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Characterisation and manufacturing of glass fibre diffuser with ultrashort pulse laser

  • In recent years, much research has been done on medical laser applications inside the human body, as they are minimally invasive and therefore have fewer side effects and are less expensive than conventional therapies. In order to bring the laser light into the human body, a glass fibre with a diffuser is needed. The goal of this master thesis is the characterization and production of fibre optic diffusers that can be used for the three therapeutic applications: photodynamic therapy, laser-induced thermotherapy and endovenous laser therapy. For this purpose the following goals have to be achieved: - Optimization of the efficiency and homogeneity of internally structured diffusers - Examine damage thresholds of the diffusers in the tissue using a crash test - Achieving a better understanding of the decouple mechanism with a simulation Using an ultra-short pulse laser, modifications could be introduced into the fibre in this way that the radiation profile is homogeneous and the decoupling efficiency is 68.3 %. It was discovered that the radiation profile depends on the wavelength. Attempts have been made to improve the decoupling efficiency by mirroring the distal end of the fibre. The mirror reflects the remaining light back into the fibre, so that it is also decoupled lateral on the modifications. Vapor-deposited aluminum with physical vapor deposition is a promising approach. However, the adhesion of the coating must be improved or the coating must be protected by a mechanical cover, otherwise it will flake off too quickly. In a crash test, it was shown that the glass fibre diffusers can withstand 20 W laser power for 300 s without visible change. In an ex vivo test, the coagulation zone in the tissue was examined and it was showed that the diffusers radiate radially homogeneously. Using a ray trace simulation, the course of the light rays in the fibre was examined and the correlation of modification width and length with the decoupling efficiency was investigated. It was discovered that there are helical light rays in the fibre, which cannot be decoupled by modifications in the fibre centre.

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Author:Beat Dominik Abelein
Advisor:Matthias Domke, Kristian Muri Knausgard
Document Type:Master's Thesis
Year of publication:2020
Publishing Institution:FH Vorarlberg (Fachhochschule Vorarlberg)
Granting Institution:FH Vorarlberg (Fachhochschule Vorarlberg)
Release Date:2020/12/21
Tag:Diffuser; Photodynamic therapy
Number of pages:IX, 41
DDC classes:600 Technik, Medizin, angewandte Wissenschaften
Open Access?:ja
Course of Studies:Mechatronics
Licence (German):License LogoUrhG - The Austrian Copyright Act applies - Es gilt das österr. Urheberrechtsgesetz