Inertial Sensors for Ground Based Gravitational Wave Detectors

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The research for seismic isolation aims to continue on the work from Dr Conor Mow-Lowry and Dr Denis Martynov of the University of Birmingham. They have proposed a 6D inertial isolator which is a device that consists of a proof mass that is softly suspended from a platform (linked to the ground) which remains inertial above its resonant frequencies. 6D is sensitive to ground motion in 6 degrees of freedom (3 translational and 3 rotational) which are detected via interferometric readout. Current isolation systems and seismometers have an inherent issue with tilt-to-horizontal coupling, effecting the output signal. The goal is to measure the platform motion in all degrees of freedom, therefore removing the tilt from the translational motion. This work will be beneficial in improving the seismic isolation at the detector sites of aLIGO and future upgrades to detect gravitational waves down to 5Hz (LIGO-LF). My research will involve modelling the dynamics of this system and working on control mechanisms to stabilise the suspended mass. Another aspect of the research will be designing and constructing a 6-axis stage platform. This will be similar to the Inertial Seismic Isolation (ISI) platforms used in Advanced LIGO (aLIGO). The final goal would be to create a prototype of the system.The rotational sensor will potentially be a whispering gallery mode optical gyroscope based on stimulated Brillouin Scattering and dispersion using the Sagnac effect. An optical gyroscope has the benefit of no losses due to friction, thereby increasing their reliability compared to their mechanical counterparts. The project will involve construction of the device and experimentally testing its sensitivity. Detection of ground rotation or rotational drift of suspended masses will likely be the application of this device. Other applications will be position sensing on space instruments. However, the gyroscope may also have commercial uses (such as navigation) as it will be a small (currently unspecified) size which can potentially be deployed on many systems as an aftermarket attachment.