This reprint is aimed at presenting strategic and design elements for the development of low-cost, low-size Free Electron Lasers. Different points of view are considered here, attempting to consider ...technologies and design conceptions that are fairly mature and may be viable solutions in the near or midterm future. The design conceptions proposed here are based on the so-called hybrid (or broader-approach) technologies, which put together, e.g., combinations of oscillator and amplifier configurations. These solutions, although developed almost thirty years ago, appear nowadays within the present technological capabilities. Other possibilities offered, for example , by the recirculated wave undulator FELs, represent border line technologies, which are worth carefully studying as the architecture of the mid-term future. Finally, the reprint addresses both theoretical and design considerations regarding proposals for the enhancement of coherent emission on higher harmonics.
•A quantum mechanical treatment is developed to describe the low-gain slow-wave free-electron laser.•The quantum nature of electrons has a significant effect on the gain.•The gain follows two ...different behaviors basing on the ratio between the spreading width of electron and laser wavelength.•There is an optimum wave packet width at which the maximum gain is reached.•The results of this paper can be used in resolving the particle-wave duality.
A quantum mechanical treatment is presented to describe slow–wave free–electron lasers (FELs) operating in the low–gain regime. Here, we address the quantum effect of electrons on the FEL operation where each electron is represented as a Gaussian wave packet with an arbitrary width. It is shown that this quantum effect should be described in two different regimes. The first regime is realized when the initial width of the electron wave packet σz0 is comparable to (larger or smaller than) the radiation wavelength λL. In this regime, the gain degrades significantly as σz0 increases and approaches λL. The latter regime is realized when σz0 is quite smaller than λL (i.e., approximately when σz0<λL/3) where the behavior of the gain is opposite to that in the first regime since it decreases with decreasing σz0. Therefore, it is predicted that there is an optimum initial width of the electron wave packet at which the gain is maximum.
A seeded FEL driven by a linac based on super conducting cavities, generating 108-1010 coherent photons per shot at 2-5 keV with 0.2-1 MHz of repetition rate, can address the need of a source devoted ...to fine analysis of matter using the linear spectroscopy technique. The seeding scheme described hereafter is a multi-stage cascade upshifting the radiation frequency by a factor 20-40. The x-ray range can be achieved with a seed constituted by a coherent flash in the extreme ultraviolet range provided by an FEL oscillator operating at 12-14 nm. The whole chain of x-ray generation is described by means of start-to-end three-dimensional simulations.
Dynamics and kinetics in soft matter physics, biology, and nanoscience frequently occur on fast (sub)microsecond but not ultrafast timescales which are difficult to probe experimentally. The European ...X-ray Free-Electron Laser (European XFEL), a megahertz hard X-ray Free-Electron Laser source, enables such experiments via taking series of diffraction patterns at repetition rates of up to 4.5 MHz. Here, we demonstrate X-ray photon correlation spectroscopy (XPCS) with submicrosecond time resolution of soft matter samples at the European XFEL.We show that the XFEL driven by a superconducting accelerator provides unprecedented beam stability within a pulse train. We performed microsecond sequential XPCS experiments probing equilibrium and nonequilibrium diffusion dynamics in water. We find nonlinear heating on microsecond timescales with dynamics beyond hot Brownian motion and superheated water states persisting up to 100 μs at high fluences. At short times up to 20 μs we observe that the dynamics do not obey the Stokes–Einstein predictions.
X-ray free-electron lasers provide femtosecond-duration pulses of hard X-rays with a peak brightness approximately one billion times greater than is available at synchrotron radiation facilities. One ...motivation for the development of such X-ray sources was the proposal to obtain structures of macromolecules, macromolecular complexes, and virus particles, without the need for crystallization, through diffraction measurements of single noncrystalline objects. Initial explorations of this idea and of outrunning radiation damage with femtosecond pulses led to the development of serial crystallography and the ability to obtain high-resolution structures of small crystals without the need for cryogenic cooling. This technique allows the understanding of conformational dynamics and enzymatics and the resolution of intermediate states in reactions over timescales of 100 fs to minutes. The promise of more photons per atom recorded in a diffraction pattern than electrons per atom contributing to an electron micrograph may enable diffraction measurements of single molecules, although challenges remain.
Ultrafast optical manipulation of magnetic phenomena is an exciting achievement of mankind, expanding one's horizon of knowledge toward the functional nonequilibrium states. The dynamics acting on an ...extremely short timescale push the detection limits that reveal fascinating light–matter interactions for nonthermal creation of effective magnetic fields. While some cases are benchmarked by emergent transient behaviors, otherwise identifying the nonthermal effects remains challenging. Here, a femtosecond time‐resolved resonant magnetic X‐ray diffraction experiment is introduced, which uses an X‐ray free‐electron laser (XFEL) to distinguish between the effective field and the photoinduced thermal effect. It is observed that a multiferroic Y‐type hexaferrite exhibits magnetic Bragg peak intensity oscillations manifesting entangled antiferromagnetic (AFM) and ferromagnetic (FM) Fourier components of a coherent AFM magnon. The magnon trajectory constructed in 3D space and time domains is decisive to evince ultrafast field formation preceding the lattice thermalization. A remarkable impact of photoexcitation across the electronic bandgap is directly unraveled, amplifying the photomagnetic coupling that is one of the highest among AFM dielectrics. Leveraging the above‐bandgap photoexcitation, this energy‐efficient optical process further suggests a novel photomagnetic control of ferroelectricity in multiferroics.
Femtosecond time‐resolved resonant magnetic X‐ray diffraction experiment using an X‐ray free electron laser visualizes a light‐induced coherent magnon in a multiferroic. The magnon trajectory in time and 3D space unveils the photomagnetic coupling largely enhanced by above‐bandgap photoexcitation, distinguished from a laser‐heated magnetic behavior. This energy‐efficient photoexcitation process suggests the potential for a novel photomagnetic control of ferroelectricity in multiferroics.
The SwissFEL X-ray Free Electron Laser (XFEL) facility started construction at the Paul Scherrer Institute (Villigen, Switzerland) in 2013 and will be ready to accept its first users in 2018 on the ...Aramis hard X-ray branch. In the following sections we will summarize the various aspects of the project, including the design of the soft and hard X-ray branches of the accelerator, the results of SwissFEL performance simulations, details of the photon beamlines and experimental stations, and our first commissioning results.
Infrared spectroscopic study of neutral water clusters is crucial to understanding of the hydrogen-bonding networks in liquid water and ice. Here we report infrared spectra of size-selected neutral ...water clusters, (H₂O)n (n = 3–6), in the OH stretching vibration region, based on threshold photoionization using a tunable vacuum ultraviolet free-electron laser. Distinct OH stretch vibrational fundamentals observed in the 3,500–3,600-cm−1 region of (H₂O)₅ provide unique spectral signatures for the formation of a noncyclic pentamer, which coexists with the global-minimum cyclic structure previously identified in the gas phase. The main features of infrared spectra of the pentamer and hexamer, (H₂O)n (n = 5 and 6), span the entire OH stretching band of liquid water, suggesting that they start to exhibit the richness and diversity of hydrogenbonding networks in bulk water.
The design and performance of a soft X‐ray free‐electron laser (FEL) beamline of the SPring‐8 Compact free‐electron LAser (SACLA) are described. The SPring‐8 Compact SASE Source test accelerator, a ...prototype machine of SACLA, was relocated to the SACLA undulator hall for dedicated use for the soft X‐ray FEL beamline. Since the accelerator is operated independently of the SACLA main linac that drives the two hard X‐ray beamlines, it is possible to produce both soft and hard X‐ray FEL simultaneously. The FEL pulse energy reached 110 µJ at a wavelength of 12.4 nm (i.e. photon energy of 100 eV) with an electron beam energy of 780 MeV.
The status of a soft X‐ray free‐electron laser beamline at SACLA is reported.
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