The free-electron laser FLASH at DESY can produce SASE-FEL pulses in the extreme ultraviolet to the soft X-ray region. The flexibility of the variable gap undulators in the FLASH2 beamline opens a wide range of scientific opportunities. Different advanced lasing schemes have been tested in the past years, like the frequency doubler scheme, two-color lasing, and ``harmonic lasing...
In Self-Amplified Spontaneous Emission Free Electron Laser (SASE FEL) based short-pulse schemes, pulse duration is limited by FEL coherence time. For hard X-ray FELs, coherence time is in a few hundred attosecond range while for XUV and soft X-ray FELs it is in the femtosecond regime. In this paper the modification of so-called chirp-taper scheme is developed that allows to overcome the...
X-ray free-electron lasers (FELs) rely on SASE due to the lack of seed lasers and the difficulty in obtaining mirrors. Progress in diamond crystal Bragg mirrors enables the design of x-ray FEL oscillators. Regenerative amplifiers (RAFELs) are high gain/low-Q oscillators that out-couple most of the optical power. An x-ray RAFEL based on the LCLS-II at SLAC using a six-mirror resonator...
This paper provides a summary of the analyses that led to the definition of the 2-color upgrade of the IR FEL at FHI Berlin. We briefly cover several different aspects of the design, beginning with the beam dynamics of the second far-IR beamline, engineering considerations of that physics design, and the FEL physics that defined the short-Rayleigh range undulator as well as aspects of the...
Free-electron lasers (FELs) operate at wavelengths from millimeter waves through hard x-rays. At x-ray wavelengths, FELs typically rely on self-amplified spontaneous emission SASE emission which contains multiple temporal “spikes” that limit the longitudinal coherence of the optical output; hence, alternate methods that improve on the longitudinal coherence of the SASE emission are of...
Genesis is widely used in the free electron laser community as a simulation tool for studying both simple and complex FEL systems. Until now, this has necessitated learning the command line interface, which can be challenging for new users. Sirepo Genesis provides an intuitive graphic interface for building Genesis simulations in the browser that can then be run using our cloud computing...
Fresh-slice lasing using wakefield induced time-dependent orbit oscillation is capable of producing high intensity two-color XFEL pulses and high power short pulses at femtosecond level. At the European XFEL, a corrugated structure system for fresh-slice applications for both the hard x-ray beamline SASE1 and the soft x-ray SASE3 beamline is being developed and implemented. In this...
X-ray absorption spectroscopy (XAS) with a SASE signal can be improved if the full XAS and reference spectrum are taken on a shot-to-shot basis, thus eliminating the impact of the intrinsic SASE fluctuations in the spectrum. This can be further improved if the FEL pulse has the frequency information encoded in its spatial position. The spatial encoding is achieved when a spatially tilted...
THz free electron laser at SANKEN, Osaka university generates a train of THz pulses with the interval of 27 MHz in the repetition of 5 Hz. The number of pulses in a train is about 100. Single pulse energy exceeds 200 \muJ at the carrier frequency of 4.5 THz. To extract a single pulse from the train, the reflective switch of the electron-hole plasma on the surface of Gallium Arsenide wafer...
The typical layout adopted in a seeded harmonic generation free-electron laser is based on radiator undulators placed immediately after the dispersive section, where the bunching is created.
With the advent of new and more complex seeding schemes, this solution cannot always be implemented and cases, where the bunched beam needs to be propagated in free space before entering the radiator,...
The AQUA beamline of the EuPRAXIA@SPARC_LAB infrastructure consists of a Free-Electron Laser facility driven by an electron beam with 1 GeV energy, produced by an X-band normal conducting LINAC followed by a plasma wakefield acceleration stage, with the goal to deliver variable polarization photons in the 3-4 nm wavelength range. Two undulator options were considered for the AQUA FEL...
Research and development of an accelerator-based THz source prototype for pump-probe experiments at the European XFEL are ongoing at the Photo Injector Test Facility at DESY in Zeuthen (PITZ). A proof-of-principle experiment to generate THz SASE FEL radiation using an LCLS-I undulator driven by an electron bunch from the PITZ accelerator has been prepared. After four years of designs and...
We report on the first demonstration of generating high-power and short FEL pulses using the fresh-slice multi-stage amplification scheme at Athos, the soft X-ray beamline of SwissFEL. We use a transversely tilted electron beam traveling through the unique Athos layout with magnetic chicanes between every two undulator modules. Our first results show the production of FEL radiation with pulse...
A major challenge in single-linac - multiple undulator setups like EuXFEL is the generation of individual shaped photon pulses, in particular, when working in a mode where a single pulse train, or cw stream, feeds all undulator lines. This work presents the experimental verification of a flexible delivery scheme producing photon pulses for each of the three undulator lines with their electron...
We propose a computationally-efficient algorithm to calculate the field of partially coherent synchrotron radiation pulses from undulators. Wavefront propagation simulations play a pivotal role in designing beamline optics at new synchrotron radiation sources. However, they do not account for the stochastic behaviour of the initial radiation field, which is due to shot noise in the electron...
Light with orbital angular momentum (OAM) provides new insights into a wide range of physical phenomena and has engendered advanced applications in various fields. Additionally, research interest in X-ray OAM has been rapidly increasing. Here, we report a straightforward method capable of generating intense OAM beams from an X-ray free-electron laser oscillator (XFELO). This method leverages...
We (PAL-XFEL) have improved the PAL-XFEL performances remarkably since the user-service operation in 2017. We achieved the self-seeded XFEL with a peak brightness of 3.2 × 10^35, the highest to date, and reached a SASE FEL intensity of 3.2 mJ due to the improved beam emittance of 0.3 mm-mrad. The statistics of the SASE FEL intensities over the past three years show that the SASE FEL...
Laser-induced breakdown has been observed in various combination of gases and lasers. It is known from previous studies that breakdown occurs when the number of electrons exceeds a threshold value through the following stages: generation of seed electrons, acceleration of electrons by inverse Bremsstrahlung, and avalanche multiplication of electrons by impact ionization.
We have observed...
The European XFEL operates with 3 different SASE FELs served by variable gap undulators. In addition, the electron energy of the superconducting linear accelerator is varied between 8.5 and 16.5 GeV to cover a photon energy range from 500 eV to 30 keV. We will present SASE performance data collected over the past 5 years of operation and compare them with theoretical predictions.
The SACLA linear accelerator has been successfully used as a full-energy injector of the SPring-8 storage ring since 2020. In order to perform the beam injection in parallel with XFEL operation, three accelerators are virtually constructed in a control system. Thus the electron beam parameters, such as the beam energy, are independently tuned for the beam injection and the two XFEL beamlines....
MINERVA is a 3-D, time-dependent simulation code of FEL amplifiers, low-gain/high-Q and high-gain/low-Q oscillators, optical klystrons (including high-gain harmonic generation) and SASE configurations [1-7]. Oscillator simulations are done in conjunction with OPC [8]. MINERVA uses the Message Passing interface on Linux, Macintosh and Windows systems and has been successfully benchmarked...
Previous studies of FEL oscillators typically use averaged simulation codes which cannot model sub-wavelength effects, such as Coherent Spontaneous Emission from the electron pulse. In this paper, the unaveraged FEL simulation code Puffin is used with the optics code Optical Propagation Code to model the FEL in three dimensions, enabling sub-wavelength effects to be modelled at the FEL...
TeraFERMI is a THz beamline at the free-electron laser (FEL) FERMI. After passing the FEL's undulator, the electron bunches are refocused on a thin dielectric slab and generate coherent transition radiation (CTR), namely strong THz pulses. TeraFERMI provides single-cycle pulses with a broadband spectrum in the range from 0.1 THz to 6 THz and strong peak electric fields with up to 4 MV/cm or...
More and more high-gain SASE FELs operate at high repetition rates, either in burst or in continuous wave mode of operation, offering an unprecedented number of electron bunches per second. External seeding techniques provide high quality FEL pulses of full coherence and shot-to-shot stability but cannot keep up with MHz repetition rates of such FELs due to their dependence on the seed laser...
At KAERI we are developing compact Terahertz(THz) Free Electron Laser(FEL) for a commercial application like security inspection. We are using a waveguide-based optical resonator for our FEL system. Firstly, we report on the selection of low loss and small cross-section waveguide candidate to enhance the gain of THz FEL. We performed a detailed analysis of waveguides with different shapes and...
Echo-Enabled Harmonic Generation (EEHG) became a very promising and very popular technique after original publication [1]. As it commonly happens, this was the reinvention of already known technique, which was not broadly known in FEL community. EEHG vaguely reminded me of theory developed at Novosibirsk Institute of Nuclear Physics (BINP), but I was not sure that my memory is correct....
Infrared FEL oscillators generally use hole-coupling to extract intracavity laser power. The hole-coupling inherently causes a non-Gaussian beam profile at user stations, which are more than 10 m apart from the coupling hole. It is due to the existence of the Airy pattern in the extracted laser beam. We demonstrated that the beam profile can be changed from a non-Gaussian to a nearly Gaussian...
Compact sources offering high-brightness radiation in the EUV to X-ray regime are highly desired. Thomson scattering, in which an electron beam colliding with a laser pulse produces radiation, is a source of X-rays of increasing prevalence in modern labs, complementing large scale facilities like synchrotrons and X-ray free electron lasers. By imposing a density modulation on the electron beam...
The existing MAX IV 3 GeV linac could drive, with minor improvements, a soft X-ray Free Electron Laser and the aim of the SXL project has been so far to deliver a conceptual design of such a facility in the 1—5 nm wavelength range.
The project was initiated by a group of Swedish users of FEL radiation and the design work was supported by the Knut and Alice Wallenberg foundation and by...
In a storage ring free-electron laser (FEL) the cavity mirrors have to resist the harsh operational conditions due to high-energetic and background radiation in an ultra-high vacuum environment. For the wavelength between 120 and 190 nm only fluoride materials are suitable as coating material for high reflective mirrors. However, used in the bare form, they are not stable for extreme FEL...
The coherence of free-electron laser (FEL) radiation has so far been accessed mainly through first and second order correlation functions. Instead, we propose to reconstruct the energy state occupation number distribution of FEL radiation, avoiding the photo-counting drawbacks with high intensities, by means of maximum likelihood techniques based on the statistics of no-click events. The...
The FELIX Laboratory, located at Radboud University in Nijmegen, The Netherlands, is operating a suite of FELs serving an international user community with infrared and THz radiation from 5 to 1500 micron operating three FELs in parallel and providing beam to 16 dedicated user end stations. Recently, FELIX has upgraded its most frequently used FEL-2 beamline. The 38 period, 65 mm Halbach-type...
The free-electron laser FLASH at DESY can produce SASE-FEL pulses in the extreme ultraviolet to the soft X-ray regime. A superconducting linear accelerator drives two undulator lines (FLASH1 and
FLASH2). The FLASH1 undulator beam line contains six fixed gap undulator which implies that the SASE wavelength can only be changed via the electron beam energy, while FLASH2 contains twelve variable...
High-resolution emission/absorption spectroscopy with picosecond time resolution appears to be strategic in fundamental matter physics investigation as well as in functional materials characterization. Such a method typically requires a pulsed radiation source and high energy resolution, along with a large data statistic. In this work we demonstrate the possibility to retrieve high resolution...
FEL pulses with an easily tunable duration are of great benefit to user experiments with high requirements on the temporal resolution. A transverse beam tilt is well suited to shorten the pulse duration in a controlled manner. We consider three methods of tilt generation: rf deflecting structures, lattice dispersion in combination with an energy chirp, and transverse wakefields from C-band...
Cavity-based x-ray free-electron lasers (CBXFEL) will allow use of
optical cavity feedback to support generation of fully coherent x-rays
of high brilliance and stability by electrons in undulators. CBXFEL
optical cavities comprise Bragg-reflecting flat crystal mirrors, which
ensure x-rays circulation on a closed orbit, and x-ray refractive
lenses, which stabilize the orbit and refocus...
Intense attosecond pulses generated by x-ray free-electron lasers (XFEL) are promising for attosecond science, for example, to study the quantum mechanical motion of electrons in molecules. This paper presents numerical simulations of the generation of attosecond soft and hard x-ray FEL pulses with the chirp-taper and Enhanced SASE schemes, based on the parameters of the European XFEL. To...
European XFEL is a multi-beamline x-ray free-electron laser (FEL) user facility driven by a superconducting accelerator with a nominal photon energy range from 250 eV to 25 keV. An afterburner undulator based on superconducting undulator technology is currently being planned to enable extension of the photon energy range towards harder x-rays. This afterburner undulator would be installed...
A tunable, tabletop, Inverse Compton Scattering (ICS) hard X-ray source is being designed and built at Eindhoven University of Technology as part of a European Interreg program between The Netherlands and Belgium. This compact X-ray source will bridge the gap between conventional lab sources and synchrotrons: The X-ray photon energy will be generated between 1 and 100 keV with a brilliance...
Accurate measurements of the x-ray pulse duration produced by x-ray free-electron lasers (XFELs) typically rely on longitudinal electron beam phase space diagnostics, e.g. in a transverse deflecting cavity or TCAV, or from measurements of spectral correlations. All of the known spectral methods share the weakness that they will underestimate the pulse length in the case that the FEL spectrum...
FLASH, the free-electron laser user facility at DESY, delivers XUV and soft X-ray radiation for photon experiments since 2005. It is driven by a superconducting linear accelerator, and has two undulator lines (FLASH1 and FLASH2). A third electron beam line hosts the plasma wakefield experiment FLASHForward. Presently, the FLASH facility is undergoing an extensive refurbishment and a...
Laser pulses of sub-femtosecond duration can be used to track the motion of electrons in the inner shell, which is needed in a variety of advanced experiments. Although this has been accomplished in XUV and hard X-rays in a free-electron-laser facility, it remains a challenge in the soft X-ray region due to the relatively high photon energies and large slippage in the undulator. In this...
Topological insulators are a class of materials which have raised a great interest over the last decade, thanks to their intriguing conduction properties. Indeed, they are insulating in the bulk and metallic at the surface. Moreover, these metallic surface states have linear Dirac dispersion [1], thanks to which topological insulators show nonlinear THz behaviour similar to the case of...
Since coming on-line in November 2013, the Fritz-Haber-Institut (FHI) der Max-Planck-Gesellschaft (MPG) Free-Electron Laser (FEL) has provided intense, tunable infrared radiation to FHI user groups. It has enabled experiments in diverse fields ranging from bio-molecular spectroscopy to studies of clusters and nanoparticles, nonlinear solid-state spectroscopy, and surface science, resulting in...
A novel and noninvasive method for two-color x-ray emission is demonstrated at SwissFEL. In the setup, a laser emittance spoiler pulse is overlapped with the primary photocathode laser to locally spoil the beam emittance and the FEL emission. This results, together with a chirped electron pulse, in X-ray emission at two colors. High-energy, high stability, independent control of the duration...
Generation of few-cycle FEL pulses with a high extraction efficiency was achieved at JAERI-FEL [1] and KU-FEL [2]. The observed lasing can be understood as superradiance, radiation from bunched electrons in the slippage region. In the superradiance FEL oscillators, the high-extraction efficiency is accompanied by significant energy variation of the electrons during the undulator. Therefore,...
Free-electron lasers (FELs) produce different optical polarizations including linear, elliptic and circular polarizations corresponding to the polarizations of the undulators used. X-ray FELs depend upon long undulator lines consisting of a sequence of short undulators. Linearly polarized undulators are most commonly used; hence the optical output is linearly polarized. Elliptic or circular...
