Soft X-ray coherence and coherent diffractive imaging
- The increased brightness of third-generation synchrotron X-ray sources using undulator insertion devices has opened up new fields for coherent lensless imaging experiments. While in the optical regime, coherent light sources allowed the pursuit of holography and imaging of non-periodic micron-sized objects, hard X-ray crystallography relied on the constructive interference of periodic lattices to image atomic structures. In the intermediate regime of soft X-rays, we now have the capability to coherently image non-periodic nanoscopic structures. Several elemental resonances, from carbon, nitrogen and oxygen to iron, cobalt and nickel, fall into the soft X-ray range of 100 eV to 1 keV. In order to pursue soft X-ray coherent imaging experiments at a synchrotron, an understanding of the origin of coherence is required. The first part of this work thus addresses the coherence properties of the undulator source. Imaging in this regime is both photon and spatial coherence thirsty and there is an inherent trade-off between these two resources. The incoherent source structure and the Heisenberg uncertainty principle lie at the heart of this matter. In reconstructing images of materials from intensity diffraction patterns, one faces the well-known phase problem. The second part of this work addresses two imaging techniques that were extended to the imaging of magnetic domains using X-ray magnetic circular dichroism. Fourier transform holography encodes the lost phase information into the intensity diffraction pattern, while multi-wavelength anomalous diffraction utilizes the energy dependence of the material's refractive index to regain the phase information. This latter method simplifies the sample preparation process and has the potential for coherent scanning microscopy.
|Type of resource
|electronic; electronic resource; remote
|1 online resource.
|Rick, Ramon, Mr
|Stanford University, Department of Applied Physics
|Brünger, Axel T
|Brünger, Axel T
|Statement of responsibility
|Submitted to the Department of Applied Physics.
|Thesis (Ph.D.)--Stanford University, 2011.
- © 2011 by Ramon Rick
- This work is licensed under a Creative Commons Attribution Non Commercial 3.0 Unported license (CC BY-NC).
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