Frank Siewert

A single pass FEL amplifier can produce extremely in- tense and fully coherent radiation at short... more A single pass FEL amplifier can produce extremely in- tense and fully coherent radiation at short wavelengths if it is seeded by a coherent light beam resonant with the mag- netic structure and collinear with the electron beam. Since at the present time a single pass SASE 1 FEL is the only source of sufficiently intense, tunable radiation in the

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A new soft x‐ray autocorrelator—direct evaluation of the temporal properties of FEL pulses at 24 nm

To provide two jitter-free soft x-ray pulses for femtosecond x-ray pump and probe experiments a s... more To provide two jitter-free soft x-ray pulses for femtosecond x-ray pump and probe experiments a split and delay unit (autocorrelator) has been constructed for the VUV-FEL in Hamburg (FLASH). Here we report experiments applying this autocorrelator to examine the average temporal properties of FEL pulses delivered from FLASH at 24 nm (51.8 eV). In a linear autocorrelation experiment the spatio-temporal

The holography endstation of beamline P10 at PETRA III

We present the design and instrumentation of a novel holography endstation for the P10 coherence ... more We present the design and instrumentation of a novel holography endstation for the P10 coherence beamline at PETRA III at DESY. The experimental imaging scheme is based on a highly coherent and divergent (cone) beam illumination, achieved by fixed curvature focusing mirrors with additional spatial and coherence filtering by x-ray waveguides. The optical elements along the beam path and the

Micro-imaging performance of multilayers used as monochromators for coherent hard X-ray synchrotron radiation

by Frank Siewert and Alexander Rack

Advances in X-Ray/Euv Optics and Components V, 2010

We present a systematic study in which multilayers of different composition (W/Si, Mo/Si, Pd/B 4 ... more We present a systematic study in which multilayers of different composition (W/Si, Mo/Si, Pd/B 4 C), periodicity (from 2.5 to 5.5 nm), and numbers of layers have been characterised. Particularly, we investigated the intrinsic quality (roughness and reflectivity) as well as the performance (flatness and coherence of the outgoing beam) as a monochromator for synchrotron radiation hard X-ray micro-imaging. The results indicate that the material composition is the dominating factor for the performance. This is of high importance for synchrotron-based hard X-ray imaging which has become a widely applied tool for probing the microstructure of bulk samples. The high spatial resolution and different contrast modalities available here strongly depend on using coherent beams from highly brilliant sources. In order to satisfy the demand for a high flux of quasi-monochromatic photons, multilayer-coated mirrors are commonly used as monochromators. Their properties present a good tradeoff between spectral bandwidth and photon flux density. Since the photon flux density at the sample position is higher than with standard crystal monochromators, better spatial resolution can be reached. This comes at the cost of reduced energy resolution and stronger non-uniformities in the incoming beam profile. By helping scientists and engineers specify the design parameters of multilayer monochromators, our results can contribute to a better exploitation of the advantages of multilayer monochromators over crystal-based devices; i.e., larger spectral bandwidth and high photon flux density for X-ray imaging.

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Fully automated, fixed exit, in vacuum double-multilayer monochromator for synchrotron-based hard X-ray micro-imaging applications

Sri 2009: the 10th International Conference on Synchrotron Radiation Instrumentation, 2010

We present a double multilayer monochromator (DMM) design which has been realized for the BAMline... more We present a double multilayer monochromator (DMM) design which has been realized for the BAMline (BESSY-II light source, Germany) as well as in an updated version for the TopoTomo beamline (ANKA light source. Germany) [1-4]. The latter contains two pairs of multilayer stripes in order to avoid absorption edges of the coating material. For both DMMs, the second multilayer offers a meridional bending option for beam compression to increase the available photon flux density. Each multilayer mirror is equipped with a vertical stage for height adjustments allowing for compensation of varying incoming beam heights and giving a certain flexibility choosing the offset. The second multilayer can be moved in the beam direction in order to cover the full energy range available. Furthermore, a white beam option is available.

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Performance of Multilayer Monochromators for Hard X-Ray Imaging with Coherent Synchrotron Radiation

10th International Conference on X-Ray Microscopy, 2011

We present a study in which multilayers of different periodicity (from 2.5 to 5.5 nm), compositio... more We present a study in which multilayers of different periodicity (from 2.5 to 5.5 nm), composition (W/Si, Mo/Si, Pd/B 4 C, Ru/B 4 C), and numbers of layers have been compared. Particularly, we chose mirrors with similar intrinsic quality (roughness and reflectivity) to study their performance (flatness and coherence of the outgoing beam) as monochromators in synchrotron radiography. The results indicate that material composition is the dominating factor for the performance. This is important to consider for future developments in synchrotron-based hard x-ray imaging methods. In these techniques, multilayer monochromators are popular because of their good tradeoff between spectral bandwidth and photon flux density of the outgoing beam, but sufficient homogeneity and preservation of the coherent properties of the reflected beam are major concerns. The experimental results we collected may help scientists and engineers specify multilayer monochromators and can contribute to better exploitation of the advantages of multilayer monochromators in microtomography and other full-field imaging techniques.

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Development of a high-performance gantry system for a new generation of optical slope measuring profilers

A new high-performance metrology gantry system has been developed within the scope of collaborati... more A new high-performance metrology gantry system has been developed within the scope of collaborative efforts of optics groups at the US Department of Energy synchrotron radiation facilities as well as the BESSY-II synchrotron at the Helmholtz Zentrum Berlin (Germany) and the participation of industrial vendors of x-ray optics and metrology instrumentation directed to create a new generation of optical slope measuring systems (OSMS) [1]. The slope measurement accuracy of the OSMS is expected to be o 50 nrad, which is strongly required for the current and future metrology of x-ray optics for the next generation of light sources.

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Sub-nm accuracy metrology for ultra-precise reflective X-ray optics

Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 2011

The transport and monochromatization of synchrotron light from a high brilliant laser-like source... more The transport and monochromatization of synchrotron light from a high brilliant laser-like source to the experimental station without significant loss of brilliance and coherence is a challenging task in X-ray optics and requires optical elements of utmost accuracy. These are wave-front preserving plane mirrors with lengths of up to 1 m characterized by residual slope errors in the range of 0.05 mrad (rms) and values of 0.1 nm (rms) for micro-roughness. In the case of focusing optical elements like elliptical cylinders the required residual slope error is in the range of 0.25 mrad rms and better. In addition the alignment of optical elements is a critical and beamline performance limiting topic. Thus the characterization of ultraprecise reflective optical elements for FEL-beamline application in the free and mounted states is of significant importance. We will discuss recent results in the field of metrology achieved at the BESSY-II Optics Laboratory (BOL) of the Helmholtz Zentrum Berlin (HZB) by use of the Nanometer Optical Component Measuring Machine (NOM). Different types of mirror have been inspected by line-scan and slope mapping in the free and mounted states. Based on these results the mirror clamping of a combined mirror/grating set-up for the BL-beamlines at FLASH was improved.

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Preparation and characterization of x-ray mirrors with three single layers of a-C, B 4 C, and Ni onto two 820-mm long Si substrate

by Frank Siewert and Kai Tiedtke

Advances in X-Ray/EUV Optics and Components IX, 2014

ABSTRACT Advanced research light sources, such as free-electron lasers, require ultra-precise and... more ABSTRACT Advanced research light sources, such as free-electron lasers, require ultra-precise and long x-ray mirrors that provide high reflectivity, high flux and a wide wavelength range. An X-ray mirror is a combination of a substrate and a coating. The demand for large mirrors has increased during the last few years, since surface finishing technology is able to process longer substrate lengths on the rms-level of a few nanometers. A state-of-the-art X-ray mirror could be coated with more than one single layer to allow a selection of thin-film materials suitable for the large wavelength range of a free-electron laser. Presented here is an X-ray mirror fabrication method to achieve low variation in thickness of less than 1 nm (peak-to-valley) over the whole mirror length of about 1 m. Low figure errors and low roughness are essential for a wave front preserving transport of photons and a high reflectance of a mirror surface. At FLASH II, the new extension of the Free-electron LASer in Hamburg (FLASH) at DESY, Germany, the wavelength range will be 4-80 nm. It is further expected that the photon beam will possess average single pulse energy of 1-500 μJ, pulse duration of 10-300 fs (FWHM), and peak power of 1-5 GW. At the Helmholtz-Zentrum Geesthacht, an in-house designed magnetronsputtering facility enabled us to deposit single layers and multilayers on up to 1.5 m long substrates. Earlier results confirmed the excellent uniformity of X-ray optical coating properties in the tangential and sagittal direction of the mirrors. Moreover, the deposition facility provided the simultaneous fabrication of two mirrors to achieve identical properties. Thin films of amorphous carbon (a-C), boron carbide (B4C) and nickel (Ni) are deposited by means of magnetron sputtering. The thin-film properties were investigated and analyzed by means of X-ray reflectometry (XRR), atomic force (AFM), and interference microscopy. The experimental results were analysed using simulations for the determination of layer thickness, density and roughness.

PERFORMANCE TESTS OF THE PHOTON MONOCHROMATOR FOR SELF-SEEDING AT FLASH

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A new soft x‐ray autocorrelator—direct evaluation of the temporal properties of FEL pulses at 24 nm