Optomechanical accelerometers for geodesy

We report on the progress of our novel low-frequency optomechanical accelerometer. This device is designed to be compact and portable, comprised of a monolithically fabricated mechanical resonator and a compact heterodyne laser interferometer. The resonator is made from fused-silica, which is a low-loss material that provides very low mechanical losses near room temperature. The oscillating test mass is read-out with the highly sensitive heterodyne interferometer. With a measured Q of 4.77x10⁵, an mQ-product above 1200 kg, a fundamental mechanical resonance of 4.7 Hz, we can estimated an acceleration noise floor near 1x10^-11 m s^-2/√Hz, which makes this device a good potential candidate for future applications in gravimetry, geodesy, geophysics, and hydrology.

A prototype packaging has been developed to reduce losses caused by typical mechanical mounts. We have conducted comparison measurements with commercial low-frequency systems to an excellent agreement. Recent measurements taken with the resonator mounted in this packaging atop a vibration isolation platform have indicated that our system is seismically limited above 1 mHz. Noise floors in the order of 82 pico-g/√Hz at 0.4 Hz has been demonstrated in our laboratory.

We will present recent updates on this optomechanical accelerometer, including up to date measurements of the resonator and interferometer sensitivity, as well as that of the combined system.