Abstract
Femtosecond pulse x-ray imaging is demonstrated in a sample-multiplexed Fourier transform holography scheme. Parallel imaging of multiple samples over an extended field of view is achieved by exploiting the coherence properties of the free-electron laser (FEL) source and the large profile of the unfocused x-ray pulse. The resulting photon flux density per pulse allows for damage-free single-pulse imaging with moderate image resolution. We envision the application of the method for femtosecond time-resolved pump–probe experiments with the feasibility of recording multiple steps in time with a single pulse. Furthermore, the scheme presented allows for a characterization of FEL radiation pulse parameters.
Highlights
The coherence properties of the free-electron laser (FEL) radiation, we are able to simultaneously image several samples over a large field of view (FOV)
Parallel imaging of multiple samples over an extended field of view is achieved by exploiting the coherence properties of the free-electron laser (FEL) source and the large profile of the unfocused x-ray pulse
Taking the intensity fluctuation of the FEL and the finite detector size into account, this value is in good agreement with our previous estimate and corresponds to a mean density of detected photons on the sample of 1.1 × 104 photons μm−2
Summary
The development of FTH in the x-ray wavelength range was largely promoted by the increasing availability of highly coherent intense x-ray beams at modern third-generation synchrotrons and by the increasing capabilities in nano-fabrication. The distance between the sample and the reference hole has to be smaller than the transverse coherence length of the beam, in order to allow interference between the scattered waves. If the distance between the samples is increased and becomes much longer than the x-ray coherence length, the diffraction patterns of the samples will add up incoherently on the detector and the cross-correlation terms will vanish in the reconstruction [15]. A reference pinhole should be associated with each sample within the coherence length, in order to achieve an image reconstruction with high contrast. Another limitation related to the object–reference distance is given by the number of detector pixels used in the experiment. With respect to femtosecond imaging applications at FELs, holography concepts can be employed to realize time-resolved experiments [8, 15]
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