Carsten Michaelsen

Total reflection amorphous carbon mirrors for vacuum ultraviolet free electron lasers

Sputter-deposited amorphous carbon coatings of high optical quality and very high radiation stability will be used as reflecting optical elements for free electron laser (FEL) applications in the vacuum ultraviolet (VUV) and soft x-ray spectral regions. Their reflectivity at grazing angles of 2° is typically 94–96% for photon energies between 50 and 250 eV. Using the focused radiation (λ=98 nm) of the VUV FEL at Deutsches Elektronen-Synchrotron DESY the damage threshold of such coatings was determined to 0.07 J/cm2. Ripples with a spatial period of 76 nm were found on the surfaces damaged by the FEL radiation.

Multilayer optics for Mo-radiation-based crystallography

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.

Optimized performance of graded multilayer optics for x-ray single-crystal diffraction

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.

Characterization of amorphous carbon films as total-reflection mirrors for XUV free-electron lasers

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.

Recent developments of multilayer mirror optics for laboratory x-ray instrumentation

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.

Development of thin-film total-reflection mirrors for the XUV FEL

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.

New developments in laboratory-based x-ray sources and optics

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.

Absolute configuration determination for light-atom structures using low-power microfocus X-ray source

The determination of the absolute configuration for light-atom structures has become central to research in pharmaceuticals and natural products synthesis. In the absence of elements heavier than silicon, it is often problematic to make a significant assignment of absolute configuration, especially for smaller crystals. Besides the introduction of new mathematical methods to evaluate the Bijvoet differences, the assignment of the absolute structure for light atom compounds has become easier with the advent of high-intensity microfocus sources, as the increased flux density improves the anomalous signal through improvements in counting statistics. In this presentation, we will be reviewing the current performance levels of different low power microfocus X-ray sources, such as the IμS and the METALJET X-ray source. Further, we will be discussing the main features of the newest generation of the IμS. We will be presenting selected results to demonstrate the impact of these modern microfocus X-ray sources on the data quality for applications in chemical and biological crystallography.

Multilayer optics and scatterless apertures for high-brilliance X-ray sources

Scatterless apertures, such as scatterfree pinholes, are usually made of oriented single crystals, such as Ge or Ta, and show a significant reduction of parasitic scattering commonly associated with conventional metal apertures. Therefore, such pinholes allow an improvement of X-ray analytical instruments as the number of necessary pinholes can be reduced. Further, the use of scatterfree pinholes enables a significant reduction of the background. This improves the data quality at low resolution which is beneficial for small angle scattering, as well as for crystallography applications. Our SCATEX pinholes are either made of Germanium for energies below 11.2 keV or of Tantalum for energies above 11.2 keV and are available with diameters ranging from 2 mm down to 20 μm and below. Therefore, these novel apertures are applicable to a wide range of different applications. We will be showing new results about development and use of these pinholes.

Improvement of SAXS Lab Equipment by Using Scatterless Apertures

Parasitic scattering caused by apertures is a well-known problem in X-ray analytics, which forces users and manufacturers to adapt their experimental setup to this unwanted phenomenon. Increased measurement times due to lower photon fluxes, a lower resolution caused by an enlarged beam stop, a larger beam defining pinhole-to-sample distance due to the integration of an antiscatter guard and generally a lower signal-to-noise ratio leads to a loss in data quality. In this presentation we will explain how the lately developed scatterless pinholes called SCATEX overcome the aforementioned problems. SCATEX pinholes are either made of Germanium or of Tantalum and momentarily have a minimum diameter of 30μm. Thus, these novel apertures are applicable to a wide range of different applications and X-ray energies. We will show measurements which were performed either at home-lab small angle X-ray scattering (SAXS) systems such as the NANOSTAR of Bruker AXS or at synchrotron beamlines. At the PTB four-crystal monochromator beamline at BESSY II data was collected for a comparison of conventional pinholes, scatterless Germanium slit systems and SCATEX pinholes. At the Nanofocus Endstation P03 beamline at PETRA III we compared the performance of our SCATEX apertures with conventional Tungsten slit systems under high flux density conditions.