Reducing Scattered Light in LIGO's Third Observing Run

TL;DR

This paper characterizes and mitigates scattered light noise in LIGO's third observing run, improving gravitational wave detection by identifying noise sources and implementing motion reduction and detection algorithms.

Contribution

It provides a detailed analysis of scattering noise sources in LIGO O3 and introduces techniques to reduce motion-induced scatter and identify noise presence.

Findings

Identified two populations of scattering noise.

Correlated surface motion with scattered light presence.

Implemented a motion reduction technique and a noise detection algorithm.

Abstract

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'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.