Abstract
This study theoretically analyzes an increase in X-ray absorption by a grazing incidence mirror due to its surface roughness. We demonstrate that the increase in absorption can be several hundred times larger than predicted by the Nevot-Croce formula. As a result, absorption enhances by several times compared to a perfectly smooth mirror despite the extremely small grazing angle of an incident X-ray beam (a fraction of the critical angle of the total external reflection) and the high quality of the reflecting surface (the roughness height was 0.5 nm in modeling). The main contribution to the absorption increase was dictated by the mid-scale roughness (waviness) of the virgin substrate surface, whose quality thus defines an absorption enhancement. The approach was applied to the analysis of two real mirrors used in a synchrotron (BESSY-I) and a European X-ray free-electron laser (XFEL) beamline. The modern surface finishing technology of elastic emission machining provides extremely low substrate waviness, guaranteeing the negligible effect of the surface roughness on the absorption increase.
Highlights
The mirrors placed in beamlines of 3rd generation synchrotrons and, especially, X-ray free electron lasers must withstand an extremely high radiation load and should absorb as small a portion of the incident radiation power as possible
The surface roughness scatters part of the incident beam into the mirror depth, resulting in increasing radiation absorption and enhancing the thermal deformation of a mirror placed in a synchrotron, especially X-ray free-electron laser (XFEL) beamlines
We first analyzed the general principles of the roughness effect on the X-ray absorption based on a simplified roughness model using the power spectral density (PSD) function determined in Eq (6)
Summary
The mirrors placed in beamlines of 3rd generation synchrotrons and, especially, X-ray free electron lasers must withstand an extremely high radiation load and should absorb as small a portion of the incident radiation power as possible. For this purpose, the mirrors should be installed with respect to the incident beam at a very small grazing angle θ0, which should be a fraction of the critical angle θc of the total external reflection (TER). According to Eq (3), the radiation absorption is increased and the absorptivity is written at very small grazing incidence angles as
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
