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ABSTRACTIn spite of abundant experimental evidences supporting the viability of the laser
induced shock wave plasma model for the explanation of the important features ofthe
plasma and the associated spectroscopic characteristics, a controversy on the atomic
excitation mechanism in the plasma has remained to be completely resolved. In this
study the contributions of the shock wave model and two other most popular models,
the electron-ion recombination model and thc electron collision model were
thoroughly investigated. For that purpose, a special technique has been developed for
the direct detection of the charge current in conjunction with plasma emission
measurement dining the laser plasma generation and expansion. The current detection
was performed by placing a partially transmitting metal mesh electrode at a distance
in front of the sample surface with the sample target sewing as the counter electrode.
The electric Held between the mesh and sample surface was set up and varied by
applying a variable DC voltage (0-400 Volt) between them. The laser plasma was
generated by a YAG laser (64 ml, 8 ns) tightly focused on a Cu target through the
mesh electrode in low-pressure surrounding gas. It was found that the charge current
time profiles obtained at various gas pressures invariably exhibit a lack of consistent
correlation with the emission time profile of the plasma throughout most of the
emission period. The result of this study has thus practically eliminated any
significant roles ofthe electron-ion recombination and electron collision models in the
excitation process. We are therefore led to conclude that the shock wave model
proposed earlier is most plausible for the consistent explanation of the secondary
plasma emission, while the other two models may have some contribution only at the
very initial stage ofthe secondary plasma generation.
Key words: charge current, shock wave, electron-ion recombination and electron
collision.
Praiseci is to the Lord for He is my reason in everything I do.
This manuscript is never be done without the guidance by Pro£ Tjia May On, to
whom I am extremely grateful. He also provided the support without which this thesis
would not possible. He is more than just a teacher for me for his words have deeply
touched me. Moreover, he also introduced me that knowledge is something we should
share among others and to improve the education in my country.
I am also indebted to Prof. Kiichiro Kagawa at the Fukui University for providing
the atmosphere and the physical resources to make thesis writing in these times of fast
paced research. I am also thankful for the opportunity which is given to me to join
research together with him in his laboratory in Japan.
Extra special thanks go to Dr. Hendrik Kurniawan for providing me with
encouragement and support for this project. He is the first one who encouraged me to
take Doctor Cotuse Program which seemed impossible at the beginning. His
companion during research at Applied Spectroscopy Laboratory at University of
Indonesia is a leading experience in research for me.
I am particularly grateful to the excellent team of referees who provided critical
comments on this thesis. Their feedback was a great benefit to me.
I gratefully acknowledge all my colleagues: Rinda Hedwig, Mangasi A.
Marpaung, Hery Suyanto, MM. Suliyanti, Wahyu S. Budi, and Emon in Applied
Spectroscopy Laboratory at University of Indonesia, for their assistance and support
during my study.
My never-ending thanks to my beloved family, especially to my parents who
exhibited thoughtful patience over extended periods of time when I seemed to be
invisible. Thanks also to Loviana who helped me in all situations which I no longer
can resist by myselfl
Finally, I apologize to all those who helped that I did not acknowledge specifically.
I know there were many and greatly appreciate your assistance.
August, 2002
Author
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