Timm Weitkamp

Using a high-efficiency grating interferometer for hard X rays (10-30 keV) and a phase-stepping technique, separate radiographs of the phase and absorption profiles of bulk samples can be obtained from a single set of measurements. Tomographic reconstruction yields quantitative three-dimensional maps of the X-ray refractive index, with a spatial resolution down to a few microns. The method is mechanically robust, requires little spatial coherence and monochromaticity, and can be scaled up to large fields of view, with a detector of correspondingly moderate spatial resolution. These are important prerequisites for use with laboratory X-ray sources.

A computer program named ANKAphase is presented that processes X-ray inline phase-contrast radiographs by reconstructing the projected thickness of the object(s) imaged. The program uses a single-distance non-iterative phase-retrieval algorithm described by David Paganin et al. [(2002), J. Microsc. 206, 33-40]. Allowing for non-negligible absorption in the sample, this method is strictly valid only for monochromatic illumination and single-material objects but tolerates deviations from these conditions, especially polychromaticity. ANKAphase is designed to be applied to tomography data (although it does not perform tomographic reconstruction itself). It can process series of images and perform flat-field and dark-field correction. Written in Java, ANKAphase has an intuitive graphical user interface and can be run either as a stand-alone application or as a plugin to ImageJ, a widely used scientific image-processing program. A description of ANKAphase is given and example applications are shown.

Direct beam x-ray imaging, with intense coherent monochromatic synchrotron radiation and a fast readout low noise detector has been used for in situ studies of cellular and dendritic solidification of Sn-Pb alloys. Temporal and spatial resolutions down to $\ensuremath{\sim}0.7\mathrm{s}$ and $\ensuremath{\sim}2.5\ensuremath{\mu}\mathrm{m}$, respectively, with a field of view up to $1{\mathrm{mm}}^{2}$ were obtained. The collected images display features from both phase and amplitude contrast which, combined with the attainable temporal resolution, provide a method with the potential to uncover dynamic processes in nonequilibrium solidification.