Kevin ROSENZIVEIG : "From acoustic wave cavities to optomechanics"

Abstract : This PhD work continues and reinforces recent investigations on bulk acoustic wave resonators at cryogenic temperature (typically 4 Kelvins). In such operating conditions their unique properties open up new applications in different fields, from ultra-stable oscillators to hybrid quantum systems. For all these areas of research, new low-loss devices can play a game changing role. This work, which is oriented towards optomechanics, explores the possibilities of light-based actuation of an acoustical cavity with the horizon of building a cryogenic oscillator with such a cavity. Without loss of generality, the selected cavity is a quartz crystal resonator, adapted to the usage requirements with cryogenic environment. The first part of this thesis focuses on the theoretical and experimental study of optical Fabry-Perot cavities with absorptive mirrors, most notably with a novel method to extract the index of refraction of thin metallic films based on their particular properties when used in an optical cavity, i.e. a broadened Full Width at Half Maximum with respect to the non-absorptive case, as well as a frequency shift between the transmitted and the reflected peaks. In the second part, an analysis is performed on different means of mechanical actuation by light, i.e. by the photothermal force, the radiation pressure force and the electrostrictive force. An experimental study of the former demonstrates in particular the feasability of photothermal actuation at frequencies exceeding some Megahertz. The conclusion opens gives way to some perspectives, and specifically about other geometries which may potentially optimize the optomechanical coupling.

Jury Composition :

M. Serge GALLIOU Professeur des universités Université Bourgogne Franche-Comté - PhD Director
M. Pierre-François COHADON Maître de conférences Ecole Nationale Supérieure - PhD co-director
M. Nicolas PASSILLY Chargé de recherche CNRS - PhD Co-supervisor
M. Gilles TESSIER Professeur Sorbonne-Université, Institut de la Vision - Reviewer
M. Olivier LLOPIS Directeur de recherche CNRS, LAAS Reporter
M. Ludovic BELLON Chargé de recherche ENS Lyon Reporter

Localization : Amphithéâtre Jules Haag - ENSMM 26, Rue de l'Epitaphe 25000 Besançon