Laser-induced breakdown spectroscopy (LIBS) is an elemental characterisation
technique using spectrally resolved emission froma laser-induced plasma
to determine the composition of a sample. Due to limited quantitifcation of
emission levels, in the literature, it is difficult to compare results between different
lab groups, and only qualitative comparisons can be made with theory.
As a result, understanding of the underlying physical processes which govern
LIBS has lagged the growth of applications.
Most applications of the LIBS technique have employed laser pulse energies
in the range of 10 - 100mJ, focal spot sizes of ��� 100 ��m, and an accumulation
of 10 - 100 spectra for a single measurement. The high energies, large focal
spots and number of shots acquired improves the sensitivity of LIBS. The
primary focus of this thesis is the quantification of the LIBS technique, LIBS
equipment and the extension of LIBS to much lower pulse energies. This new
regime, referred to as ��LIBS, utilises pulse energies below 100 ��J.
In this thesis a theory of LIBS detector systems is developed, and used
to define responsivity, noise-equivalent integrated spectral brightness and
noise-equivalent spectral brightness in terms useful for the LIBS experimentalist.
Four LIBS detection systems have been characterised.
Laser ablation plume dynamics and absolute emission levels from a millijoule
energy LIBS system were studied and compared with simple physical
models for shock wave expansion and stagnation. A simple model for the
emission is compared with the absolute emission levels of the LIBS plasma.
The scaling of LIBS emission below 100 ��J pulse energies is investigated.
The number of photons emitted is found to be a small fraction of the number
of atoms ablated for the energy range between 100 nJ and 100 ��J. Using a thin
film target, it is found that the ablated region which contributes to the LIBS
emission is restricted to a layer much shallower than the ablation crater.
Finally, two applications of the ��LIBS technique are presented. Surface
mapping of Al alloys with sub-microjoule laser pulses is demonstrated. Latent
fingerprint detection and imaging is demonstrated using the ��LIBS technique
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:AEU.uuid#c81f3cd6-1835-407d-a687-77fad124d59f |
| Creators | Taschuk, Michael Thomas |
| Publisher | University of Alberta |
| Source Sets | Library and Archives Canada ETDs Repository / Centre d'archives des thèses électroniques de Bibliothèque et Archives Canada |
| Language | English |
| Detected Language | English |
| Type | Research Material |
| Format | application/pdf |
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