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Plasma Temperature Measurements in the Context of Spectral Interference University of Central Florida STARS Honors Undergraduate Theses UCF Theses and Dissertations 2016 Plasma Temperature Measurements in the Context of Spectral Interference Brandon Seesahai University of Central Florida Part of the Analytical Chemistry Commons, Optics Commons, and the Plasma and Beam Physics Commons Find similar works at: https://stars.library.ucf.edu/honorstheses University of Central Florida Libraries http://library.ucf.edu This Open Access is brought to you for free and open access by the UCF Theses and Dissertations at STARS. It has been accepted for inclusion in Honors Undergraduate Theses by an authorized administrator of STARS. For more information, please contact [email protected]. Recommended Citation Seesahai, Brandon, "Plasma Temperature Measurements in the Context of Spectral Interference" (2016). Honors Undergraduate Theses. 140. https://stars.library.ucf.edu/honorstheses/140 PLASMA TEMPERATURE MEASUREMENTS IN THE CONTEXT OF SPECTRAL INTERFERENCE by BRANDON SEESAHAI A thesis submitted in partial fulfillment of the requirements for the Honors in the Major Program in Photonic Science and Engineering in the College of Optics and Photonics and in the Burnett Honors College at the University of Central Florida Orlando, Florida Fall Term, 2016 Thesis Chair: Matthieu Baudelet, Ph.D. © 2016 Brandon Seesahai ii ABSTRACT The path explored in this thesis is testing a plasma temperature measurement approach that accounts for interference in a spectrum. The Atomic Emission Spectroscopy (AES) technique used is called Laser Induced Breakdown Spectroscopy (LIBS) and involves focusing a laser pulse to a high irradiance onto a sample to induced a plasma. Spectrally analyzing the plasma light provides a "finger print" or spectrum of the sample. Unfortunately, spectral line broadening is a type of interference encountered in a LIBS spectrum because it blends possible ionic or atomic transitions that occur in plasma. To make use of the information or transitions not resolved in a LIBS spectrum, a plasma temperature method is developed. The basic theory of a LIBS plasma, broadening mechanisms, thermal equilibrium and distribution laws, and plasma temperature methods are discussed as background support for the plasma temperature method tested in this thesis. In summary, the plasma temperature method analyzes the Full Width at Half the Maximum (FWHM) of each spectral line for transitions provided from a database and uses them for temperature measurements. The first implementation of the temperature method was for simulated spectra and the results are compared to other conventional temperature measurement techniques. The temporal evolution of experimental spectra are also taken as a function of time to observe if the newly developed temperature technique can perform temporal measurements. Lastly, the temperature method is tested for a simulated, single element spectrum when considering interferences from all the elements provided in an atomic database. From stimulated and experimental spectra analysis to a global database consideration, the advantages and disadvantages of the temperature method are discussed. iii TABLE OF CONTENTS Introduction ..................................................................................................................................... 1 CHAPTER 1 Laser Induced Breakdown Spectroscopy (LIBS) ..................................................... 3 1.1 LIBS Introduction, History, and Applications ................................................................. 3 1.2 LIBS Plasma Concepts ..................................................................................................... 4 1.3 Spectral Acquisition from LIBS Setup............................................................................. 7 1.4 Spectral Analysis .............................................................................................................. 8 1.5 Line Broadening Mechanisms and Spectral Profiles ....................................................... 9 CHAPTER 2 Plasma Temperature and its Measurement ............................................................. 14 2.1 Plasma Temperature Introduction .................................................................................. 14 2.2 Thermodynamic Equilibrium and Distribution Laws .................................................... 14 2.2.1 Boltzmann Population Distribution Law ................................................................ 14 2.2.2 Maxwellian Velocity Distribution Law .................................................................. 16 2.2.3 Saha Ionization Equilibrium ................................................................................... 17 2.2.4 Photon Energy Distribution Law ............................................................................ 18 2.2.5 Local Thermodynamic Equilibrium (LTE) ............................................................. 18 2.3 Measuring Plasma Temperature ..................................................................................... 20 2.3.1 Boltzmann Plot Method .......................................................................................... 20 2.3.2 Saha-Boltzmann Plot Method ................................................................................. 24 2.3.3 Multi-Element Saha-Boltzmann Plot ...................................................................... 26 CHAPTER 3 Plasma Temperature of Known Samples ................................................................ 32 3.1 Broadening as an Interference ........................................................................................ 32 3.2 Plasma Temperature Methods ........................................................................................ 33 3.2.1 Attribution to a Single Transition ........................................................................... 34 3.2.2 Attribution to Multiple Transitions ......................................................................... 34 3.2.3 Example of 4 Temperature Methods from Simulated Spectrum ............................ 35 3.3 Experimental Application of Sharing of Intensities ....................................................... 38 3.3.1 Aluminum Sample .................................................................................................. 38 iv 3.3.2 Copper Sample ........................................................................................................ 46 3.4 Summary ........................................................................................................................ 54 CHAPTER 4 Plasma Temperature with Global Database (Simulated Spectra) ........................... 56 4.1 Global Database ............................................................................................................. 56 4.2 Filtering .......................................................................................................................... 59 4.2.1 Temperature Filter .................................................................................................. 59 4.3 Matching Factor (MF) .................................................................................................... 61 4.3.1 MF as a Filter .......................................................................................................... 63 4.4 Summary ........................................................................................................................ 65 Overall Conclusion ....................................................................................................................... 67 APPENDIX A: WAVELENGTH CALIBRATION ..................................................................... 70 APPENDIX B: SPECTRAL RESPONSE CALIBRATION ........................................................ 79 APPENDIX C: SAMPLE MATLAB CODE ............................................................................... 83 REFERENCE ................................................................................................................................ 87 v LIST OF FIGURES Figure 1: Plasma Life Cycle from a nanosecond laser pulse. ......................................................... 5 Figure 2: Spectrum dependence on lifetime of LIBS plasma from a nanosecond laser pulse (intensity is not drawn to scale). The blue curve is the plasma intensity as a function of time. ..... 6 Figure 3: Stark broadening and shift resulting from split energy levels. ...................................... 11 Figure 4: Gaussian, Lorentzian, and Pseudo-Voigt Fit for a spectral line. ................................... 13 24 -3 Figure 5: Simulated Aluminum spectrum from 250-400 nm at 3.0 eV with Ne = 10 m . The upper and lower energy level transitions are shown and the Al III peaks that are formed as a result. ............................................................................................................................................. 23 Figure 6: a) The relative population of electrons in Al III with respect to the upper energy level. b) The intensity of an emission line with respect to the upper energy level. c) Boltzmann Plot .. 23 Figure 7: Boltzmann, Saha-Boltzmann, and Multi-Element Saha Boltzmann plots for a simulated Aluminum and Calcium spectrum at 1.5 eV. ................................................................................ 30 Figure 8: Al II transitions within the FWHM of an Al II peak. .................................................... 33 Figure 9: Simulated
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