Vibration isolation for gravitational wave detection

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Abstract
Through a combination of experiment and numerical modelling, we show that vibration isolators using cantilever springs can be used to achieve vibration levels below 10-20 m/ square root Hz for frequencies above 100 Hz, and that this performance can probably be achieved for frequencies as low as 25 Hz. Damping or high Q normal modes in all metal isolator structures can be relatively easily achieved by a combination of active and narrow band eddy current damping while the use of a single-stage ultra-low-frequency pre-isolator can eliminate the need for such damping. Utilizing an improved sapphire transducer, new measurements of the isolator's performance are presented. The measurement noise floor reaches 10-15 m/ square root Hz for vertical displacements and 10-14 m/ square root Hz for horizontal displacements.