Report/Dissertation / PhD Thesis

PUBDB-2015-04615

http://join2-wiki.gsi.de/foswiki/pub/Main/Artwork/join2_logo100x88.png Quantum effects in nonresonant x-ray scattering

Slowik, J. M. (Corresponding author)CFEL*DESY*

2015
Verlag Deutsches Elektronen-Synchrotron Hamburg

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Please use a persistent id in citations: doi:10.3204/DESY-THESIS-2015-045

Report No.: DESY-THESIS-2015-045

Abstract: Due to their versatile properties, x rays are a unique tool to investigate the structure and dynamics of matter. X-ray scattering is the fundamental principle of many imaging techniques. Examples are x-ray crystallography, which recently celebrated one hundred years and is currently the leading method in structure determination of proteins, as well as X-ray phase contrast imaging (PCI), which is an imaging technique with countless applications in biology, medicine, etc. The technological development of X-ray free electron lasers (XFEL) has brought x-ray imaging at the edge of a new scientific revolution. XFELs offer ultrashort x-ray pulses with unprecedented high x-ray fluence and excellent spatial coherence properties. These properties make them an outstanding radiation source for x-ray scattering experiments, providing ultrafast temporal resolution as well as atomic spatial resolution. However, the radiation-matter interaction in XFEL experiments also advances into a novel regime. This demands a sound theoretical fundament to describe and explore the new experimental possibilities. This dissertation is dedicated to the theoretical study of non resonant x-ray scattering. As the first topic, I consider the near-field imaging by propagation based x-ray phase contrast imaging (PCI). I devise a novel theory of PCI, in which radiation and matter are quantized. Remarkably, the crucial interference term automatically excludes contributions from inelastic scattering. This explains the success of the classical description thus far. The second topic of the thesis is the x-ray imaging of coherent electronic motion, where quantum effects become particularly apparent. The electron density of coherent electronic wave packets –important in charge transfer and bond breaking – varies in time, typically on femto- or attosecond time scales. In the near future, XFELs are envisaged to provide attosecond x-ray pulses, opening the possibility for time-resolved ultrafast x-ray scattering experiments. In the quantum theory it has however been revealed that x-ray scattering patterns of electronic motion are related to complex spatio-temporal correlations, instead of the instantaneous electron density. I scrutinize the time-resolved scattering pattern from coherent electronic wave packets. I show that time-resolved PCI recovers the instantaneous electron density of electronic motion. For the far-field diffraction scattering pattern, I analyze the influence of photon energy resolution of the detector. Moreover, I demonstrate that x-ray scattering from a crystal of identical wave packets also recovers the instantaneous electron density. I point out that a generalized electron density propagator of he wave packet can be reconstructed from a scattering experiment. Finally, I propose time-resolved Compton scattering of electronic wave packets. I show that x-ray scattering with large energy transfer can be used to recover the instantaneous momentum space density of the target. The third topic of this dissertation is Compton scattering in single molecule coherent diffractive imaging (CDI). The structure determination of single macromolecules via CDI is one of the key applications of XFELs. The structure of the molecule can be reconstructed from the elastic diffraction pattern. Inelastic x-ray scattering generates a background signal, which I determine for typical high-intensity imaging conditions. I find that at high x-ray fluence the background signal becomes dominating, posing a problem for high resolution imaging. The strong ionization by the x-ray pulse may ionize several electrons per atom. Scattering from these free electrons makes amaj or contribution to the background signal. I present and discuss detailed numerical studies for different x-ray fluence and photon energy.

Note: Universität Hamburg, Diss., 2015

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Contributing Institute(s):

1. CFEL-Theory (FS-CFEL-3)

Research Program(s):

1. 6211 - Extreme States of Matter: From Cold Ions to Hot Plasmas (POF3-621) (POF3-621)

Experiment(s):

1. No specific instrument

Appears in the scientific report 2015

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Database coverage:

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