Laboratory-based multi-modal X-ray microscopy and micro-CT with Bragg magnifiers.

We report on the successful demonstration of X-ray phase contrast microscopy and micro computed tomography (CT) with a Bragg magnifier microscope (BMM) in a laboratory setup. The Bragg magnifiers, constituted by two channel-cut crystals in asymmetric diffraction, produced a 15X magnification of the X-ray beam, thus enabling high resolution imaging to be attained. The angular sensitivity of the crystals was used to implement analyzer-based phase contrast imaging: acquiring images at different angular positions and the three parametric images (apparent absorption, differential phase and scattering) have been obtained. Micro-CT, with resolution of about 5 µm is demonstrated with the same system. The main limitations, as well as the ways to mitigate them, are discussed with the aid of the experimental data. The technique demonstrated herein extends high-resolution, multi-modal, x-ray imaging and micro-CT to compact laboratory setups, with the potential of broadening the reach of these techniques outside the community of synchrotron users.

X-ray Bragg magnifier microscope as a linear shift invariant imaging system: image formation and phase retrieval.

We present the theoretical description of the image formation with the in-line germanium Bragg Magnifier Microscope (BMM) and the first successful phase retrieval of X-ray holograms recorded with this imaging system. The conditions under which the BMM acts as a linear shift invariant system are theoretically explained and supported by the experiment. Such an approach simplifies the mathematical treatment of the image formation and reconstruction as complicated propagation of the wavefront onto inclined planes can be avoided. Quantitative phase retrieval is demonstrated using a test sample and a proof of concept phase imaging of a spider leg is also presented.

Potential use of V-channel Ge(220) monochromators in X-ray metrology and imaging.

While channel-cut crystals, in which the diffracting surfaces in an asymmetric cut are kept parallel, can provide beam collimation and spectral beam shaping, they can in addition provide beam compression or expansion if the cut is V-shaped. The compression/expansion ratio depends in this case on the total asymmetry factor. If the Ge(220) diffraction planes and a total asymmetry factor in excess of 10 are used, the rocking curves of two diffractors will have a sufficient overlap only if the second diffractor is tuned slightly with respect to the first one. This study compares and analyses several ways of overcoming this mismatch, which is due to refraction, when the Cu Kα1 beam is compressed 21-fold in a V21 monochromator. A more than sixfold intensity increase was obtained if the matching was improved either by a compositional variation or by a thermal deformation. This provided an intensity gain compared with the use of a simple slit in a symmetrical channel-cut monochromator. The first attempt to overcome the mismatch by introducing different types of X-ray prisms for the required beam deflection is described as well. The performance of the V-shaped monochromators is demonstrated in two applications. A narrow collimated monochromatic beam obtained in the beam compressing mode was used for high-resolution grazing-incidence small-angle X-ray scattering measurements of a silicon sample with corrupted surface. In addition, a two-dimensional Bragg magnifier, based on two crossed V15 channel monochromators in beam expansion mode and tuned by means of unequal asymmetries, was successfully applied to high-resolution imaging of test structures in combination with a Medipix detector.