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 a vital component in inertial sensing and geodesy, gravitational physics, seismic noise detection, hydrology, and other fields requiring precision measurements. Our group develops compact low and high frequency optomechanical inertial sensors to measure acceleration for various applications. Our sensors measure the linear displacement of an oscillating test mass with displacement laser interferometers that are fiber-coupled or free space. The observed external acceleration is recovered from the displacement of the test mass. Our compact 5 Hz resonator will operate as a relative gravimeter and be read out by a compact, highly sensitive free-space heterodyne laser interferometer. It has demonstrated low mechanical losses with quality factors above 4.77 × 105 and mQ-products greater than 1200 kg. Our millimeter scale higher frequency resonators are made of fused silica for operation at room temperature and Si for operation at cryogenic temperatures. They will be readout with fiber based Fabry-Perot cavities or waveguide ring resonators that are currently under development. We are working to fabricate the Si resonators and are optimizing the process using Bosch and cryo-Si DRIE etching. Here, we report our progress on design and fabrication along with preliminary measurement results for all resonator prototypes.
Inertial sensors are used in a variety of applications including inertial navigation and precision measurements. Optical measurement of test mass displacement in a resonator allows for the creation of compact accelerometer systems. Fused silica resonators allow for excellent acceleration sensitivities due to their high mechanical quality factor, Q, at room temperature, but this changes significantly at lower temperatures. The Q factor of crystalline silicon, however, remains high at low temperatures. We work with compact fused silica resonators that operate at room temperature and aim to fabricate compact comparable mechanical resonators from Si wafers. We will report on the fabrication progress of these resonators and results from ringdown and sensitivity measurements.
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.
The design of next generation gravitational wave observatories considers operation at cryogenic temperatures to enhance their sensitivity by reducing thermal noise fluctuations. Inertial sensors are used on the observatory platforms to measure local seismic noise and counteract its effects by active control or subtraction in post-processing. Measuring the displacement of a test mass in a resonator system allows for creation of a compact accelerometer system. Currently, there are no commercial inertial sensors available that are capable of operating at cryogenic temperatures and providing the required sensitivities for gravitational wave observatories. Materials such as fused silica exhibit very low losses at room temperature. However, this changes significantly at lower temperatures. Unlike fused silica, the Q factor of crystalline silicon structures is expected to remain high at low temperatures, making it a likely candidate for use in these types of inertial sensors. We are working to fabricate compact mechanical resonators from Si wafers to test their mechanical response. Micro-fabrication consists of optimizing the photolithography and Bosch etching processes for through-wafer Si etching on a 280 μm, 500 μm, and 1 mm wafer. Successful etching on 280 μm wafers has been achieved. We report on the design, model, and fabrication progress of these resonators.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.