Laser Absorptance of Metallic Alloys to Nd:YAG and Nd:YLF Laser Light

149 Pages·2005·5.59 MB·English

by  David Bergström

2005:89
LICENTIATE T H E S I S
The Absorptance of Metallic Alloys
to Nd: YAG and Nd: YLF Laser Light

David Bergström
Luleå University of Technology
Department of Applied Physics and Mechanical Engineering
Division of Manufacturing Systems Engineering
2005:89|: 02-757|: -c -- 05⁄89 -- 
Licentiate Thesis
The Absorptance of Metallic Alloys
to Nd:YAG and Nd:YLF Laser Light
David Bergström
Division of Manufacturing Systems Engineering
Department of Applied Physics and Mechanical Engineering
Luleå University of Technology
Luleå, Sweden
in cooperation with
Department of Engineering, Physics and Mathematics
Mid Sweden University
Östersund, Sweden
Luleå, November 2005

Dedicated to the Curious Mind.

Preface
The work presented in this Licentiate thesis is devoted to the theoretical and
experimental study of the light absorption mechanisms in laser processing of
metals and metallic alloys. The Licentiate thesis consists of a short introduction
and a series of five papers, all dealing with different aspects of this topic.
This work has been carried out at the Division of Manufacturing Systems
Engineering at Luleå University of Technology and at the Department of
Engineering, Physics and Mathematics at Mid Sweden University in Östersund,
Sweden, from 2003 to 2005.
I would like to express my gratitude to my supervisors Prof. Alexander Kaplan
(LTU) and Prof. Torbjörn Carlberg (MIUN) for their advice and guidance during
this intial phase of my PhD. My deepest thanks also to Dr. John Powell (Laser
Expertise Ltd., Nottingham, UK) for our fruitful discussions, his proof reading of
all my written work and his neverending curiosity and devotion to the subject
which has worked as an inspiration for me.
Thanks are also due to M.Sc. Rickard Olsson and his colleagues at LaserNova AB
in Östersund, for their expertise and for letting me use parts of their machine park
in my experiments. I would also like to thank Patrik Frihlén of Azpect Photonics
AB and M.Sc. Ingemar Eriksson for helping me setting up the equipment for the
laser lab at my university in Östersund. Further thanks goes to Doc. Mats Tinnsten
and Dr. Leon Dahlén for providing the financial circumstances in making this
work possible.
Finally I would like to thank my family and especially my girlfriend Ulrika for her
understanding, support and her sincere interest in what I do.
Östersund, November 2005
David Bergström
i

Abstract
In Laser Material Processing of metals, an understanding of the fundamental
absorption mechanisms plays a vital role in determining the optimum processing
parameters and conditions. The absorptance, which is the fraction of the incident
laser light which is absorbed, depends on a number of different parameters. These
include laser parameters such as intensity, wavelength, polarisation and angle of
incidence and material properties such as composition, temperature, surface
roughness, oxide layers and contamination. The vast theoretical and experimental
knowledge of the absorptance of pure elements with smooth, contamination-free
surfaces contrasts with the relatively sparse information on the engineering
materials found in real processing applications. In this thesis a thorough
investigation of the absorption mechanisms in engineering grade materials has
been started. The Licentiate thesis consists of 5 papers.
Paper 1 is a short review of some of the most important mathematical models used
in describing the interaction between laser light and a metal.
Paper 2 is a review of a few experimental methods of measuring the absorptance
of an opaque solid such as a metal.
Papers 3 and 4 are experimental investigations of the absorptance of some of the
most frequently found metallic alloys used in Laser Material Processing today.
Paper 5 is a co-authored paper on the cleaning of copper artefacts with the use of
second harmonic generated Nd:YAG laser light.
ii

List of Papers
Paper 1
Bergström, D.; Kaplan, A.; Powell, J.: ”Mathematical Modelling of Laser
Absorption Mechanisms in Metals: A Review”. Presented at the M4PL16
workshop, Igls, Austria, January 2003.
Paper 2
Bergström, D.; Kaplan, A.; Powell, J.: ”Laser Absorption Measurements in
Opaque Solids”. Presented at the 10th Nordic Laser Materials Processing
(NOLAMP) Conference, Piteå, Sweden, August 17-19, 2005, ed: A. Kaplan,
published by Luleå TU, Sweden.
Paper 3
Bergström, D.; Kaplan, A.; Powell, J.: ”The absorptance of steels to Nd:YAG and
Nd:YLF laser light at room temperature”. Paper accepted for the 2nd Pacific
International Conference on Applications of Lasers and Optics (PICALO), April
3-5, 2006, Melbourne, Australia, published by LIA, and submitted to Journal of
Physics D: Applied Physics.
Paper 4
Bergström, D.; Kaplan, A.; Powell, J.: ”The absorptance of non-ferrous alloys to
Nd:YAG and Nd:YLF laser light at room temperature”. Paper accepted for the
2nd Pacific International Conference on Applications of Lasers and Optics
(PICALO), April 3-5, 2006, Melbourne, Australia, published by LIA, and
submitted to Applied Surface Science.
Paper 5
Koh, Y.S.; Bergström, D.; Powell, J.; Åberg, G.; Grahn, J.; Kaplan, A.: ”Cleaning
oxides from copper artifacts using a frequency-doubled Nd:YAG laser”. Paper
accepted for the 2nd Pacific International Conference on Applications of Lasers
and Optics (PICALO), April 3-5, 2006, Melbourne, Australia, published by LIA,
and submitted to Studies in Conservation.
iii