Multistage active vibration isolation system

The major obstacle to the detection of low-frequency gravitational waves with an earth-based interferometer is seismic noise. The current design of the initial Laser Interferometer Gravitational-Wave Observatory (LIGO) receiver, now under construction, projects that ground noise will limit the operating band to frequencies above 40 Hz. In this article, we describe recent progress on the JILA active vibration isolation system. This device is being constructed to demonstrate the technology needed for useful reduction of low-frequency seismic noise in a gravitational wave interferometer. It consists of three spring-mounted stages, each of which provides both active and passive isolation. To date, all of the control loops on the first two of the three stages have been closed. Together they can reduce large vibrations by at least 70 dB in both vertical and horizontal directions at 1.5 Hz and above. (C) 1998 American Institute of Physics. [S0034-6748(98)04506-7]