two-color schemes are proposed for the experiment,such as the realization of two-photon spectrometer, pump-probe spectrometer.In this work,we investigate the optical radiation of the atom irradiated by a combined laser pulse,whose energies are higher than the ionization energy of the atom.It is found that the odd harmonics of the two high frequencies are shown in the emission spectra,and many satellite peaks appear in the vicinity of these odd harmonics.Furthermore,the intensities of the satellite peaks are enhanced exponentially with the increase of the incident laser intensity,and the frequency difference between the two adjacent peaks is the frequency difference between the two incident laser pulses.We study the time-frequency profile of the harmonic emission by analyzing the wavelets.With the two-color scheme one can achieve coherent soft X-ray and produce short coherent pulse. We also calculate the high-order harmonic spectrum of hydrogen in the two-color laser pulse,the multi-peak structure in the emission spectra can also be found,and the positions and intensity distribution of the emission peaks are consistent well with those from the one-dimensional calculation.In our two-color scheme,by changing the peak intensity and frequency of one of the combined laser pulses,the multi-plateau structure can be shown in the harmonic spectra.Taking advantage of the harmonic plateau,the soft X-ray radiation and ultra-short attosecond pulse chain can be generated.

Control of the Swiss Free Electron Laser: Methods for Precision Control of Pulsed-Mode Accelerator Beams

Free electron laser (FEL) machines generate highpower, coherent, and tunable radiation in the X-ray range. They are used to study molecular structural and dynamic processes at the Ångstrom-femtosecond spatiotemporal scale. The Swiss Free Electron Laser (SwissFEL) facility–under development at the Paul Scherrer Institut and scheduled to begin operation in 2017– will generate intense and short pulses of X-ray light, enabling researchers to observe extremely fast processes, such as the creation of new molecules in chemical reactions or to study the detailed structure of proteins. This article introduces FEL technology from a control systems perspective and provides insight into the types of control problems that arise in pulsedmode accelerators and beams. Although developed here for the SwissFEL machine, the control approaches are expected to be transferable to other systems as well. See Summary for an overview of the article.

Attosecond interferometry with self-amplified spontaneous emission of a free-electron laser

Light-phase-sensitive techniques, such as coherent multidimensional spectroscopy, are well-established in a broad spectral range, already spanning from radio-frequencies in nuclear magnetic resonance spectroscopy to visible and ultraviolet wavelengths in nonlinear optics with table-top lasers. In these cases, the ability to tailor the phases of electromagnetic waves with high precision is essential. Here we achieve phase control of extreme-ultraviolet pulses from a free-electron laser (FEL) on the attosecond timescale in a Michelson-type all-reflective interferometric autocorrelator. By varying the relative phase of the generated pulse replicas with sub-cycle precision we observe the field interference, that is, the light-wave oscillation with a period of 129 as. The successful transfer of a powerful optical method towards short-wavelength FEL science and technology paves the way towards utilization of advanced nonlinear methodologies even at partially coherent soft X-ray FEL sources that rely on self-amplified spontaneous emission.

A strong diffusive ion mode in dense ionized matter predicted by Langevin dynamics

The state and evolution of planets, brown dwarfs and neutron star crusts is determined by the properties of dense and compressed matter. Due to the inherent difficulties in modelling strongly coupled plasmas, however, current predictions of transport coefficients differ by orders of magnitude. Collective modes are a prominent feature, whose spectra may serve as an important tool to validate theoretical predictions for dense matter. With recent advances in free electron laser technology, X-rays with small enough bandwidth have become available, allowing the investigation of the low-frequency ion modes in dense matter. Here, we present numerical predictions for these ion modes and demonstrate significant changes to their strength and dispersion if dissipative processes are included by Langevin dynamics. Notably, a strong diffusive mode around zero frequency arises, which is not present, or much weaker, in standard simulations. Our results have profound consequences in the interpretation of transport coefficients in dense plasmas.

Reconstructing three-dimensional helical structure with an X-ray free electron laser

Recovery of three-dimensional structure from single-particle X-ray scattering of completely randomly oriented diffraction patterns as predicted a few decades ago has been realized owing to the advent of the new emerging X-ray free electron laser (XFEL) technology. Since the world's first XFEL started operation in June 2009 at SLAC National Laboratory at Stanford, the first few experiments have been conducted on larger objects such as viruses. Many of the important structures of nature such as helical viruses or DNA consist of helical repetition of biological subunits. Hence development of a method for reconstructing helical structure from collected XFEL data has been a top research priority. This work describes the development of a method for solving helical structures such as tobacco mosaic virus from a set of randomly oriented simulated diffraction patterns exploiting the symmetry and Fourier space constraint of the diffraction volume.

Picosecond dissociation of amyloid fibrils with infrared laser: A nonequilibrium simulation study.

Recently, mid-infrared free-electron laser technology has been developed to dissociate amyloid fibrils. Here, we present a theoretical framework for this type of experiment based on laser-induced nonequilibrium all-atom molecular dynamics simulations. We show that the fibril is destroyed due to the strong resonance between its amide I vibrational modes and the laser field. The effects of laser irradiation are determined by a balance between fibril formation and dissociation. While the overall rearrangements of the fibril finish over short time scales, the interaction between the peptides and the solvent continues over much longer times indicating that the waters play an important role in the dissociation process. Our results thus provide new insights into amyloid fibril dissociation by laser techniques and open up new venues to investigate the complex phenomena associated with amyloidogenesis.

A Review on Ab Initio Approaches for Multielectron Dynamics

In parallel with the evolution of femtosecond and attosecond laser as well as free-electron laser technology, a variety of theoretical methods have been developed to describe the behavior of atoms, molecules, clusters, and solids under the action of those laser pulses. Here, we review major ab initio wave-function-based numerical approaches to simulate multielectron dynamics in atoms and molecules driven by intense long-wavelength and/or ultrashort short-wavelength laser pulses. Direct solution of the time-dependent Schrodinger equation, though its applicability is limited to He, ${\rm H}_2$ , and Li, can provide an exact description and has been greatly contributing to the understanding of dynamical electron-electron correlation. Multiconfiguration self-consistent-field (MCSCF) approach offers a flexible framework from which a variety of methods can be derived to treat both atoms and molecules, with possibility to systematically control the accuracy. The equations of motion of configuration interaction coefficients and molecular orbitals for general MCSCF ansatz have recently been derived. Time-dependent extension of the $R$ -matrix theory, originally developed for electron-atom collision, can realistically and accurately describe laser-driven complex multielectron atoms.

Two-colour pump–probe experiments with a twin-pulse-seed extreme ultraviolet free-electron laser

Exploring the dynamics of matter driven to extreme non-equilibrium states by an intense ultrashort X-ray pulse is becoming reality, thanks to the advent of free-electron laser technology that allows development of different schemes for probing the response at variable time delay with a second pulse. Here we report the generation of two-colour extreme ultraviolet pulses of controlled wavelengths, intensity and timing by seeding of high-gain harmonic generation free-electron laser with multiple independent laser pulses. The potential of this new scheme is demonstrated by the time evolution of a titanium-grating diffraction pattern, tuning the two coherent pulses to the titanium M-resonance and varying their intensities. This reveals that an intense pulse induces abrupt pattern changes on a time scale shorter than hydrodynamic expansion and ablation. This result exemplifies the essential capabilities of the jitter-free multiple-colour free-electron laser pulse sequences to study evolving states of matter with element sensitivity.

Magnetic Performance of a Laser Structured YBCO Tape Suitable for Insertion Devices Technology

Recent intensive development of high-temperature superconducting (HTS) materials resulted in the availability of various commercial HTS tapes, in particular coated conductors. Technological progress in this field and up-coming market will reduce the costs of the tape. One very promising application for free electron laser technology considers a new concept of meander-like structured stacked HTS tapes to provide the desired magnetic field pattern with periodic changing field orientation. For the first time, we report in this paper on the magnetic field performance of such an HTS tape, structured with picosecond laser pulses, which prevent damage of the superconducting layer by overheating and lead to very precise structure.

Exotic Dense-Matter States Pumped by a Relativistic Laser Plasma in the Radiation-Dominated Regime

In high-spectral resolution experiments with the petawatt Vulcan laser, strong x-ray radiation of KK hollow atoms (atoms without n = 1 electrons) from thin Al foils was observed at pulse intensities of 3 × 10(20) W/cm(2). The observations of spectra from these exotic states of matter are supported by detailed kinetics calculations, and are consistent with a picture in which an intense polychromatic x-ray field, formed from Thomson scattering and bremsstrahlung in the electrostatic fields at the target surface, drives the KK hollow atom production. We estimate that this x-ray field has an intensity of >5 × 10(18) W/cm(2) and is in the 3 keV range.

Crystallization of a self-assembled three-dimensional DNA nanostructure.

The powerful and specific molecular-recognition system present in the base-pairing of DNA allows for the design of a plethora of nanostructures. In this work, the crystallization of a self-assembling three-dimensional B-DNA nanostructure is described. The DNA nanostructure consists of six single-stranded oligonucleotides that hybridize to form a three-dimensional tetrahedron of 80 kDa in molecular mass and 20 bp on each edge. Crystals of the tetrahedron have been successfully produced and characterized. These crystals may form the basis for an X-ray structure of the tetrahedron in the future. Nucleotide crystallography poses many challenges, leading to the fact that only 1352 X-ray structures of nucleic acids have been solved compared with more than 80,000 protein structures. In this work, the crystallization optimization for three-dimensional tetrahedra is also described, with the eventual goal of producing nanocrystals to overcome the radiation-damage obstacle by the use of free-electron laser technology in the future.

Potential of the FLASH free electron laser technology for the construction of a kW-scale light source for next-generation lithography

The driving engine of the free electron laser in Hamburg (FLASH) is an L-band superconducting accelerator. It is designed to operate in burst mode with an 800-ms pulse duration at a repetition rate of 10 Hz. The maximum accelerated beam current during the macropulse is 9 mA. Our analysis shows that the FLASH technology has great potential since it is possible to construct a FLASH-like free electron laser operating at the wavelength of 13.5 and 6.8 nm with an average power of up to 2.6 kW. Such a source meets the physical requirements for the light source for next-generation lithography.