Wavelength–angle characterization of high-energy X-ray beams from lapped Si(111) double-crystal monochromators using rocking-curve tomography

Lapping the surfaces of Si(111) crystals in a double-crystal monochromator (DCM) has recently been shown to increase the 100 keV X-ray beam intensity by nearly an order of magnitude, raising the need for a reliable experimental evaluation of the resulting beam quality, particularly wavelength spread (energy bandwidth) and angular divergence. To address this need, a method for determining the wavelength-angle distribution of high-energy X-ray beams is developed by interpreting rocking-curve measurements as projections in wavelength-angle (DuMond) space and reconstructing the distribution using an iterative computed-tomography approach. When applied to beams produced with polished and lapped Si(111) DCMs, the method reproduces the DuMond prediction for perfect crystals and reveals systematic changes in wavelength spread while the angular divergence remains nearly unchanged. These results demonstrate a practical framework for experimentally characterizing the wavelength-angle distributions of high-energy X-ray beams, providing a basis for understanding and optimizing beam properties beyond conventional one-dimensional metrics.