rafaelcelestre / celestre_phd_thesis

PhD thesis presented by Rafael CELESTRE (01/02/2021)

Investigations of the effect of optical imperfections on partially coherent X-ray beam by combining optical simulations with wavefront sensing experiments

PhD thesis presented by Rafael CELESTRE (01/02/2021)

Key-words: Optical simulations, X-ray lenses, CRL, at-wavelengh metrology, speckle-tracking, physical optics

In physical optics, weakly focusing elements are usually simulated as a single thin element. While a single X-ray lens at typical operation conditions can often be represented in this way, simulating a full lens stack with a similar approach lacks versatility. This work proposes decomposing a lens stack into its lenslets separated by a free-space propagation, similar to the multi-slicing techniques already used for optical simulations. Attention is given to modelling the single lens element by adding additional degrees of freedom allowing the modelling of typical misalignments and fabrication errors. Orthonormal polynomials for optical aberrations as well as metrology data obtained with X-ray speckle vector tracking (XSVT) are also used to obtain realistic simulation results, which are presented in several coherent- and partially-coherent simulations throughout this work. Implementing a model of X-ray lenses using metrology data allows extraction of the accumulated figure errors and enables the calculation of phase corrections. Finally, this thesis presents a methodology for calculating the profile of refractive correctors, which is applied to produce phase plates ablated from diamond. Early experimental results show an improvement on the beam profile. This project addressed important aspects of the ESRF-EBS X-ray optics R&D programme as laid out in the strategic upgrade plan (Orange book).