@article{OpolkaMuellerFellaetal.2021, author = {Opolka, Alexander and M{\"u}ller, Dominik and Fella, Christian and Balles, Andreas and Mohr, J{\"u}rgen and Last, Arndt}, title = {Multi-lens array full-field X-ray microscopy}, series = {Applied Sciences}, volume = {11}, journal = {Applied Sciences}, number = {16}, issn = {2076-3417}, doi = {10.3390/app11167234}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-244974}, year = {2021}, abstract = {X-ray full-field microscopy at laboratory sources for photon energies above 10 keV suffers from either long exposure times or low resolution. The photon flux is mainly limited by the objectives used, having a limited numerical aperture NA. We show that this can be overcome by making use of the cone-beam illumination of laboratory sources by imaging the same field of view (FoV) several times under slightly different angles using an array of X-ray lenses. Using this technique, the exposure time can be reduced drastically without any loss in terms of resolution. A proof-of-principle is given using an existing laboratory metal-jet source at the 9.25 keV Ga K\(_α\)-line and compared to a ray-tracing simulation of the setup.}, language = {en} } @article{DittmannBallesZabler2018, author = {Dittmann, Jonas and Balles, Andreas and Zabler, Simon}, title = {Optimization based evaluation of grating interferometric phase stepping series and analysis of mechanical setup instabilities}, series = {Journal of Imaging}, volume = {4}, journal = {Journal of Imaging}, number = {6}, issn = {2313-433X}, doi = {10.3390/jimaging4060077}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-197723}, pages = {77}, year = {2018}, abstract = {The diffraction contrast modalities accessible by X-ray grating interferometers are not imaged directly but have to be inferred from sine-like signal variations occurring in a series of images acquired at varying relative positions of the interferometer's gratings. The absolute spatial translations involved in the acquisition of these phase stepping series usually lie in the range of only a few hundred nanometers, wherefore positioning errors as small as 10 nm will already translate into signal uncertainties of 1-10\% in the final images if not accounted for. Classically, the relative grating positions in the phase stepping series are considered input parameters to the analysis and are, for the Fast Fourier Transform that is typically employed, required to be equidistantly distributed over multiples of the gratings' period. In the following, a fast converging optimization scheme is presented simultaneously determining the phase stepping curves' parameters as well as the actually performed motions of the stepped grating, including also erroneous rotational motions which are commonly neglected. While the correction of solely the translational errors along the stepping direction is found to be sufficient with regard to the reduction of image artifacts, the possibility to also detect minute rotations about all axes proves to be a valuable tool for system calibration and monitoring. The simplicity of the provided algorithm, in particular when only considering translational errors, makes it well suitable as a standard evaluation procedure also for large image series.}, language = {en} } @article{MuellerGraetzBallesetal.2021, author = {M{\"u}ller, Dominik and Graetz, Jonas and Balles, Andreas and Stier, Simon and Hanke, Randolf and Fella, Christian}, title = {Laboratory-Based Nano-Computed Tomography and Examples of Its Application in the Field of Materials Research}, series = {Crystals}, volume = {11}, journal = {Crystals}, number = {6}, issn = {2073-4352}, doi = {10.3390/cryst11060677}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-241048}, year = {2021}, abstract = {In a comprehensive study, we demonstrate the performance and typical application scenarios for laboratory-based nano-computed tomography in materials research on various samples. Specifically, we focus on a projection magnification system with a nano focus source. The imaging resolution is quantified with common 2D test structures and validated in 3D applications by means of the Fourier Shell Correlation. As representative application examples from nowadays material research, we show metallization processes in multilayer integrated circuits, aging in lithium battery electrodes, and volumetric of metallic sub-micrometer fillers of composites. Thus, the laboratory system provides the unique possibility to image non-destructively structures in the range of 170-190 nanometers, even for high-density materials.}, language = {en} } @phdthesis{Balles2021, author = {Balles, Andreas}, title = {In-line phase contrast and grating interferometry at a liquid-metal-jet source with micrometer resolution}, doi = {10.25972/OPUS-23591}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-235917}, school = {Universit{\"a}t W{\"u}rzburg}, year = {2021}, abstract = {As a non-destructive testing method, X-ray imaging has proved to be suitable for the examination of a variety of objects. The measurement principle is based on the attenuation of X-rays caused by these objects. This attenuation can be recorded as shades of intensity using X-ray detectors and thus contains information about the inner structure of the investigated object. Since X-rays are electromagnetic waves, they also experience a change of phase in addition to their attenuation while penetrating an object. In general, imaging methods based on this effect are referred to as phase contrast imaging techniques. In the laboratory, the two mainly used methods are the propagation based phase contrast or in-line phase contrast and the grating interferometry. While in-line phase contrast - under certain conditions - shows edge enhancement at interfaces due to interference, phase contrast in the grating interferometry is only indirectly measurable by the use of several gratings. In addition to phase contrast, grating interferometry provides access to the so-called dark-field imaging contrast, which measures the scattering of X-rays caused by an object. These two imaging techniques, together with a novel concept of laboratory X-ray sources, the liquid-metal-jet, form the main part of this work. Compared to conventional X-ray sources, the liquid-metal-jet source offers higher brightness. The term brightness is defined by the number of X-ray photons per second, emitting area (area of the X-ray spot) and solid angle at which they are emitted. On the basis of this source, a high resolution in-line phase contrast setup was partially developed in the scope of this work. Several computed tomographies show the feasibility of in-line phase contrast and the improvement of image quality by applying phase retrieval algorithms. Moreover, the determination of optimized sample positions for in-line phase contrast imaging is treated at which the edge enhancement is maximized. Based on primitive fiber objects, this optimization has proven to be a good approximation. With its high brightness in combination with a high spatial coherence, the liquid-metal-jet source is also interesting for grating interferometry. The development of such a setup is also part of this work. The overall concept and the characterization of the setup is presented as well as the applicability and its limits for the investigation of various objects. Due to the very unique concept of this grating interferometer it was possible to realize a modified interferometer system by using a single grating only. Its concept and results are also presented in this work. Furthermore, a grating interferometer based on a microfocus X-ray tube was tested regarding its performance. Thereby, parameters like the anode material, acquisition geometry and gratings were altered in order to find the advantages and disadvantages of each configuration.}, subject = {Phasenkontrastverfahren}, language = {en} }