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The European X-ray Free-Electron Laser Facility in Germany delivers x-ray pulses with femtosecond pulse duration at a repetition rate of up to 4.5 MHz. The free-electron laser radiation is created by the self-amplified spontaneous emission (SASE) process, whose stochastic nature gives rise to shot-to-shot fluctuations in most beam properties, including spectrum, pulse energy, spatial profile, wavefront, and temporal profile. Each spectrum consisting of many spikes varies in width and amplitude that appear differently within the envelope of the SASE spectrum. In order to measure and study the SASE spectrum, the HIgh REsolution hard X-ray single-shot (HIREX) spectrometer was installed in the photon tunnel of the SASE1 undulator beamline. It is based on diamond gratings, bent crystals as a dispersive element, and a MHz-repetition-rate strip detector. It covers a photon energy range of 3 keV–25 keV and a bandwidth of 0.5% of the SASE beam. The SASE spikes are resolved with 0.15 eV separation using the Si 440 reflection, providing a resolving power of 60 000 at a photon energy of 9.3 keV. The measured SASE bandwidth is 25 eV. In this paper, we discuss the design specifications, installation, and commissioning of the HIREX spectrometer. The spectral results using Si (110), Si (111), and C (110) crystals are presented. [ABSTRACT FROM AUTHOR]

In this work we report on the ionization of a gaseous neon target by combining extreme ultraviolet (XUV) radiation from the Free Electron Laser in Hamburg with an intense synchronized optical laser. Applying energy-resolved photoelectron spectroscopy, the dependence of the electrons ejected from singly charged neon (Ne+) on the relative polarization of the XUV and optical laser fields was investigated. The electron spectra exhibit a strong dependence on the degree of the relative orientation of the linear polarization vectors. A quantitative analysis was undertaken using multichannel time-dependent perturbation theory in order to reproduce the magnitude of the ejected low kinetic energy electrons as a function of the relative polarization directions and explicitly taking into account the influence of the residual Ne2+ cores (1D,3P). It is concluded that the variation of the photoelectron spectrum with the deviation of XUV and optical field directions is mainly related to the different responses of the magnetic substates of the ejected electrons in their interaction with the laser field. [ABSTRACT FROM AUTHOR]

Abstract: Activities on free-electron laser (FEL) X-ray sources, based on linear accelerators, to produce spatially coherent, ultra-short (∼100fs) pulses with very high peak brilliance (1028–1032 photons/s/mm2/mrad2/0.1% BW) are summarized, with special emphasis on the European XFEL project in Hamburg. The scientific case includes time-resolved studies of dynamics on sub-ps scales, structural studies by imaging of non-periodic systems, and investigation of high energy-density phenomena such as non-linear X-ray optics and the production of warm dense matter. Examples are presented, with reference to the experience gained on the presently operational facilities, FLASH at DESY, Hamburg and LCLS in Stanford, California. [Copyright &y& Elsevier]

Abstract: Pulse intensities greater than 1017 Watt/cm2 were reached at the FLASH soft X-ray laser in Hamburg, Germany, using an off-axis parabolic mirror to focus 15 fs pulses of 5–70 μJ energy at 13.5 nm wavelength to a micron-sized spot. We describe the interaction of such pulses with niobium and vanadium targets and their deuterides. The beam produced craters in the solid targets, and we measured the kinetic energy of ions ejected from these craters. Ions with several keV kinetic energy were observed from craters approaching 5 μm in depth when the sample was at best focus. We also observed the onset of saturation in both ion acceleration and ablation with pulse intensities exceeding 1016 W/cm2, when the highest detected ion energies and the crater depths tend to saturate with increasing intensity. A general difficulty in working with micron and sub-micron focusing optics is finding the exact focus of the beam inside a vacuum chamber. Here we propose a direct method to measure the focal position to a resolution better than the Rayleigh length. The method is based on the correlation between the energies of ejected ions and the physical dimensions of the craters. We find that the focus position can be quickly determined from the ion time-of-flight (TOF) data as the target is scanned through the expected focal region. The method does not require external access to the sample or venting the vacuum chamber. Profile fitting employed to analyze the TOF data can extend resolution beyond the actual scanning step size. [Copyright &y& Elsevier]

Abstract: We propose a two-color pump–probe Thomson scattering experiment at the FLASH facility in Hamburg to characterize warm dense matter states. The fundamental free electron laser wavelength of 40.5 nm is used to pump a liquid hydrogen jet that is subsequently probed with the third harmonic at 13.5 nm. We have considered the laser–target interaction in the pump and probe phase by using the radiation hydrodynamics code HELIOS. The calculation of the Thomson scattering spectrum is based on the Chihara formula which is evaluated using the Born–Mermin approximation for the free electron dynamic structure factor and the Debye–Hückel static structure factor for the elastic scattering part. We consider the full density- and temperature-dependent Thomson scattering cross section throughout the inhomogeneous target. The results indicate that the electron–ion equilibration rate can be extracted by measuring the electron and ion feature with varying time delays between the pump and the probe pulse. [Copyright &y& Elsevier]

The European X-ray Free Electron Laser (XFEL) under construction in Hamburg (Germany) will be able to deliver high intensity X-ray pulses of few tens of femto seconds of duration, at 5 MHz pulse repetition rate. Thanks to its characteristics, this instrument will open up new research opportunities for experiments in femto chemistry, structural biology and material research. A high speed focal plane detector system has been presented, based on a novel non-linear DEPFET as a detector. DEPFETs have been chosen since they can provide excellent energy resolution and high speed readout, a fundamental property to cope with the very demanding pulse time structure of XFEL. Full parallel readout is required, with every channel comprising analog filtering, data conversion and memory storage. In this paper we show results for the first prototype of the analog front end that implements the current readout of the DEPFET pixel. The circuit is based on the Flip Capacitor Filter technique, here briefly presented, and has been designed in 130 nm 1.2 V CMOS technology from IBM. Careful characterization of the individual circuit alone and also connected to a single pixel linear detector has been carried out and the measured performance is summarized. [ABSTRACT FROM AUTHOR]

ivities on free-electron laser (FEL) x-ray sources, based on linear accelerators, to produce spatially coherent, ultra-short (∼100 fs) pulses with very high peak brilliance (10-10 photons/s/mm/mrad/0.1% BW) are summarized. The scientific case includes time-resolved studies of dynamics on sub- ps scales, structural studies by imaging of non-periodic systems, and investigation of high energy-density phenomena such as non-linear x-ray optics and the production of warm dense matter. Examples are presented, with emphasis on the operational facilities, FLASH at DESY, Hamburg and LCLS in Stanford, California, and on the European XFEL project in Hamburg. [ABSTRACT FROM AUTHOR]

Abstract: With the scientific successes of the soft X-ray FLASH facility in Germany and the recent spectacular commissioning of the Linac Coherent Light Source at SLAC, free electron lasers are poised to take center stage as the premier source of tunable, intense, coherent photons of either ultra-short time resolution or ultra-fine spectral resolution, from the far infrared to the hard X-ray regime. This paper examines the state of the art in FEL performance and the underlying enabling technologies. It evaluates the state of readiness of the three basic machine architectures—SASE FELs, seeded FELs, and FEL oscillators—for the major X-ray science user facilities on the 5–10 years time scale and examines the challenges that lie ahead for FELs to achieve their full potential throughout the entire spectral range. In soft and hard X-rays, high longitudinal coherence, in addition to full transverse coherence, will be the key performance upgrade; ideas using laser-based or self-seeding or oscillators can be expected to be qualitatively superior to today''s SASE sources. Short pulses, from femtoseconds to attoseconds, can be realistically envisioned. With high repetition rate electron sources coupled to superconducting radiofrequency linear accelerators, unprecedented average beam brightness will be possible and many users would be served simultaneously by a single accelerator complex. [Copyright &y& Elsevier]

Abstract: High spectral resolution and nanometer sized foci of 3rd generation SR beamlines can only be achieved by means of ultra precise optical elements. The improved brilliance and the coherence of free electron lasers (FEL) even push the accuracy limits and make the development of a new generation of ultra precise reflective optical elements mandatory. Typical elements are wave front preserving plane mirrors (lengths of up to 1m, residual slope errors ∼0.05μrad (rms) and values of 0.1nm (rms) for the micro-roughness) and curved optical elements like spheres, toroids or elliptical cylinder (residual slope error ∼0.25μrad (rms) and better). These challenging specifications and the ongoing progress in finishing technology need to be matched by improved accuracy metrology instruments. We will discuss the results of recent developments in the field of metrology made in the BESSY-II-optics laboratory (BOL) at the Helmholtz Zentrum Berlin (HZB), by the use of vertical angle comparator (VAC) in use to calibrate the nanometer optical component measuring machine (NOM). The BESSY-NOM represents an ultra accurate type of slope measuring instruments characterized by an accuracy of 0.05μrad (rms) for plane substrates and 0.2μrad (rms) for significant curved surfaces. [Copyright &y& Elsevier]

Abstract: The FLASH free-electron laser at DESY, Hamburg, has been equipped with an infrared electromagnetic undulator which provides radiation in the mid- and far-infrared range. It will be used both for electron beam diagnostic purposes and as a powerful radiation source synchronized to the VUV and soft X-ray pulses of the FEL. This paper summarizes the undulator construction, the main design features, and the magnetic measurements undertaken to verify the device performance prior to installation. [Copyright &y& Elsevier]

Lasers have long played a critical role in the advancement of aerosol science. A new regime of ultrafast laser technology has recently be realized, the world's first soft x-ray free electron laser. The Free electron LASer in Hamburg, FLASH, user facility produces a steady source of 10 femtosecond pulses of 7-32 nm x-rays with 1012 photons per pulse. The high brightness, short wavelength, and high repetition rate (> 500 pulses per second) of this laser offers unique capabilities for aerosol characterization. Here we use FLASH to perform the highest resolution imaging of single PM2.5 aerosol particles in flight to date. We resolve to 35 nm the morphology of fibrous and aggregated spherical carbonaceous nanoparticles that existed for less than two milliseconds in vacuum. Our result opens the possibility for high spatial- and time-resolved single particle aerosol dynamics studies, filling a critical technological need in aerosol science. [ABSTRACT FROM AUTHOR]

Fermilab is building a cryomodule containing four 3.9 GHz superconducting radio frequency (SRF) cavities for the Free electron LASer in Hamburg (FLASH) facility at the Deutsches Elektronen-SYnchrotron (DESY) laboratory. Before assembling the cavities into the cryomodule, each individual cavity is tested at Fermilab's Horizontal Test Stand (HTS). The HTS provides the capability to test fully-dressed SRF cavities at 1.8 K with high-power pulsed RF in order to verify that the cavities achieve performance requirements under these conditions. The performance at the HTS of the 3.9 GHz cavities built for FLASH is presented here. [ABSTRACT FROM AUTHOR]

Abstract: FLASH, the free electron laser at DESY in Hamburg, is the first facility of its kind providing intense, femtosecond radiation pulses in the vacuum ultraviolet and soft X-ray range for user experiments. A broad science program has been started in summer 2005 with applications in atomic and molecular physics, cluster physics, the study of warm dense matter and surface dynamics, and diffraction imaging of small structures and biological samples with nanometer resolution. A selection of first experimental results is highlighted in this paper. [Copyright &y& Elsevier]

The article discusses the operation of the free-electron laser at Hamburg (FLASH) in Germany. The operation of the first FLASH for vacuum ultraviolet and soft x-ray radiation started in the summer of 2005. This is based on a single-pass free-electron laser (FEL) relying on the self-amplified spontaneous emission principle. The electron bunches of the FEL facility are generated by a laser driven photocathode radio frequency gun and accelerated by a superconducting linear accelerator.

This article reports that more than 90 participants from Europe, the U.S. and Japan gathered from April 27 to 29, 2005, in Berlin, Germany, to hold a lively international meeting on time-resolved soft X-ray science. The meeting continued the series of preceding workshops held in 2002 in Napa, California and in 2003 in Montreux, Switzerland. The aim of the workshop was to bring together the existing ultrafast laser community and the emerging ultrafast X-ray community in order lo discuss recent scientific highlights from both fields and to outline new directions for the application of ultrafast X-rays. In turn, it was hoped that this would help define the source characteristics of future ultrafast X-ray sources such as X-ray Free Electron Lasers.

The article offers information on X-ray science and the development of new equipment. Topics discussed include the Linac Coherent Light Source (LCLS) of the SLAC National Accelerator Laboratory, X-ray free-electron lasers (XFELs) built by Japan, and the Free-Electron Laser in Hamburg (FLASH) built by Germany. Also mentions about physicist Claudio Pellegrini who built machines at the SLAC.

The article offers information about the European x-ray free electron laser (XFEL) created by scientists from Hamburg, Germany.

Discusses the results of the first experiments with the free-electron lasers at the TESLA test facility at the high-energy physics research center in Hamburg, Germany. Strength of absorption of the laser radiation by atomic clusters; Nonlinear optical interaction between light and matter at ultraviolet wavelengths.

An endstation for pump-probe small-angle X-ray scattering (SAXS) experiments at the free-electron laser in Hamburg (FLASH) is presented. The endstation houses a solid-state absorber, optical incoupling for pump-probe experiments, time zero measurement, sample chamber, and detection unit. It can be used at all FLASH beamlines in the whole photon energy range offered by FLASH. The capabilities of the setup are demonstrated by showing the results of resonant magnetic SAXS measurements on cobalt-platinum multilayer samples grown on freestanding Si3N4 membranes and pump-laser-induced grid structures in multilayer samples. [ABSTRACT FROM AUTHOR]

Abstract: We present results of damage studies performed at the Free-Electron LASer in Hamburg (FLASH) on amorphous carbon (a-C). The experiment was performed in the total external reflection geometry representing the working configuration of X-ray mirrors. The 177eV photon laser beam was focused on a 40nm thin layer of a-C coated on a silicon substrate. Single-shot damages were produced at two different grazing angles (4.3° and 7.7°) below the critical angle (θ c=8°) calculated for this photon energy. The corresponding damage fluence thresholds were determined to be 43.7 and 74mJ/cm2. No evidence of delamination or mechanical damages (cracks) under grazing angles on the 40nm thin sample was observed. The results are compared with the results of the previous experiment done on thicker layers (900nm) of a-C with the same experimental conditions . [Copyright &y& Elsevier]

Abstract: We describe the optical pump–probe laser system at the XUV free-electron laser FLASH at DESY. A growing interest in optical laser pulses combined with the free-electron laser (FEL) beam for time-resolved experiments raise high demands on the stability of operation and knowledge on the status of synchronization between the XUV and optical pulses. In this publication we describe this system, the characterization of the optical pulses, synchronization and timing schemes as well as beamlines that transport beam to experimental stations. [Copyright &y& Elsevier]

Abstract: For the diagnostics of Free Electron Laser (FEL) it is necessary to obtain accurate information on the position and profile of the electron and/or the photon beam. For these tasks, one promising method is the use of the so-called Ionization Profile Monitor (IPM). An essential advantage of this method is that the FEL beam is not influenced by the IPM, so it is possible to analyze the beam parameters without beam destruction. Moreover, the monitor is able to determine the relative position and the spatial profile of the photon beam with the precision of a few μm. In this paper, the design and first implementation of an Ionization Profile Monitor as a photon diagnostic tool at the FLASH accelerator in Hamburg is presented. In addition, the first measurements taken at FLASH are analyzed and good measuring accuracy of the IPM is obtained. [Copyright &y& Elsevier]

Abstract: The Free Electron Laser at Hamburg (FLASH) facility at the Deutsches Elektronen-Synchrotron (DESY) is a linear accelerator that is operated in superconducting technology and produces soft X-ray laser light from 4.5 to 47nm. Several switching mirrors, located in the experimental hall, provide different beam lines with laser light, where the switching procedure lasts up to 1h and is performed at intervals of days or sometimes weeks. Since the experiments would be sufficient even with a lower repetition rate of the beam, a new kind of switching mirror has been invented. In this paper, the design and implementation of a fast switching mirror at FLASH are presented where focussed and unfocussed beam trains can be distributed between two beam lines with a frequency of up to 2.5Hz. The challenge lies in the precise repetition accuracy of position (few μm) and angle (about 1arcsec) of the mirror. In addition, first measurements taken at FLASH are analyzed and they show only little influence of the developed switching mirror on the beam position. [Copyright &y& Elsevier]

Abstract: A high resolution online grating spectrometer has been set up at the free electron laser in Hamburg FLASH at DESY in Hamburg. This new photon diagnostic device allows to parasitically measure the spectral distribution of the FEL laser pulses on a single shot basis and therefore gives complementary spectral and temporal pulse information for user experiments and FEL operation. The spectrometer combines a plane mirror and two plane variable line spacing (VLS) gratings and is installed at the non-monochromized beamline branch at FLASH. In contrast to a standard grating the blaze angle is optimized for the zero-order radiation transferred to the experimental stations, leaving approximately 1–10% intensity for recording the wavelength in the spectrometer. The detector, an intensified CCD camera imaging the dispersed beam on a Ce:YAG crystal, can follow the focal plane of the gratings covering a wavelength ranging from 6 to 60nm. The resolving power of the spectrometer is expected to range from 500 to 8000 depending on the FEL wavelength. [Copyright &y& Elsevier]

The free electron laser (FEL) FLASH at DESY in Hamburg is the first x-ray FEL ever built. Many new developments were necessary in order to exploit the unique properties of this novel light source for scientific experiments. The facility has constantly been improved and several major upgrades have been made or are currently underway. This paper reviews the main characteristics of the user facility as well as the major developments and upgrades. [ABSTRACT FROM AUTHOR]

Multiple ionization (MI), induced by a few EUV photons at energies of 28.2 eV, 38 eV and 44 eV from FLASH (the free-electron laser at Hamburg), has been studied for atoms (He, Ne, Ar) and N2 molecules utilizing our multi-hit coincident technology--the reaction microscope. At comparably low intensities of I [?] 1011-1013 W cm[?]2 we find the non-sequential (NS) MI mechanism dominating Ar3+ and Ar4+ production. Inspecting recoil ion and electron momentum distributions evidence is provided (i) for preferential back-to-back emission of electrons for NS double ionization of He and (ii) for angular entanglement between two outgoing electrons in sequential ionization (SI). In contrast to atoms, SI is observed to be most effective for MI of N2 molecules at an intensity of [?]1013 W cm[?]2 leading, among others, to N2+2 - N+ + N+, N3+2 - N2+ + N+, N4+2 - N2+ + N2+ Coulomb explosion channels. Fragment ion momentum distributions are investigated and are demonstrated to allow tracing SI pathways. [ABSTRACT FROM AUTHOR]

High flux extreme ultraviolet (XUV) sources like the free electron laser (FEL) in Hamburg (FLASH) offer the possibility of diffractive imaging of small objects. Irrespective of whether the diffraction is based on the detection of photons or photoelectrons, it is required that the measurement is done in the reference frame of the molecule meaning that, for a sample of several molecules, it is necessary to pre-align the molecules in the sample. As a step towards performing molecular frame diffraction experiments, we report experiments on field-free molecular alignment performed at FLASH. The impulsive alignment induced by a 100 fs near-infrared laser pulse in a rotationally cold CO2 sample is characterized by ionizing and dissociating the molecules with a time-delayed XUV-FEL pulse. The time-dependent angular distributions of ionic fragments measured by a velocity map imaging spectrometer exhibit rapid changes associated with the induced rotational dynamics. The experimental results show hints of a dissociation process that depends nonlinearly on the XUV intensity. [ABSTRACT FROM AUTHOR]

An interview with scientist Mikhail Yurkov is presented. Yurkov claims that free-electron laser is related to vacuum-tube devices which offers an alternative approach to create short pulses of high-intensity light. He states that the device has an electromagnetic wave which is faster than the electrons. He argues that the free-electron laser facility in Hamburg, Germany can produce a gigawatt-level, laser-like radiation pulses which shows a solid foundation in terms of radiation.

Reports on the decision of Germany's science ministry to half the cost of x-ray free electron laser from German Electron Synchroton (DESY) in Hamburg. Comment of DESY Director Albrecht Wagner; Role of superconducting accelerator cavities; Plan of Germany to participate in a next-generation linear collider.

Reports on the German government's proposal to construct an X-ray Free-Electron Laser Laboratory in Hamburg. Investment cost of the project.

We have proposed to build a 100 T/10 ms, 70 T/100 ms, 60 T/I s pulsed field user facility with a 50 MJ capacitor bank at the Forschungszentrum Rossendorf near Dresden. This would provide the appealing possibility to have access to Zeeman energies in the energy range of the infrared free-electron-lasers (5 µm to 150 µm; 2 ps; cw; >10 W) now under construction at the radiation source ELBE (superconducting electron linear accelerator; 40 MeV; 1 mA; 2 ps; cw) in Rossendorf. The work is accompanied by computer simulations of the planned coil systems, of the power supply, and by the development of high-strength conductors aiming at a tensile strength of about 1.5 GPa at δ = δ Cu/2 (microcomposite CuAg alloys and Cu-steel macro compounds). With a view of gaining experience in the construction and operation of pulsed magnets, a pilot pulsed field laboratory was established at the Institute of Solid State and Materials Research Dresden (IFW Dresden). The laboratory includes short pulse magnets with peak field up to 60 T in a 24 mm bore and a rise time of about 10 ms (coil from NHMFL, Tallahassee), and a 40 T long pulse magnet with 24 mm bore and rise time of about 80 ms (coil from METIS, Leuven). The repetition rate of 20 min between pulses is limited by the cooling time of the coils. The coils are energized by a 1 MJ, 10 kV capacitor bank with some special features. With this set-up measurements of magnetization and magnetotransport on 4f-electron systems, for example RECu2, have been carried out in the temperature range of 1.5 to 300 K and at fields up to 52 T using high precision pick-up coils. [ABSTRACT FROM AUTHOR]