Table Of ContentSpringer Series in Optical Sciences 182
Sergio Musazzi
Umberto Perini Editors
Laser-Induced
Breakdown
Spectroscopy
Theory and Applications
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Ludwig-Maximilians-UniversitätMünchen
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AmCoulombwall1
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Max-Planck-InstitutfürQuantenoptik
Hans-Kopfermann-Straße1
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Sergio Musazzi Umberto Perini
•
Editors
Laser-Induced Breakdown
Spectroscopy
Theory and Applications
123
Editors
SergioMusazzi
Umberto Perini
Ricerca sulSistema Energetico—RSE SpA
TTD
Milan
Italy
ISSN 0342-4111 ISSN 1556-1534 (electronic)
ISBN 978-3-642-45084-6 ISBN 978-3-642-45085-3 (eBook)
DOI 10.1007/978-3-642-45085-3
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Preface
Laser-Induced Breakdown Spectroscopy (LIBS) also known as laser-induced
plasma spectroscopy (LIPS) or laser spark spectrometry (LSS) is a relatively
new type of atomic emission spectroscopy made possible by the invention of the
laser. More precisely, the use of laser-induced spark emission for elemental
analysis of materials originated from the pioneering work of D. A. Kremers and
L. J. Radziensky at Los Alamos National Laboratory (USA) in the early 1980s,
about 20 years after the invention of the laser. Since then, LIBS has developed
into a major analytical tool capable of providing real-time measurements of
constituents in almost any kind of material.
TheLIBSprincipleofoperationisquitesimple,althoughthephysicalprocesses
involved in the laser–matter interaction are complex and still not completely
understood. The technique relies on the use of a pulsed laser source (with energy
per pulse ranging from tens to hundreds of mJ and pulse durations typically
smaller than 10 ns) and a measuring chain for the analysis of the plasma emitted
spectrum. In detail, the laser pulses are focused down to a target (solid, liquid
as well as gas samples have so far been analyzed) so as to generate a high-
temperature plasma that vaporizes a small amount of material. A portion of the
light emitted by the excited atomic and ionic species in the plasma is then
collectedandspectrallyanalyzed todeterminethesampleelemental composition.
Quantitative LIBS analysis can also be performed when the assumptions of local
thermal equilibrium (LTE) and optically thin plasma are satisfied.
Becauseofitsuniquefeatures,liketheabsenceofsamplepreparation,theability
to perform real-time, and in situ analysis as well as the quasi non-destructive and
micro-analysischaracterofthemeasurements,thenumberofLIBSapplicationshas
dramatically increased in the last years. For this reason, the main purpose of this
book is toprovide an overview ofthe latest developments and applications of the
LIBS technique as well as to recall (especially for readers not familiar with these
topics)sometheoreticalandexperimentalaspectsofthelaser–matterinteractionin
LIBS experiments.
The book is divided into two main parts: the first part deals with some
fundamental aspects of the technique and the second part is dedicated to the
descriptionofthemostimportantapplicationsofLIBSindifferentdisciplinesand
areas of interest. In Part I of the book (Fundamentals of LIBS), the physical
processesoccurringduringtheformationandexpansionofalaser-inducedplasma
v
vi Preface
are described in the Chap. 1, where the role of the various effects characterizing
theenergyflowfromthelaserpulsetotheobservedspectroscopicquantities(e.g.,
thermal diffusion, electron and ion temperatures, particle ablation, and kinetics)
areelucidated.OtheraspectsofthesametopicarealsodiscussedinChap.2where
different features of the physical mechanisms involved in optical emission spec-
troscopy (OES) are analyzed in equilibrium and non-equilibrium conditions. The
contentofChap.3dealswiththeinstrumentalaspectsofLIBS.Thepurposeofthis
chapteristoprovideadescriptionofthebasiccomponentsofaLIBSsystem(laser
source, focusing optics, ablation chamber, and detection system) and how their
technical features as well as their experimental arrangement may affect the mea-
surements.Newdevelopmentsinlasersourcesandfiberopticstechnologyarealso
highlighted.LIBSperformanceundernon-standardpressuresandwithsurrounding
atmospheric gases other than air is the content of Chap. 4. The interest for this
topic has been mainly driven by the applications of LIBS for space exploration
(described in more detail elsewhere in the book) but the gained experience has
provedfruitfulinimprovingLIBSmeasurements.Infact,alteringtheatmospheric
pressure and gas composition can dramatically change the observed spectra, such
as modifying (and in many cases improving) the spectral resolution, the signal
intensity,andtheoverallsignal-to-noiseratio.MorerecentLIBStechniqueswhere
multiple laser pulses and ultrashort laser pulses are used to excite the plasma are
alsodiscussedinthissection(Chaps.5and6).Chapter5coversseveralimportant
aspectsofdoubleandmultiplepulseLIBS,includingthephysicalprinciplesofthe
laser–target plasma interactions, an overview of the currently available instru-
mentation, and some examples of representative applications of this technique (e.
g., the analysis of metallic alloys, soils, underwater materials, etc.). Chapter 6
deals with the use offemtosecond lasers in LIBS. Since the duration of a femto-
second laser pulse is shorter than the electron-to-ion energy transfer time and the
heat conduction time in sample lattice, the resulting laser ablation and heat dis-
sipation mechanisms are very different from those observed when more conven-
tional nanosecond laser pulses are used. The basics offemtosecond laser ablation
processes and the application of this technique are presented in this chapter.
PartIIofthebook(ApplicationsofLIBS)showshowLIBScanbeconveniently
used to provide analytical information about different disciplines. Applications of
LIBS to the analysis of solid targets, like metals and different alloy types, is the
subject matter of Chap. 7, while LIBS analysis of liquids at gas–liquid interface
as well as the underwater analysis of both solid and soft targets are described in
Chap.8.TheuseofLIBSfordeterminingthechemicalcompositionofaerosolsis
presentedinChap.9whereparticularemphasisisgiventotheanalysisoffineand
ultra-fineaerosols.SpaceutilizationofLIBS,oneofthemoreexoticapplicationsof
thistechnique,formsthesubjectmatterofChap.10.Inthischapterthecapabilities
of LIBS for geological analysis at close-up and stand-off distances as well as for
atmospheric pressures and compositions (simulating the Mars, Venus, and Moon
environments) are discussed. The elementalanalysis ofsoils andthe geochemical
fingerprintingusingLIBSarethecontentofChaps.11and12.Althoughapparently
verysimilar,thesetwotopicscovertwodifferentaspectsofgroundanalysis.While
Preface vii
soil testing and analysis has an impact on both crops yield and environment, the
importance of geochemical fingerprinting stems from its ability to determine
the geographical provenience of a large variety of minerals, gemstones, and
volcanicrocks.ThedetectionofexplosivesintracesbymeansofLIBSisdiscussed
in Chap. 13. The advantages and disadvantages of using LIBS as a technique for
forensic evidence analysis are presented in Chap. 14 together with examples of
current applications of LIBS to the analysis of materials offorensic interest (e.g.,
paperandinks,counterfeitcurrency,gun-shotresidues,fingerprints,etc.).Chapter
15dealswiththeutilizationofLIBSfortheidentificationoforganiccompounds(in
particularpolymermaterials)whileChap.16includestheapplicationsofLIBSin
research related to globally important aspects such as climate change, carbon
sequestration,phytoremediation,anddendrochemistry.Lifescienceapplicationsof
LIBS are the subject matter of Chap. 17 where the use of LIBS for the elemental
signatureofbiomedicalspecimensisdiscussed.CombustionapplicationsofLIBS
aswellastheuseofLIBSfortheanalysisofcoalarediscussedinChaps.18and19.
Both these chapters are of great interest in view of the future developments in
LIBS-based diagnostic techniques aimed at improving the efficiency of industrial
boilersutilizedincoal-firedpowerplants.Analysisofculturalheritagematerialsby
means of LIBS is the content of the last chapter of the book. In this chapter, in
addition to a number of case studies (such as the use of LIBS techniques in
museums, in archeological conservation labs, and in excavation sites), particular
emphasis is given to mobile/portable instrumentation to be used in outdoors
applications.
We believe that this book will be of interest to the large community of con-
sumers, researchers, and developers of the LIBS technique, working in academic
institutes, research centers, as well as in industrial laboratories.
We gratefully thank all the co-authors who spared time from their demanding
research and teaching activities for contributing to this book.
Milan Sergio Musazzi
Umberto Perini
Contents
Part I Fundamentals of LIBS
1 Laser–Matter Interaction in LIBS Experiments. . . . . . . . . . . . . . 3
Andrea Marco Malvezzi
1.1 Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.2 Laser Interaction with Gases . . . . . . . . . . . . . . . . . . . . . . . . 6
1.2.1 Multiphoton Ionization . . . . . . . . . . . . . . . . . . . . . . 7
1.2.2 Cascade Ionization . . . . . . . . . . . . . . . . . . . . . . . . . 10
1.3 Laser Interaction with Solid Materials from Milliseconds
to Nanoseconds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
1.3.1 Heating and Melting. . . . . . . . . . . . . . . . . . . . . . . . 15
1.3.2 Vaporization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
1.4 Laser Interaction with Solid Materials:
Ultrashort Laser Pulses . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
1.5 Conclusions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
2 Physical Processes in Optical Emission Spectroscopy. . . . . . . . . . 31
Mario Capitelli, Gianpiero Colonna, Giuliano D’Ammando,
Rosalba Gaudiuso and Lucia Daniela Pietanza
2.1 Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
2.2 LTE Plasmas: The Few Level Approximation
for the Partition Function and Thermodynamic
Properties of Atomic Species. . . . . . . . . . . . . . . . . . . . . . . . 34
2.3 Non-LTE Plasmas: Collisional Radiative Models Coupled
with Electron Energy Distribution Function
and Radiation Transfer . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
2.4 Fluid Dynamics of Laser-Plasma Expansion in Gas
and Liquids: Modeling and Validation . . . . . . . . . . . . . . . . . 45
2.5 Conclusions and Perspectives. . . . . . . . . . . . . . . . . . . . . . . . 53
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55
ix
x Contents
3 LIBS Instrumental Techniques . . . . . . . . . . . . . . . . . . . . . . . . . . 59
Sergio Musazzi and Umberto Perini
3.1 Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59
3.2 The Laser Source. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61
3.2.1 Laser Sources Utilized in LIBS Systems. . . . . . . . . . 63
3.2.2 Laser–Matter Interaction: Dependence
on Wavelength and Pulse Duration. . . . . . . . . . . . . . 65
3.3 The Focusing Optics. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67
3.4 The Target Container . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70
3.5 The Light Collection System. . . . . . . . . . . . . . . . . . . . . . . . 72
3.6 Spectral Detection Systems . . . . . . . . . . . . . . . . . . . . . . . . . 73
3.6.1 Wavelength Selectors . . . . . . . . . . . . . . . . . . . . . . . 74
3.6.2 Detectors. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79
3.6.3 Spectrometer-Detector Combination:
The Right Trade Off. . . . . . . . . . . . . . . . . . . . . . . . 82
3.7 Control Electronics. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85
3.8 Conclusions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 86
4 Influence of Atmospheric Pressure and Composition on LIBS . . . 91
Jill R. Scott, Andrew J. Effenberger and Jeremy J. Hatch
4.1 Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91
4.2 Spectral Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 94
4.2.1 Resolution. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95
4.2.2 Signal Intensity . . . . . . . . . . . . . . . . . . . . . . . . . . . 97
4.2.3 Signal-to-Noise Ratio . . . . . . . . . . . . . . . . . . . . . . . 102
4.3 Material Ablation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103
4.4 Experimental Issues . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 106
4.4.1 General Considerations . . . . . . . . . . . . . . . . . . . . . . 106
4.4.2 Field of View. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 107
4.4.3 Multiple Pulse Configurations . . . . . . . . . . . . . . . . . 108
4.5 Overview of Applications . . . . . . . . . . . . . . . . . . . . . . . . . . 109
4.5.1 Isotope Measurements. . . . . . . . . . . . . . . . . . . . . . . 109
4.5.2 LIBS in Space . . . . . . . . . . . . . . . . . . . . . . . . . . . . 110
4.5.3 Process Monitoring. . . . . . . . . . . . . . . . . . . . . . . . . 110
4.6 Conclusions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 112
5 Double and Multiple Pulse LIBS Techniques. . . . . . . . . . . . . . . . 117
Stefano Legnaioli, Giulia Lorenzetti, Lorenzo Pardini,
Gildo H. Cavalcanti and Vincenzo Palleschi
5.1 Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117
