Enhanced grating characterization method for absorbing X-ray gratings by bidirectional angular X-ray transmission

High-quality X-ray absorption gratings are essential for grating-based X-
ray phase-contrast imaging. Bidirectional angular X-ray transmission measurements,
as proposed in this work, allow for large-area and nondestructive characterization of
these gratings.
A custom setup consisting of two rotational axes is used to measure the transmission
of X-ray absorption gratings under rotation. From the transmission values and rotation
angles, pixelwise transmission profiles are reconstructed. From these transmission
profiles, parameter maps that carry information about the microstructure of the
grating are retrieved via a fitting procedure. Compared to unidirectional angular X-
ray transmission measurements, more detailed and complementary parameter maps
are obtained, revealing more defects and parameter variations. Apart from duty
cycle, absorber height, and absorber inclination, the bidirectional measurements also
provide access to grating lamella rotation on the substrate and to auxiliary structures
introduced to increase grating stability.
Furthermore, a novel correction technique is introduced to address projective
distortions in individual radiographs caused by the rotations. ... mehrThis method relies
on calibration phantom measurements to track the movement of registration points
under the same rotations as the gratings. Based on the movement of the registration
points, the distortions are reconstructed, and appropriate deformation vector fields are
calculated and applied to measurement data, achieving a correction with a precision
of about two pixels.