Theses and Dissertations

Date of Award

7-1-2026

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Physics

First Advisor

Volker Quetschke

Second Advisor

Teviet Creighton

Third Advisor

Mario C. Diaz

Abstract

The LIGO detectors are part of a global network of gravitational-wave detectors. The calibration of the most sensitive instrument to length changes on Earth comes with numerous sources of systematic errors. This uncertainty on the calibration of the detector couples directly to the astrophysical parameters of the source that is detected.

The Photon Calibrator (Pcal) is the primary calibration system of the Laser Interferometer Gravitational-Wave Observatory (LIGO). The system uses the radiation pressure of a laser to produce a displacement of the interferometer end test masses (ETMs). The uncertainty of the displacement provided by the Pcal system is split into the uncertainty in measuring the laser power at the ETM and the unknown amount of rotation that is sensed as displacement due to imperfect alignment of the Pcal beams. The location of the Pcal beams incident on the test mass has become the dominant source of error in the Pcal uncertainty budget. This dissertation addresses this limitation by developing a method to directly measure the center-of-force location of the Pcal beams on the ETMs using the interferometer response function. By moving the Pcal beams at the LIGO Hanford detector, we compared the measured beam offsets with the interferometer’s main beam location and experimentally confirmed the modeled force-to-displacement equation. The measurements were taken during observing runs O4b and O4c, demonstrating the viability of this method for reducing the dominant source of Pcal uncertainty, while maintaining science mode operation.

Supporting this primary work, comprehensive characterization of the Pcal power sensors was performed to maintain calibration accuracy. This included improvements to the responsivity ratio measurement setup at the laboratories at UTRGV and LIGO Hanford. A low-level Python data acquisition system to replace legacy LabVIEW software was implemented, and investigation of temperature-dependent sensor response were undertaken. These improvements ensure the Pcal sensors remain the reliable absolute reference for the network of gravitational-wave detectors calibration.

Finally, the refined calibration tools and improved understanding of the Pcal system were used to apply detector improvements during O4.

Comments

Copyright 2026 Francisco Llamas. All Rights Reserved. https://proquest.com/docview/3409025203

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