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@PHDTHESIS{Dresselhaus:646127,
      author       = {Dresselhaus, Jan Lukas},
      othercontributors = {Bajt, Sasa},
      title        = {{C}haracterization and correction of multilayer {X}-ray
                      optics},
      school       = {University of Hamburg},
      type         = {Dissertation},
      reportid     = {PUBDB-2026-00727},
      pages        = {160},
      year         = {2025},
      note         = {Dissertation, University of Hamburg, 2025},
      abstract     = {Highest resolution X-ray microscopy requires high numerical
                      aperture (NA) optics ofexcellent quality which allow to
                      focus X-ray beams to small focal points. MultilayerLaue
                      lenses (MLLs) are a new type of diffractive optic with the
                      capability to focushard X-rays with high efficiency to
                      nanometer spots. However, they are currentlylimited by
                      wavefront aberrations caused by layer misplacements during
                      their fab-rication process. The determination and correction
                      of wavefront aberration aretherefore crucial aspects for the
                      development and improvement of MLLs designedto achieve the
                      highest possible resolutions. Wavefront characterization for
                      lensdevelopment cannot rely solely on access to
                      synchrotrons, as beamtime must beapplied for and is
                      therefore only available to a limited extent. For that
                      reason, theaim of this thesis was to determine the
                      requirements that have to be met in orderto enable fast and
                      precise wavefront characterization of MLLs using a
                      laboratory-based setup. This requires a dedicated table top
                      X-ray system and a suitable software.To determine the
                      optimal structure for MLLs, periodic multilayer gratings
                      withdifferent layer thicknesses on the scale of a few
                      nanometers were studied. It wasfound that high quality and
                      high efficiency (> 60 $\%$ at 17.5 keV and > 80 $\%$ at60
                      keV) periodic multilayers can be fabricated, which are
                      mainly limited by theinterdiffusion of the layers. The
                      interdiffusion depth was found to be around 0.4nm for WC/SiC
                      multilayer-based optics, the material pair our MLLs are
                      typicallymade of. Based on these findings, high NA (>0.01)
                      MLLs were produced for highestresolution microscopy. To
                      determine the wavefront aberrations of the MLLs in
                      alaboratory setup, a phase retrieval algorithm with low
                      requirements on coherenceand monochromaticity was needed.
                      Ptychographic X-ray speckle tracking (PXST)is an in-house
                      developed phase gradient reconstruction algorithm that was
                      foundto fulfill these requirements and was recently
                      augmented to incorporate machinelearning techniques, which
                      allow accurate phase retrieval even in noisy and
                      lowintensity environments. It is based on the X-ray speckle
                      tracking approach and can beunderstood as a generalized
                      Hartmann sensor that tracks sample features
                      betweenoverlapping images to determine local phase
                      gradients. It was found that due tothe robustness of the
                      algorithm, wavefront reconstructions are largely
                      accurateregardless of the measurement conditions, as long as
                      the lens and a suitable sampleare aligned with respect to
                      each other. This has reduced the time required for
                      theviicharacterization of MLLs from >10 hours to a few
                      minutes, allowing feedback on alens’ performance on the
                      same day it is manufactured.The wavefront error of an MLL is
                      a map of the relative deviation from the wavefrontof an
                      ideal lens, which can be related to the misplacements of its
                      layers, allowingsubsequent fabrication cycles to be improved
                      based on previous lens characteriza-tions. However, residual
                      aberrations remain that have to be corrected externally.
                      Asit becomes increasingly difficult to produce high NA MLLs
                      with the required preci-sion, they tend to have larger
                      aberrations. To correct these, a compound
                      refractivecorrector consisting of an array of individual
                      refractive elements had been proposed.For the first time,
                      such a design was realized based on nano-scale 3D printing
                      tocorrect an MLL pair for hard X-ray high-resolution
                      imaging, resulting in a recordfocusing of 2.9 nm ×2.8 nm at
                      17.5 keV.The well characterized and aberration corrected
                      MLLs were then used in a seriesof imaging schemes at the
                      PETRA III synchrotron and the European X-ray free elec-tron
                      laser. There, imaging techniques such as projection
                      holography and near-fieldptychography, which benefit from
                      the strong focusing of the lenses, were used withimproved
                      MLLs to achieve resolutions well below 10 nm. Novel imaging
                      techniquesthat are now possible due to high NA MLLs such as
                      convergent beam crystallographyhave been successfully
                      implemented. At high photon energies, where MLLs becomemore
                      efficient in contrast to other optics, the dark-field
                      imaging method of scanningCompton X-ray microscopy was
                      successfully used, allowing high-resolution imagingof
                      biological samples with minimal radiation dose. This method
                      in particular willbenefit significantly from fourth
                      generation synchrotrons, as their higher brightnessand
                      larger coherence in combination with better X-ray optics
                      allows for both higherresolution and faster data acquisition
                      times. This should enable 3D imaging ofmicroscopic samples
                      at high resolutions and low radiation doses.},
      cin          = {FS-ML / CFEL-I},
      cid          = {I:(DE-H253)FS-ML-20120731 / I:(DE-H253)CFEL-I-20161114},
      pnm          = {632 - Materials – Quantum, Complex and Functional
                      Materials (POF4-632) / 6G3 - PETRA III (DESY) (POF4-6G3) /
                      Ex-Net-0002-Phase2-3 - Advanced Imaging of Matter:
                      Structure, Dynamics and Control on the Atomic Scale - AIM
                      $(2018_Ex-Net-0002-Phase2-3)$},
      pid          = {G:(DE-HGF)POF4-632 / G:(DE-HGF)POF4-6G3 /
                      $G:(DE-HGF)2018_Ex-Net-0002-Phase2-3$},
      experiment   = {EXP:(DE-H253)P-P11-20150101 / EXP:(DE-H253)P-P07-20150101},
      typ          = {PUB:(DE-HGF)11},
      urn          = {urn:nbn:de:gbv:18-ediss-126347},
      doi          = {10.3204/PUBDB-2026-00727},
      url          = {https://bib-pubdb1.desy.de/record/646127},
}