We create inertial sensors by using displacement interferometry techniques to measure motion of our low resonance monolithic resonators. Supported by the National Geospatial-Intelligence Agency (NGA), LASSO is currently improving this technology by making it more compact. The goal of this system is a field deployable gravimetric sensor (able to measure gravity at a point on earths surface) that is precise, reliable, compact, and relatively lightweight.
Displacement interferometry utilizes laser interferometers to measure the displacement, or change in position relative to an arbitrary starting point. Our monolithic resonators oscillate in one constrained direction, and can be viewed as a test mass on the end of a spring. When the direction of motion is aligned downward, gravity can act on the mass in the measurement direction. When gravity levels change, for example during the different phases of ocean tides which is an effect of lunar gravity, the pull gravity exerts on the test mass changes. In times of increased gravity, the test mass will be pulled lower, and when gravity decreases the test mass will rise up. Knowing the designed system parameters and measuring this change in relative position using displacement interferometry, we can determine the acceleration due to gravity.
LASSO has demonstrated the concept of creating inertially sensitive systems in this manner before, but the current goal is to make the system more compact. The current interferometer uses large optical components which are in turn mounted to the optical table. This uses a lot of space and allows noise to enter the measurements through vibrations in each separate element. The current research is focused on utilizing compact prism optics mounted on the frame of the resonator. This will decrease both the size and noise associated with the sensor, leading to an improved, compact system.
Inertially sensitive optomechanical sensors make excellent relative inertial sensors, however, they are prone to long term drifts. By combining an optomechanical sensor with an absolute inertial sensor, such as an atom interferometer, we can form an extremely sensitive hybrid sensor with broad measurement bandwidth. LASSO is currently in the process of developing an optomechanical retro-reflector for just such a purpose. By combining the optomechanical sensor at the intertial reference of the atom interferometer, the retro-reflector, we can eliminate any mechanical mismatch between the two sensors. With the careful design of the optomechanical sensor, we can tune the resonance of the optomechanical oscillator to optimize hybrid sensor performance. Such a sensor would be able to perform inertial measurements in high noise environments.
A demonstration of how an optomechanical retro-reflector could be placed into an atom interferometer.
“Quantum hybrid optomechanical inertial sensing,” Appl. Opt. 59, G160-G166 (2020) – Logan Richardson, Adam Hines, Andrew Schaffer, Brian P. Anderson, and Felipe Guzman