To meet the overall isolation and alignment requirements for the optics in Advanced LIGO, the planned upgrade to LIGO, the US laser interferometric gravitational wave observatory, we are developing three sub-systems: a hydraulic external pre-isolator for low frequency alignment and control, a two-stage active isolation platform designed to give a factor of ~1000 attenuation at 10 Hz, and a multiple pendulum suspension system that provides passive isolation above a few hertz. The hydraulic stage uses laminar-flow quiet hydraulic actuators with millimeter range, and provides isolation and alignment for the optics payload below 10 Hz, including correction for measured Earth tides and the microseism. This stage supports the in-vacuum two-stage active isolation platform, which reduces vibration using force feedback from inertial sensor signals in six degrees of freedom. The platform provides a quiet, controlled structure to mount the suspension system. This latter system has been developed from the triple pendulum suspension used in GEO 600, the German/UK gravitational wave detector. To meet the more stringent noise levels required in Advanced LIGO, the baseline design for the most sensitive optics calls for a quadruple pendulum, whose final stage consists of a 40 kg sapphire mirror suspended on fused silica ribbons to reduce suspension thermal noise.
The GEO 600 laser interferometer with 600m armlength is part of a worldwide network of gravitational wave detectors. GEO 600 is unique in having advanced multiple pendulum suspensions with a monolithic last stage and in employing a signal recycled optical design. This paper describes the recent commissioning of the interferometer and its operation in signal recycled mode.
The GEO600 laser interferometric gravitational wave detector is approaching the end of its commissioning phase which started in 1995.
During a test run in January 2002 the detector was operated for 15 days in a power-recycled michelson configuration. The detector and environmental data which were acquired during this test run were used to test the data analysis code. This paper describes the subsystems of GEO600, the status of the detector by August 2002 and the plans towards the first science run.
The detection of gravitational waves by the first generation of ground-based interferometric detectors, like LIGO, relies on sophisticated data analysis techniques. For the inspiral phase of binary compact objects, the optimal one is the so-called matched-filtering technique. The output of the detector is cross-correlated with a bank of templates. The closer the templates are to the real signal, the higher the S/N of the detection is. In this paper we quantify the loss of S/N that occurs when one tries to detect a precessing binary using non-precessing templates. To do so, we compute the fitting factor which is a measure of the mismatch between the signal and the templates. The precessing signal is obtained using a 1.5 PN analytical approximation of the real solution called simple precession. We found regions of the parameter space for which the detection could be jeopardized if precession is not accounted in the templates. The solution of this problem could be to use more complete templates, that could capture the main features of the precession. Specifically we examine such a family of 'mimic' templates, that requires only three additional parameters, first proposed by Apostolatos. However we find that this family does not recover the main part of the signal. We conclude that a more efficient template family will be needed in the near future.