Testing compact, fused silica resonator based inertial sensors in a gravitational wave detector prototype facility

Future gravitational wave observatories require significant advances in all aspects of their seismic isolation; inertial sensors being a pressing example. Inertial sensors using gram-scale high mechanical Q factor (Q) glass resonators combined with compact interferometric readout are promising alternatives to kilogram-scale conventional inertial sensors. We have produced fused silica resonators suitable for low frequency inertial sensing and demonstrated that Qs of over 150 000 are possible. One resonator we produced was combined with a homodyne quadrature interferometer (HoQI) to read out the test mass displacement to form an inertial sensor. This is the first time a HoQI was used with a high Q resonator. The resulting sensor was tested against other commercial, kilogram scale inertial sensors at the AEI 10 m Prototype facility. Despite the dynamic range challenges induced by the test mass motion, we can match the excellent noise floors HoQIs have achieved so far with slow-moving or stationary test masses, showing HoQIs as an excellent candidate for the readout of such sensors. We evaluate the setup as an inertial sensor, showing the best performance demonstrated by any gram-scale sensor to date, with comparable sensitivity to the significantly bulkier sensors used in gravitational wave detectors today. These sensors’ compact size, self-calibration, and vacuum compatibility make them ideal candidates for the inertial sensing requirements in future gravitational wave detectors.