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Published January 8, 2015 | public
Journal Article

Noise and control decoupling of Advanced LIGO suspensions


Ground-based interferometric gravitational wave observatories such as Advanced LIGO must isolate their optics from ground vibrations with suspension systems to meet their stringent noise requirements. These suspensions typically have very high quality-factor resonances that require active damping. The sensor noise associated with this damping is a potential significant contributor to the sensitivity of these interferometers. This paper introduces a novel scheme for suspension damping that isolates much of this noise and permits greater amounts of damping. It also decouples the damping feedback design from the interferometer control. The scheme works by invoking a change from a local coordinate frame associated with each suspension, to a coordinate frame aligned with the interferometric readout. In this way, degrees of freedom invisible to the readout can employ effective, but noisy damping. The degree of freedom measured by the readout is then damped using low noise interferometer signals, eliminating the need to use the usual noisy sensors. Simulated and experimental results validate the concepts presented in this paper.

Additional Information

© 2015 IOP Publishing Ltd. Received 11 September 2014, revised 27 October 2014. Accepted for publication 29 October 2014. Published 3 December 2014. This work was supported by funding from the National Science Foundation under cooperative agreements PHY-0107417 and PHY-1068596. The design of the quadruple pendulum was developed by groups at the University of Glasgow, Rutherford Appleton Laboratory, the University of Birmingham, and the University of Strathclyde, in collaboration with the LIGO Laboratory. The authors would like to acknowledge the contributions of Professors Bob Byer and Dan DeBra to this work. Public internal LIGO documents are found at https://dcc.ligo.org/cgi-bin/DocDB/DocumentDatabase/.

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