Degree

Doctor of Philosophy (PhD)

Department

Department of Physics and Astronomy

Document Type

Dissertation

Abstract

Gravitational waves are “ripples” in the fabric of spacetime and create a minuscule change in the distance between two points. After publishing his theory of general relativity in 1915, Albert Einstein predicted the existence of gravitational waves as a consequence of the theory. Almost 100 years after the theoretical prediction, gravitational waves were detected for the first time in 2015 by the Advanced LIGO detectors in Livingston, Louisiana, and Hanford, Washington. Gravitational waves have a very small amplitude, making it very challenging to detect them. Different types of noise sources either of instrumental or environmental origin can reduce the astrophysical sensitivity of the detectors. For this reason, it is very important to characterize these noise sources so that they can be mitigated. This dissertation is based on characterizing one of such noise sources which is created by scattered light inside the detector. This noise is transient in nature and creates “glitches” in the detector data.

Two types of scattered light noise had appeared during the third observation run (O3) in the detector. Their sources were found and mitigated by implementing instrumental changes. But the scattered light noise appeared again during the fourth observation run (O4) in the frequency range 10-40 Hz, from some other sources. First, I discuss the characteristics of the scattered light noise that appeared during O4 and how they are different than before. From our analysis, we have found two groups of glitches caused by scattered light, one having higher signal-to-noise ratio (SNR) than the other. We developed two models of possible coupling mechanisms of the high SNR glitches and simulated noise from both of these seem to match well with the observed noise in the detector. Next, we performed a statistical correlation analysis which predicts the source of the noise to be located at the corner station of the detector. After performing some tests in the detector, some evidence of scattered light was found from the corner station. For the low SNR glitches, we suspected the high frequency ground motion to be coupled through a vacuum chamber at the corner station. After installing an additional seismic isolation platform in that vacuum chamber, the low SNR glitches have not appeared again. A set of baffles, installed very close to the test mass mirrors helped to reduce the rate and SNR of the high SNR glitches as well. Overall, these changes helped to improve the low frequency (10-40 Hz) sensitivity of the detector, where we expect to see gravitational waves from high mass binary black hole mergers.

Date

7-15-2026

Committee Chair

Gabriela Gonzalez

LSU Acknowledgement

1

LSU Accessibility Acknowledgment

1

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