Laserinduced breakdown spectroscopy (LIBS) is a rapidly growing elemental analyses technique that uses a short laser pulse to create a microplasma, so called laserinduced plasma (LIP), on the sample surface. The principle of LIBS is quite simple however although the physical processes involved in the lasermatter interaction are quite complex and still not completely explained. In LIBS, the laser pulses are focused onto the surface of sample target (solid, liquid as well as gas samples) so as to generate a high temperature microplasma (LIP) that vaporizes a small amount of samples material. The light emission from LIP, which contains the excited atomic and ionic species, is then collected and spectrally analyzed to determine the elemental constituents of target material. LIBS analysis can also provide the quantitative information provided the assumptions of local thermal equilibrium (LTE) and optically thin
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Laser Induced Breakdown Spectroscopy (LIBS)
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Laser Induced Breakdown Spectroscopy (LIBS)
Concepts, Instrumentation, Data Analysis and Applications
Volume 1
Edited by Vivek K Singh
University of LucknowLucknow, India
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This edition first published 2023
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Cover Design: Wiley Cover Images: © Georgy Shafeev/Shutterstock; Roxana Bashyrova/Shutterstock Set in 9.5/12.5pt STIXTwoText by Straive, Chennai, India
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Contents
Volume 1 Preface xix
Part I Fundamental Aspects of LIBS and Laser-Induced Plasma 1
1 Nanosecond and Femtosecond Laser-Induced Breakdown
Spectroscopy: Fundamentals and Applications 3
K M Muhammed Shameem, Swetapuspa Soumyashree, P Madhusudhan, Vinitha Nimma, Rituparna Das, Pranav Bhardwaj, Prashant Kumar and Rajesh K Kushawaha
2.3 Plasma Characteristics and Elementary Processes 35
2.4 Plasma in Thermodynamic Equilibrium 37
2.5 Plasma Emission Features 39
2.6 Conclusion 41
References 41
3 Diagnostics of Laser-Induced Plasma 45
Charles Ghany, Kyung-Min Lee, Herve K Sanghapi and Vivek K Singh
Trang 73.2.2 Plasma Temperature Measurements 46
3.2.3 Electron Density Measurements 47
3.2.3.1 Nonlinear Stark Broadening 47
3.2.3.2 Linear Stark Broadening 48
3.2.4 Additional Comments on the Characteristics of LIBS Plasmas 48
3.2.4.1 Matrix Effect 48
3.2.4.2 McWhirter Criterion 49
3.3 Factors Affecting the LIBS Plasma 49
3.3.1 Laser Characteristics 49
3.3.2 Wavelength and Pulse Duration of Laser 50
3.3.3 Properties of Target Material 50
3.3.4 Time Window of Observation 50
3.3.5 Geometric Setup 50
3.3.6 Ambient Gas 50
3.4 Methods of Enhancing LIBS Sensitivity 51
3.5 LTE Plasmas and Non-LTE Plasmas 52
3.6 Laser–Plasma Expansion in Gas and Liquids: Modeling and
4 Double and Multiple Pulse LIBS Techniques 65
Francesco Poggialini, Asia Botto, Beatrice Campanella, Simona Raneri, Vincenzo Palleschi and Stefano Legnaioli
4.2.4 Variable Pulse Duration in DP-LIBS 72
4.2.5 Variable Pulse Wavelength in DP-LIBS 73
4.2.6 Multiple Pulse LIBS 75
4.3 Signal Enhancement in DP-LIBS: Principles and Theory 77
4.4 Applications of DP-LIBS 80
4.4.1 DP-LIBS of Archaeological Artifacts 80
4.4.2 DP-LIBS for the Stand-Off Detection of Explosives 81
4.4.3 DP-LIBS for the Analysis of Biological Materials 81
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5 Calibration-Free Laser-Induced Breakdown Spectroscopy 89
Jörg Hermann
5.1 Introduction 89
5.2 Validity Conditions of the Physical Model 90
5.2.1 Congruent Mass Transfer from the Solid Sample Toward Plasma 90
5.2.2 Local Thermodynamic Equilibrium 92
5.2.3 Spatial Distribution of Plasma 93
5.2.4 Self-Absorption 94
5.2.5 Chemical Reactions 95
5.3 Methods of Calibration-Free Measurements 98
5.3.1 The Mathematical Problem of a Multielemental Equilibrium Plasma 98
5.3.2 First CF-LIBS Method for Ideal Plasma 99
5.3.3 Amended Methods 100
5.3.4 Methods Based on Spectra Simulation 101
5.3.4.1 Calculation of Spectral Radiance 101
5.3.4.2 Implementation in Measurement Algorithm 104
5.3.4.3 Illustration for Alloy 105
5.4 Critical Review of Analytical Performance 107
5.4.1 Model Validity 107
5.4.2 Error Evaluation 107
5.4.2.1 Minor and Trace Element Quantification 107
5.4.2.2 Error due to Self-Absorption 109
5.4.3 Recommendations 111
5.4.3.1 Apparatus Requirements 111
5.4.3.2 Setting the Experimental Conditions 111
5.4.3.3 Selection of Spectral Lines 113
Part II Molecular LIBS and Instrumentation Developments 123
6 Molecular Species Formation in Laser-Produced Plasma 125
K M Muhammed Shameem, Swetapuspa Soumyashree, P Madhusudhan, Vinitha Nimma, Rituparna Das, Pranav Bhardwaj and Rajesh K Kushawaha
6.1 Introduction 125
6.2 Atmospheric Contribution in LIBS Spectra 127
6.3 CN and C2Molecular Formation in LIP 127
References 134
Trang 97.2 Laser Systems Used 137
7.3 Instrumentation in Standoff LIBS 138
7.4 Gated and Non-Gated CCDs/Spectrometers 139
7.5 Experimental Setup 139
7.6 Reviews on Standoff LIBS 140
7.7 Studies in Standoff LIBS 140
7.8 Variants in Standoff LIBS 146
7.9 Machine-Learning for Data Analysis in Standoff Mode 149
7.10 Advancements in Standoff LIBS Methods 150
7.11 Ongoing Study at ACRHEM, University of Hyderabad 153
7.12 Conclusions and Outlook 158
8.2.1 Plasmon Excitation in NPs During NELIBS 166
8.2.2 Broadening of the Plasmon Frequency due to Plasmon Coupling 167
8.2.3 Local Field Enhancement 168
8.2.4 Influence of Sample Properties on Laser Ablation Mechanism During
8.3.1 Sample Preparation and Setup 174
8.3.2 Application in the Field of Analytical Chemistry 175
9.4 Enhancement Via Different Conditions 185
9.5 Perspectives on the Mechanism(s) of Enhancement 191
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9.6 Variations in NE-LIBS 199
9.7 Beyond NE-LIBS 200
9.8 Further Application of Nanoparticles in LIBS 202
9.9 Ongoing Study in the Lab 203
9.10 Conclusions 204
References 205
Part III Data Analysis and Chemometrics in LIBS 211
10 Full-Spectrum Multivariate Analysis of LIBS Data 213
Catherine E McManus and Nancy J McMillan
10.1 Introduction 213
10.2 Full-Spectrum Multivariate Analysis 215
10.3 Analysis of Geologic Samples 216
11 Chemometrics for Data Analysis 229
Manoj Kumar Gundawar and Rajendhar Junjuri
11.1 Introduction 229
11.2 Data 230
11.3 Machine Learning 231
11.3.1 Principal Component Analysis 234
11.4 Classification of the Data 236
11.4.1 Artificial Neural Network 236
11.5 Conclusion 237
References 238
12 Chemometric Processing of LIBS Data 241
J El Haddad, A Harhira, E Képeš, J Vrábel, J Kaiser and P Poˇrízka
12.1 Introduction 241
12.2 Exploratory Analysis Methods for Visualization 243
12.2.1 Principal Component Analysis 244
12.3 Quantitative Analysis Methods 249
12.3.1 Main Steps of Multivariate Calibration Before and After LIBS
Measurements 250
12.3.2 Multiple Linear Regression 251
12.3.3 Principal Component Regression 251
12.3.4 Partial Least Squares 252
12.4 Classification 254
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xii Contents
12.4.1 Soft Independent Modeling of Class Analogy 255
12.4.2 Partial Least Squares-Discriminant Analysis 256
12.5 Data Preprocessing 257
12.5.1 Baseline Correction 257
12.5.2 Normalization 258
12.5.2.1 Normalization to the Background 258
12.5.2.2 Normalization to the Total Area 258
12.5.2.3 Normalization to an Internal Standard 259
12.5.2.4 Standard Normal Variate 259
12.6.3.1 Figures of Merit for Quantitative Models 265
12.6.3.2 Figures of Merit for Classification Models 267
12.7 Conclusions 268
Acknowledgments 269
References 269
13 How Chemometrics Allowed the Development of LIBS in the
Quantification and Detection of Isotopes: A Case Study of Uranium 277
Carlos A Rinaldi, Norberto Boggio and Juan Vorobioff
13.1 Introduction 277
13.2 The LIBS Method 278
13.3 Detection and Quantification 279
14 Application of Multivariate Analysis to the Problem of the
Provenance of Gem Stones (Ruby, Sapphire, Emerald, Diamond) 287
Nancy J McMillan and Catherine E McManus
14.1 Introduction 287
14.1.1 The Problem of Gem Provenance 287
14.1.2 Analytical Methods Employed in the Determination of Gem Provenance 288
14.2 Gem Mineral Genesis 289
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14.2.1 Corundum: Ruby and Sapphire Genesis 289
14.2.2 Diamond Genesis 291
14.2.3 Emerald Genesis 292
14.2.4 Characteristics of a System to Determine Gem Provenance 292
14.3 Laser-Induced Breakdown Spectroscopy and Multivariate Analysis 293
14.3.1 Laser-Induced Breakdown Spectroscopy 293
14.3.2 Multivariate Data Analysis 293
14.4 Gem Provenance Studies 294
14.4.1 Ruby and Sapphire 294
15.2 Fundamental Concepts of Machine Learning 306
15.3 Decision Trees and Related Ensemble Methods 307
15.3.1 Decision Trees 307
15.3.2 Ensemble Models 309
15.4 Support Vector Machines 311
15.5 Artificial Neural Networks 314
15.5.1 Artificial Neuron 314
15.5.2 Fully Connected Multilayer Perceptrons 314
15.5.3 Convolutional Neural Networks 316
15.5.4 Training of Artificial Neural Networks 317
16.2 LIBS Coal and Biomass Laboratory Experimental Results 334
16.3 Application of Artificial Intelligence Techniques to LIBS Spectral Data 337
16.3.1 LIBS Biomass Spectral Analysis Using Back-Propagation Neural Networks and
Self-Organizing Map Networks 338
16.3.1.1 Model Inputs 342
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17 Lasing in Optically Pumped Laser-Induced Plasma 355
Lev Nagli, Michael Gaft and Yosef Raichlin
17.1 Introduction 355
17.2 Experimental Setups and Samples 357
17.3 Lasing Effects in a LIP Plume; 13thGroup Elements 360
17.3.1 Al; Ground Term 3s23p2P1,2;3/2; ΔLS=0.013 eV 360
17.3.1.1 Plasma Parameters 360
17.3.1.2 Stimulated Emission and Lasing, Intensities, and Directionality 360
17.3.2 Other 13th Group Elements LIPL 367
17.3.2.1 Ga; Ground-State Term 3s24p2P1,2;3/2; ΔLS=0.1 eV 367
17.3.2.2 In; Ground-State Term 3s25p2P1,2;3/2; ΔLS≈0.27 eV 368
17.3.2.3 Tl; Ground-State Term 3s26p2P1,2;3/2; ΔLS≈0.94 eV 368
17.4 Polarization of the LIPLs: the UV–VIS Generation 370
17.4.1 Al LIPL 370
17.4.1.1 Vector EpNormal to the Generation Direction kg 373
17.4.1.2 Vector EpParallel to the Generation Direction kg 374
17.4.2 UV–VIS Generation of Other Elements from the 13th Group 375
17.4.2.1 In LIPL 3s25p Ground State 375
17.4.2.2 Tl LIPL 3s26p Ground State 375
17.5 External Magnetic Field Effects 376
17.6 Fourteenth GROUP Elements LIPL (Ground-State Configuration 4s2np23P0,
n =4,5,6) 377
17.7 LIPLs Tunability 379
17.8 Conclusions 382
References 382
18 LIBS Analysis of Optical Surfaces and Thin Films 387
Christoph Gerhard and Jörg Hermann
18.1 Introduction 387
18.2 Sensitivity-Improved Calibration-Free LIBS 389
18.3 Analysis of Optical Materials and Surfaces 392
18.3.1 Depth-Resolved Analysis of Impurities 392
18.3.2 Accuracy of Sensitivity-Improved Calibration-Free LIBS on Glasses 395
18.4 Elemental Analysis of Thin Films 395
18.4.1 Need of Quality Control in Thin Film Manufacturing Technology 395
18.4.2 Monitoring of Thin Film Synthesis 397
18.4.3 Probe Volume in LIBS Analysis of Thin Films 400
18.4.4 Accurate Analysis of Thin Films via Calibration-Free LIBS 400
18.4.4.1 Analyses in Ambient Air 400
18.4.4.2 Analyses in Argon Background Gas 404
Trang 1419.4 Detection of RE Using LIBS 418
19.5 Detection of RE Using Other Techniques 423
20.2 Biofouling Sample Preparation 431
20.3 Experimental LIBS Setup 432
20.4 Analysis and Discussion 432
20.5 Biomineralization and Elemental Mapping Studies 437
20.6 LIBS Spectra for Biofouling Sample 437
20.7 LIBS Spatial Elemental Mapping 440
20.8 Conclusion 444
Acknowledgement 444
References 444
21 Hyphenated LIBS Techniques 447
U K Adarsh, V S Dhanada, Santhosh Chidangil and V K Unnikrishnan
21.2.3 Hyphenated LIBS Systems 452
21.3 Conclusion and Future Directions 457
References 457
22 Comparison of LIBS with Other Analytical Techniques 461
Muhammad Aslam Baig, Rizwan Ahmed and Zeshan Adeel Umar
22.1 Introduction 461
22.2 Quantitative Analysis by LIBS 462
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xvi Contents
22.2.1 Energy-Dispersive X-ray Spectroscopy 471
22.2.2 Proton-Induced X-ray Emission 473
22.2.3 X-ray Fluorescence Spectroscopy 474
22.2.4 Inductively Coupled Plasma – Optical Emission Spectrometry 475
22.3 Laser-Ablation Time-of-Flight Mass Spectrometry 476
22.4 Conclusion 482
References 482
23 Combining Laser-Induced Breakdown Spectroscopy and Raman
Spectroscopy: Instrumentation and Applications 487
Vasily N Lednev
23.1 Introduction 487
23.2 Instrumentation 489
23.2.1 Laser System 489
23.2.2 Optical Systems for Laser Beam Delivery and Signals Collection 493
23.2.3 Spectra Resolution Systems and Detectors 494
23.2.4 Integrated Raman and LIBS Instruments 496
23.2.4.1 Laboratory Systems 496
23.2.4.2 Remote Systems for Raman and LIBS 498
23.3 Applications 502
23.3.1 Geology Applications 502
23.3.2 Cultural Heritage and Archaeology Applications 510
23.3.3 Dangerous Materials Detection 511
23.3.4 Biology and Ecology 512
Part V Novel Applications of LIBS 531
24 Application of LIBS to the Analysis of Metals 533
Francesco Poggialini, Asia Botto, Beatrice Campanella, Vincenzo Palleschi, Simona Raneri and Stefano Legnaioli
25 LIBS Analysis of Metals Under Extreme Conditions 551
Mohamed Abdel-Harith and Raghda Hosny El-Saeid
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26 LIBS Applications to Liquids and Solids in Liquids 559
Chet R Bhatt, Daniel Hartzler, Jinesh Jain and Dustin L McIntyre
27 Coal Analysis by Laser-Induced Breakdown Spectroscopy 581
Shunchun Yao
28 Application of LIBS to Terrestrial Geological Research 593
Giorgio S Senesi and Russell S Harmon
29 Plastic Waste Identification Using Laser-Induced Breakdown
Spectroscopy 615
Rajendhar Junjuri and Manoj Kumar Gundawar
30 Cultural Heritage Applications of Laser-Induced Breakdown
Spectroscopy 623
Duixiong Sun and Yaopeng Ying
31 Nuclear Applications of Laser-Induced Breakdown Spectroscopy 643
Gábor Galbács and Éva Kovács-Széles
32 Applications of Laser-Induced Breakdown Spectroscopy for Trace
Detection in Explosives 667
Qianqian Wang and Geer Teng
33 Geochemical Fingerprinting Using Laser-Induced Breakdown
Spectroscopy 683
Pengju Xing and Zhenli Zhu
34 Laser-Induced Breakdown Spectroscopy for the Analysis of Chemical
and Biological Hazards 701
Lianbo Guo
35 Development of a Simple, Low-Cost, and On-Site Deployable LIBS
Instrument for the Quantitative Analysis of Edible Salts 715
Sandeep Kumar, Hyang Kim, Jeong Park, Kyung-Sik Ham, Song-Hee Han, Sang-Ho Nam and Yonghoon Lee
36 Bioimaging in Laser-Induced Breakdown Spectroscopy 729
Pavlina Modlitbová, Pavel Poˇrízka and Jozef Kaiser
37 Laser-Induced Breakdown Spectroscopy for the Identification of
Bacterial Pathogens 745
Somenath Ghatak, Gaurav Sharma, Prashant Kumar Rai, Suman Yadav and Geeta Watal
Trang 17Gang Xiong and Stephen D Tse
39 Laser-Induced Breakdown Spectroscopy for the Analysis of Cultivated
Soil 767
R K Aldakheel, M A Gondal and M A Almessiere
40 Laser-Induced Breakdown Spectroscopy in Food Sciences 781
J Naozuka and A P Oliveira
41 Capabilities and Limitations of Laser-Induced Breakdown
Spectroscopy for Analyzing Food Products 807
R K Aldakheel, M A Gondal and M A Almessiere
42 Laser-Induced Breakdown Spectroscopy and Its Application
Perspectives in Industry and Recycling 823
Reinhard Noll
43 Development of Laser-Induced Breakdown Spectroscopy for
Application to Space Exploration 851
Zhenzhen Wang and Han Luo
44 Femtosecond Laser-Induced Breakdown Spectroscopy of Complex
Materials 863
Mathi Pandiyathuray
45 Application of LIBS for the Failure Characteristics Prediction of
Heat-Resistant Steel 883
Meirong Dong, Junbin Cai, Shunchun Yao and Jidong Lu
46 Scope for Future Development in Laser-Induced Breakdown
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Preface
Laser-induced breakdown spectroscopy (LIBS) is a rapidly growing elemental analysestechnique that uses a short laser pulse to create a micro-plasma, so called laser-inducedplasma (LIP), on the sample surface The principle of LIBS is quite simple howeveralthough the physical processes involved in the laser-matter interaction are quite complexand still not completely explained In LIBS, the laser pulses are focused onto the surface
of sample target (solid, liquid as well as gas samples) so as to generate a high temperaturemicro-plasma (LIP) that vaporizes a small amount of samples material The light emissionfrom LIP, which contains the excited atomic and ionic species, is then collected andspectrally analyzed to determine the elemental constituents of target material LIBSanalysis can also provide the quantitative information provided the assumptions of localthermal equilibrium (LTE) and optically thin plasma are satisfied
Uniqueness of LIBS is that it is capable of providing distinct spectral signatures acteristic of all chemical species in all environments Because of its unique features, such
char-as no or minimal sample preparation, real-time, and in situ analysis char-as well char-as the quchar-asinon-destructive and micro-analysis character of the measurements, the applications ofLIBS has dramatically increased in the last few years During the past decade, LIBS has gonethrough major changes in the field of biological sciences In this book, our aim is to providethe detailed overview of the latest developments and applications of the LIBS technique and
an up-to-date review of LIBS for biological, medical, food, environmental, and plant scienceresearchers We have tried to include the chapters for theoretical and experimental aspects
of LIBS experiments as well as the chemometrics methods with applications that are beingused for LIBS data interpretation especially for beginners those who are not familiar withthese topics The chapters are contributed by independent LIBS groups in the world
The book is divided into two volumes Vol.1 and Vol 2 Volume 1 comprises of four(04) parts (Part I-IV) which contains 23 chapters Volume 1 of the book basically includesthe chapters related to the fundamental processes and underlying physics of LIBS andlaser-induced plasma, molecular LIBS and instrumentation developments, data analysisand chemometrics in LIBS, and special topics and comparison with other methods
Volume 2 comprises of only one part (Part V) which contains 23 chapters that isparticularly dedicated to the novel applications of LIBS of different disciplines and areas
of interest In this volume (Vol 2), the chapters contain recent advances in the field,such as molecular LIBS, self-calibrated methods, high-energy materials, LIBS imaging,food science, coal, flame, defense, matrix effects, LIBS for planetary science, analysis of
Trang 19Part I (Fundamental Aspects of LIBS and Laser-Induced Plasma) consists of five (05)chapters which include the chapters related to the fundamental aspects of LIBS cover-ing nanosecond and femtosecond LIBS, calibration-free LIBS (CF-LIBS), and diagnostics
of laser-induced plasma (LIP) Chapter 1 describes the fundamentals of nanosecond andfemtosecond LIBS with pertinent applications Chapter 2 discusses about the elementaryprocesses and emission spectra in LIP Chapter 3 presents the diagnostics of LIP Chapter 4discusses in details about double and multiple pulse LIBS Chapter 5 highlighted the details
of CF-LIBS along with the proposed physical models, their validity conditions, and theexperimental requirements
Part II (Molecular LIBS and Instrumentation Developments) consists of four (04)chapters which concern about the molecular LIBS and recent developments in LIBS
Chapter 6 discusses about the molecular formation in laser-induced plasma of LIBS
Chapter 7 highlighted the recent developments in Standoff-LIBS In chapter 8, thebasic concepts ad fundaments of nanoparticle enhanced-LIBS (NE-LIBS) are discussedwith important applications Chapter 9 highlights the concepts of NE-LIBS for SensingApplications
Part III (Data Analysis and Chemomertics in LIBS) consists of seven (07) chapters whichdescribe in details the chapters of LIBS data analysis using different chemometric meth-ods such as machine learning, artificial intelligence etc Chapter 10 discusses about themultivariate analysis of LIBS data Chapter 11 describes about the chemometrics, whichrefers to the whole array of data analysis methods, for data analysis in LIBS Chapter 12
highlights about the chemometric processing of LIBS data In this chapter, examples of
chemometric applications in LIBS for different fields are presented Chapter 13 presentsthe application of chemometrics and their application in the development of LIBS in thequantification and detection of isotopes particularly in case of uranium (U) Chapter 14discusses the application of multivariate analysis to the problem of the provenance of Gemstones (ruby, sapphire, emerald, diamond) Chapter 15 gives the detailed introduction ofmodern machine learning (ML) techniques in context of LIBS Chapter 16 discusses theuse of artificial intelligence techniques for the analysis of LIBS data from coal and biomass
Part IV (Special Topics and Comparison with Other Methods) consists of seven (07)chapters which cover some special topics and comparison of LIBS with other exist-ing analytical methods Chapter 17 discusses in details the lasing in optically pumpedlaser-induced plasma (LIP) which provides the information of nonlinear effects in opticallypumped LIP Chapter 18 emphasizes the use and application of LIBS towards the analysis
of thin films and optical surfaces Chapter 19 gives the overview of LIBS technique forthe detection of rare earth elements and comparison with other techniques Chapter 20presents laboratory-scale LIBS technique to analyze biofouling samples temporally andspatially Chapter 21 gives the overview of hyphenated LIBS techniques Chapter 22 is thecomparison of LIBS technique with other analytical techniques Chapter 23 presents indetails the instrumentation and application of LIBS combined with Raman spectroscopy
Part V (Novel Applications of LIBS) consists of twenty three (23) chapters This sectionincludes the chapters of the possible novel applications of LIBS technique Chapter 24
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presents the application of LIBS to analysis of metals Chapter 25 gives the details of LIBSfor the analysis of metals under extreme conditions Chapter 26 presents the outstandingcapability of LIBS technique for real-time measurements of liquids and suspended solidsinside liquids Chapter 27 is the coal Analysis using LIBS technique Chapter 28 presentsthe application of LIBS to terrestrial geological research Chapter 29 gives the overview
of plastic waste identification using LIBS technique Chapter 30 highlights the culturalheritage applications of LIBS Chapter 31 presents the nuclear applications of LIBStechnique Chapter 32 emphasizes the use and application LIBS for trace detection inexplosives Chapter 33 gives the overview of geochemical fingerprinting using LIBS
Chapter 34 highlights the application of LIBS to analyze chemical and biological hazards
Chapter 35 presents the development of a simple, low-cost, and on-site deployable LIBSinstrument for salt analysis applications Chapter 36 is the LIBS bio-imaging which arefocused on LIBS elemental imaging of biotic samples Chapter 37 briefly gives LIBS basedidentification of bacterial pathogens Chapter 38 discusses the phase-selective LIBS ofmetal-oxide nanoaerosols Chapter 39 presents the use of LIBS technique for the analysis ofcultivated soil Chapter 40 gives the overview of the applications of LIBS in food sciences
Chapter 41 presents the capabilities and limitations of LIBS for analyzing food products
Chapter 42 highlights about the LIBS techniques and it’s application perspectives inindustry and recycling Chapter 43 briefly gives the development of LIBS for application
to space exploration Chapter 44 discusses about femtosecond-LIBS (fs-LIBS) for
com-plex materials Chapter 45 highlighted the use and application of LIBS for the failurecharacteristics prediction of heat-resistant steel Chapter 46 presents the scope of futuredevelopment in laser-induced breakdown spectroscopy
We gratefully acknowledge the most valuable and imaginative contributions by theauthors who spared time from their busy schedule of teaching and research for this book
We hope the readers will enjoy this book “Laser Induced Breakdown Spectroscopy (LIBS):
Concepts, Instrumentation, Data Analysis and Applications” and that it contributes tothe continued instrumental developments of LIBS and it’s applications We also hopethat it encourages and inspires the beginners to the field in exploring the multifacetedaspects of LIBS Finally, the critical evaluations and recommendations by the reviewersfor the applicability of the LIBS in different field of science and technology will make thisbook a valuable asset for anyone employing or improving upon these techniques VivekKumar Singh (VKS) finds the words inadequate to express his gratefulness to his parents
Dr Markandeya Singh and Mrs Chandratara Devi who encouraged and supported himthroughout academic life and waited along to see this achievement come true VKS greatlyappreciates his wife Dr (Mrs.) Priyanka Rai for her patience and encouragement and hisdaughters Ms Vandita Singh and Ms Anika Singh for amusing him during the preparation
of the book VKS is thankful to all his family members, friends and well wishers whodirectly and indirectly helped him to complete this book
Dr Durgesh K Tripathi Prof Yoshihiro Deguchi
Dr Zhenzhen Wang
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Laser Induced Breakdown Spectroscopy (LIBS)
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Laser Induced Breakdown Spectroscopy (LIBS)
Concepts, Instrumentation, Data Analysis and Applications
Volume 2
Edited by Vivek K Singh
University of LucknowLucknow, India
Zhenzhen Wang
Xi’an Jiaotong UniversityXi’an, China
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This edition first published 2023
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Library of Congress Cataloging-in-Publication Data Applied for
[Hardback ISBN: 9781119758402]
Cover Design: Wiley Cover Images: © Georgy Shafeev/Shutterstock; Roxana Bashyrova/Shutterstock Set in 9.5/12.5pt STIXTwoText by Straive, Chennai, India
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Contents
Volume 1 Preface xix
Part I Fundamental Aspects of LIBS and Laser-Induced Plasma 1
1 Nanosecond and Femtosecond Laser-Induced Breakdown
Spectroscopy: Fundamentals and Applications 3
K M Muhammed Shameem, Swetapuspa Soumyashree, P Madhusudhan, Vinitha Nimma, Rituparna Das, Pranav Bhardwaj, Prashant Kumar and Rajesh K Kushawaha
2 Elementary Processes and Emission Spectra in Laser-Induced
Plasma 33
V Gardette, Z Salajkova, M Dell’Aglio and A De Giacomo
3 Diagnostics of Laser-Induced Plasma 45
Charles Ghany, Kyung-Min Lee, Herve K Sanghapi and Vivek K Singh
4 Double and Multiple Pulse LIBS Techniques 65
Francesco Poggialini, Asia Botto, Beatrice Campanella, Simona Raneri, Vincenzo Palleschi and Stefano Legnaioli
5 Calibration-Free Laser-Induced Breakdown Spectroscopy 89
Jörg Hermann
Part II Molecular LIBS and Instrumentation Developments 123
6 Molecular Species Formation in Laser-Produced Plasma 125
K M Muhammed Shameem, Swetapuspa Soumyashree, P Madhusudhan, Vinitha Nimma, Rituparna Das, Pranav Bhardwaj and Rajesh K Kushawaha
7 Recent Developments in Standoff Laser-Induced Breakdown
Spectroscopy 137
Trang 25Zita Salajková, Marcella Dell’Aglio, Vincent Gardette and Alessandro De Giacomo
9 Nanoparticle-Enhanced Laser-Induced Breakdown Spectroscopy for
Sensing Applications 183
Linga Murthy Narlagiri and Venugopal Rao Soma
Part III Data Analysis and Chemometrics in LIBS 211
10 Full-Spectrum Multivariate Analysis of LIBS Data 213
Catherine E McManus and Nancy J McMillan
11 Chemometrics for Data Analysis 229
Manoj Kumar Gundawar and Rajendhar Junjuri
12 Chemometric Processing of LIBS Data 241
J El Haddad, A Harhira, E Képeš, J Vrábel, J Kaiser and P Poˇrízka
13 How Chemometrics Allowed the Development of LIBS in the
Quantification and Detection of Isotopes: A Case Study of Uranium 277
Carlos A Rinaldi, Norberto Boggio and Juan Vorobioff
14 Application of Multivariate Analysis to the Problem of the
Provenance of Gem Stones (Ruby, Sapphire, Emerald, Diamond) 287
Nancy J McMillan and Catherine E McManus
15 Machine Learning in the Context of Laser-Induced Breakdown
Spectroscopy 305
E Képeš, J Vrábel, J El Haddad, A Harhira, P Poˇrízka and J Kaiser
16 Analysis of LIBS Data from Coal and Biomass Using Artificial
Intelligence Techniques 331
Carlos E Romero and Robert De Saro
Part IV Special Topics and Comparison with Other Methods 353
17 Lasing in Optically Pumped Laser-Induced Plasma 355
Lev Nagli, Michael Gaft and Yosef Raichlin
18 LIBS Analysis of Optical Surfaces and Thin Films 387
Christoph Gerhard and Jörg Hermann
Trang 2621 Hyphenated LIBS Techniques 447
U K Adarsh, V S Dhanada, Santhosh Chidangil and V K Unnikrishnan
22 Comparison of LIBS with Other Analytical Techniques 461
Muhammad Aslam Baig, Rizwan Ahmed and Zeshan Adeel Umar
23 Combining Laser-Induced Breakdown Spectroscopy and Raman
Spectroscopy: Instrumentation and Applications 487
Vasily N Lednev
Volume 2 Preface xix
Part V Novel Applications of LIBS 531
24 Application of LIBS to the Analysis of Metals 533
Francesco Poggialini, Asia Botto, Beatrice Campanella, Vincenzo Palleschi, Simona Raneri and Stefano Legnaioli
24.1 Introduction 533
24.2 Laser-Induced Ablation on Metal Targets 534
24.2.1 Wavelength and Pulse Duration Dependence 534
24.2.2 Laser Pulse Energy Dependence 535
24.3 LIBS Application to the Analysis of Metals 536
25 LIBS Analysis of Metals Under Extreme Conditions 551
Mohamed Abdel-Harith and Raghda Hosny El-Saeid
25.1 Introduction 551
25.2 LIBS Analysis of Metals Under Extreme Conditions 552
25.2.1 Effects of Ambient Gas and Its Pressure on LIBS Signal Intensity and Plasma
Parameters 552
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x Contents
25.2.2 Effects of Sample Temperature on LIBS Analysis of Metals 552
25.3 Under water LIBS Analysis 554
25.4 Conclusion 555
References 556
26 LIBS Applications to Liquids and Solids in Liquids 559
Chet R Bhatt, Daniel Hartzler, Jinesh Jain and Dustin L McIntyre
26.3.4 Measurements on Pretreated Samples (Concentrated Liquids) 568
26.4 Field-Deployable LIBS Sensor 569
27.2 Key Role of LIBS in the Analysis of Coal 581
27.3 Challenges to Coal Analysis by LIBS 582
27.3.1 Signal Uncertainty 582
27.3.2 Matrix Effect 582
27.3.3 Establishing Quantitative Analysis Model of Coal Property 583
27.4 Optimization Methods 584
27.4.1 Signal Stabilization Methods 584
27.4.2 Matrix Effect Correction 585
27.4.3 Chemometrics Methods 586
27.4.4 LIBS Combined with Infrared Spectroscopy 588
References 588
28 Application of LIBS to Terrestrial Geological Research 593
Giorgio S Senesi and Russell S Harmon
28.1 Introduction: Why Is Laser-Induced Breakdown Spectroscopy Important for the
Geosciences? 593
28.1.1 Attributes of LIBS for Geomaterial Analysis 593
28.2 Applications of LIBS Across Geosciences 594
28.2.1 Minerals 594
28.2.1.1 Gem Minerals 594
Trang 2829.3 Results and Discussion 617
29.3.1 Principal Component Analysis 618
29.3.2 Partial Least Squares Discriminant Analysis (PLS-DA) 619
30.2 Case Studies of LIBS in Cultural Heritage 623
30.2.1 Pottery, Stone, Glass 623
31 Nuclear Applications of Laser-Induced Breakdown Spectroscopy 643
Gábor Galbács and Éva Kovács-Széles
31.1 Introduction 643
31.2 Analytical Potential of LIBS in the Nuclear Field 644
31.3 Applications Related to Nuclear Fission Facilities 645
31.3.1 Quantitative Elemental Analysis 646
31.3.1.1 Nuclear Materials 646
31.3.1.2 Structural and Engineering Materials 648
Trang 2932.4.1 Feature Analysis and Selection 673
32.4.2 Spectral Identification Methods 676
32.5 Conclusions and Outlooks 678
33.2 Geochemical Fingerprints and LIBS 683
33.3 LIBS for Geochemical Fingerprinting 685
33.3.1 Qualitative and Quantitative Elemental Analysis of Geological Samples Using
LIBS 685
33.3.2 Identification and Classification of Geological Samples by LIBS 687
33.3.3 Imaging of Geological Samples Using LIBS 688
33.4 Prospect of LIBS for Geochemical Fingerprints 689
References 690
34 Laser-Induced Breakdown Spectroscopy for the Analysis of Chemical
and Biological Hazards 701
Lianbo Guo
34.1 Introduction 701
34.2 LIBS for Chemical Hazards Analysis 701
34.2.1 Introduction to Chemical Hazards 701
34.2.2 Detection of Inorganic Chemical Hazards by LIBS 701
34.2.2.1 Detection of Metallic Elements 702
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34.2.2.2 Detection of Nonmetallic Elements 702
34.2.3 Detection of Organic Chemical Hazards by LIBS 703
34.3 LIBS for Biological Hazards Analysis 705
34.3.1 Introduction to Biological Hazards 705
34.3.2 Detection of Bacteria by LIBS 705
34.3.2.1 Discrimination and Classification of Bacteria by LIBS 705
34.3.2.2 Quantification of Bacteria by LIBS 708
34.3.3 Detection of Virus by LIBS 710
34.4 Conclusion 711
References 711
35 Development of a Simple, Low-Cost, and On-Site Deployable LIBS
Instrument for the Quantitative Analysis of Edible Salts 715
Sandeep Kumar, Hyang Kim, Jeong Park, Kyung-Sik Ham, Song-Hee Han, Sang-Ho Nam and Yonghoon Lee
35.1 Chemical Composition of Salts: Introduction 715
35.2 Laser-Induced Breakdown Spectroscopy for Salt Analysis 717
35.3 Quantitative Analysis Using LIBS 719
35.3.1 Sample Preparation Method and the Related Effects 719
35.3.2 An Inexpensive Medium-Performance LIBS Instrument for Analysis of Mg, Ca,
and K in Edible Salts 723
35.3.3 A Compact On-Site Deployable LIBS Instrument for Analysis of Mg, Ca, and K
in Edible Salts 725
35.4 Conclusion 727
References 727
36 Bioimaging in Laser-Induced Breakdown Spectroscopy 729
Pavlina Modlitbová, Pavel Poˇrízka and Jozef Kaiser
36.1 Introduction 729
36.2 Plants 730
36.3 Animal and Human Soft Tissues 733
36.4 Animal and Human Calcified Tissues 737
37.2 Standard Methodologies for Identifying Bacterial Species 745
37.3 Identifying Bacterial Strains Using Laser-Induced Breakdown
Spectroscopy 747
Trang 3139.2.2 Physical Characteristics (Soil Texture Class) 769
39.3 LIBS System for Soil Classification 770
39.4 LIBS Elemental Analysis for Cultivated Soil 772
39.5 Conclusions 777
Acknowledgment 778
References 778
40 Laser-Induced Breakdown Spectroscopy in Food Sciences 781
J Naozuka and A.P Oliveira
40.1 Introduction 781
40.1.1 LIBS Applications in Food Sciences 784
40.1.1.1 Adulterations, Quality Control, and Classification 784
40.1.1.2 Agricultural Applications 796
40.1.1.3 Geographical Origin Identification 797
40.1.1.4 Biological and Microbiological Assessment 797
40.1.1.5 LIBS: Challenges and Limitations With Regard to Food Analysis 798
References 799
41 Capabilities and Limitations of Laser-Induced Breakdown
Spectroscopy for Analyzing Food Products 807
R K Aldakheel, M A Gondal and M A Almessiere
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41.3 The Multielemental Analytical LIBS Tool for Food-Analysis Applications 809
41.3.1 Meat 809
41.3.2 Milk and Its Products 810
41.3.3 Vegetables and Fruits 811
42 Laser-Induced Breakdown Spectroscopy and Its Application
Perspectives in Industry and Recycling 823
Reinhard Noll
42.1 Introduction 823
42.2 Examples of Applications 824
42.2.1 Fast, Spatially Resolved Material Analysis 824
42.2.2 Mix-Up Inspection in a Rolling Mill 827
42.2.3 Sorting of Refractories 829
42.2.4 Sorting of Alloyed Metal Scrap 832
42.2.5 LIBS as Key Methodology for Inverse Production of End-of-Life
Electronics 834
42.2.6 Compact LIBS Analyzers 843
Acknowledgment 846
References 847
43 Development of Laser-Induced Breakdown Spectroscopy for
Application to Space Exploration 851
Zhenzhen Wang and Han Luo
43.1 Introduction 851
43.2 Laser-Induced Breakdown Spectroscopy System 852
43.2.1 Basic Principles of LIBS 852
43.2.2 LIBS Instrument Structure 852
43.2.3 Comparison of LIBS with Other Analysis Methods for Spacecraft 853
43.3 Overview of Development of LIBS Application to Space Exploration 853
43.3.1 Early Research Based on LIBS 853
43.3.2 The ChemCam Onboard NASA’s Mars Rover Curiosity 856
43.3.3 Improvements of LIBS Technique for Space Exploration 857
43.4 Conclusions and Prospects 858
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xvi Contents
44.3 Characterization of the fs-Laser-Induced Plasma and Quantitative Estimation of
Pt and Pd Loaded on Cordierite Substrate 865
44.4 LIBS Abilities for Paleoclimatic Investigations in Speleothems 870
44.5 fs-LIBS Studies in High-Energy Materials 873
44.5.1 Trend in CN/C2in the Para Series 876
44.5.2 Trend in CN/C2in the Ortho Series 877
44.5.3 Trend in CN/C2with Respect to the Position of the Substituent (Para vs
45.2 Properties and Failure Mechanism of Heat-Resistant Steel 884
45.3 Sample Preparation for LIBS Measurement 886
45.3.1 20G with Different Microstructure 887
45.3.2 12Cr1MoV with Different Structure Changes 888
45.3.2.1 Metallographic Structure 888
45.3.2.2 Pearlite Spheroidization 889
45.3.2.3 Grain Size Grade 889
45.3.3 T91 Steel with Different Aging Grade 890
45.4 Spectral Characteristics of Heat-Resistant Steel with Different
Properties 893
45.4.1 Microstructure 893
45.4.2 Grade of Pearlite Spheroidization 894
45.4.3 Aging Grade 895
45.4.3.1 Correlation Between Emission Ratios and Aging Grade 895
45.4.3.2 Spatial and Temporal Characteristics 896
45.5 Application and Optimization of Multivariate Methods in the Failure
Characteristics Prediction 902
45.5.1 Classification Analysis of 20G with Different Microstructures 902
45.5.2 Classification of 12Cr1MoV with Different Grades of Pearlite
Spheroidization 904
45.5.3 Estimation of the Aging Grade of T91 907
45.5.4 Estimation of the Hardness of T91 Steel 910
45.5.5 Improvement of Feature Selection Methods 914
45.5.6 Combination of Spectral Pretreatment with Feature Selection Methods and
Multi-Feature Coupling Modeling 919
45.6 Practical Application of Aging Grade Assessment in Industry 927
45.7 Conclusion and Outlook 932
References 933
Trang 3446.2 Development of LIBS Techniques 940
46.3 Hybrid Method of LIBS and Other Methods 942
References 944
Index 947
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1 Nanosecond and Femtosecond Laser-Induced Breakdown Spectroscopy: Fundamentals and Applications
1 Atomic, Molecular and Optical Physics Division, Physical Research Laboratory, Ahmedabad, Gujarat, India
2 Department of Physics, Indian Institute of Technology, Gandhinagar, Gujarat, India
The interaction of a high-power laser with the analyte is a topic of interest since the firstobservation of laser-produced plasmas (LPPs), and it has played an increasingly importantrole in many material process technologies, plasma physics, and analytical chemistry[1, 2] Interaction of intense laser light with matter is a complex phenomenon that involves
a series of processes, such as coupling of light with material, absorption, heat diffusion,material ejection, ionization, high-energy particle emission, surface modification, andgeneration of transient plasma, followed by the emission of radiations The light–matterinteractions and the underlying physical mechanisms are significantly varied with respect
to the time duration of the excitation pulse Some of the characteristic processes associatedwith light–matter interaction for a nanosecond (ns) to attosecond pulse are schematicallyshown in Figure 1.1
The characteristics of laser ablation (LA) and LPP have been studied thoroughly over aperiod in order to understand the mechanism of LA and plasma formation Consequently,many oblivious processes involved in the ablation mechanism are revealed and explained
However, the complete mechanism of LA and its associated effects are still not fullyunderstood in the scientific community Laser ablation occurs in the picosecond (ps)timescale after the irradiation of laser pulses having a fluence higher than the ablationthreshold of the target material During the ablation process, the target undergoes sev-eral stages, such as melting, liquefaction, evaporation, Coulomb Explosion (CE), phaseexplosion, fragmentation, and ionization The mechanism and the outcome of intenselight–matter interaction depend on many factors, including laser properties (pulse dura-tion, wavelength, and fluence), ambient condition (nature of gas, pressure, temperature,and flow rate), and material properties (metal, semiconductor and dielectrics) [3, 4]
Trang 37ps
ps fs
fs as
as
Plasma
Processes and time scales Ablation and Plasma formation through surface heating/metal excitation, and plume evolution.
Nuclear dynamics/Coulomb explosion, ionic species collision, and eˉ-lattice heating.
Multi-photon absorption/
ionization/tunneling, electron recollision, HHG process, etc.
Electron dynamics in atom/molecules are in as.
Therefore, it becomes imperative to understand the basic properties and mechanisms of
LA, plasma formation, and its evolution dynamics Several techniques in combination with
LA have been used for diagnosing laser-produced transient micro-plasma to understandthe physical properties of ablated species, including optical emission spectroscopy (OES),laser absorption spectroscopy, and laser-induced fluorescence spectroscopy (LIF), massspectrometry, time-gated imaging, shadowgraphy, Langmuir probing and time of flight(TOF) [5–12]
Laser ablation and plasma production have a broad variety of applications, such
as pulsed laser deposition, high harmonic generation, nanoparticle (NP) production,surface modification, micromachining, broad sources for spectroscopy, narrowband wave-length for lithography and microscopy, analytical applications, including matrix-assistedlaser deposition/Ionization (MALDI), laser ablation-inductively coupled plasma massspectrometry (LA-ICP-MS), laser-induced breakdown spectroscopy (LIBS), etc [13–18]
Among the spectroscopy techniques, LIBS is the most widely adopted technique for ing the elemental emission from LPP and the plasma characteristics due to its simplicity
study-in the experimental setup, like it needs only optical access to and from the analyte andthe relatively fast detection capability
This chapter is intended to give a brief description of the physics behind LA and theplasma formation enabled by short (ns) and ultrashort (femtosecond [fs]) laser pulses
The chapter begins with a short introduction to the LIBS technique and discusses thefundamental difference between the traditional nano-LIBS (ns-LIBS) and the relativelynew femto-LIBS (fs-LIBS) Plasma formation and its evolution along with the associatedshockwave generation are also highlighted and discussed Moreover, the unique advantage
of fs-pulses in generating filaments in the air is explained Finally, the techniques employedfor enhancing the overall sensitivity and detection limits of the LIBS signals are presentedhere along with some of the potential applications of fs-LIBS
Trang 38k k
Nowadays, LIBS has become a mainstream analytical technique in analytical chemistrydue to its extraordinary advantages of rapid, online, and multi-elemental material analysiswithout extensive sample preparations In general, LIBS is an atomic emission spectroscopytechnique that uses focused energetic laser pulses to create an expanding micro-plasmawith high temperature The laser-produced plasma is a mixture of ions, electrons, neu-tral and excited species, and molecules of the ablated target material [19, 20] Partially
or fully ionized plasma emits radiations characteristic of the material constituents of thesample Optical emissions from the transient plasma can be detected and analyzed at aparticular time delay after the formation of plasma in order to identify the elemental com-position and their chemical abundance The spectrally resolved emission from the plasmayields fast qualitative and semi-quantitative multi-elemental information from any kind
of sample regardless of its physical phases such as solid, liquid, gas, and aerosol [21–23]
Spectrally resolved plasma emission can further be resolved temporally and spatially forunderstanding various potentially important physical mechanisms, such as plasma dynam-ics, plasma–laser, and plasma–ambient interactions, shock wave dynamics, etc In addition,LIBS is considered as a quasi-destructive technique because only a very little amount (∼ ng
to μg) of the sample is consumed for vaporization and atomization, and hence can be usedfor easily fragile, potentially harmful, and precious samples Other main advantages of LIBSare the simultaneous multi-elemental detection with reasonable precision, low detectionlimits (part-per-million), feasibility of standoff detection and fieldability (portable system
to work in the field), and the capability of layer-by-layer (depth profile) analysis of thesuccessive layers without extended or sophisticated sample preparations [22, 24] Neverthe-less, the analytical prediction capability of LIBS strongly depends on several experimentalconditions, such as irradiation wavelength, pulse width, fluence, time interval chosen forobserving the spectral lines, atmospheric conditions, and target properties [25]
Nanosecond pulsed solid-state lasers are the typical “workhorse” for LIBS setups due totheir various advantages, such as being compact, relatively inexpensive, stable, and robust
The ns Q-switch Nd:YAG lasers with different harmonics (1064, 532, 355, 266 nm) have beenused extensively for many LIBS applications However, ns lasers possess some major limi-tations such as the huge background continuum at the initial stages of plasma, poor repro-ducibility, thermal and mechanical damage during the ablation process, and relatively poordetection limits compared with their competitive elemental techniques, etc Moreover, thematrix effects and the atmospheric conditions strongly contribute to line intensity, whichcan reduce the accuracy of quantitative measurements [26] These limitations often restrictthe use of the LIBS technique alone to determine the highly heterogeneous samples, such aspigments, organic and biological samples, etc On the other hand, a wide range of method-ologies has been proposed by scientists to strengthen the analytical prediction capability ofLIBS for identifying complex samples even in adverse environments Among these, the mostpowerful approaches are the double-pulse configuration, NP-enhanced LIBS (NE-LIBS),resonant excitation, spatial confinement, fs-LIBS, hyphenated instruments, etc [25, 27–31]
In addition, the LIBS technique has been coupled with more advanced statistical tools
Trang 39k
6 1 Nanosecond and Femtosecond Laser-Induced Breakdown Spectroscopy: Fundamentals and Applications
for classifying complex samples [32] These techniques have already proven the ability toenhance the signal strength and to overcome some of the potential limitations associatedwith the traditional ns-LIBS technique Compared with all other approaches mentionedabove, fs-LIBS has gained considerable research attention in recent years The fs-LIBS hasopened up the scope of investigating complex organic mixtures effectively, which otherwisewas not efficiently interrogated with the ns-LIBS
Lower ablation threshold, higher ablation efficiency, and small ablated mass, less heat,and thermal damages, high spatial resolution, improved signal-to-noise (S/N) ratio, highreproducibility, and sensitivity, high lateral, and depth resolution, low continuum emission,and environmental contribution to the signals are the main advantages of the ultrashortlaser pulses over conventional ns pulses for LIBS measurements [33–35] Another addedadvantage of ultrashort laser pulses for LIBS measurements is that they can be focusedlongitudinally and transversely in the air at standoff distances (> km) to carry high inten-sities for ionizing the analyte Longitudinal pulse compression is attained by introducing
a negative frequency chirp on the laser pulse, whereas the nonlinear optical Kerr effect isresponsible for transverse focusing [36, 37] Also, peak power of these pulses is relativelyvery high to ionize a wide range of materials regardless of their physical property
The pulse duration (τp) influences the ablation efficiency and the formation of plasma to
a large extent The physics of laser-induced ablation dramatically changes when ultrashort(femto) pulses are used for ablation compared with the conventional ns “long pulse” due
to the change in mechanism that governs the laser–matter interaction During the initialstages of light–matter interaction, the laser energy is absorbed by the target regardless ofthe spatial and temporal profile of the pulse Nevertheless, the energy absorption and theablation processes for short (> ps) and ultrashort pulses (< ps) are significantly different
The absorption process is linear and follows the Beer–Lambert law in the case of typical
ns pulses, whereas the nonlinear process dominates significantly in the case of fs-pulsesdue to the high peak power of the ultrashort pulses [38] Hence the long pulses induceboth thermal and nonthermal ionization (multiphoton absorption and ionization, tunnel-ing, and avalanche ionization) while fs-pulses induce only nonthermal ionization (interactonly with the electron subsystem) [39] A schematic representation of ns and fs-laser pulsesinteracting on a solid surface is shown in Figure 1.2
Figure 1.2 Schematic representation of nanosecond and femtosecond laser pulses interacting on
a solid surface: IB, incident beam; P, plasma; PT, particle; CR, crater.
Trang 40k k
In the case of ns pulses, the ablation process is governed by heat conduction, melting,evaporation, ionization, and plasma formation [40] The electron lattice heating time ismuch shorter than the pulse duration of ns pulses; hence, the thermal effects dominatethe ionization If the power density is much higher than the ionization threshold, the non-thermal effect is also added up Hence, at higher irradiance, both thermal and nonthermaleffects ionize the atoms Moreover, the leading edge of the pulse generates the plasma,which eventually gets heated up by the trailing edge of the pulse At the time scale of
10−8–10−9seconds, the plasma becomes opaque to the laser radiation (plasma shielding)[41] Hence, the trailing end of the laser pulse persists even after the formation of theplasma, thereby interacting with the plasma and getting absorbed or reflected as shown inFigure 1.2 Thus, plasma shielding reduces the rate of ablation since all radiations from theexcitation source do not reach the sample surface (attenuation of incident laser radiation)
On the other hand, the prolonged exposure of the plasma with comparatively long nspulses reheats the plasma to a high temperature through collisional absorption (inverseBremsstrahlung), which, in turn, increases the lifetime and size of the plasma The plasmashielding strongly depends on both environmental (atmospheric gases or vacuum) andexperimental (irradiance and wavelength) conditions [41, 42]
The atoms in the analyte get ionized in the timescale of a few fs (∼100 fs) Characteristicrelaxation, such as electron–ion interaction time, lattice relaxation, heat conduction, andhydrodynamics, often occur at a much longer time scale on the order of ps (∼10−12seconds)rather than the ultrashort laser pulse duration (fs) [40] Therefore, in the case of the sub-nsregime, such as ps and fs-pulses, the laser energy is predominantly deposited onto thesample surface within a short period of time (before the material undergoes any change inthe thermodynamic state) causing fast evaporation before the plasma formation, thereby,resulting in efficient ablation [43] Hence, there is no interaction between the incominglaser beam and plasma in this case (the nonthermal process will dominate the ionization)
The negligible heat conduction effect of fs-laser offers reduced thermal damage andheat-affected zone in the target material Because of the absence of the thermal effect,well-defined (even walls without clear rims) craters can be made by using ps or fs laserscompared with ns lasers [44] Also, fs-pulses can be used to produce well-defined structures
in diameter and depth However, the small energy content in the plasma leads to the weakemission of lines Coulomb explosion and thermal vaporization are the two competingmechanisms responsible for fs-induced material removal and ablation [45, 46] Existing lit-erature suggests that the CE dominates the ablation at low laser fluence (below 0.5 J/cm2),while the ablation mechanism depends on thermal ablation at high laser fluence [47]
In contrast, Zhao et al reported that CE is the dominant mechanism for fast ion ejection inthe early stages of silicon ablation at high fluence, whereas thermal ejection dominates inlower fluence [48] Electron impact ionization and strong-field ionization are the majormechanisms for generating free electrons during fs ablation The ejection of electrons fromthe target materials prompts a charge imbalance on the surface due to the accumulation ofpositively charged ions, forming a strong electric field If the electric field strength is strongenough to overcome the bond between the ions, the ions are pulled out from the surface,which is known as “Coulomb explosion” [46, 48] The CE process leads to the removal
of a few monolayers (nm in depth) from the material surface while the material ablationefficiency rate per pulse is one order of magnitude higher in thermal vaporization [38]