David A. Cremers, Applied Research Associates Inc, Albuquerque, NM, USA

Leon J. Radziemski , Tucson, AZ, USA

Acronyms, Constants, and Symbols xv

1 Introduction 1

1.1 Atomic Optical Emission Spectrochemistry (OES) 1

1.1.1 Conventional OES 1

1.1.2 Laser OES 1

1.2 Laser-Induced Breakdown Spectroscopy (LIBS) 2

1.3 LIBS History 1960–1980 7

1.4 LIBS History 1981–1990 9

1.5 LIBS History 1991–2000 11

1.6 LIBS History 2001–2012 14

References 18

2 Basics of the LIBS Plasma 29

2.1 LIBS Plasma Fundamentals 29

2.1.1 Spectral Lines and Line Profiles 32

2.1.2 Determining Electron Densities from Spectral Line Widths 34

2.1.3 Plasma Opacity 37

2.1.4 Temperature and Thermodynamic Equilibrium 38

2.2 Laser-Induced Breakdown 46

2.2.1 Breakdown in Gases 46

2.2.2 Post-Breakdown Phenomena in Gases 48

2.2.3 Breakdown in and on Solids, Aerosols, and Liquids 48

2.2.4 Post-Breakdown Phenomena on Solid Surfaces 50

2.3 Laser Ablation from Surfaces and Aerosols 53

2.4 Nanosecond and Femtosecond Double- or Multiple-Pulse LIBS 58

2.5 Summary 63

2.6 Problems 63

References 64

3 LIBS Apparatus Fundamentals 69

3.1 Basic LIBS Apparatus 69

3.2 Lasers 70

3.2.1 Laser Fundamentals 70

3.2.2 Types of Lasers 72

3.2.3 Properties of Laser Light Important for LIBS 76

3.2.4 Generation of Additional Wavelengths 78

3.2.5 Double-Pulse Operation 78

3.3 Optical Systems 80

3.3.1 Focusing and Light Collection 80

3.3.2 Lenses 82

3.3.3 Fiber Optic Cables 82

3.4 Methods of Spectral Resolution 86

3.4.1 Introduction 86

3.4.2 Spectral Resolution Devices 88

3.5 Detectors 102

3.6 Detection System Calibrations 109

3.6.1 Wavelength Calibration 109

3.6.2 Spectral Response Calibration 110

3.7 Timing Considerations 114

3.8 Methods of LIBS Deployment 115

3.9 Problems 117

References 118

4 LIBS Analytical Figures of Merit and Calibration 123

4.1 Introduction 123

4.2 Basics of a LIBS Measurement 123

4.3 Precision 129

4.4 Calibration 131

4.4.1 Calibration Curves 131

4.4.2 Calibration Standards 138

4.4.3 Calibration-Free LIBS 140

4.5 Detection Limit 144

4.6 Accuracy 144

4.7 Problems 146

References 148

References for Detection Limits 150

5 Qualitative LIBS Analysis 151

5.1 Introduction 151

5.2 Identifying Elements 151

5.3 Material Identification 156

5.4 Process Monitoring 159

5.4.1 Introduction 159

5.4.2 Experimental 162

5.4.3 Results 163

5.4.4 Conclusions 169

5.5 Material Sorting/Distinguishing 169

5.5.1 Surface Condition 169

5.5.2 Type of Analysis 171

5.5.3 Sorting Materials of Close Composition 173

5.5.4 Other Examples of Material Identification 174

5.6 Site Screening Using LIBS 177

5.7 Semiquantitative Analysis 178

5.8 Problems 180

References 182

6 Quantitative LIBS Analysis 185

6.1 Introduction 185

6.2 Effects of Sampling Geometry 185

6.3 Other Sampling Considerations 189

6.4 Incomplete Vaporization and Ablation Stoichiometry 193

6.5 Use of Internal Standardization 194

6.6 Chemical Matrix Effects 196

6.7 Example of LIBS Measurement: Impurities in Lithium-Containing

Solutions 198

6.7.1 Objective 198

6.7.2 Experimental 198

6.7.3 Results 201

6.7.4 Discussion of Results 205

6.8 Example of LIBS Measurement: Detection of Materials on Swipes 206

6.8.1 Objective 206

6.8.2 Experimental 206

6.8.3 Results 209

6.9 Reported Figures of Merit for LIBS Measurements and Comparison

with Standard Methods 211

6.10 Enhancing Quantitative Analysis via Sophisticated Signal Processing 219

6.11 Conclusions 220

References 221

7 Chemometric Analysis in LIBS 223

7.1 Introduction 223

7.2 Chemometric Terms 227

7.3 Chemometric Analysis/Model Development 232

7.3.1 Data Collection 232

7.3.2 Data Preprocessing: Selection of Variables 234

7.3.3 Train the Model (Calibration) 236

7.3.4 Selecting the Criteria for Classification 238

7.3.5 Test the Model (Validation) 239

7.3.6 Refine the Model Parameters 239

7.3.7 Using the Model 240

7.3.8 Improve the Training Data 241

7.4 Summary 241

References 241

8 Remote LIBS Measurements 257

8.1 Introduction 257

8.2 Conventional Open-Path LIBS 259

8.2.1 Apparatus 259

8.2.2 Focusing the Laser Pulse 260

8.2.3 Collecting the Plasma Light 264

8.2.4 Results Using Conventional Open-Path LIBS 265

8.3 Standoff LIBS Using Femtosecond Pulses 270

8.3.1 Conventional Remote LIBS Using Femtosecond Laser Pulses 270

8.3.2 Remote Analysis by Filamentation Produced by Femtosecond

Pulses 271

8.4 Fiber Optic LIBS 276

8.4.1 Fiber Optics for Light Collection 276

8.4.2 Fibers for Laser Pulse Delivery 277

8.4.3 Applications of Fiber Optics 280

References 284

9 Selected LIBS Applications 289

9.1 Introduction 289

9.2 LIBS and the CBRNE Threats 289

9.2.1 Background 289

9.2.2 Nuclear Material and Isotope Detection 291

9.2.3 Detection of Explosives 294

9.2.4 Chemical and Biological Agent Detection 295

9.3 LIBS Analysis of Liquids and Solids in Liquids 297

9.4 Transportable LIBS Instrument for Stand-off Analysis 303

9.4.1 Instrument Design 303

9.4.2 Instrument Capabilities 307

9.4.3 Consideration of Detection Scenarios 312

9.5 LIBS for Space Applications 313

9.5.1 Background 313

9.5.2 Laboratory Studies of LIBS for Space Missions 313

9.5.3 ChemCam LIBS Instrument on MSL Rover 322

References 325

A Safety Considerations in LIBS 333

B Major LIBS References 337

C Detection Limits from the Literature 341

D Examples of LIBS Spectra 377

E Solutions to Problems 387

Index 397

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