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Title of Thesis

Nek Muhammad Shaikh
Institute/University/Department Details
Department of Physics/ Quaid-i-Azam University Islamabad
Number of Pages
Keywords (Extracted from title, table of contents and abstract of thesis)
plasma diagnostics, laser-induced breakdown spectroscopy, cadmium plasma, laser ablation, laser induced zinc plasma

Laser-induced breakdown spectroscopy (LIBS) is a technique that can provide qualitative and quantitative measurement of metals in various environments. In the present work, we have studied the spatial and temporal evolution of the plasma parameters of the zinc (Zn), cadmium (Cd) and mercury (Hg) plasma, produced by the fundamental (1064 nm), second (532 nm) and third(355 nm) harmonics of a Q-switched pulsed Nd:Y AG laser. The experimentally observed line profiles of several atomic and ionic species have been used to extract the excitation temperature and electron number density. The excitation temperature is estimated from the intensity ratio method and from the Boltzmann plot method. The electron temperature of the zinc plasma has determined using the transitions 4s4d 3D3†’ 4s4p 3P2 at 334.5 nm and 4s5s 3S1†’ 4s4p 3P2 at 481.0 nm of neutral zinc. In the case of cadmium plasma, eight transition lines 228.80 nm (5p 1P1 †’ 5s2 1S0), 283.74 nm (6d 3D1†’ 5p 3p0), 298.06 nm (6d 3D3†’5p 3P2), 346.78 nm (5d 3D2 †’ 5p 3p1), 361.05 nm (5d 3D3 †’5p 3P2), 467.81 nm (6s 3S1 †’ 5p 3p0), 479.99 nm (6s 3S1 †’ 5p 3p1), and 508.58 nm (6s 3S1 †’ 5p 3P2) of neutral cadmium have used in the Boltzmann plot method. The ion temperature is estimated from the relative intensity ratio method of the ionic and atomic transitions using the Saha equation. In the case of mercury plasma, six transition lines at, 296.72 nm (6s6d 3D1†’ 6s6p 3p0), 365.01 nm (6s6p 3D3 †’ 6s6p 3P2), 404.66 nm (6s7s 3S1 †’ 6s6p 3p0), 435.83 nm (6s7s 3S1 †’ 6s6p 3Pl), 576.96 nm (6s6d 3D2 †’ 6s6p 1p1) and 579.07 nm (6s6d 1D2 †’6s6p 1pl) have been used for the determination of the excitation temperature. Stark broadened profiles of the neutral and singly ionized species have been utilized for the electron number density measurements. The electron number density of the Zn, Cd and Hg plasma has been deduced from the Zn (I) line at 334.5 nm, Cd (II) line at 226.50 nm and Hg (II) line at 398.39 run respectively. The experiments have been performed in air at atmospheric pressure as well as in the presence of different ambient gases (Ar, Ne and He) to investigate the effect ambient gas environments on the emission intensity of the atomic and ionic transition lines and on the plasma parameters. Besides, we present experimental relative transition probabilities of the Zn (4s5s 3S1 †’4s4p 3p0,1,2) and Cd (5s6s 3S1 †’ 5s5p 3p0,1,2) triplets and compare our data with that listed in the NIST data base. In addition we have studied the variation of the excitation temperature and electron number density as a function of laser irradiance at atmospheric pressure and estimated the inverse bremstrahlung (IB) absorption and photo ionization (PI) absorption coefficients. The validity of the assumption of local thermodynamic equilibrium is discussed in the light of the results obtained.

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2690.77 KB
S. No. Chapter Title of the Chapters Page Size (KB)
1 0 Contents
281.05 KB
2 1 Introduction 11
633.52 KB
  1.1 Laser Induced Breakdown Spectroscopy (LIBS ) 11
  1.2 Advantages And Disadvantages Of LIBS 12
  1.3 LIBS Plasma Precipitation Mechanism 13
  1.4 Effect Of Physical Variables LIBS 17
  1.5 Laser Absorption In The Plasma 21
  1.6 Line Broadening Mechanism LIBS 23
  1.7 Determination Of Electron Number Density From Stark Broadening Of Spectral Lines 27
  1.8 Determination Of Excitation / Electron Temperature 28
  1.9 Local Thermodynamic Equilibrium 30
  1.10 Self Absorption 31
  1.11 Zinc 31
  1.12 Cadmium 32
  1.13 Mercury 33
3 2 Experimental Setup 35
192.25 KB
  2.1 N d : Yag Laser 37
  2.2 LIBS 2000+Spectrometer 38
  2.3 Hr2000 High Resolution Spectrometer 39
  2.4 Optics Fiber 40
  2.5 Measurements Of Error In The Electron Number Density And The Excitation Temperature 41
4 3 Measurement Of Electron Density And Temperature Of The Laser Induced Zinc Plasma 42
584.07 KB
  3.1 Summary Of The Work 42
  3.2 Historical Background 42
  3.3 Results And Discussion 43
5 4 Diagnostics Of Cadmium Plasma Produced By Laser Ablation 66
523.14 KB
  4.1 Summary Of The Work 66
  4.2 Historical Background 66
  4.3 Results And Discussion 67
6 5 Optical Emission Studies Of The Mercury Plasma Generated By The Fundamental Second And Third Harmonics Of The N d Yag Lasers 87
405.23 KB
  5.1 Summary Of The Work 87
  5.2 Historical Background 87
  5.3 Results And Discussion 89
7 6 Conclusions 103
208.86 KB
  6.2 Future Plan : 105
  6.3 References 106