Femtosecond Laser Inscribed Calibration Phantoms for Optical Coherence Tomography


The thesis describes work using a femtosecond laser to fabricate high precision microstructures as multipurpose 3D OCT calibration phantoms that can be used to quantitatively characterise and calibrate across different OCT systems. The research has been focused on three areas in developing the OCT calibration phantom - laser power characterisation, fabrication optimisation and novel multipurpose OCT phantom development and phantom application. For the laser power characterisation process, a detailed in-depth study was performed investigating the correlation between laser power and inscription size. Test phantoms were inscribed with different laser pulse energies. The results showed that with increased laser pulse energy, both the linewidth and the cross-inscription height were increased. The critical power of self-focusing was exceeded when the laser power was around 63% of the total laser average output power. As the non-linear effect caused unexpected control of the inscription size along the axial direction, a laser power range below the self-focusing threshold was selected to inscribe the phantoms which was still enough to extend the design to reach greater depths. The phantom fabrication optimisation with a layer-by-layer inscription method has allowed inscriptions at a greater depth up to 2mm whilst keeping the inscription size uniform and consistent for all depths. For the inscription method, the laser power was reset at beginning of the inscription for each layer which allowed a customised option to be made to get the desired inscription size that can be kept consistent and uniform for all depths. In order to address the challenges of inscribing non-planar samples, a series of multipurpose of OCT phantoms were designed and fabricated. A non-planar phantom was initially proposed that comprised of a grid-like pattern inscribed inside a planoconvex lens as the planar side provided a standard non-distorted image and the curved side provided a distorted image which can be used to detect the scanning errors and the post-processing algorithms of the OCT system for distortion correction. However, the grid-like pattern required a highly degree of alignment under the OCT system. Subsequently, a circle-like pattern was proposed to overcome this angular issue with a landmark layer consisting of a series of radial lines inscribed at the top of the test pattern to guide the location. To investigate the impact of OCT image distortion, a planar phantom was designed and used as a reference to correct the distortion due to the scanning errors caused by the OCT system itself. With a known reference, a phantom-based distortion correction method is possible with the reduction of the scan spacing error by 82% which extends the potential use of the OCT phantoms beyond a qualitive measurement tool.

Publication DOI: https://doi.org/10.48780/publications.aston.ac.uk.00046022
Divisions: College of Engineering & Physical Sciences > Aston Institute of Photonics Technology (AIPT)
Additional Information: Copyright © Yang Lu, 2021. Yang Lu asserts their moral right to be identified as the author of this thesis. This copy of the thesis has been supplied on condition that anyone who consults it is understood to recognise that its copyright rests with its author and that no quotation from the thesis and no information derived from it may be published without appropriate permission or acknowledgement. If you have discovered material in Aston Publications Explorer which is unlawful e.g. breaches copyright, (either yours or that of a third party) or any other law, including but not limited to those relating to patent, trademark, confidentiality, data protection, obscenity, defamation, libel, then please read our Takedown Policy and contact the service immediately.
Institution: Aston University
Uncontrolled Keywords: optical coherence tomography (OCT),femtosecond laser inscription,OCT calibration phantom,femtosecond laser direct writing,OCT image distortion correction
Last Modified: 08 Feb 2024 15:11
Date Deposited: 08 Feb 2024 15:11
Completed Date: 2021
Authors: Lu, Yang

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