Theses and Dissertations

Issuing Body

Mississippi State University

Advisor

Monts, David L.

Committee Member

Arnoldus, Hendrik F.

Committee Member

Singh, Jagdish P.

Committee Member

Berg, Matthew J.

Committee Member

Krishnan, Sundar Rajan

Date of Degree

12-9-2016

Document Type

Dissertation - Open Access

Major

Applied Physics

Degree Name

Doctor of Philosophy

College

James Worth Bagley College of Engineering

Department

Applied Physics Program

Abstract

Laser-induced breakdown spectroscopy (LIBS) is an efficient tool for identification of elemental composition and characterization of materials. The concept of this technique is to focus a laser pulse of sufficiently high power on to a sample to create a plasma plume of atoms, ions, and molecules. The measurement of the resulting optical emission from these species provides the basis of the spectral analysis. Spectroscopic analysis of the plasma generated by Nd:YAG laser irradiation of wheat flour tortillas was carried out. A careful selection of spectral lines of Ca, Na and K which do not suffer from spectral interference was made. Among the spectral lines selected for analysis, the Na I 589.00 and 589.60-nm doublet lines were found to show the same intensity ratio values. A study on combustion was carried out with the use of LIBS. The main focus of this study was to compare results previously obtained using a rectangular slot burner with new results using a McKenna burner for equivalence ratios measurement in atmospheric premixed methane-air flames with ungated LIBS and also obtaining a temperature profile for our new burner. The Mckenna burner has a steady and less turbulent flame. Fortyive equivalence ratios were calculated. LIBS spectra of helium, argon and nitrogen were acquired using samples of pure gases at low pressures. The spectra from the three species showed continuum contributions which differ from one gas to the other. To better understand LIBS of gaseous samples, we have performed a study of the laser-induced plasmas in three gases, i.e., Ar, He, N2 and their mixtures. The evolution of plasma intensity and electron density, with time was studied at different laser pulse energies. Samples containing cerium, cesium and strontium were made with known concentrations and analyzed using laser-induced breakdown spectroscopy (LIBS). Powder samples are more challenging to analyze using LIBS than pellets. Spectra resulting from these samples under various experimental conditions were compared for possible interferences and other properties, placing particular interest in Ce II 418.65-nm, Cs I 852.11-nm and Sr I 460.73-nm atomic emission spectra lines because these were outstanding strong lines of these three aforementioned elements.

URI

https://hdl.handle.net/11668/19814

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