0.1% uncertainty multicolor calibration scheme for gravitational wave detectors

Advanced LIGO (aLIGO) achieves detection of gravitational waves (GWs) originating in distant astrophysical events by reducing the detector measurement noise below the signal strength in the frequency band they arrive. However, the lower the detector noise becomes, the more the uncertainty of a measurement outcome depends on systematic rather than statistical errors. For example, strain in aLIGO is currently calibrated using a standardized laser radiation pressure on the end test masses with an uncertainty of about 5%, highly dominated by systematic error. With next-generation cryogenic GW detectors aiming to bring the detector noise floor further down, new calibration procedures ensuring statistical uncertainty limited measurements are required. Here, we describe a calibration procedure that uses stable oscillating auxiliary fields in the 4-km long arms as a reference to calibrate the differential arm length fluctuations of the interferometer. With this new method, we aim to achieve 0.1% relative uncertainty in the calibration under similar signal-to-noise conditions. Our calibration method will directly impact the precision in compact binary merger parameters and rate estimates, self-calibrated Hubble constant measurement, tests of general relativity, and limits on continuous GW sources and stochastic GW background.