Perspective: Towards single shot time-resolved microscopy using short wavelength table-top light sources
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Abstract:
Time-resolved imaging allows revealing the interaction mechanisms in the microcosm of both inorganic and biological objects. While X-ray microscopy has proven its advantages for resolving objects beyond what can be achieved using optical microscopes, dynamic studies using full-field imaging at the nanometer scale are still in their infancy. In this perspective, we present the current state of the art techniques for full-field imaging in the extreme-ultraviolet- and soft X-ray-regime which are suitable for single exposure applications as they are paramount for studying dynamics in nanoscale systems. We evaluate the performance of currently available table-top sources, with special emphasis on applications, photon flux, and coherence. Examples for applications of single shot imaging in physics, biology, and industrial applications are discussed.Keywords:
Single shot
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We demonstrate a single shot measurement technique to quantify ground state coherence in atomic system. The quantifier identifies the transition from EIT to Autler- Townes regime. Furthermore, we demonstrate phase coherent control and freezing coherence against decoherence. © 2019 The Author(s)
Single shot
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We formulate coherent diffractive imaging in the framework of partially spatially coherent diffraction. We find that the reconstruction can be critically dependent on the degree of coherence in the illuminating field and that even a small departure from full coherence may invalidate the conventional assumption that a mapping exists between an exit surface wave of finite support and a far field diffraction pattern. We demonstrate that the introduction of sufficient phase curvature in the illumination can overcome the adverse effects of partial coherence.
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Coherent Diffraction Imaging (CDI) is an experimental technique to get images of isolated structures by recording the light scattered off the sample. Thanks to the extremely bright and short coherent light pulses provided by X-ray Free Electron Lasers, CDI makes it possible to study nanostructures in the gas phase and get time-resolved snapshots of their ultrafast dynamics with unprecedented resolution. In principle, the sample density can be recovered from the scattered light field through a straightforward Fourier Transform operation. However, only the amplitude of the field is recorded, while the phase is lost during the measurement process and has to be retrieved by means of suitable, well-established, phase retrieval algorithms. We present the Memetic Phase Retrieval (MPR) method, an improved approach to the phase retrieval problem, which makes use of a combination of existing phase retrieval algorithms and evolutionary algorithms to mitigate the shortcomings of conventional approaches. We benchmark the method on experimental data acquired in two experimental campaigns at SwissFEL and European XFEL. Imaging results on isolated nanostructures reveal considerable stability of the algorithm's behavior on the input parameters, as well as the capability of identifying the solution in challenging conditions. A user-friendly implementation of the MPR method is released as open-source software, aiming at being a reference tool for the FEL imaging community.
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Coherent diffraction imaging
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Phase imaging
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Coherent diffraction imaging
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Coherent diffraction imaging
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The complete characterization of spatial coherence is difficult because the mutual coherence function is a complex-valued function of four independent variables. This difficulty limits the ability of controlling and optimizing spatial coherence in a broad range of key applications. Here we propose a method for measuring the complete mutual coherence function, which does not require any prior knowledge and can be scaled to measure arbitrary coherence properties for any wavelength. Our method can also be used to retrieve objects illuminated by partially coherent beam with unknown coherence properties. This study is particularly useful for coherent diffractive imaging of nanoscale structures in the X-ray or electron regime. Our method is not limited by any assumption about the illumination and hence lays the foundation for a branch of new diffractive imaging algorithms.
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Coherence theory
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Coherence time
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The evolution from 3rd to 4th generation synchrotron radiation (SR) sources significantly enhanced their coherence, making coherent scattering techniques such as coherent X-ray diffraction imaging (CXDI) and X-ray photon correlation spectroscopy (XPCS) more accessible. We take advantage of a coherent modes decomposition and propagation model to carry out coherence analysis and simulations of CXDI experiments for the coherent Hard X-ray Coherent Scattering (HXCS) beamline at High Energy Photon Source.
Coherent diffraction imaging
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Coherence time
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