The Advanced Virgo Gravitational Wave Detector: Study of the optical design and development of the mirrors

Gravitational waves have been predicted by Einstein in his General Relativity theory. They are perturbation of the space-time metric and we try to reveal them by laser interferometry. More precisely, gravitational wave detectors are km long Michelson interferometers combined with Fabry-Perot cavities. The network of first generation detectors (Virgo, LIGO, GEO) did not permit a direct detection after several observational runs in coincidence at the nominal sensitivity. A second generation of detectors is in preparation with in particular the European project Advanced Virgo. This detector should have a sensitivity increased by an order of magnitude compared to Virgo. The interferometer mirrors play a crucial role in the Advanced Virgo sensitivity as it is limited by the mirror thermal noise in the mid-frequency region and by the amount of photons collected in the interferometer cavities at high frequencies. The high power circulating in the Fabry-Perot cavities induces important thermal lensing effect. This thesis is interested first in the thermal lensing effect in the interferometer for different optical configurations. Then we are interested in the mirrors composing the Fabry-Perot arm cavity from the calculation of the requirements in terms of flatness to the realization of the mirrors flatness and its measurement. The mirror flatness should be sub-nanometric in order to limit the optical losses in the Fabry-Perot cavities to reduce the effect of the shot noise and of the diffused light. We will see the correction of the substrates flatness by the so-called corrective coating technique. Finally, we study the uniformity of the dielectric multilayer coating deposition necessary to obtained high-reflective mirrors. We study in particular the planetary motion of the substrates in the coating machine. (author)