The Optical Truss Interferometer: A Convenient Solution for Picometer Sensitivity in the LISA Telescopes and Beyond

Abstract

The Laser Interferometer Space Antenna (LISA) is a planned space-based gravitational wave detector whose purpose is to observe the gravitational spectrum between 0.1 mHz - 1 Hz. The detector is formed by three spacecraft, each separated by 2.5 million km in a heliocentric orbit trailing behind the Earth. Each spacecraft is equipped with two telescopes that expand outgoing laser beams and compress a small fraction of large incoming beams from the other two spacecraft. These laser relays form the basis of the interferometry that will measure fluctuations in the distance between free-flying test masses aboard each spacecraft with a sensitivity goal of 10 pm/√Hz. Dimensional changes in the telescopes will contribute directly to the optical path of the interferometers, leading to a 1 pm/√Hz stability requirement for each telescope. The optical truss interferometer (OTI) is a contingent subsystem proposed for the LISA telescopes to aid in the verification of a 1 pm/√Hz optical path length stability. By mounting compact fiber-coupled units to the telescope structure to form Fabry-Perot cavities whose baselines are proportional to the telescope length, the dimensional stability of each cavity can be monitored with heterodyne readout methods. We have designed and developed prototype OTI units to demonstrate the capability of measuring stable structures, such as the LISA telescope, with a 1 pm/√Hz sensitivity using a set of freely mountable fiber-injected cavities. This dissertation will detail the design, development, and proof-of-concept for the optical truss interferometer as a powerful ``plug and play'' solution for the LISA telescope and ground testing of prototype stable structures.