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@PHDTHESIS{Trost:596416,
      author       = {Trost, Fabian},
      othercontributors = {Chapman, Henry N. and Roehlsberger, Ralf},
      title        = {{I}maging via photon-photon correlation of {X}-ray
                      fluorescence},
      school       = {University of Hamburg},
      type         = {Dissertation},
      reportid     = {PUBDB-2023-06144},
      pages        = {146},
      year         = {2023},
      note         = {Dissertation, University of Hamburg, 2023},
      abstract     = {This work discusses and demonstrates the imaging method
                      ‘photon-photon correlation of X-ray fluorescence’, also
                      called ‘Incoherent Diffraction Imaging (IDI)’. This
                      method corresponds to the ‘intensity interferometry’,
                      known from astronomy. However, this method requires
                      measurement or exposure times that are on the order of the
                      coherence time of the measured radiation; for Kα
                      fluorescence of light transition metals, this is on the
                      order of a femtosecond – a temporal length that can be
                      achieved by modern X-ray free electron lasers (XFELs).In
                      addition to the exposure time requirement, this work
                      discusses other influencing factors that can cause a
                      reduction in the useful correlation signal. These are the
                      temporal shape of the excitation pulse, the sample size, the
                      (non) polarization of the detected photons, and others.
                      These factors, collectively called ‘visibility factor’,
                      also manifest as ‘speckle contrast’ and can be measured
                      without the need to perform intensity correlation. A
                      weighting method is presented to determine the speckle
                      contrast from a data set consisting of images with very low
                      photon counts that fluctuate significantly from image to
                      image. This method is applied to compare the speckle
                      contrast of iron Kα fluorescence excited by 3 fs and 15 fs
                      XFEL pulses. An increase in speckle contrast was found for
                      the short pulses compared to the longer ones – a
                      fundamental requirement for the IDI method.Furthermore,
                      inherent noise sources affecting the IDI are discussed. A
                      model is derived to estimate the dependence of the
                      signal-to-noise ratio (SNR) on the photon number per pixel,
                      temporal coherence (or visibility factor), and the shape of
                      the imaged object. In addition, simulations in two and three
                      dimensions were performed to validate the model’s
                      predictions. Unlike coherent imaging methods, more detected
                      photons do not always result in higher SNR. Moreover, larger
                      and more complex objects generally yield poorer SNR, even
                      when the number of measured photons is proportional to the
                      object size or complexity.Finally, an experiment that uses
                      the photon-photon correlation of X-ray fluorescence photons
                      for the first time to reconstruct a nontrivial
                      (noncontinuous) fluorescence emitter distribution is
                      presented. In the course of this experiment, the application
                      of IDI to determine XFEL beam parameters such as focus and
                      temporal pulse length is demonstrated.},
      cin          = {FS-CFEL-1},
      cid          = {I:(DE-H253)FS-CFEL-1-20120731},
      pnm          = {633 - Life Sciences – Building Blocks of Life: Structure
                      and Function (POF4-633) / DFG project 390715994 - EXC 2056:
                      CUI: Advanced Imaging of Matter (390715994)},
      pid          = {G:(DE-HGF)POF4-633 / G:(GEPRIS)390715994},
      experiment   = {EXP:(DE-H253)CFEL-Exp-20150101 /
                      EXP:(DE-H253)XFEL-MID-20150101 /
                      EXP:(DE-MLZ)External-20140101},
      typ          = {PUB:(DE-HGF)11},
      urn          = {urn:nbn:de:gbv:18-ediss-112508},
      doi          = {10.3204/PUBDB-2023-06144},
      url          = {https://bib-pubdb1.desy.de/record/596416},
}