Under previous grants, the University of Colorado group has designed and constructed an active seismic isolation platform that uses a combination of active and passive seismic isolation to reduce the mechanical noise at a test-mass suspension's mounting point over a frequency range beginning at 1 Hz. In each of the now-functioning cascaded stages, motion in each of the six degrees-of-freedom (DOF's) is sensed against an inertial reference (a seismometer) and reduced with a non-contacting forcer. At 1 Hz, vertical and horizontal vibration transmission through the two stages is reduced by a factor of 3000 for large drives. The group will complete work on and document performance of the two operating stages, with the goal of measuring a displacement noise in the first main stage of approximately 3x10^(-13) m/(Hz)^(1/2). Close collaboration will continue with the LIGO Science Collaboration (LSC) in studying the needs of advanced LIGO detector systems.
The Colorado active seismic isolation platform has been developed primarily to demonstrate techniques that can be used to reduce the mechanical noise at a test-mass suspension's mounting point over a frequency range beginning at 1 Hz, significantly lower than is currently planned for the first generation of interferometric gravitational wave observatories. If such technology can be used in future LIGO detectors, low-frequency sources such as coalescing binary systems involving several hundred solar mass black holes might be observable. Active isolation techniques are likely to also have a role in reducing the noise load on the systems used to hold the LIGO detector's optical elements in alignment and position. As the LSC works to design a consistent set of improvements to implement in LIGO several years after its initial commissioning, the knowledge and experience gained in studying this active isolation demonstration system is expected to be useful. ***
