Interferometric mapping of test mass surfaces for precise position determination in inertial sensors

• Autor(a) principal: Vilas, João Pedro Bento
• Data de Publicação: 2018
• Tipo de documento: Dissertação
• Idioma: eng
• Título da fonte: Repositório Científico de Acesso Aberto de Portugal (Repositórios Cientìficos)
• Texto Completo: http://hdl.handle.net/10362/36899
• topic: Interferometry; heterodyne interferometry; surface measurements; center of mass determination; Domínio/Área Científica::Engenharia e Tecnologia::Outras Engenharias e Tecnologias

Novel inertial reference sensors for space applications using optical readout of a Spherical proof mass (SPM), which enable full drag-free operations, are being studied for future space programs such as Laser Interferometer Space Antenna (LISA) and Big Bang Observer. Using this concept results in the reduction of residual acceleration noise by the proof mass, but with the SPM under rotation the surface topography induces errors in the center of mass position determination due to factors like surface finish, that changes the optical path length on a nanometer scale, and the reflection angle. To determine successfully the center of mass position with picometer accuracy, a surface map of the proof mass is necessary in order to correct the measurement data, thus improving the precision of the position determination. An experimental setup using double heterodyne interferometer in opposing configuration developed by Airbus, Friedrichshafen, is used to map one single surface circumference of a continuously rotating proof mass. In this thesis, enhancements were done to allow a complete surface map of the SPM with picometer accuracy at relevant angular frequencies. Enhancements made were: The inertial-mass degrees of freedom were increased by adding a second rotational stage. Overall software performance has been improved by implementing fast angle read-out by the encoders. Code in LabVIEW and MATLAB has been developed, capable of making a full 2D surface map of the SPM for calibration of errors in the determination of the position of the center of mass. Data acquisition has been sped up to enable low-noise full 2D surface maps.