Sensitivity and control of a 6-axis fused-silica seismometer

TL;DR

This paper introduces a compact, vacuum-compatible 6-axis fused-silica seismometer with interferometric sensors that achieve high sensitivity and low-frequency measurement capabilities, suitable for applications like gravitational-wave detection.

Contribution

The work presents a novel fused-silica seismometer design with improved tilt stability and sensitivity, enabling better low-frequency seismic measurements and potential enhancements for gravitational-wave observatories.

Findings

Achieved tilt sensitivity surpassing commercial sensors

Demonstrated stable operation with fused-silica design

Extended sensing band towards millihertz frequencies

Abstract

We present a pair of seismometers capable of measurement in all six axes of rigid motion. The vacuum-compatible devices implement compact interferometric displacement sensors to surpass the sensitivity of typical electrical readout schemes. Together with the capability to subtract the sensitivity-limiting coupling of ground tilt into horizontal motion, our seismometers can widen the sensing band towards mHz frequencies. This has notable applications across a range of fields requiring access to low-frequency signals, such as seismology and climate research. We particularly highlight their potential application in gravitational-wave observatories (LIGO) in improving their observation capability of intermediate-mass black holes ($\sim 1000\,M_\odot$). The sensors are based on a near-monolithic fused-silica design consisting of a fused-silica mass and fibre, showing improved stability and robustness to tilt drifts, alignment, and control compared to all-metal or mixed metal-silica designs. We demonstrate tilt sensitivity that surpasses the best commercial alternatives in a significantly reduced footprint compared to our previous iterations of these sensors.