Improving LIGO calibration accuracy by tracking and compensating for slow temporal variations

Understand

Calibration of the second-generation LIGO interferometric gravitational-wave detectors employs a method that uses injected periodic modulations to track and compensate for slow temporal variations in the differential length response of the instruments.

• These detectors utilize feedback control loops to maintain resonance conditions by suppressing differential arm length variations.
• We describe how the sensing and actuation functions of these servo loops are parameterized and how the slow variations in these parameters are quantified using the injected modulations.
• We report the results of applying this method to the LIGO detectors and show that it significantly reduces systematic errors in their calibrated outputs.