Study of quality factor and hysteresis associated with the state-of-the-art passive seismic isolation system for Gravitational Wave Interferometric Detectors

Seismic isolation systems, consistent of passive attenuators, based on mechanical harmonic oscillators with resonant frequencies below the frequency region of interest, are being used by multiple Gravitational wave (GW) detectors. We conduct a study of the fundamental limitations present due to the properties of the material such as Maraging steel, used in some of the seismic attenuation systems for GW detectors. We tentatively interpret the main effects observed in our system, such as the anomalous damping and the hysteresis, in terms of movement of dislocations trapped between Maraging steel intermetallic precipitates. In light of our understanding, we further discuss and propose ideas to overcome these limitations and improve the performance of these systems, which may allow for passive attenuation at even lower-frequency regimes than achieved so far. These advanced performances would help further reduce the requirements on the mirror suspension control actuators and could reduce their associated noise in the present Gravitational Wave Interferometric Detectors (GWID). This advancement can lead to more suitable seismic attenuation systems for the future instruments with lower frequency sensitivity requirements.