Characterization of an indirect X-ray imaging detector by simulation and experiment.

We describe a comprehensive model of a commercial indirect X-ray imaging detector that accurately predicts the detector point spread function and its dependence on X-ray energy. The model was validated by measurements using monochromatic synchrotron radiation and extended to polychromatic X-ray sources. Our approach can be used to predict the performance of an imaging detector and can be used to optimize imaging experiments with broad-band X-ray sources.

Combined synchrotron X-ray tomography and X-ray powder diffraction using a fluorescing metal foil.

This study realizes the concept of simultaneous micro-X-ray computed tomography and X-ray powder diffraction using a synchrotron beamline. A thin zinc metal foil was placed in the primary, monochromatic synchrotron beam to generate a divergent wave to propagate through the samples of interest onto a CCD detector for tomographic imaging, thus removing the need for large beam illumination and high spatial resolution detection. Both low density materials (kapton tubing and a piece of plant) and higher density materials (Egyptian faience) were investigated, and elemental contrast was explored for the example of Cu and Ni meshes. The viability of parallel powder diffraction using the direct beam transmitted through the foil was demonstrated. The outcomes of this study enable further development of the technique towards in situ tomography∕diffraction studies combining micrometer and crystallographic length scales, and towards elemental contrast imaging and reconstruction methods using well defined fluorescence outputs from combinations of known fluorescence targets (elements).

Using coherent X-ray ptychography to probe medium-range order.

Characterization of microscopic structural order and in particular medium range order (MRO) in amorphous materials is challenging. A new technique is demonstrated that allows analysis of MRO using X-rays. Diffraction data were collected from a sample consisting of densely packed polystyrene-latex micro-spheres. Ptychography is used to reconstruct the sample transmission function and fluctuation microscopy applied to characterize structural order producing a detailed `fluctuation map' allowing analysis of the sample at two distinct length scales. Independent verification is provided via X-ray diffractometry. Simulations of dense random packing of spheres have also been used to explore the origin of the structural order measured.

Phase-diverse Fresnel coherent diffractive imaging of malaria parasite-infected red blood cells in the water window.

Phase-diverse Fresnel coherent diffractive imaging has been shown to reveal the structure and composition of biological specimens with high sensitivity at nanoscale resolution. However, the method has yet to be applied using X-ray illumination with energy in the so-called 'water-window' that lies between the carbon and oxygen K edges. In this range, differences in the strength of the X-ray interaction for protein based biological materials and water is increased. Here we demonstrate a proof-of-principle application of FCDI at an X-ray energy within the water-window to a dehydrated cellular sample composed of red blood cells infected with the trophozoite stage of the malaria parasite, Plasmodium falciparum. Comparison of the results to both optical and electron microscopy shows that the correlative imaging methods that include water-window FCDI will find utility in studying cellular architecture.

Nanoscale Fresnel coherent diffraction imaging tomography using ptychography.

We demonstrate Fresnel Coherent Diffractive Imaging (FCDI) tomography in the X-ray regime. The method uses an incident X-ray illumination with known curvature in combination with ptychography to overcome existing problems in diffraction imaging. The resulting tomographic reconstruction represents a 3D map of the specimen's complex refractive index at nano-scale resolution. We use this technique to image a lithographically fabricated glass capillary, in which features down to 70nm are clearly resolved.

Diffractive imaging using partially coherent x rays.

The measured spatial coherence characteristics of the illumination used in a diffractive imaging experiment are incorporated in an algorithm that reconstructs the complex transmission function of an object from experimental x-ray diffraction data using 1.4 keV x rays. Conventional coherent diffractive imaging, which assumes full spatial coherence, is a limiting case of our approach. Even in cases in which the deviation from full spatial coherence is small, we demonstrate a significant improvement in the quality of wave field reconstructions. Our formulation is applicable to x-ray and electron diffraction imaging techniques provided that the spatial coherence properties of the illumination are known or can be measured.

Phase imaging using a polychromatic x-ray laboratory source.

We describe a quantitative phase imaging process using an x-ray laboratory-based source with an extremely broad bandwidth spectrum. The thickness of a homogeneous object can be retrieved by using separately spectrally weighted values for the attenuation coefficient and the decrement of the real part of the refractive index. This method is valid for a wide range of object types, including objects with an absorption edge in the used energy range. The accessibility of conventional x-ray laboratory sources makes this method very useful for quantitative phase retrieval of homogeneous objects. We demonstrate the application of this method for quantitative phase retrieval imaging in tomographic measurements.