15 April 2018


Torsten Lauridsen

A thesis for the degree of Doctor of Philosophy defended April 2018.

The PhD School of Science, Faculty of Science, Theoretical Particle Physics and Cosmology, Niels Bohr Institute, University of Copenhagen

Academic advisors:
Robert Feidenhans’l, Niels Bohr Institute, UCPH and European XFEL 
Kell Mortensen, Niels Bohr Institute, UCPH

New Methods in X-ray Imaging

A couple of decades ago, x-ray tomography was a technique largely reserved for a few specialists from the hospitals' diagnostic departments and university based reseach groups. But during the last 20 years x-ray imaging has become much more available outside these narrow circles as a method to help the advancement of many di erent academic and industrial elds. In this thesis I describe my work on developing the techniques within the eld and studying their possible applications as well as my collaboration with external researchers, applying x-ray imaging methods to answer scienti c questions within their particular elds. For the sake of completeness I start my thesis from the electric eld equation. From there I derive the transport of intensity equation, the Fresnel propagator function and the basic formula of propagated intensity used in holotomography. I also sketch the principles behind the magni cation e ect and interactions between x-rays and matter.

From these fundamental formulas and principles, I move on to describe the practical aspects of xray imaging in more detail. I describe the basis of the di erent contrast mechanisms in absorption, holotomography and grating interferometry. I have also included a description of the basic principles behind tomogram reconstruction. Next, I describe my work relating to image construction from grating interferometer data, both the adaptive-period sine tting method and the anisotropic tomogram reconstruction algorithm I have developed.

Thereafter I move on to describe my work investigating the applicability of the grating interferometer dark- eld signal for detecting sub-resolution sized cracks in a solid material and for detecting misaligned bers in a ber composite material. In the next chapter I introduce the ideas and main conclusions from my collaboration with researchers from other academic elds. Finally, I sum up my work and give my view on the future possibilities and challenges within the field.

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