LISA long-arm interferometry

The Laser Interferometer Space Antenna (LISA) will observe gravitational radiation in the millihertz band by measuring picometer-level fluctuations in the distance between drag-free proof masses over baselines of approximately 5 × 10 9 m. The measurement over each baseline will be divided into three parts: two ‘short-arm’ measurements between the proof masses and a fiducial point on their respective spacecraft, and a ‘long-arm’ measurement between fiducial points on separate spacecraft. This work focuses on the technical challenges associated with these long-arm measurements and the techniques that have been developed to overcome them.