Coherent diffraction imaging using a high harmonic source at 40 eV

Abstract

This thesis presents the current status of coherent diffractive imaging and ptychography using the high harmonic at the University of Southampton. The full system used to generate the 40 eV radiation and collect the far-field speckle patterns is outlined and critical criteria discussed. The algorithms used to re-phase the data are outlined and some simple 1-dimensional examples are given. The question of how to appropriately state the resolution of a coherent diffraction system is addressed and the concluding results are applied to the work in the experimental chapters, of which this thesis contains two.
The first, is a published result which investigates the treatment of partial temporal coherence through the coherent diffraction process. Partial coherence for a high harmonic source is slightly more complex to treat than standard broad-bandwidth sources since the spectrum is modulated by the narrow-bandwidth harmonic comb underneath a broad-bandwidth envelope. An experimental investigation is presented by illuminating the same amplitude mask under broad-band and narrow band conditions using the same imaging systems. The results are discussed and conclude that a much greater than expected (20%) relative bandwidth can used for such an experiment and still reproduce a reliable and fairly stable reconstruction. This construction is not a solution to the phase problem however, and hence only provides an improved support constraint for potential further processing.
The second experimental chapter presents novel and currently unpublished work using the high harmonic source to obtain iterative ptychograms of complex-valued extended samples. This represents the first documented result of ptychography using a lab-based source of short wavelength radiation. Defects in the Molybdenum pinhole used to define the illumination function are investigated and provide a thickness for the defect area of 6 nm x 1 nm with a pixel size of 90 nm. The sample under investigation for this experiment was a substrate with fixed cultured hippocampal neurons. An investigation of one of the neurite processes of this sample is made and identification of the neurite as an axon is deduced via analysis of the samples dielectric loss tangent.

More information

Identifiers

ORCID for W.S. Brocklesby: orcid.org/0000-0002-2123-6712

Catalogue record

Export record