The search for gravitational waves has led to the development of km-scale interferometers with sub attometre
displacement sensitivity. The challenge of meeting this goal is divided into two aspects. First the main optical
components of the interferometer - the test masses - must be sufficiently quiet, and then the interferometric
measurement of the relative test mass positions must be performed to the required degree of sensitivity. Key design
elements of modern interferometers are discussed, reviewing the most important aspects. Gravitational astronomy will
require 10 to 100 times improved sensitivity beyond that of the initial instruments and potential techniques are
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 LIGO Laboratory 40m prototype interferometer at Caltech is being commissioned to prototype an optical configuration for Advanced LIGO. This optical configuration has to control five length degrees of freedom, and its control topology will be significantly more complicated than any other present interferometers. This paper explains the method of sensing, controls and lock acquisition.
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 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.
Conference Committee Involvement (2)
Gravitational Wave and Particle Astrophysics Detectors