Ghost Tomography

Ghost tomography using single-pixel detection extends the emerging field of ghost imaging to three dimensions, with the use of penetrating radiation. In this work, a series of spatially random x-ray intensity patterns is used to illuminate a specimen in various tomographic angular orientations with only the total transmitted intensity being recorded by a single-pixel camera (or bucket detector). The set of zero-dimensional intensity readings, combined with knowledge of the corresponding two-dimensional illuminating patterns and specimen orientations, is sufficient for three-dimensional reconstruction of the specimen. The experimental demonstration of ghost tomography is presented here using synchrotron hard x-rays. This result expands the scope of ghost imaging to encompass volumetric imaging (i.e., tomography), of optically opaque objects using penetrating radiation. For hard x-rays, ghost tomography has the potential to decouple image quality from dose rate as well as image resolution from detector performance

Boosting spatial resolution by incorporating periodic boundary conditions into single-distance hard-x-ray phase retrieval

A simple coherent-imaging method due to Paganin et al. is widely employed for phase-amplitude reconstruction of samples using a single paraxial x-ray propagation-based phase-contrast image. The method assumes that the sample-to-detector distance is sufficiently small for the associated Fresnel number to be large compared to unity. The algorithm is particularly effective when employed in a tomographic setting, using a single propagation-based phase-contrast image for each projection. Here we develop a simple extension of the method, which improves the reconstructed contrast of very fine sample features. This provides first-principles motivation for boosting fine spatial detail associated with high Fourier frequencies, relative to the original method, and was inspired by several recent works employing empirically-obtained Fourier filters to a similar end

Impact failure in two silicates revealed by ultrafast, in situ, synchrotron X-ray microscopy

From Springer Nature via Jisc Publications RouterHistory: received 2019-12-31, accepted 2020-05-28, registration 2020-06-03, pub-electronic 2020-06-25, online 2020-06-25, collection 2020-12Publication status: PublishedAbstract: To travel safely behind screens that can protect us from stones and hail, we must understand the response of glass to impact. However, without a means to observe the mechanisms that fail different silicate architectures, engineering has relied on external sensors, post-impact examination and best-guess to glaze our vehicles. We have used single and multi-bunch, X-ray imaging to differentiate distinct phases of failure in two silicates. We identified distinct micromechanisms, operating in tandem and leading to failure in borosilicate glass and Z-cut quartz. A surface zone in the amorphous glass densifies before bulk fracture occurs and then fails the block, whilst in quartz, fast cracks, driven down cleavage planes, fails the bulk. Varying the rate at which ejecta escapes by using different indenter tip geometries controls the failed target’s bulk strength. This opens the way to more physically based constitutive descriptions for the glasses allowing design of safer, composite panels by controlling the impulses felt by protective screens

Fast x-ray radiography to study the dynamic compaction mechanisms in a rigid polyurethane foam under plate impact

International audienceThis article presents results of plate impact experiments coupled to in situ X-ray radiography, performed on a polyurethane foam, to visualize its deformations during the propagation of a stress wave. A two-wave structure associated with the propagation of an elastic precursor and pores compaction has been observed. A phenomenological compaction model, implemented in a dynamic explicit one-dimensional hydrocode, was used to simulate the dynamic macroscopic response of the foam. By using this model, which has previously been calibrated and validated by performing dedicated dynamic experiments, it is possible to compare calculated and experimental waves velocities and improve interpretations. Quasi-static tests coupled to in situ X-ray tomography have also been performed to study the mechanical behavior under low strain rates. Experimental results show that the compaction is due to bending and buckling of cell edges, and then matrix failure. Strain rate dependence of the foam behavior has been observed

Towards a practical implementation of X-ray ghost imaging with synchrotron light

An experimental procedure for transmission X-ray ghost imaging using synchrotron light is presented. Hard X-rays from an undulator were divided by a beamsplitter to produce two copies of a speckled incident beam. Both beams were simultaneously measured on an indirect pixellated detector and the intensity correlation between the two copies was used to retrieve the ghost image of samples placed in one of the two beams, without measuring the samples directly. Aiming at future practical uses of X-ray ghost imaging, the authors discuss details regarding data acquisition, image reconstruction strategies and measure the point-spread function of the ghost-imaging system. This approach may become relevant for applications of ghost imaging with X-ray sources such as undulators in storage rings, free-electron lasers and lower-coherence laboratory facilities