Spatial coherence determination from the Fourier analysis of a resonant soft X-ray magnetic speckle pattern

Abstract

We present a method to determine the two-dimensional spatial coherence of synchrotron radiation in the soft X-ray regime by analyzing the Fourier transform of the magnetic speckle pattern from a ferromagnetic film in a multidomain state. To corroborate the results, a Young's double-pinhole experiment has been performed. The transverse coherence lengths in vertical and horizontal direction of both approaches are in a good agreement. The method presented here is simple and gives a direct access to the coherence properties of synchrotron radiation without nanostructured test objects.

Direct 2D spatial-coherence determination using the Fourier-analysis method: multi-parameter characterization of the P04 beamline at PETRA III

“…Due to the simple and fast analysis, spatial-coherence measurements for various beamline settings can be carried out in a short time to optimize beam properties and re-check them during an experiment. The wavelength limitation present in our previous study [36] is overcome by using a nano-structured sample producing small-angle X-ray scattering from a charge inhomogeneity instead of a magnetic one. For this purpose, a highly spatially disordered nanodot array is used.…”

“…For this purpose, a highly spatially disordered nanodot array is used. Exploiting the small-angle X-ray scattering from a charge inhomogeneity for the Fourier-analysis method allows for a 2D spatial-coherence analysis not only for certain energies in the soft X-ray range, as in our previous study [36], but for arbitrary energies into the tender X-ray range, as presented here. Extension into hard X-rays should be feasible with adapted samples.…”

“…Amplitude interferometric techniques are based on amplitude-correlation measurements and thus on first-order correlation functions. The most prominent candidate is Young's double-pinhole experiment, but more advanced techniques have been developed over the last decades, which even allow for a direct two-dimensional analysis of the coherence properties in a short time, e.g., near-field speckle pattern analysis [33,34], circular phase-grating interferometry [35], or the Fourier-analysis method [36]. Intensity interferometry exploits second-order intensity correlation functions.…”

“…A significant reduction of the vertical spatial coherence compared to theoretical expectations is found and sources of this degradation are identified. We use the Fourier-analysis method detailed in [36] that allows for the determination of the full two-dimensional spatial (transverse) coherence function and hence the transverse coherence length of the X-ray radiation directly from a single far-field X-ray speckle pattern. Due to the simple and fast analysis, spatial-coherence measurements for various beamline settings can be carried out in a short time to optimize beam properties and re-check them during an experiment.…”

Employing soft x-ray resonant magnetic scattering to study domain sizes and anisotropy in Co/Pd multilayers

“…To measure the coherence of the beam we performed a Young´s double-pinhole experiment. Using the 40-μm illumination pinhole and a monochromator exit slit of 200 μm, a transverse coherence length of more than 15 μm in both horizontal and vertical directions was obtained [33].…”