Techniques for in-situ birefringence characterisation of gravitational wave detector optics

Pearce, Terri 2025. Techniques for in-situ birefringence characterisation of gravitational wave detector optics. PhD Thesis, Cardiff University. Item availability restricted.

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Abstract

This thesis presents the development of a Polarisation Phase Camera (PPC) for spatially resolved birefringence measurements of optical components relevant to gravitational-wave detectors. The work begins with the design and construction of the experimental system, including beam preparation, scanning, and detection, followed by the implementation of two measurement approaches. An initial heterodyne (RF) method was developed to enable phase-sensitive de- tection through interference between a frequency-shifted reference beam and the sample beam. However, this approach was found to be limited by slow phase drift between the optical paths, preventing stable phase reconstruction. A direct-current (DC) method was therefore implemented as a robust alternative, reconstructing bire- fringence parameters from intensity measurements at multiple analyser orientations. The system was calibrated using a quarter-wave plate of known parameters, demonstrating recovery of fast-axis orientation to within approximately 1° and re- tardation to within tenths of a radian under stable conditions. Measurements of a sapphire sample were also performed to assess the applicability of the technique to realistic optics. Overall, this work demonstrates the feasibility of birefringence mapping with a PPC, while identifying phase stability and polarisation control as key limitations to be addressed in future implementations.

Item Type:	Thesis (PhD)
Date Type:	Completion
Status:	Unpublished
Schools:	Schools > Physics and Astronomy
Subjects:	Q Science > QB Astronomy Q Science > QC Physics
Uncontrolled Keywords:	‘Birefringence', 'Gravitational-wave detectors’, ‘Polarisation optics’, ‘Interferometry’, 'Heterodyne detection’, 'Phase drift’
Date of First Compliant Deposit:	14 April 2026
Last Modified:	14 Apr 2026 10:01
URI:	https://orca.cardiff.ac.uk/id/eprint/186306

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