Coherent small-angle scattering on a bending-magnet beamline at the ESRF

Area of Science:

• Synchrotron Radiation and X-ray Optics
• Materials Science and Condensed Matter Physics

Background:

• Coherent X-ray beams are crucial for advanced imaging and scattering experiments.
• The D2AM bending-magnet beamline (BM2) at the European Synchrotron Radiation Facility (ESRF) provides X-ray radiation.
• Achieving high coherence from bending magnet sources requires careful optical design and beam selection.

Purpose of the Study:

• To characterize the coherence properties of the X-ray beam generated at the D2AM BM2 beamline.
• To assess the suitability of the beam for quantitative analysis in small-angle scattering experiments.
• To identify sources of incoherence and propose improvements.

Main Methods:

• Utilized permanent convergent optics and an Si(111) double monochromator to select a coherent portion of the X-ray beam.
• Employed a high-resolution direct-illumination CCD area detector for data acquisition.
• Performed quantitative analysis of the small-angle scattering setup stability and compared calculated and measured coherence degrees.

Main Results:

• A high degree of coherence was achieved, compensating for low beam intensity (10^6 X-rays/s).
• The X-ray beam was found to be composed of approximately two-thirds coherent and one-third incoherent parts.
• The incoherent component was identified as originating from Kapton windows in the beamline.

Conclusions:

• The experimental setup enables quantitative analysis due to its stability.
• The presence of Kapton windows significantly contributes to beam incoherence.
• Removal of Kapton windows is expected to further enhance beam coherence in future experiments.