Hard X-ray free electron lasers provide almost fully transverse coherent X-rays. Though the natural divergence of these X-rays is a few micro-radians, they still need to be collimated or focused while traveling up to 1km towards the sample. This can be done with beryllium compound refractive lenses (CRLs). Due to the coherence of the beam, it is important that the impurities or granular boundaries in these CRLs do not distort the wavefront of the X-ray beam to a measurable extend. We measured the SAXS signal of various beryllium grades and of 2D parabolic lenses made of IF-1 beryllium. Then, we imaged these samples using X-ray computed laminography at a resolution of around 1 micrometer. Computed laminography is a 3D imaging technique similar to computed tomography, but particularly adapted for at extended objects. These measurements are used to characterize the voids and granular boundaries in the beryllium samples. Boundaries between the former powder particles are easily seen for beryllium grades produced via powder metallurgy methods. This is not the case for cast ingots. Common to all samples are voids with diameters in the 10 micrometer range as well as smaller sized, denser impurities. Finally, we use wavefront propagation simulations in order to analyze the effect of voids in the CRLs on the wavefront of the XFEL beam. If the distance "lens to focus and sample" is large enough, the diffraction patterns emerging from the voids smoothen out.

Date Published: 5 September 2014
PDF: 12 pages
Proc. SPIE 9207, Advances in X-Ray/EUV Optics and Components IX, 920702 (5 September 2014); doi: 10.1117/12.2061127

Published in SPIE Proceedings Vol. 9207:
Advances in X-Ray/EUV Optics and Components IX
Christian Morawe; Ali M. Khounsary; Shunji Goto, Editor(s)