The precise calibration of the strain readout of the LIGO gravitational wave observatories is paramount to the accurate interpretation of gravitational wave events. This calibration is traditionally done by imparting a known force on the test masses of the observatory via radiation pressure. Here we describe the implementation of an alternative calibration scheme: the Newtonian Calibrator. This system uses a rotor consisting of both quadrupole and hexapole mass distributions to apply a time-varying gravitational force on one of the observatory's test masses. The force produced by this rotor can be predicted to <1% relative uncertainty and is well-resolved in the readout of the observatory. This system currently acts as a cross-check of the existing absolute calibration system.
@article{arxiv.2107.00141,
title = {Initial Results from the LIGO Newtonian Calibrator},
author = {Michael P. Ross and Timesh Mistry and Laurence Datrier and Jeff Kissel and Krishna Venkateswara and Colin Weller and Kavic Kumar and Charlie Hagedorn and Eric Adelberger and John Lee and Erik Shaw and Patrick Thomas and David Barker and Filiberto Clara and Bubba Gateley and Tyler M. Guidry and Ed Daw and Martin Hendry and Jens Gundlach},
journal= {arXiv preprint arXiv:2107.00141},
year = {2021}
}