A novel interferometrically read out inertial sensor for future gravitational wave detectors

We present a novel inertial sensor designed and developed at Nikhef that features an interferometric readout for a horizontal monolithic accelerometer. It is the first time this class of mechanics and this type of optical readout are combined. It will be able to measure 3 × 10-15 m/√HZ displacement levels from 20 Hz onwards. Current results show (self) noise levels of 8×10-15 m/√Hz from 30 Hz onwards. Despite these unprecedented results, the result is worse than the sum of modeled noise contributions. Several possible unmodeled noise sources and possible solutions have been identified