On environment-related instrumental effects of ROMY (ROtational Motions in seismologY): A prototype, multi-component, heterolithic ring laser array.

Abstract

Large-scale ring laser gyroscopes (RLGs) are essential scientific instruments to study a variety of geophysical phenomena. The first and so far only large-scale RLG array ROMY (ROtational Motions in seismologY) comprises four triangular, heterolithic, active RLGs and can provide high-quality, three-component rotational ground motion observations. Compared to other RLGs, often being located in underground laboratories, ROMY is a near-surface installation that is more exposed to environmental influences. The prototype design of ROMY could serve as a blueprint for high-sensitivity, six degree-of-freedom stations for geoscientific rotation sensing. Understanding and quantifying instrumental effects caused by its environment is, therefore, essential to enhance the design toward a stable and continuous operation. Geometric deformation of a heterolithic optical ring resonator introduces undesired instrumental drifts that are challenging to mitigate. Applying a classic correction for backscatter-induced errors, we achieve a reduction in short-term Sagnac frequency fluctuations of several millihertz. A new sensor network inside ROMY monitors key environmental parameters such as barometric pressure and temperature. In order to quantify deformation of the resonator, we use camera-based beam tracking and free spectral range measurements. Based on these observations, we discuss the current operational stability of ROMY and recovery methods. We relate the observed instrumental drifts to dominant environmental drivers. Using a linear, multivariate modeling approach, we can identify dominant drivers and reduce long-term drifts of the Sagnac frequency. A quantification and better understanding of environment-induced instrumental effects allows to develop strategies for a further improvement in operational stability.