Validation of optical pathlength stability in a LISA test-bench demonstrator

The Laser Interferometer Space Antenna (LISA) observatory is a future L3 mission of the European Space Agency to detect gravitational waves, set to launch in 2035. The detector constellation will conduct interferometry to extreme precision over an unprecedented armlength of 2.5 million kms. In this paper, we present the development and testing results for the Zerodur interferometer (ZIFO), an optical demonstrator built to validate critical technology for the test setup of LISA’s interferometric core. Optical pathlength stability measurements on the ZIFO demonstrate successful reduction of bench noise to maintain the 10 pm Hz−1 specification across the 1 mHz to 1 Hz frequency band. We also identify and characterize dominant noise sources from phasemeters and correlations of beam tilt into the pathlength that are observed during the test campaign.