VIBRATION ISOLATION FOR GRAVITATIONAL-WAVE DETECTION

Through a combination of experiment and numerical modelling, we show t hat vibration isolators using cantilever springs can be used to achiev e vibration levels below 10(-20) m/square-root Hz for frequencies abov e 100 Hz, and that this performance can probably be achieved for frequ encies as low as 25 Hz. Damping of high Q normal modes in all metal is olator structures can be relatively easily achieved by a combination o f active and narrow band eddy current damping while the use of a singl e-stage ultra-low-frequency pre-isolator can eliminate the need for su ch damping. Utilizing an improved sapphire transducer, new measurement s of the isolator's performance are presented. The measurement noise f loor reaches 10(-15) M/square-root Hz for vertical displacements and 1 0(-14) m/square-root Hz for horizontal displacements.