Abstract
The optical metrology system (OMS) of the LISA Pathfinder mission is measuring the distance between two free-floating test masses with unprecedented precision. One of the four OMS heterodyne interferometers reads out the phase difference between the reference and the measurement laser beam. This phase from the reference interferometer is common to all other longitudinal interferometer read outs and therefore subtracted. In addition, the phase is fed back via the digital optical pathlength difference (OPD) control loop to keep it close to zero. Here, we analyse the loop parameters and compare them to on-ground measurement results.
Highlights
LISA Pathfinders (LPF) main measurement [1] is the acceleration between two test masses (TM)
The relative TM positions are determined by the optical metrology system (OMS) using heterodyne interferometry [2]
The phase difference of the so-called reference and the measurement laser beam is measured at the heterodyne frequency of fhet = 1 kHz. Both beams are generated from a single laser source (Nd:YAG, λ=1064 nm) at the laser modulator unit (LMU)
Summary
LISA Pathfinders (LPF) main measurement [1] is the acceleration between two test masses (TM). 1. Introduction LISA Pathfinders (LPF) main measurement [1] is the acceleration between two test masses (TM). This results in a variation of the optical pathlength difference (OPD) between the reference and the measurement beam. The varying phase (Ψr) between the beams is measured in the reference interferometer.
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