Precision Mechanical Rotation Sensors for Terrestrial Gravitational Wave Observatories

Abstract

The LIGO gravitational-wave observatories are comprised of 4-km long dual-recycled Fabry-Perot Michelson interferometers. Each observatory deploys a multi-stage seismic isolation system to isolate from terrestrial seismic motion. These systems use seismometers to measure motion at a wide range of frequencies. Seismometers are inherently susceptible to contamination due to tilts arising from wind acting on the walls of the observatory. This contamination dominates seismometer readings at low frequency which limits the performance of LIGO's seismic isolation. We developed low-frequency inertial rotation sensors to subtract this tilt-contamination from ground seismometers. These sensors were deployed at both LIGO observatories which allowed the observatories to operate during high wind speeds. In addition, a compact inertial rotation sensor was developed with the capability of being deployed on the LIGO seismic isolation platforms. A prototype was built and tested. A theoretical control model was designed to exploit this novel sensor. This model predicts a significant decrease in control-noise leakage in the gravitational wave frequency band. These sensors have found application in a number of auxiliary fields. The ground rotation sensors have allowed for novel seismological studies while the compact rotation sensor has been applied to the study of Newtonian noise.