The LTP interferometer and phasemeter

The LISA Technology Package (LTP), to be launched by ESA in 2006/2007, is a technology demonstration mission in preparation for the LISA space-borne gravitational wave detector. A central part of the LTP is the optical metrology package (heterodyne interferometer with phasemeter) which monitors the distance between two test masses with a noise level of 10 pm Hz-1/2 between 3 mHz and 30 mHz. It has a dynamic range of >100 μm without any actuators for the pathlength. In addition to the longitudinal measurements, it provides alignment measurements with an expected noise level of <10 nrad Hz-1/2. While the basic design has been described previously by Heinzel et al (2003 Class. Quantum Grav. 20 S153-61), this paper gives new details on the laser stabilization, the phasemeter and recent prototype results