Laser Induced Breakdown Spectroscopy LIBS is a fast non-contact technique for the
analysis of the elemental composition using spectral information of the emission from
a laser-induced plasma. For the LIBS studies in this thesis the focus has been in using
very low energy, microjoule pulses in order to give high spatial resolution and minimize
the laser system requirements. This is a regime that we refer to as microLIBS. Under
such conditions it is important to maximize the signal detected to give the lowest
limit of detection LOD possible.
One technique to improve the signal to noise ratios is by coupling LIBS with
Laser Induced Fluorescence. This is a technique where the _rst pulse creates a vapor
plume and the second pulse tuned to a resonant absorption line of the species of
interest re-excites the plume. We term this technique as Laser ablation Laser Induced
Fluorescence LA-LIF. We have been investigating the performance of LA-LIF at low
pulse energies (_ 1 mJ for both pulses) for the detection of elemental contaminants in
water. This technique allows reasonable performance compared to high energy singlepulse
LIBS, but at a much reduced total energy expenditure. This allows LODs in the
parts per billion range ppb range which typically cannot be obtained with low energy
single pulse probing of the systems. This approach or exceeds the sensitivities which
can be obtained with many shots using much larger energy systems. In this thesis
we investigated the performance of LIBS at low pulse energies for the detection of
Pb as a contaminant in water. An LOD of 70 ppb was obtained for an accumulation
of 100 shots with the ablation laser pulse energy of 250 _J and an excitation laser
pulse energy of 8 _J. A systematic study of the detector conditions was made for the
system for the detection of Pb. Scaling laws for the LOD in terms of the pump and
probe energies were measured and also the e_ect of detector gain, the gate delay and
the gate width were studied.
In this thesis LIBS and LA-LIF were also used to analyze ultralow volumes of
analyte in liquids in microuidic geometries. LIBS was applied for the detection of
Na in liquid droplets in a microuidic system. The detection of Na as low as 360
femtograms was demonstrated for 100 shots integrated in this system. An LOD of 7
ppm for Pb for 100 shot accumulation was demonstrated using the LA-LIF technique
on an 18 _m diameter microdroplet.
To study the laser interaction with the water targets the MEDUSA one dimensional
hydrocode was used. The propagation of the shockwave and plume dynamics
were studied using this modeling code. The expansion of the plume was studied and
compared to experimentally measured values and to physical models for blast wave
expansion and stagnation.
Two preconcentration techniques were also studied, one of which used a wood-chip
as a substrate to absorb the analyte liquid and wick the salt on to the surface for
analysis and the other used an electroplating technique to plate the analyte metal as
a thin _lm on a substrate metal used as a cathode. The electroplating method for
preconcentration was also studied using a microchip laser and a LOD of 6.4 ppb for
Pb in water was obtained for an accumalation of 200,000 shots. / Photonics and Plasmas
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:AEU.10048/1353 |
| Date | 11 1900 |
| Creators | Godwal, Yogesh |
| Contributors | Fedosejevs, Robert (Electrical and Computer Engineering), Tsui, Ying (Electrical and Computer Engineering), Elezabbi, Abdul (Electrical and Computer Engineering), Tulip, John (Electrical and Computer Engineering), Marchand, Richard (Electrical and Computer Engineering), Singh, Jagdish (DIAL, Mississippi State University) |
| Source Sets | Library and Archives Canada ETDs Repository / Centre d'archives des thèses électroniques de Bibliothèque et Archives Canada |
| Language | en_US |
| Detected Language | English |
| Type | Thesis |
| Format | 7862600 bytes, application/pdf |
| Relation | Yogesh Godwal, Govind Kaigala, Viet Hoang, Siu-Lung Lui, Christopher Backhouse, Ying Tsui, and Robert Fedosejevs. Elemental analysis using micro Laserinduced Breakdown Spectroscopy (m-LIBS) in a microfluidic platform. Optics Express, Vol.16:12435-12445, 2008., Zhijiang Chen, Yogesh Godwal, Ying Yin Tsui, and Robert Fedosejevs. Sensitive detection of metals in water using laser-induced breakdown spectroscopy on wood sample substrates. Applied Optics, 49:87-94, 2010., Y. Godwal, S.L. Lui, M.T. Taschuk, Y.Y. Tsui and R. Fedosejevs. Determination of lead in water using laser ablationlaser induced uorescence. Spec- trochimica Acta Part B, Vol.62:1443-1447, 2007., Y. Godwal, M.T.Taschuk, S.L. Lui, Y.Y. Tsui and R. Fedosejevs. Development of laser-induced breakdown spectroscopy for microanalysis applications. Laser and Particle Beams, Vol.26:95-104, 2008., S.L. Lui, Y. Godwal, M.T. Taschuk, Y.Y. Tsui, R. Fedosejevs. Detection of Lead inWater Using Laser-Induced Breakdown Spectroscopy and Laser-Induced Fluorescence. Analytical Chemistry, Vol.80:1995-2000, 2008., Lucas M. C. Silva Celio Pasquini, Juliana Cortez and Fabiano B. Gonzaga. Laser induced breakdown spectroscopy. J. Braz. Chem. Soc., Vol. 18:463-512, 2007. |
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