X-ray topography of diffracting crystal optics at the Diamond Light Source

Abstract

Diffracting crystals are extensively used at synchrotron beamlines as X-ray monochromators and phase retarders. Imperfect growth processes, surface damage occurring during fabrication, and strain caused by poor clamping methods can all degrade the quality of these crystals and the X-ray beams diffracted by them. Because X-ray topography of these crystals can reveal both the location and the magnitude of these defects, it is now regularly used as an acceptance test for diffracting crystal optics at the Diamond Light Source synchrotron. Before installation on beamlines, crystal optics are inspected at the versatile bending-magnet B16 Test Beamline, where a variety of topographic techniques have been implemented with both white and monochromatic X-ray beams. A set of digital detectors permits rocking curve imaging with a choice of fields of view and spatial resolution down to 2 µm. Test crystals may be mounted in a variety of geometries according to need. For inspecting monochromator crystals fabricated for imaging applications, both on-the-fly scans and stitching techniques have been used to compose maps of surface defects. First crystals of multi-crystal monochromators have been tested under realistic cryocooled conditions, and their design has been improved to minimize strain. The Diamond Light Source's X-ray topography program serves not only its own beamlines, but also industrial users and other X-ray synchrotron facilities.