A new imaging setup, aimed to perform differential X-ray phase contrast (DPC) imaging with a Talbot interferometer
on a microfocus X-ray tube, is demonstrated. The main features compared to recently proposed setups
are an extremely short source to detector distance, high spatial resolution and a large field of view. The setup
is designed for an immediate integration into a industrial micro CT scanner. In this paper, technical challenges
of a compact setup, namely the critical source coherence and divergence, are discussed. A theoretical analysis
using wave optics based computer simulations is performed to estimate the DPC signal visibility and the size
of the field of view for a given setup geometry. The maximization of the signal visibility as a function of the
inter-grating distance yields the optimal grating parameters. Imaging results using the optimized grating parameters
are presented. The reduction of the field of view, being a consequence of the high beam divergence,
was solved by fabricating new, cylindrically bent diffraction gratings. The fabrication process of these gratings
required a change of the currently used wafer materials and an adaption of the manufacturing techniques. The
implementation of the new setup represents a major step forward for the industrial application of the DPC
technique.
In this paper we describe the design of different X-ray Talbot interferometers that have been built at the tomography
beamline ID19 of the European Synchrotron Radiation Facility (ESRF) in Grenoble, France, and give a short review of
performance characteristics, of current developments, and of the results obtained with these instruments so far. Among the
applications so far, soft-tissue imaging has been a particular focus, as demonstrated in a recent paper by Schulz et al. (J.
Roy. Soc. Interface, in press).
Phase contrast imaging with conventional X-ray tubes as e.g. in computer tomography scanners (CTscanners)
requires a setup of three different types of optical gratings. One grating is used to obtain
a spatially coherent radiation, the second grating defines a periodic phase shift and the third is used
as a periodic absorption grating. In order to absorb high energy radiation, absorption gratings with
periods of a few microns only and extreme aspect ratios (>80) are fabricated, employing a modified
LIGA process. However, above a critical structural height, structures collapse due to e.g. capillary
effects. To overcome this limitation a new variant of the LIGA process has been developed. It is
characterized by structuring of a resist on both sides of a membrane, resulting in a moderate aspect
ratio on both sides of the membrane instead of an extreme aspect ratio on one side. To get a perfect
overlay of both structures the grating structure on the front side of a membrane patterned by the
standard LIGA-process is used as the mask for structuring the second resist layer on the backside of
the membrane. A second electroforming step fills the gaps on the backside.
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