Enhanced Energy Resolution of Synchrotron Multispectral CT based on a Silicon Wafer Edge as Spectral‑Splitting Optics

Multispectral imaging at synchrotrons is of great importance since it enables the simultaneous acquisition of structural and chemical information while reducing implicitly beam hardening artefacts. This allows complex samples from the fields of materials sciences, biology, cultural heritage and others to be analyzed non-destructively. Such a comprehensive approach provides deeper insights into processes and properties that are not accessible with standard integrating detectors alone. At synchrotrons, multispectral imaging is usually based on spectral-dispersive optics for high photon fluxes, as energy-resolved detectors suffer from pile-up under synchrotron radiation. The flagship BM18 beamline at the ESRF, with a beam width of over 300 mm and a spectral width of up to 400 keV, is an ideal source of radiation for such a multispectral imaging approach. In this paper, we propose a 90° cut Si wafer edge as an effective, low-cost refractive optic compared to the Si prism array (100 prisms) inspired by prism-based setups in the literature. For the tungsten K-edge (69.5 keV), the prism array produces a beam shift of 25 pixels, while the wafer edge produces 174 pixels, which corresponds to a 7-fold higher refraction. The wafer edge thus enables shorter distances between the optics and the detector or higher energy resolution.