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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 10nm will already translate into signal uncertainties of one to ten percent 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.

Laboratory-based X-ray computed tomography (CT) with resolutions around 100nm per line pair is technically feasible since a few years [1]. However, this measurement principle is still not widely usedespecially not for industrial and medical applications. Reasons for this are high costs, the complex operation of systems based on optical elements, as well as the restricted flexibility of their field-of-view. As applied development center for X-ray technology, the Fraunhofer EZRT is currently developing an easy-to-handle, flexible setup for industrial use. The setup uses standard projection geometry, a small Xray source and large detector pixel; thus it operates using high geometric magnification. Due to significant advances made on the component side combined with a high stability of the setup, we are able to resolve in standard operation 150nm lines and spaces. Compared to modified SEM X-ray sources, the sample does not need to be placed in vacuum [3]. Moreover, due to the source's peak energy of 60kV, sample diameter and material can be chosen relatively flexible.For our setup we utilize an X-ray tube developed by Excillum in the framework of the NanoXCT Project, which is now commercially available as "NanoTube". In our acquisition geometry, the penumbral blurring of the source's focal spot defines the achievable resolution. Besides a thin transmission target combined with a suited design of the electron optics to guarantee a small source size, also high spatial spot stability is required for computed tomography. The latter is established by advanced temperature and noise control. In order to provide good heat dissipation, the transmission target is made of tungsten deposited on a 100µm diamond window. With this, we reach a source size diameter of a few hundred nanometers.Although the brightness of the spot is high, the total emitted flux is still relatively low, which is a major drawback compared to an optics-based setup [4]. Thus, we need an efficient detector and a large solid angle to achieve reasonably short exposure times. Therefore, we use 750µm CdTe as sensor material with a quantum efficiency greater than 80% over the full spectrum. The Hybrid Photon Counting "SANTIS" detector possesses 2048 x 514 pixel with 75µm edge length, and was provided by DECTRIS. Each pixel of a dedicated readout chip is directly bonded to a semiconducting X-ray sensor [2]. Besides the high efficiency due to the photon counting technique, it possesses virtually zero noise. Furthermore, two energy thresholds enable us to perform dual-energy computed tomography without additional filters. Moreover, the quasi-rectangular point spread function of the detector supersedes oversampling.Large solid angles are obtained by a short source-detector-distance of minimum 380mm. This also requires small distances between the source and sample. Therefore, an optical collision avoidance system is implemented to be able to adjust source-object-distances below 500µm without risking a damage of the source's window. In combination with this, the syst...

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