High-sensitivity accelerometers are key for many applications including ground-based gravitational wave (GW) detectors, in-situ or satellite gravimetry measurements, and inertial navigation systems. We will present our work on the development of optomechanical accelerometers based on the micro-fabrication of mechanical resonators and their integration with laser interferometers to read out their test mass dynamics under the presence of external accelerations. We will discuss the latest developments on compact millimeter-scale resonators made of fused silica and silicon, optimized for frequencies below 1 kHz and exhibiting low mechanical losses. While fused silica has demonstrated high mechanical quality factors at room temperature, silicon devices perform significantly better at very low temperatures, which is particularly relevant for future ground-based gravitational wave detectors where cryogenic environments will be used to improve the sensitivity of the observatories. We will report on our design, modeling, and fabrication process for the silicon-based resonators and present their characterization by means of highly compact fiber-based Fabry-Perot cavities.
Accelerometers are key sensors in many fields and applications such as precision metrology, gravimetry measurements, gravitational wave observatories, and navigation where position and attitude need to be determined accurately. A combination of six accelerometers provides all the necessary information to estimate position and orientation of a rigid body and thus serves as an inertial navigation system for autonomous navigation. Fusedsilica based mechanical resonators paired with laser interferometric read-outs enable compact high-accuracy accelerometers. In this talk, we will present a wide-band accelerometer based on a double resonator with two test masses of different sizes in a single frame. One of the resonators has a resonance frequency of about 50 Hz, while the other is optimized for lower frequencies and has a nominal frequency of about 10 Hz. The combination of the two resonators allows for excellent long-term precision while maintaining good measurement bandwidth. We will show the experimental characterization in air and in vacuum of the double-resonator using a heterodyne laser interferometer and a fiber interferometer and its expected performance as an inertial sensor.
Our work in the Laboratory of Space Systems and Optomechanics (LASSO) at Texas A&M University involves using optomechanical resonators coupled with compact, high-precision interferometers to create novel inertial sensors. These resonators are etched from monolithic fused silica, which is known to have very low internal losses, allowing for high mechanical quality factors and low thermal acceleration noise in the test mass. Previous measurements at mTorr pressures have demonstrated Q’s of 1.91 x 105, corresponding to estimated thermal acceleration noise floor on the order of 10-10 m s- 2/√Hz for frequencies above 30 mHz. In this pressure regime, gas damping is still the dominant loss mechanism. At sufficiently low pressures such that gas damping is negligible, we anticipate mechanical quality factors of the order of 106 and thermal acceleration noise at levels of 10-11 m s-2/√Hz in the sub-Hz regime. As expected, previous measurements have shown significant ambient vibrations that limit our ability to observe the noise floor of the resonator. Hence, we have developed a dedicated vibration isolation platform to mitigate external disturbances, which consists of a pendulum with a magnetic anti-spring to lower the resonant frequency. Sensors constructed with these resonators would be lightweight and cost-effective, making them promising candidates for field applications in geophysics, navigation, and site exploration.
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