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Imaging and spectroscopy of laser produced annular plasmas

Delaney, Ben (2019) Imaging and spectroscopy of laser produced annular plasmas. PhD thesis, Dublin City University.

Abstract
Laser induced breakdown spectroscopy (LIBS) has emerged as a commonly used analytical technique for both qualitative elemental identification and quantitative concentration determination in various academic and industrial fields. The ultimate performance of LIBS is dependent on the signal to background ratio (SBR) of the spectra which are acquired from a sample and is quantified as the limit of detection (LOD) of the technique. A significant body of work has already been reported in the literature aimed at lowering of the LOD of LIBS. This work includes investigations into the effects of; laser fluence, wavelength and pulse length as well as space and time optimization, along with double pulse plasma formation and reheating arrangements. The aim of the work presented here is to generate and investigate the stagnation layer formed in vacuo, at the centre of an annular plasma, and to employ it in a LIBS experiment on trace Cu in Al. This is achieved by retrofitting a single optical element, namely an axicon, to the focusing lens normally used for point plasma formation. Spatially and temporally resolved imaging and spectroscopy are employed to track the formation and evolution of a stagnation layer at the centre of an annular plasma. Comparisons of these imaging and spectroscopy measurements are drawn with those obtained for a stagnation layer formed between two point seed plasmas, as well as for single laser produced plasma. An off axis parabolic mirror was used to carry out imaging and spectroscopy along the plasma expansion axis, normal to the target. A simple relay lens system was used for imaging and spectroscopy parallel to the target surface. The former is, to the best of my knowledge, the first time such an investigation into stagnation layers has been undertaken. The targets used were slabs of aluminium with trace amounts of copper. Point, dual colliding and annular colliding plasmas were investigated to determine their relative merits in laser induced breakdown spectroscopy. It found that the limit-of-detection for trace amounts of Cu in Al is lowest for annular plasmas formed at low laser pulse energies of ca. 25 – 30 mJ.
Metadata
Item Type:Thesis (PhD)
Date of Award:November 2019
Refereed:No
Supervisor(s):Costello, John T. and Kennedy, Eugene T.
Uncontrolled Keywords:Plasma diagnostics; Annular Plasmas; Colliding Plasmas; Time-Resolved Spectroscopy; Gated Imaging
Subjects:Physical Sciences > Laser plasmas
Physical Sciences > Physics
Physical Sciences > Spectrum analysis
Physical Sciences > Plasmas
DCU Faculties and Centres:DCU Faculties and Schools > Faculty of Science and Health > School of Physical Sciences
Use License:This item is licensed under a Creative Commons Attribution-NonCommercial-No Derivative Works 3.0 License. View License
Funders:Irish Research Council, Science Foundation Ireland
ID Code:23725
Deposited On:20 Nov 2019 12:07 by John Costello . Last Modified 13 Dec 2019 15:30
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