Dissertation Defense: Yanqi Zhang, "Optical Readout Systems for Optomechanical Inertial Sensors"

    Friday, May 13, 2022 - 1:00pm

    Zoom link: https://arizona.zoom.us/j/85368160516

    Password: lasso


    The advancement of a compact optomechanical inertial sensor with ultra-high acceleration sensitivity in the sub-Hz regime requires its optical readout system to have a small footprint, low noise floor, and large dynamic range. In this dissertation, three optical readout systems are designed based on common-mode heterodyne interferometry, including a compact interferometer with off-the-shelf optical components, a customized quasi-monolithic interferometer assembly, and a two-wavelength fiber-based interferometer. A benchtop prototype of each configuration is developed and tested in the lab. Preliminary measurements show that all three instruments reached single-digit picometer level sensitivity above 1 Hz and sub-nanometer level sensitivity in the millihertz regime.

    Investigations are conducted regarding common noise sources in the low-frequency regime, such as laser frequency noises and temperature fluctuations. The corresponding post-processing algorithms are developed to mitigate these noise effects and improve the instrument sensitivity.

    Furthermore, the optical readout systems are integrated with a tunable optomechanical inertial sensor design to provide a sub-picometer level of sensitivity and large bandwidth capable of measuring seismic activities. Details of the feedback damping system in this inertial sensor are designed with a novel cascaded cooling system to improve the cooling efficiency with less radiation pressure actuation.