Reducing scattered light in LIGO's third observing run

Noise due to scattered light has been a frequent disturbance in the advanced LIGO gravitational wave detectors, hindering the detection of gravitational waves. The non stationary scatter noise caused by low frequency motion can be recognized as arches in the time-frequency plane of the gravitational wave channel. In this paper, we characterize the scattering noise for LIGO and Virgo's third observing run O3 from April, 2019 to March, 2020. We find at least two different populations of scattering noise and we investigate the multiple origins of one of them as well as its mitigation. We find that relative motion between two specific surfaces is strongly correlated with the presence of scattered light and we implement a technique to reduce this motion. We also present an algorithm using a witness channel to identify the times this noise can be present in the detector.

Automated summary

In this paper, the scattering noise in the advanced LIGO and Virgo gravitational wave detectors during the third observing run from April 2019 to March 2020 is characterized. It is found that there are at least two different populations of scattering noise, and the origins of one of them are investigated along with mitigation techniques. Additionally, a strong correlation is observed between relative motion of two specific surfaces and the presence of scattered light, leading to the implementation of a technique to reduce this motion.