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

Abstract

We present a systematic 2D spatial-coherence analysis of the soft-X-ray beamline P04 at PETRA III for various beamline configurations. The influence of two different beam-defining apertures on the spatial coherence properties of the beam is discussed and optimal conditions for coherence-based experiments are found. A significant degradation of the spatial coherence in the vertical direction has been measured and sources of this degradation are identified and discussed. The Fourier-analysis method, which gives fast and simple access to the 2D spatial coherence function of the X-ray beam, is used for the experiment. Here, we exploit the charge scattering of a disordered nanodot sample allowing the use of arbitrary X-ray photon energies with this method.

Enabling time-resolved 2D spatial-coherence measurements using the Fourier-analysis method with an integrated curved-grating beam monitor

“…This result is in very good agreement with a beamvibration analysis performed using a beam-diagnostic tool specifically designed to map out the full photon-beam caustic. The beam-vibration analysis using this tool revealed vertical beam-vibration amplitudes of around 125 nm in the horizontal and 500 nm in the vertical directions [10]. From simulated SAXS experiments using the disordered nanodots, we found that vibrations of 680 nm do not have any effect on the extracted spatial-coherence properties using the Fourier-analysis method.…”

“…Using the obtained transverse coherence lengths in horizontal and vertical directions l s,x = (1.18 ± 0.04) µm and l s,y = (5.95 ± 0.53) µm, respectively, global degrees of coherence of ζ x = (13 ± 1)% and ζ y = (50 ± 3)% are determined. This results in a total degree of coherence of ζ t = ζ x ζ y = (6.5 ± 2)%, which reflects mainly the large horizontal source size of PETRA III when using the full beam [10].…”

“…As a consequence, spatial-coherence degradation effects caused by optics vibrations can be uncovered and investigated. In our previous studies [9,10], the beam-intensity distribution required for the Fourier-analysis method had to be determined separately by scanning a 1 µm pinhole in front of a photodiode, which makes time-resolved spatial-coherence measurements feasible only under certain conditions. Recently, it has been demonstrated that a sample carrying a grating that forms an off-center zoneplate segment can be used for photon-beam monitoring in X-ray transmission experiments, allowing the detection of the photonbeam position as well as its 2D intensity distribution [11,12].…”

Photoelectron circular dichroism in angle-resolved photoemission from liquid fenchone

“…The minimum spot size of the beamline (using smaller exit-slit openings than 30 μm) has been measured as 10 × 10 μm 2 ( h × v ) in the nominal focus position of the optics. 44,45 For our experiment, due to spatial constraints, the interaction region had to be placed approximately 220 mm downstream of that position; the vertical focus however was shifted accordingly using a pair of Kirkpatrick–Baez mirrors. 43 We correspondingly estimate the beam spot size at the point of interaction to be 180 × 35 μm 2 ( h × v ).…”

The PERCIVAL detector: first user experiments

“…5(a) shows a series of speckle patterns from a static sample. The sample was a spatially disordered nanodot array made from a homogeneous metallic multilayer (Co 1.65 nm /Pt 2 nm ) 2 fabricated by nanosphere lithography (Bagschik et al, 2020). In the experiment, a series of 1000 patterns was taken with an exposure time of Át min = 0.12 s per pattern.…”