Triple Pendulum Suspensions
The central elements in all gravitational wave detectors are mirrors weighing several kilograms, which are used to direct the laser beams. These mirrors are suspended as multi-stage pendulums to isolate them from seismic motion of the ground, which would render the measurement of gravitational waves impossible. The mirror suspensions must meet several special requirements: they have to hold the heavy mirrors securely and must not cause disturbances of their own.
The triple-stage pendulums used in GEO600 served as prototypes for the four-stage pendulum system of Advanced LIGO, which were developed by GEO collaboration members from the Institute for Gravitational Research (IGR) at the University of Glasgow. The suspensions meeting the requirements of gravitational-wave detection: thin threads made of quartz glass – fused silica fibres. Such fibres have far less internal losses than equivalent steel wires, for instance. They are bonded directly onto the mirrors and a second pendulum mass, which means there is no friction at the point of contact. This increases the overall sensitivity of gravitational-wave detectors through reduced mechanical loss.