Thesis defense of Amr MAHMOUD

Thesis defense of Amr MAHMOUD, PhD student in the Optics XUV group of the Laboratoire Charles Fabry, on Monday 25 September 2023 at 2pm in the Auditorium of the Institut d'Optique Graduate School in Palaiseau, on the topic: "Multilayer diffraction gratings with broadband efficiency in the extreme ultraviolet."

Abstract: "Recently, the development of high-density multilayer optical gratings has allowed for increased efficiency and spectral resolution in the extreme ultraviolet (EUV) spectral range, enabling the realization of ultra-high-resolution spectrometers and Spectro imagers for solar observation. This thesis presents an experimental and modeling study of high-density EUV multilayer gratings to optimize diffraction efficiency in a wavelength range from 17nm to 30nm. This work is part of the development of an EUV Spectro-imager for the Japanese Solar-C mission. The magnetron sputtering technique was used to deposit Al/Mo/SiC multilayers optimized for various wavelength ranges on lamellar gratings ( 4000 lines/mm) with depths ranging from 5nm to 20nm. All samples were characterized before and after multilayer deposition using atomic force microscopy (AFM) and grazing incidence X-ray reflectometry (GIXR) at 8.05 keV. The evolution of the surface profile with an increasing number of deposited layers was observed through AFM measurements and confirmed by cross-sectional analysis using transmission electron microscopy. The EUV diffraction efficiency of the multilayer gratings was measured in different orders using synchrotron radiation (XUV metrology beamline of the SOLEIL synchrotron). The obtained results are in excellent agreement with numerical simulations performed using rigorous coupled-wave analysis (RCWA), incorporating the structural parameters determined by AFM and GIXR. The measured first-order efficiency at normal incidence reached 8.1% in the spectral range of 17-21 nm, surpassing the efficiency of the grating used in the previous Solar B mission. Moreover, the use of aperiodic multilayer stacks on the grating demonstrated high efficiencies over an extended wavelength range. This work paves the way for the development of high-performance instruments for EUV spectroscopy with increased resolution or Spectro-imaging applications."