Many applications in the field of X-ray analytics require an X-ray beam with a high flux density at the sample position. Examples for these applications are single crystal diffraction or micro-diffraction to name but a few. An X-ray system comprising of an X-ray source with a small electron beam spot size combined with a diffracting 2-dimensional multilayer mirror is the ideal source for these applications. The mirror collects many photons from the small source, especially when it is mounted as close to the source as possible.
To achieve the goal of a high flux density the spot size on the anode of the X-ray tube should be as small as possible with a simultaneous increase of the X-ray power. A risk is the melting of the anode due to weak heat dissipation. At the same time the figure error of the multilayer mirror should be as low as possible. Large figure errors will increase the spot size of the X-ray beam at the sample position.
The increasing importance of X-ray diffractometry with one- and two-dimensional detectors for materials research has
lead to a rising demand for highly intense X-ray sources enabling the analysis of very small and weakly scattering
samples in the home-lab within a reasonable time frame. As a result, various microfocusing sealed tube X-ray sources
with focal spot sizes below 50μm are now available. Potential applications of the low-maintenance, high-brilliance
microfocus source IμS, which are equipped with different two-dimensional beam shaping multilayer optics, will be
shown. With the instrumentation that is now available, more and more crucial measurements like gracing incidence
small angle X-ray scattering or stress and pole figure measurements can be carried out in the lab, and even in-situ during
dynamic processes. Some ideas on new instrumental set-ups for customized X-ray analytics will also be shown.
X-ray sources according to the principle of the "free electron laser" (FEL), will in future, be able to provide bright
radiation with pulses in the femtosecond range. Even nowadays, home-lab X-ray sources with very short pulses in the
sub-picosecond range are already available for lab experiments. These laser-based sources need different kinds of optics
to direct the emitted X-rays onto the samples. On the one hand, the optics should transfer as much flux as possible and
on the other hand, the brilliance and timestructure of the source should not be reduced too much. These requirements are
fulfilled with 2-dimensional beam shaping multilayer optics. Their design, production and their influence on the shape of
the X-ray beam will be explained in this contribution. The optics consist of bent substrates with shape tolerances below
100 nm, upon which multilayers are deposited with single layer thicknesses in the nanometer range and up to several
hundreds of pairs of layers. Furthermore, these multilayers were designed with lateral thickness gradients within ± 1%
deviation of the ideal shape. This means that a deposition precision in the picometer range is required. We use
magnetron sputtering methods for deposition, optical profilometry in order to characterize the shape of the optics and X-ray
reflectometry to characterize the multilayers.
Selected aspects of simulation, preparation and characterization of total reflection and multilayer X-ray optics will be
discussed. The best multilayer is found by calculating the optical properties of the coating. Sophisticated improvements
in deposition technology allow the precise realization of the specified parameters when manufacturing the X-ray optics.
The quality of the shape of the substrate for the optics is measured with the aid of profilometry. X-ray reflectometry
measures both film thickness as well as their lateral gradient. Last but not least we will be showing results of the
development of carbon coatings as total reflection mirrors for FEL (free electron laser) sources. Over the past years we
have developed optimized optics for the XUV range up to 200 eV. First FEL irradiation tests have shown that carbon
coatings offer high reflectivity > 95%, high radiation stability, good uniformity in thickness and roughness. An
optimized coating of two stripes for different beam energies was produced especially for a tomography beamline, where
a Ru/C multilayer was chosen for energies between 10 and 22 keV and a W/Si multilayer for energies between 22 and 45 keV.
The multi-mJ, 21-nm soft-x-ray laser at the PALS facility was focused on the surface of amorphous carbon (a-C) coating, developed for heavily loaded XUV/x-ray optical elements. AFM (Atomic Force Microscopy) images show 3-micrometer expansion of the irradiated material. Raman spectra, measured with an Ar+ laser microbeam in both irradiated and unirradiated areas, confirm a high degree of graphitization in the irradiated layer. In addition to this highfluence (~ 1 J/cm2), single-shot experiment, it was necessary to carry out an experiment to investigate consequences of prolonged XUV irradiation at relatively low fluence. High-order harmonic (HH) beam generated at the LUCA facility in CEA/Saclay Research Center was used as a source of short-wavelength radiation delivering high-energy photons on the surface at a low single-shot fluence but with high-average power. a-C irradiated at a low fluence, i.e., < 0.1 mJ/cm2 by many HH shots exhibits an expansion for several nanometers. Although it is less dramatic change of surface morphology than that due to single-hot x-ray-laser exposure even the observed nanometer-sized changes caused by the HH beam on a-C surface could influence reflectivity of a grazing incidence optical element. These results seem to be important for estimating damages to the surfaces of highly irradiated optical elements developed for guiding and focusing the ultraintense XUV/x-ray beams provided by new generation sources (i.e., VUV FEL and XFEL in Hamburg; LCLS in Stanford) because, up to now, only melting and vaporization, but not graphitization, have been taken into account.
We present an optic for laboratory Mo-Kalpha single crystal diffraction systems. The optic is comprised of two elliptically bent focusing multilayers, which are arranged in the Montel scheme. The paper shows the design and performance of the optic. A comparison with a graphite monochromator shows a five-fold intensity enhancement. Especially small and weakly diffracting crystals benefit from the large intensity produced by the optic, as illustrated by diffraction analyses.
We present recent developments in the production of X-ray multilayer optics for Cu Kα laboratory single crystal diffraction equipment for protein crystallography and structural proteomics. The paper shows design, simulations and properties of Montel optics comprised of two elliptically bent focusing multilayers, optimized for the use with modern rotating anode X-ray generators. The multilayers are sputter deposited with a graded d-spacing along the length of the substrate.
The various beam properties such as flux density and divergence are investigated in detail. After optimization of the optic for a state-of-the-art rotating anode x-ray generator, we obtain a flux density of 1 x 1010 photons/s/mm2. Results for a typical protein structure will be shown, illustrating the advantage of Montel optics in the field of single-crystal diffraction and protein crystallography for life sciences.
As part of the TESLA (TeV-Energy Superconducting Linear Accelerator) project a free electron laser (FEL) in the XUV (Extreme Ultra-Violet, (6-200 eV)) and X-ray (0.5-15 keV) range is being developed at DESY (Deutsches Elektronen Synchrotron, Hamburg). At the TESLA Test Facility (TTF) a prototype FEL has recently demonstrated maximum light amplification in the range of 80 nm to 120 nm. It is expected that the FEL will provide intense, sub-picosecond radiation pulses with photon energies up to 200 eV in the next development stage. In a joint project between DESY and GKSS, thin film optical elements with very high radiation stability, as required for FEL applications, are currently being developed.
Sputter-deposited amorphous carbon coatings have been prepared for use as total reflection X-ray mirrors. The optical characterization of the mirrors has been carried out using the soft X-ray reflectometer at HASYLAB (Hamburger Synchrotronstrahlungslabor) beamline G1. The reflectivity of the carbon films at 2 deg incidence angle is close to the theoretical reflectivity of 95.6 %, demonstrating the high quality of the coatings. For comparison, layers produced by different methods (e.g. Chemical vapor deposition, Pulsed laser deposition) have been characterized as well.
Annealing experiments have been performed to evaluate the thermal stability of the amorphous carbon films. Further investigations concerning the radiation stability of the X-ray mirrors have also been conducted. The mirrors were irradiated in the FELIS (Free Electron Laser-Interaction with Solids) experiment at the TTF-FEL. Microscopic investigations demonstrate that the carbon mirrors are fairly stable.
In this paper we review various improvements that we made in the development of multilayer mirror optics for home-lab x-ray analytical equipment in recent years. For the detection of light elements using x-ray fluorescence spectrometry, we developed a number of new multilayers with improved detection limits. In detail, we found that La/B4C multilayers improve the detection limit of boron by 29 % compared to the previous Mo/B4C multilayers. For the detection of carbon, TiO2/C multilayers improve the detection limit also by 29 % compared to the V/C multilayers previously used. For the detection of aluminum, WSi2/Si or Ta/Si multilayers can lead to detection limit improvements over the current W/Si multilayers of up to 60 % for samples on silicon wafers. For the use as beam-conditioning elements in x-ray diffractometry, curved optics coated with laterally d-spacing graded multilayers give rise to major improvements concerning usable x-ray intensity and beam quality. Recent developments lead to a high quality of these multilayer optics concerning beam intensity, divergence, beam uniformity and spectral purity. For example, x-ray reflectometry instruments equipped with such multilayer optics have dynamic ranges previously only available at synchrotron sources. Two-dimensional focusing multilayer optics are shown to become essential optical elements in protein crystallography and structural proteomics.
A free electron laser for the XUV spectral range is currently under test at the TESLA Test Facility at DESY. High gain has been demonstrated below 100nm wavelength, and it is expected that the FEL will provide intense, sub-picosecond radiation pulses with photon energies up to 200eV. Thin film optical elements required for this facility are currently being developed by the X-ray optics group of the GKSS research center near Hamburg. Sputter-deposited coatings have been prepared for the use as total reflection X-ray mirrors for FEL beam optics. Coatings of low Z elements with the lowest possible absorption and high reflectivity have been investigated. Silicon substrates have been coated with carbon using different deposition conditions. The films were investigated using the soft X-ray reflectometer at the HASYLAB beamline G1. The measurements show that the reflectivity of the films is typically 90% at energies below 200eV and a grazing incidence angle of 4 degrees. The optical constants of these coatings obtained from the reflectivity measurements and are in agreement with tabulated values. The deposition parameters have been optimized resulting in argon contamination free films with near-theoretical performance. Preliminary investigations concerning the heat resistance of the films were also carried out.
We have fabricated La/B4C multilayer films by magnetron sputtering for the use as x-ray mirrors at energies below 190 eV, particularly for the detection of boron Ka x-rays at 183 eV, and compared them to Mo/B4C multilayers that are currently used in x-ray fluorescence spectrometers for this purpose. Transmission electron microscopy and synchrotron soft x-ray reflectometry at energies between 50 and 525 eV were used to study the structural quality and the x-ray optical performance of the multilayers. The results show a significant improvement of the reflectance at 183 eV with simultaneously improved suppression of other, undesired x-ray energies, indicating that La/B4C has a high potential to replace Mo/B4C in many x-ray optical applications below 190 eV. As an example, a comparison between La/B4C and Mo/B4C multilayers was performed by laboratory x-ray fluorescence measurements of the boron Ka emission using samples of B4C and borophosphosilicate glass. The improvements of the peak intensity and the lower limit of detection amounted to about 64% and 29%, respectively. The thermal stability of La/B4C multilayers was also investigated.
Periodic multilayers are well known as Bragg reflectors for X- rays. A high reflectivity and a wide reflection width are their outstanding features. However, if multilayers shall be used as reflective coating for X-ray optics, especially for wide acceptance angles, uniform layer thicknesses cause chromatic aberrations. These aberrations can be overcome by laterally graded multilayer optics. Their Bragg angle is matched laterally to the incidence angle so that for all points on the reflector, Bragg reflection is obtained for the same wavelength. Three major types of laterally graded multilayer mirrors ('Gobel Mirrors') are applied in X-ray diffractometry: (1) parabolic, (2) elliptic and (3) planar. In this paper, we give design criteria and formulae for these mirrors. Furthermore, we discuss the requirements on the dimensions and the fabrication process. Two different processes suitable for the fabrication, sputter coating and pulsed laser deposition (PLD), are described. The X-ray optical parameters and their characterization are presented for various mirrors designed for Cu K(alpha) , Mo K(alpha) and Cr K(alpha) radiation. From Ni/C and Ni/B4C multilayers, high-photon-flux monochromators with a Cu K(beta) /K(alpha) intensity ratio of about 1:1000 have been realized. The divergence of the 'parallel' beam reflected from parabolic mirrors is about 0.02 degrees, which is one order of magnitude lower than the divergence of polycapillary optics, monocapillary optics and waveguides. Comparing the photon flux density in a high resolution diffraction setup with and without mirror optics a gain factor of 16 was achieved for parabolic Ni/B4C multilayer mirrors.