Ultrashort pulse laser interaction with aluminium

Proctor, J. (Jonathan Kenneth)

September 2022

Thesis or dissertation

© 2022 J (Jonathan Kenneth) Proctor. All rights reserved. No part of this publication may be reproduced without the written permission of the copyright holder.

In this thesis an analysis of ultrashort pulse laser interactions with bulk aluminium and aluminium foils is presented. In particular, this thesis has the goal of understanding the laser-material interaction and applying this knowledge to the application of laser machining RFID antennae using industrial-grade samples and an LXR 100 femtosecond laser. The work is presented in a progressive manner; firstly the laser and motion control systems have been characterised with respect to their properties and then how they interact with each other. Experimental results for the fluence threshold for ablation using a Gaussian beam method are then shown for a polished, 8nm roughness average (Ra), 99% purity aluminium as the target. Resulting in a threshold fluence of 0.27±0.06 J cm−2. A two-temperature model describing the interaction is then presented, giving estimates for the fluence threshold in the range of 0.27 to 0.47 J cm−2 as well as the etch diameter of the damage site, and these calculations are then compared to the experimental results. The relationship between surface roughness and the fluence threshold is then explored, samples of 99% purity bulk aluminium were prepared so that their surfaces had a range of Ra values, and the fluence thresholds measured for each roughness. Two different regimes were found. The threshold decreased with roughness until the Ra value was larger than the laser wavelength and then increased. A prediction for the fluence threshold of an industrial sample is made from this relationship, and is predicted to have a threshold fluence of 0.165 J cm−2. Experimental results for the “real-world” sample are then presented and are compared to the predicted values. Using this information, an application for kiss-cutting the industrial foil sample on an adhesive backing paper to produce RFID antennae has been demonstrated. Electrical isolation is achieved for etch widths less than 50 μm and confirmed using SEM micrographs.

Department of Physics and Mathematics, The University of Hull
Snelling, Howard Victor
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190 MB
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