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- Kharitonov, Konstantin, et al.
(author)
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Flexible ptychography platform to expand the potential of imaging at free electron lasers
- 2021
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In: Optics Express. - 1094-4087. ; 29:14, s. 22345-22365
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Journal article (peer-reviewed)abstract
- Ptychography, a scanning coherent diffraction imaging method, can produce a high-resolution reconstruction of a sample and, at the same time, of the illuminating beam. The emergence of vacuum ultraviolet and X-ray free electron lasers (FELs) has brought sources with unprecedented characteristics that enable X-ray ptychography with highly intense and ultra-fast short-wavelength pulses. However, the shot-to-shot pulse fluctuations typical for FEL pulses and particularly the partial spatial coherence of self-amplified spontaneous emission (SASE) FELs lead to numerical complexities in the ptychographic algorithms and ultimately restrict the application of ptychography at FELs. We present a general adaptive forward model for ptychography based on automatic differentiation, which is able to perform reconstructions even under these conditions. We applied this model to the first ptychography experiment at FLASH, the Free electron LASer in Hamburg, and obtained a high-resolution reconstruction of the sample as well as the complex wavefronts of individual FLASH pulses together with their coherence properties. This is not possible with more common ptychography algorithms.
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| 2. |
- Wodzinski, Thomas, et al.
(author)
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High-harmonic generation wave front dependence on a driving infrared wave front
- 2020
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In: Applied Optics. - : Optical Society of America. - 1559-128X .- 2155-3165. ; 59:5, s. 1363-1370
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Journal article (peer-reviewed)abstract
- With high-harmonic generation (HHG), spatially and temporally coherent XUV to soft x-ray (100 nm to 10 nm) table-top sources can be realized by focusing a driving infrared (IR) laser on a gas target. For applications such as coherent diffraction imaging, holography, plasma diagnostics, or pump-probe experiments, it is desirable to have control over the wave front (WF) of the HHs to maximize the number of XUV photons on target or to tailor the WF. Here, we demonstrate control of the XUV WF by tailoring the driving IR WF with a deformable mirror. The WFs of both IR and XUV beams are monitored with WF sensors. We present a systematic study of the dependence of the aberrations of the HHs on the aberrations of the driving IR laser and explain the observations with propagation simulations. We show that we can control the astigmatism of the HHs by changing the astigmatism of the driving IR laser without compromising the HH generation efficiency with a WF quality from lambda/8 to lambda/13.3. This allows us to shape the XUV beam without changing any XUV optical element.
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