Active vibration isolation using a Suspension Point Interferometer

A suspension point interferometer (SPI) is a high-performance active vibrationisolation scheme for laser interferometric gravitational wave detectors. By making use of auxiliary interferometers installed at the suspension points of the interferometer's mirrors, this technique helps to reduce the seismic noise and to improve the stability of the interferometer. We are now constructing a Fabry-Perot interferometer equipped with an SPI to test the effectiveness of the SPI. We report on the current status of the experiment and preliminary results that demonstrate about 20 dB of vibration attenuation by the SPI below 2 Hz