Sala, Simone; (2018) Wavefront and nanostructure characterisation with X-ray ptychography. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

X-ray ptychography is a scanning diffraction microscopy technique suited for the phase-sensitive investigation of wavefronts and specimens. It returns complex-valued wave functions and transmission functions producing high-resolution (nanoscale) phase- contrast images. This work focuses on the implementation and application of X-ray ptychography in the context of synchrotron radiation facilities. It presents an experimental protocol developed for multiscale X-ray imaging and tested at the I13-1 Coherence Branchline at Diamond Light Source. This protocol combines both near-field and far-field ptychography with other imaging methods, providing a flexible way of conducting experiments on hierarchical structures at any high-brilliance X-ray facility. This work also reports ptychography experiments performed at free-electron lasers, aimed at characterising their pulsed beam. Both the average and individual wavefronts are retrieved through a novel application of a reconstruction algorithm based on singular- value decomposition, giving direct insight on pulse-to-pulse fluctuations and confirming ptychography as a powerful beam diagnostics technique. Additional ptychography experiments are also discussed, which were carried out at storage rings on flat, weakly-scattering biogenic samples to characterise their 3D nanos- tructures. Their data analysis pipeline is presented in detail, from data acquisition to rendered volumes. Furthermore, one of these last experiments constitutes the first successful 3D ptychography experiment run on real-life samples at the I13-1 Coherence Branchline at Diamond Light Source.

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