A matter of brightness: table-top X-ray generation inside waveguides and X-ray holography with single free-electron laser pulses

by Malte Julian Udo Vassholz
Doctoral thesis
Date of Examination:2021-03-26
Date of issue:2022-03-22
Advisor:Prof. Dr. Tim Salditt
Referee:Prof. Dr. Tim Salditt
Referee:Prof. Dr. Claus Ropers
Persistent Address: http://dx.doi.org/10.53846/goediss-9130

 

 

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Abstract

English

X-ray microscopy delivers insights into the structure of optically opaque bulk specimens with high spatial resolution. The source brightness poses a limit on the achievable resolution, however. While table-top X-ray sources are readily available but provide only low brightness, large-facility sources, such as synchrotrons and X-ray free-electron lasers (XFEL), generate radiation with high brightness and high coherence, but are not easily accessible. In this work, we report on and experimentally demonstrate a novel table-top X-ray source concept to generate spatially coherent X-rays with high brightness, that are emitted directly into the modes of a waveguide. Our estimate of the achievable gain increase demonstrates a substantial brightness improvement with respect to other table-top X-ray sources. In another set of experiments, we make use of the high peak brilliance of an XFEL to observe transient states of water under extreme conditions. In a pump-probe scheme, an infrared laser pulse generates a plasma after optical breakdown to seed a cavitation bubble, which we image with a single XFEL pulse. To get access to the pressure distribution within the shockwave of the cavitation bubbles, we calculate the quantitative phase shift based on a tailored phase-retrieval approach. We further complement nanofocus X-ray holography with time-resolved X-ray diffraction to obtain information on the molecular structure of water after dielectric breakdown. This combined approach delivers quantitative information from microscopic to molecular length scales with high temporal resolution.
Keywords: X-ray microscopy; X-ray sources; phase retrieval; waveguides; pump-probe; cavitation; X-ray diffraction; free-electron laser
 
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