Expanding a polarized synchrotron beam for full-field x-ray fluorescence imaging

Full-field x-ray fluorescence (XRF) imaging is an efficient technique for investigating element composition of a sample and the corresponding spatial distribution. Eliminating scattering x-rays is important for visualizing diluted/trace elements clearly. However, using the linear polarization of synchrotron radiation to remove scattering in full-field XRF imaging has not been feasible for many years because a synchrotron beam is inherently narrow in the direction perpendicular to the polarization and a large imaging area and a low scattering background cannot be simultaneously achieved. In this study, the trade-off was solved by expanding a synchrotron beam in the direction perpendicular to the polarization using an asymmetric-cut Si crystal. Large areas of samples were illuminated. In addition, a collimator plate, which only transmitted scattering x-rays that spread in the polarization direction, was used for imaging. Therefore, the detected scattering intensity was low. The present full-field XRF imaging scheme with a size-expanded polarized synchrotron beam is well suited for visualizing diluted/trace elements. It could be extended to x-ray absorption edge fine structure imaging for analyzing the chemical state of diluted/trace elements in inhomogeneous samples.