One-mile equivalent length interferometric pendulum for seismic noise reduction

Abstract

We describe the performances of a 100-kg, 1-m-long active pendulum provided with a reference arm to get rid of the effects of tilting of the ground. The pendulum displacement with respect to the suspension point is measured interferometrically. The phase signal, to be sent to the actuator which displaces the suspension point, is extracted from the interferometer using an analog phase follower. At 10 Hz we obtain a virtual pendulum length of 1.7 km with the reference arm locked and 1.2 km when the reference arm is free. This device can be used to reduce the seismic noise in an antenna for low-frequency gravitational wave detection.