Feedforward reduction of the microseism disturbance in a long-base-line interferometric gravitational-wave detector
Standing ocean waves driven by storms can excite surface waves in the ocean floor at twice the wave frequency. These traverse large distances on land and are called the double-frequency (DF) microseism. The Laser Interferometer Gravitational-wave Observatory (LIGO) detector relies on length servos to maintain optical resonance in its 4 km Fabry–Pérot cavities, which consist of seismically isolated in-vacuum suspended test mass mirrors in three different buildings. Correcting for the DF microseism motion can require tens of micrometers of actuation, a significant fraction of the feedback dynamic range. The LIGO seismic isolation design provides an external fine actuation system (FAS), which allows long-range displacement of the optical tables that support the test mass suspensions. We report on a feedforward control system that uses seismometer signals from each building to produce correction signals, which are applied to the FAS, largely removing the microseism disturbance independently of length control servos. The root-mean-squared displacement from the microseism near 0.15 Hz can be reduced by 10 dB on average.
© 2003 American Institute of Physics. Published Online: 16 January 2003 Accepted: September 2002. This work was supported by National Science Foundation Awards Nos. 9801158, 0107417 and 0071316, as well as Louisiana Board of Regents Contract No. LEQSF (2000-03)-RD-A-06. The authors also wish to thank the scientific and technical staff of LIGO, and the LSU physics shops.
Published - 1.1524717.pdf