Ultrafast X-ray absorption spectroscopy (UXAS) offers the opportunity to investigate function-structure relationships of
complex organic molecules or biological functional subunits without the need of crystallization. Of special interest from
the viewpoint of structural biology is the region of K-edges of transition metals between 5 and 10 keV. Regardless of
successful application of time-resolved diffraction techniques to investigations of crystal dynamics using synchrotron
and laboratory based sources there are only very few examples for application of UXAS to revealing the structural
dynamics in biomolecular systems. This is mainly caused by the lack of broadband ultrafast x-ray sources as well as of
appropriate optics adapted to these sources. Due to the long-data-recording time in UXAS experiments the sample
integrity is mainly determined by the average power of the pump pulses inducing the structural changes. Using a fixed
energy of the pump pulse the latter one is determined by the repetition rate of the pump laser. In this paper we discuss the
prospects of UXAS comparing fs laser plasma sources with different repetition rates in combination with tailor-made
optics based on highly annealed pyrolytic graphite (HAPG).
We have developed a 0.1-Hz-repetition-rate, 30-fs, 1.5-PW Ti:sapphire laser system for the research on high field physics. In this paper, we describe the design and output performance of the PW Ti:sapphire laser and its applications in the generation of relativistic high order harmonic generation and the acceleration of charged particles (protons and electrons). In the experiment on relativistic harmonic generation, the harmonic order dramatically extended up to 164th that corresponds to 4.9 nm in wavelength, and the dramatic extension was explained by the oscillatory flying mirror model. Recently, we could accelerate protons up to 45 MeV from a 10-nm polymer target and show the change in the acceleration mechanism from target normal sheath acceleration to radiation pressure acceleration. The femtosecond high power laser system is a good candidate for developing a compact electron accelerator as well. The generation of multi-GeV electron beam was observed from an injection scheme when a PW laser pulse was focused by a long focal length spherical mirror.
Beams of energetic negative ions and neutral atoms are obtained from water and ethanol spray targets irradiated by high
intensity (5×1019 W/cm2) and ultrashort (50 fs) laser pulses. The resulting spectra were measured with the Thomson parabola spectrometer, which enabled absolute measurements of both: positive and negative ions. The generation of a beam of energetic neutral hydrogen atoms was confirmed with CR-39 track detectors and their spectral characteristics have been measured using time of flight technique. Generation is ascribed to electron-capture and -loss processes in the collisions of laser-accelerated high-energy protons with spray of droplets. The same method can be applied to generate energetic negative ions and neutral atoms of different species.
Results of energy deposition measurement in interaction between an ultra-short laser pulse and nanostructured
target are described. As a target we used carbon nanotubes and multilayer graphene deposited on a sapphire
wafer surface and embedded in a layer of protein. A 25 fs, p-polarised pulses from a 1 kHz-Ti;sapphire laser
of energy up to 3 mJ were focused to give intensity up to 2×1016 W/cm2 on a target positioned within an
integrating sphere. The absorption measured showed a level in excess of 80 %, increasing with the intensity. The
results suggest that the host material (lysozyme) is responsible for the breakdown while the embedded material
contributes dominantly to the absorption.
Extreme Light Infrastructure (ELI), the first research facility hosting an exawatt class laser will be built with a joint
international effort and form an integrated infrastructure comprised at last three branches: Attosecond Science (in
Szeged, Hungary) designed to make temporal investigation at the attosecond scale of electron dynamics in atoms,
molecules, plasmas and solids. High Field Science will be mainly focused on producing ultra intense and ultra short
sources of electons, protons and ions, coherent and high energetic X rays (in Prague, Czech Republic) as well as laserbased
nuclear physics (in Magurele, Romania). The location of the fourth pillar devoted to Extreme Field Science, which
will explore laser-matter interaction up to the non linear QED limit including the investigation of vacuum structure and
pair creation, will be decided after 2012. The research activities will be based on an incremental development of the light
sources starting from the current high intensity lasers (APOLLON, GEMINI, Vulcan and PFS) as prototypes to achieve
unprecedented peak power performance, from tens of petawatt up to a fraction of exawatt (1018 W). This last step will
depend on the laser technology development in the above three sites as well as in current high intensity laser facilities.
Laboratory based X-ray lasers (XRL) exhibit a broad application potential in material sciences, imaging, spectroscopy and laser plasma diagnostics if two main issues are solved: a stable, well defined output of the system and a high repetition rate for fast data acquisition. During the last few years using the grazing incidence pumping (GRIP) scheme an pump energy level as low as 1 J was demonstrated for saturated XRL operation. This pump energy could be provided in principle even by commercially available Ti:Sa laser systems. However, the repetition rate of these systems is limited to
10 Hz and the output stability of the XRL follows that of the pumping laser. To overcome this situation a dedicated high
repetition rate XRL pumping laser will be introduced here. This concept is based on a fully diode pumped solid state laser using thin Yb:YAG disks as active material. In this paper we report about the first phase of the project aimed at a high average power XRL user station based on the GRIP scheme.
Output characteristics of an X-ray laser based on the GRIP geometry are analysed by both the theoretical and experimental methods. Detailed analysis of the last experiments on GRIP X-ray lasers with a single profiled pulse is given as well as the consequences of this pump variant for the injector-amplifier scheme being developed. Especially dynamics of the gain coefficient and the spontanous emission flux are important for the injector-amplifier scheme. Discussion on medium dynamics and kinetics is supported by numerical simulations. Additionally, some preliminary results on seeding a
Ni-like soft X-ray with high harmonic from neon at 13.9 nm are presented.
The present trends in the development work on X-ray lasers are shown and discussed on a background of a brief history of the collisionally pumped X-ray lasers. The presentation is focused on two variants of the transient inversion pump method succesfully applied in the experiments - slab target geometry and single profiled laser pulse. Recently, another scheme referred to as GRIP (GRazing Incidence Pumping) has been proposed and demonstrated. This pump geometry opens the new real possibility to construct a repetitive X-ray laser. Some
aspects of the pump scheme implementation are discussed in detail. Finally, a specific injector-amplifier system giving a new perspective on the future of X-ray lasers is dicussed briefly as well.
Recent development in the field of X-ray lasers is shown and discussed starting from transient inversion scheme in a double-pulse arrangement. Different variants of this scheme are discussed in detail from the point of view of reduction in the pump energy. The discussion is concentrated on the kinetic aspect of the plasma created
and heated by a profiled pulse. Recently, a scheme referred to as GRIP (GRazing Incidence Pumping) has been proposed and demonstrated. This pump geometry opens a new real possibility to construct a repetitive X-ray laser. Some aspects of the pump scheme implementation are analysed. Finally, a specific injector-amplifier system giving a new perspective on the future of X-ray lasers is dicussed briefly as well.
Technological reasons stimulated enormous interest in the spectral range between 10 nm and 15 nm. One of the most important, apart from the potential to be applied in the microlithography, was the existence of the high-efficiency, spectrally highly selective (narrow-band) reflective multi-layer (ML) optics in this spectral range. Applying these optics to plasma based XUV (extreme ultra violett) sources the debris from the plasma is a serious problem. For transmissive multi-layer optics we have additionally the low figures of merit. For example, the best beam splitters have an efficiency of about 30% (energy in both parts of the splitted beam). This type of element is crucial for efficient single-shot interferometry being the main application using table-top soft x-ray lasers.
We applied capillary optical elements, to our knowledge for the first time, to XUV radiation at 13.9 nm. These optical elements help overcome the limits discussed above or at least remarkably reduce the existing difficulties. A capillary beam splitter and a focussing capillary were applied to an incoherent XUV radiation source. For the beam splitter we measured a throughput of about 80%. With the focussing capillary we obtained a spot size of 27 μm (FWHM) with a gain (intensity in the focal spot compared to the intensity behind a pinhole of the focal spot size) of 600. Advantages and disadvantages of these optics in the discussed spectral range are analyzed.
Thin films of highly oriented pyrolytic graphite (HOPG) give the opportunity to realize crystal optics with arbitrary geometry by mounting it on a mould of any shape. A specific feature of a HOPG is its mosaicity accompanied by mosaic focusing and high integral reflectivity. These characteristics are of interest for compact x-ray diagnostic tools and spectrometers. Another interesting feature is, due to the mosaic spread of the HOPG crystals, that it is possible also with a beam of low divergence to record a spectrum in a broad energy range even within one laser shot. That means that the HOPG spectrometer can act as a polychromator. The latter feature is important if irreversible changes in samples should be investigated or, e.g., if in time-resolved pump-probe experiments a spectrum should be recorded before sample degradation takes place due to high pump intensities. Different design considerations for a compact HOPG-spectrometer based on experimental and theoretical studies will be presented. For applications in plasma diagnostics and XAFS (x-ray absorption fine structure) the attainable energy resolution plays a central role and has been intensively investigated. The results of our investigations demonstrate that HOPG can be used as powerful optics for x-ray diagnostics as well as for x-ray absorption and emission spectroscopy.
Some prospects for development of collisional X-ray lasers with a high repetition rate based on the output characteristics of a transient Ni-like Ag soft X-ray laser pumped by a single picosecond laser pulse are analysed. Such problems as target technology, new driver development and the active medium parameters are discussed.
Output characteristics of a transient Ni-like Ag X-ray laser pumped by a single picosecond laser pulse are demonstrated. The small-signal gain coefficient, beam divergence, output pulse profile and beam dimensions in the near-field were measured. The influence of the pump pulse structure on the lasing process and the output signal is analysed theoretically.
The state-of-the-art and the trends in development of table-top soft x-ray lasers (XRLs) with a special emphasis on the work of the Max Born Institute (MBI) are presented. Both, basic physics and some features of the output radiation crucial for applications are discussed as well.
With the development of EUV lithography there is an increasing need for high-accuracy at-wavelength metrology. In particular, there is an urgent need for metrology at optical components like mirrors or masks close to the production line. Sources for metrology have to fit different demands on EUV power and spectral shape than sources for steppers systems. We present the results of the radiometric characterization of a laser produced plasma (LPP)-source, newly developed at Max-Born-Institute Berlin for use in an EUV reflectometer. It is operated with a high-power pointing-stabilized laser beam (energy per pulse up to 700 mJ, 10 ns pulse duration, < ± 25 μrad pointing stability) at 532 nm which is focussed on a rotating Au target cylinder. The incident angle of the laser beam is set to 63°, the detecting angle 55° to the target normal. The source has been characterized regarding spectral photon flux, source size and source point stability. Two independently calibrated instruments, an imaging spectrometer and a double multilayer tool for in-band power measurements were used to obtain highly reliable quantitative values for the EUV emission of the Au-LPP source. Both instruments were calibrated by Physikalisch-Technische Bundesanstalt in its radiometry laboratory at the electron storage ring BESSY II. We obtained a source size of 30 μm by 50 μm (2s horizontal by vertical) and a stability of better than 2s=5 μm horizontally and 2s=9 μm vertically. A spectral photon flux of 1*10e14 /(s sr 0.1 nm) at 13.4 nm at a laser pulse energy of 630 mJ is obtained. The shot-to-shot stability of the source is about 5% (1s) for laser pulse energies above 200 mJ. For pulse energies between 200 mJ and 700 mJ, there is a linear relation between laser pulse energy and EUV output. The spectrum shows a flat continuos emission in the EUV spectral range, which is important for wavelength scanning reflectometry. High stability in total flux and spectral shape of the plasma emission as well as low debris was only obtained using a new target position for each shot. There is also a trade off between source size and EUV power. For a slightly defocused laser, an increase in EUV power up to a factor of two is obtained, while the source size also increases by about a factor of two. It is shown that an Au-LPP source provides spectrally flat reproducible emission with sufficient power at low debris conditions for the operation of a laboratory based EUV reflectometer.
The quality assurance for production of optical components for EUV lithography strongly requires at-wavelength metrology. Presently, at-wavelength characterizations of mirrors and masks are done using the synchrotron radiation of electron storage rings, e.g. BESSY II. For the production process of EUV optics, however, the immediate access to metrology tools is necessary and availability of laboratory devices is mandatory. Within the last years a stand alone laboratory EUV reflectometer for large samples has been developed It consists of a laser produced plasma (LLP) radiation source, a monochromator and a large goniometer systme. The manipulation system of the reflectometer can handle samples with diameters of up to 500 mm, thicknesses of up to 200 mm and weights of up to 30 kg. The wavelength can be varied from 10 nm to 16 nm. The spot size on the sample surface is about 2mm. The angle of incidence can be varied from 3° to 60°. In this paper, we describe the laboratory reflectometer in detail and discuss the achieved performance. First measurements of 4 inch mirrors are presented and discussed in comparison to the results obtained at the PTB soft x-ray radiometry beamline at BESSY II.
In this contribution we describe a laser plasma source for Extreme Ultraviolet Lithography (EUVL) based on a Xe-cluster target. Although Xe-clusters as target systems for EUVL are known for some time, no attempts have been made for a systematic study of the influence of the laser parameters on the EUV-emission at a well defined Xe-aggregation.
The MBI burst mode laser used offers some unique features: Within one burst (duration 800 μs) the repetition rate of single laser pulses can be adjusted between 30 and 1000 kHz. The average power per burst is about 5 kW at the maximum energy of 4 J/burst. The pulse duration of a single pulse can be adjusted from the ps- to ns-range.
We have examined the EUV-emission from the Xe-cluster target within one burst of the laser as a function of single pulse intensity and repetition rate. Based on the measured EUV-spectra the conversion efficiency at 13.4 nm wavelength in dependence on pulse duration in the range from 30 ps to 3 ns were estimated.
We present a review of new progress performed in several laboratories (Laboratoire pour l'Utilisation des lasers Intenses, Rutherford Appleton Laboratory, Prague Asterix Laser System, Institute of Laser Engineering, Laboratoire d'Optique Appliquee). Concerning the realization of x-ray lasers sources, using different laser pumping techniques (600 ps, 100 ps, ns/ps, OFI) and the optimization of their optical properties, using curved and plane half-cavity mirrors. In parallel of these developments, we present the main results obtained with x-ray laser in interferometry applications. These studies concern on the one hand the Michelson interferometry with an x-ray laser emitting at 13.9 nm (recently realized at LULI), and on the other hand the Fresnel bi-mirror with an x-ray laser emitting at 21.2 nm (recently realized at PALS).
This paper summarizes our recent progress achieved in the characterization and understanding of the Ni-like Ag transient x-ray laser pumped under traveling wave irradiation. At the Rutherford Laboratory CPA laser facility, we measured the temporal history of the 13.9 nm laser pulse with a high-resolution streak camera. A very short, approximately 2 ps x-ray laser pulse was directly demonstrated for the first time. More recently we carried out an experiment at the LULI CPA laser facility. Several diagnostics that recorded the plasma emission at the XRL wavelength or in the keV range indicate the presence of small-scale spatial structures in the emitting XRL source. Single-shot Fresnel interferograms at 13.9 nm were successfully obtained with a good fringe visibility. Strong lasing was also observed on the Ni-like 4f-4d line at 16 nm.
The Gesellschaft fuer Schwerionenforschung (GSI, Society for Heavy Ion Research) is currently the leading facility in the production of radioactive isotopes. Nuclear properties like charge radii, spin, and magnetic moments of exotic nuclei provide important data for testing of nuclear models. These properties are usually accessed by laser spectroscopy, which requires photon energies of around 100 eV in the case of lithium-like ions. We propose to use a transient gain X-ray laser (XRL) at the experimental storage ring (ESR) to perform this kind of spectroscopy. In this article we describe the planned experiments and give an overview of the current construction at GSI.
Analysis of the capillary discharge plasma as a possible preformed active medium of the collisionally pumped soft X-ray lasers (XRLs) working within the transient inversion scheme is presented. Temporal dependence of the plasma column resistance is compared with a 1D-model used in the numerical simulations of the plasma dynamics. Numerical analysis of the laser absorption determines the pump parameter range for efficient excitation of the longitudinally pumped hybrid XRLs.
Large Xe-clusters have been excited with 50 fs and 2 ps pulses from a Ti:Sa multi - TW laser at 800 nm wavelength. Additionally a 10 ns Nd:YAG laser at 1064 nm wavelength was used to heat Xe-cluster/gas and a liquid Xe-spray target. Absolute yield measurements of EUV-emission in a wavelength range between 10 nm and 15 nm in combination with target variations were carried out. The ps-laser pulse has resulted in about 30 percent enhanced and spatially more uniform EUV-emission compared to fs-laser excitation. Similar emission has been obtained with ns-pulse exposure of different target modifications which also act back to the EUV-source size. Absolute emission efficiencies at 13.4 nm of up to 0.8 percent in 2pi sr and 2.2 percent bandwidth were measured.
In this article we describe a laser plasma source for Extreme Ultraviolet Lithography (EUVL) based on a liquid water jet target. Although jet targets are known for some time now, no attempts have been made to prove the functionality of the target under conditions similar to an EUVL production-line facility, that means illumination with high average power laser systems (in the multi-kW regime) at repetition rates in the kHz region. Such systems are currently under development. We used the MBI-burst laser to simulate these extreme illumination conditions. We examined the hydrodynamic stability of the target as a function of the laser repetition rate at different average laser powers (0.6kW and 5kW per burst). Additionally, the dependence of the conversion efficiency on pulse duration in the range from 30ps to 3ns was investigated. From our results one can conclude parameters for future design of driver lasers for EUVL systems.
M. Roth, Bruno Becker-de Mos, R. Bock, Stefan Borneis, Herbert Brandt, C. Bruske, John Caird, E. Dewald, C. Haefner, D. Hoffmann, Mikhail Kalachnikov, H.-J. Kluge, Ferenc Krausz, Thomas Kuehl, Grant Logan, Dieter Marx, Paul Neumayer, Peter Nickles, M. Perry, K. Poppensieker, Irene Reinhard, Wolfgang Sandner, Roland Sauerbrey, A. Tauschwitz, Ingo Will
The unique combination of an intense heavy ion beam accelerator and a high energy laser opens the possibility of exploring new physics taking advantage of the synergy of both facilities. A variety of new fields can be addressed with this combination in plasma physics, atomic physics, nuclear- and astro-physics as well as material research. In addition, using CPA-technology, laser pulses with a pulse power of up to a petawatt opens the door to explore the regime of fully relativistic plasmas. Therefore the Gesellschaft fuer Schwerionenforschung is augmenting the current high intensity upgrade of the heavy ion accelerator facility with the construction of PHELIX. Designed with two pulse-generating front ends and send to multiple experimental areas PHELIX will serve as a highly versatile laser system for various applications. In this report, we present the design of the laser system and some key experiments that can be performed with this combination for the first time.
The absolutely calibrated K-shell spectra emitted form short-living aluminum plasma at laser intensities of 5 by 1015- 4 by 1018 W/cm2 are reported. The experiments performed with the constant energy, variable-length laser pulse are modeled by the 1D hydrodynamics code including non-linear resonance absorption of the laser radiation, fast electron acceleration and energy transfer into the target. The characteristic features of the measured and the post- processed spectra are outlined; the scaling rules for the conversion efficiency of the laser radiation into the line x-ray emission are discussed.
We discuss the results of the studies of Z-pinch sources for photolithographic applications developed by Lambda Physik. We also report the results of fundamental investigations pursued by Fraunhofer-Institut fuer Lasertechnik. Friedrich- Schiller Universitat Jena, Max-Born Institut Berlin, and Gustav August Universitat Gottingen. The later efforts are supported by German government and steered by the industrial consortium led by Lambda Physik.
Results of measurements on a plasma created by a discharge in a sulfur capillary and irradiated by a picosecond laser pulse are presented. Time-resolved transmission measurements and the corresponding XUV spectra are discussed. It is found that the transmission of the laser through the capillary decreases abruptly after the peak of the discharge current, and that the profile of the output laser beam is symmetrized before the onset of the opaque period. The spectra are evidently affected by the laser pulse and show significant intensification on the 3p-3s transition in Ne-like sulfur at 60.84 nm. This observation, combined with the fact that the emission of this line appears spatially displaced from all other lines in the detector and presents a lower divergence, suggest that lasing is occurring.
M. Roth, R. Bock, U. Funk, Matthias Geissel, D. Hoffmann, Thomas Kuehl, Grant Logan, Jurgen Meyer-ter-Vehn, Peter Nickles, Michael Perry, Wolfgang Seelig, Christian Stoeckl, S. Stoewe, W. Suess
For the development of a heavy ion driven inertial confinement fusion scenario a detailed knowledge of the interaction processes of the ions with the converter material is crucial. As this converter will be predominantly in the plasma state one of the main topics of the plasma physics group at Gesellschaft fuer Schwerionenforschung (GSI) is the interaction of heavy ions with dense hot plasma. Based on the latest result on interaction experiments with laser generated plasma targets presented here and concerning the high current upgrade of GSI a new high energy laser system is proposed. It will serve as a driver for interaction experiments with heavy ions as well as a diagnostic tool for heavy ion generated plasmas. In addition, with the combination of high current heavy ion beams and intense lasers innovative, fundamental research in the field of high energy density physics will be accessible for the first time.
Novel scheme providing for 7 J Nd-glass subpicosecond MultiTeraWatt laser pulse shortening down to 200 fs with intensity rise time of 100 fs for 2 order of magnitude and prepulse suppression down to quantum noise level are proposed. Non-linear optical two-stage converter consists of sequential second harmonic generator and stimulated raman scattering oscillator-amplifier.
The use of multi-pulse irradiation of neon-like ions has been shown to produce orders-of-magnitude enhancement of x-ray laser output. Recent results obtained at the Rutherford Appleton Laboratory are reviewed with an emphasis on understanding the reasons for the enhancement. Simulations with the fluid and atomic physics code EHYBRID are used to show that enhancement occurs because of a spatial enlargement of the gain region and consequent better propagation of the x- ray laser beam along the gain region.
Low pump energy transient gain x-ray lasers in Ti at 32.6 nm, 30.15 nm, in V at 30.4 nm and Ge at 19.6 nm using picosecond pulse heating of a long pulse preformed plasma of neonlike ions has been realized for the first time. Gain saturation was demonstrated in Ti and Ge XRL. Results of pump consumption, x- ray divergence and output energy are given.
Numerical modeling of transient inversion and capillary discharge x-ray lasers were performed for the purposes of understanding of recent experiments, improving the laser efficiency and planing their further development. The first demonstration of saturation of a low pump energy x-ray laser utilizing a transient inversion mechanism on the 3p - 3s transition at 32.63 nm in Ne-like Ti has been confirmed. A close to saturation amplification was simultaneously achieved for the 3d - 3p, J equals 1 - 1 transition at 30.15 nm. Small signal effective transient gain coefficients of g approximately equals 46 cm-1 and approximately 35 cm-1 and effective gain-length products of 16.7 and 16.9 for these lines were obtained. Experiments and calculations demonstrate that it is possible to achieve saturated laser action in a transient regime with Ne-like Ti for a pump energy as low as approximately 5 J. With such energies just recently the lasing on Ni-like Pd at 14.7 nm has been achieved. MHD simulations of capillary discharges were performed for several elements with shorter lasing wavelengths. A new approach which intends to combine advantages of electrical discharge plasma preparation with CPA-laser excitation was investigated. It will enable a kind of x-ray lasers to be built with ultrashort pulse duration and the high efficiency. In this case the well preformed cylindrical shell of discharge plasma and the transient population inversion combined with the traveling-wave excitation will enable to achieve lasing at much shorter wavelengths.
A collisionally excited transient population inversion XUV-laser on [Ne]-like titanium has been realized using a table top terawatt laser. At the lasing wavelength of 32.6 nm a high gain value of 19 plus or minus 1.4 cm-1 has been obtained using plasma columns of 2 to 5 mm length.
Laser energy requirements for the creation of active plasma media with Ne- and Ni-like ions with a `long' subnanosecond prepulse (100 - 1000 ps) and a `short' picosecond main pulse (0.1 - 10 ps) have been determined for foil and low density targets (foams, gases, vapors, etc.). RADEX hydrodynamics and atomic kinetics calculations show that X-ray laser action in the 200 - 400 A can be obtained with 1 - 2 J in 100 - 1000 ps prepulse followed of an approximately 1 ps pulse of similar energy. Transient gains of approximately 100 cm-1 level have been calculated. For the wavelengths 38 - 46 A (`red' edge of `water window' spectral band) a short pulse of only approximately 5 - 10 J is required.
X-ray emission and laser absorption have been studied with pulses of 1.5 ps duration irradiating solid targets at intensities of 1018 W/cm2. Absorption as a function of the incident laser flux and the irradiation angle in respect to the polarization reaches maximal values of 50% and is discussed in comparison to theoretical works published recently. This gives basic guidelines for efficient x-ray production which we have investigated in the hard (Ex > 50 keV, Bremsstrahlung) and soft (Ex < 1 keV, line emission of ions) spectral region. The feasibility of a short pulse and a plasma source with an extension of only some microns is proofed with an experiment using a spherically bent Mica crystal for collimation of the x-ray beam. The brightness and divergence of that x-ray beam being relevant for applications are given.
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