Laser interferometry for LISA and satellite geodesy missions

authored by
Katharina-Sophie Isleif
supervised by
Karsten Danzmann

The development and investigation of laser interferometry concepts for performing precise length measurements at frequencies below 1Hz is the main topic of this thesis. These concepts are quintessential for space-based measurements of gravitational waves or the Earth gravity field. For the Laser Interferometer Space Antenna (LISA) and future satellite geodesy missions, various interferometer types have been studied between 2014 and 2018 at the Albert Einstein Institute (AEI) in Hannover as a part of the work presented here. The first part of this thesis presents conceptual design studies of phase reference distribution systems (PRDSs) for LISA. The usage of Telescope Pointing is the baseline mechanism for the current LISA design and implies the need for a light-exchanging backlink connection between two rotating optical benches within one satellite. Different backlink implementations are presented and analyzed, the final choice however remains one of the last open questions for the LISA optical metrology. A test-bed for comparing three backlinks with each other in a single, so-called Three-Backlink interferometer (TBI) experiment, has been simulated and a detailed noise estimation, including a critical stray light analysis, is presented. A free-beam connection between two moving set-ups was established by which the full functionality of the experimental environment was validated. The design of the TBI has been completed and the experiment, consisting of two rotating quasi-monolithic optical benches, is currently under construction. The full experiment will enable to test the performance of LISA backlink candidates with a precision of 1 pm/√Hz in a relevant environment. The second part of this thesis describes alternative interferometer techniques for reducing the complexity of optical set-ups, while modern digital signal processing is applied for recovering the desired phase information. The simplifications in the optical part enables multi-channel operation and multi-degree of freedom readout, which is required for future gradiometers in satellites consisting of six or more test masses. An experiment simulating such a test mass readout with only a single optical component has been established. Interferometric readout noise levels of 1.0pm/√Hz at 100mHz were achieved by using deep frequency modulation interferometry (DFMI), a novel technique developed as part of this thesis.

QUEST-Leibniz Research School
Doctoral thesis
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