vendredi 27 août 2021
La soutenance de thèse de Maëlle LE GAL aura lieu le vendredi 3 septembre 2021 à 14h00 dans la salle de conférence du Château, à Meudon.
La thèse sera également accessible en visioconférence via le lien :
Elle sera soutenue en anglais.
"High-resolution, space spectropolarimeters for a wide ultra-violet range : design and tests"
Several space mission projects, such as LUVOIR, Arago, PolStar or CASSTOR, plan to use a spectropolarimeter op- erating in the ultraviolet (UV) range. The main goals of these instruments is the study of stars and their environment, in particular their magnetic fields and magnetospheres, as well as the interstellar medium and exoplanets. However, high-resolution spectropolarimeters operating over a wide spectral range only exist on instruments on Earth and in the visible or infrared wavelength ranges. The work carried out in this thesis aims at studying prototype polarimeters in order to design and optimize them over the wavelengths of interest. Several wavelength ranges were considered, depending on the studied instruments, between 90 and 400 nm. Two prototypes were studied : one using birefringent materials and operating by transmission, and one operating exclusively by reflection. An optimization method was developed to maximize the efficiency of the polarimeters for the chosen wavelength ranges. Finally, three experiments were set up to test these two prototypes optically and thermally. Two experiments were designed to test the transmission polarimeter. First, it was tested in the UV and in vacuum in order to measure the polarimetric efficiencies of the prototype under its operating conditions. Then, examples of the modulator used in this polarimeter underwent a series of thermal cycles to study the resistance of molecular adhesion of its plates. Finally, the third experiment tests a prototype by reflection using gold mirrors. This experiment also allows us to measure the polarimetric properties of some materials foreseen for such polarimeters and thus better simulate the studied polarimeters. The methods used to optimize and design the polarimeters as well as the experiments carried out and their results are presented in this thesis.
