Laser induced breakdown spectroscopy methods and applications: A comprehensive review

Journal Pre-proof Laser induced breakdown spectroscopy methods and applications: A comprehensive review Syed Kifayat Hussain Shah, Javed Iqbal, Pervaiz Ahmad, Mayeen Uddin Khandaker, Sirajul Haq, Muhammad Naeem PII:

S0969-806X(19)31343-X

DOI:

https://doi.org/10.1016/j.radphyschem.2019.108666

Reference:

RPC 108666

To appear in:

Radiation Physics and Chemistry

Received Date: 15 October 2019 Revised Date:

21 December 2019

Accepted Date: 25 December 2019

Please cite this article as: Hussain Shah, S.K., Iqbal, J., Ahmad, P., Khandaker, M.U., Haq, S., Naeem, M., Laser induced breakdown spectroscopy methods and applications: A comprehensive review, Radiation Physics and Chemistry (2020), doi: https://doi.org/10.1016/j.radphyschem.2019.108666. This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. © 2019 Published by Elsevier Ltd.

Laser Induced Breakdown Spectroscopy Methods and Applications: A Comprehensive Review Syed Kifayat Hussain Shah1, Javed Iqbal1, Pervaiz Ahmad*1, 2, Mayeen Uddin Khandaker3, Sirajul Haq4, Muhammad Naeem5 1

Department of Physics, University of Azad Jammu and Kashmir, 13100 Muzaffarabad Pakistan Department of Physics, Faculty of Science University of Malaya 50603 Kuala Lumpur Malaysia 3 Center for Biomedical Physics, School of Healthcare and Medical Sciences, Sunway University, 47500 Bandar Sunway, Selangor, Malaysia 4 Department of Chemistry, University of Azad Jammu and Kashmir, 13100 Muzaffarabad Pakistan 5 Department of Physics, Women University of Azad Jammu and Kashmir, Bagh Pakistan 2

ABSTRACT Laser induced breakdown spectroscopy has become an established analytical atomic emission spectroscopic technique. It has analytical and technical advantages over other existing techniques. It is a rapid, non-contact technique which is capable of providing qualitative and quantitative analytical information for any sample without any sample preparation. The instrumentation is simple, rebuts, compact and even provides remote analysis. The aim of the current study is to provide a critical review of “laser induced breakdown spectroscopy” in several aspects. First part focuses on the comparison of the “laser induced breakdown spectroscopy” with other well established techniques. In this section, the sensitivity, accuracy and sample preparation are compared and summarized. The second parts is a discussion on the experimental setup and instrumentation. In third part, a complete review of qualitative and quantitative analysis has been summarized. In addition, the effects of different experimental parameters and potential applications of “laser induced breakdown spectroscopy” in different fields of modern technologies have also been described in the current study.

Corresponding author. Tel.: +923459493879. E-mail: [email protected], [email protected] (Dr. Pervaiz Ahmad)

1

Keywords: Laser spectroscopy; LIBS; Analytical technique; experimental setup.

2

1. INTRODUCTION During past few decades so many analytical techniques (such as inductively coupled atomic emission spectroscopy (ICP-AES), atomic absorption spectroscopy (AAS), X-ray fluorescence (XRF) and energy dispersive x-ray spectroscopy (EDX) have been developed to analyze composition of different materials in a sample. Although, these techniques have good detection limits and measurement accuracy, however, it is found that they require a complex sample preparation and long detection time. In addition, majority of them are found destructive in nature [1-3]. Laser induced breakdown spectroscopy (LIBS) is comparatively a new atomic emission spectroscopic method. LIBS technique has a key role in elemental analysis of a wide range of samples. It is a multi-element analytical approach that has been recognized as a powerful sensor technology for both laboratory and field going systems. LIBS has many advantages over conventional analytic techniques. It provides rapid analysis, requires minimal or no sample preparation, non-destructive in nature, simple in operation and equally applied to solids, liquids, gases and aerosols [4-15]. LIBS can perform elemental analysis both in-situ and remotely by using portable and standoff LIBS instruments [16]. LIBS is a spectrochemical analytical technique employing light emitted by laser produced plasma (LPP) to produce spectra of the sample for composition analysis of materials [17, 18]. In LIBS a high energy laser pulse is utilized to generate plasma by excitation and ionization of atoms of the sample [19]. Most commonly Nd:YAG (Neodymium doped Yttrium Aluminum Garnet) lasers are employed for generation of plasma. Light produced by plasma is utilized to produce spectra of sample with the help of spectrometer [20]. The process is to focus a high energetic laser beam on sample which ablates a small amount of material of sample and a luminous plasma 3

is generated. Light from LPP is collected and directed to a spectrometer with the help of an optical fiber to generate spectrum which facilitate the elemental detection. The spectrum has a certain specific wavelengths depending upon the type of elements present in the specimen. Each atom has different energy levels so it could be recognized by its wavelengths. LIBS can also be deployed for knowing amount of each element in a sample by measuring spectral intensities. Presence of a wavelength of an element provides a clue that the element is existing in the sample and its intensity determine the amount of an element in the sample [21]. Spectral line are compared with online database provided by National Institute of Standards and Technology (NIST). For quantification of each element either calibration curves are developed (for each element and measurements are acquired under similar circumstances) or calibration free LIBS (CF-LIBS) methodology is utilized [22, 23]. Overall process of LIBS can be summarized in the word as below (and schematically as shown in Fig. 1: •

A short pulse of laser is focused on the specimen.

•

Energy from laser beam is absorbed by the atoms and molecules of the specimen. A small amount of sample is evaporated and forms a vaporous plume near the surface of the target.

• •

Interaction of laser beam with plume generates luminous plasma. Light is collected from the plasma with the help of an optics and directed towards a spectrometer which spreads it to form the spectrum.

•

Spectrum is analyzed for detection and quantitative analysis [24]

LIBS has been in use since early 1960s when ruby laser was developed [25]. In 1963, with the development of Q-switched lasers, LIBS techniques came into practical uses [24]. Debras-Guendon et al. in 1963 reported the first analytical used of LIBS [26]. In early 1970s, 4

Moenke-Blankenberg wrote a paper on LIBS [27]. During 1980s, the Nd: YAG lasers gained popularity and become the most commonly laser system. After 1980s, a significant development has been reported in laser and detectors technology. Reliable instruments were developed with the passage of time which further improved LIBS for qualitative and quantitative study of a variety of materials [28] including metal alloys for metallurgy and jewelry [29, 30]. Cultural heritage materials [31, 32], soil, rocks, sediments [33], mixture of gases and aerosol sprays were also analyzed by LIBS technique [34, 35]. Solutions were also studied by using this technique [31, 36]. Qualitative analysis and elemental detection of insecticides in spinach and rice samples were also studied by LIBS. Using this analytical technique, fresh and stored vegetables [37], soil (in powder form) [38], plants [39], food [40], fossils and nuclear combustions were also analyzed [41]. After the introduction of calibration-free LIBS (CF-LIBS) during 1999, LIBS has become one of the best technique for qualitative and quantitative analysis. CF-LIBS has been widely applied for quantitative investigation of materials [42-46]. LIBS is an important analytical technique used for analysis of a wide range of materials. The aims of this study is to compare LIBS with other analytical techniques with respect to its methodology, effects of laser parameters and applications for qualitative and quantitative analysis in different fields.

2. COMPARISION OF LIBS AND OTHER SPECTROSCOPIC TECHNIQUES Most commonly used techniques for the elemental analysis and composition study of different materials are based on atomic or mass spectroscopy. These included: Atomic absorption spectroscopy (AAS), inductively coupled atomic emission spectroscopy (ICP-AES), X-ray fluorescence spectroscopy (XRF), energy dispersive x-ray spectroscopy (EDX) and laser in-

5

duced break down spectroscopy (LIBS). Although majority of these analytical techniques are highly sensitive and precise but produces huge amount of noxious wastes. In addition, they require regents, sample dissolution and very complex sample preparation. As compared to these techniques, LIBS is simple, safe and has been proven to be free from sample preparation. A comparison of LIBS and other analytical techniques on the basis of sample preparation, sampling rate, limit of detection (LOD), accuracy and portability is given in Table.1. 2.1. Atomic Absorption Spectroscopy (AAS) AAS is a spectrochemical technique used for determination of chemical compositions via absorption of light by the atoms. Electrons in an atom absorb a definite amount of light and jumps to some higher energy state. On de-excitation, the electron emits photons with a specific wavelengths corresponds to the type of elements. AAS is used to detect the existence and to calculate amount of atoms in dilute solutions [47]. The concentration is determined through calibration curves. The sample solution can also be atomized by passing current through a graphite tube containing sample solution. Sensitivity of AAS can be increased up to 1000 folds by using graphite furnace AAS [48]. Limit of detection (LOD) for atomic absorption spectroscopy (AAS) ranges from 0.003 ppm to 20 ppm and precision ranges from 1 - 2%. Higher precision and LOD make this technique more appealing but complex (dissolved solution), use of atomizers, selection of suitable monochromator, complex sample preparation, non-portability, large Quantity of sample and long sample time make it less appealing [49].

6

Table. 1. Comparison of LIBS with other spectroscopic techniques.

Technique

Sample preparation

Sample pretreatment

Sampling rate

Limit of detection (LOD)

Precision Accuracy

Absorption spectroscopy AAS

Dissolved acetified solution is required. Atomization is required Dissolved sample

Required

Minuteshours

0.00320 ppm

Required

Minuteshours

No sample preparation

Not required

EDX

No or little sample preparation

LIBS

No or little sample preparation

Inductively coupled atomic emission spectroscopy ICP-AES X-ray florescence XRF

/

Potability

Advantages

Disadvantages

Refer erence

1-2%

No

High accuracy and low LOD

1. Complex sample preparation, atomization 2. Non-portable 3. Time consuming

[50, 51]

10 ppb

1-5%

No

High accuracy and low LOD

1. Complex sample preparation 2. Matrix problems 3. Spectral interference

[52] [53]

Few minutes

Ppm%

3-23%

No

1.

Low accuracy and high LOD

[20, 5457]

required

Few minutes

1000 – 3000 ppm

Up to 95%

No

Matrix effect, SEM is required, overlape of spectral lines

[5860]

Not required

3-60 onds

Ppm%

5-20%

Yes

Low accuracy and LOD

[7, 50, 54,

2.

sec-

7

1.

No sample preparation and pretreatment. fast detection 1. Easy sample preperation 2. Easy to perform with high accuracy No/little sample preparation.

high

2. 3. 4.

5.

8

Fast detection. Portability. Remote measurement and Nondestructive

61]

2.2. Inductively Coupled Atomic Emission Spectroscopy (ICP-AES) ICP-AES is also referred to as inductively-coupled plasma optical emission spectrometry. ICP-OES is an analytical technique used for the detection of chemical elements. It is a type of emission spectroscopy that uses the inductively-coupled plasma to produce excited atoms and ions that emit electromagnetic radiation at wavelengths representative of a specific element, by isolating these photon wavelengths type of elements and their concentrations could be measured. [62, 63]. To generate plasma argon gas is introduced into the tube, a high frequency current is passed which ionizes argon gas, this plasma has high temperature and it is responsible for excitation-emission of sample. Solution sample is introduced into the plasma in an atomized state. This technique measures the intensities of light emitted by atoms as they are ionized in the plasma. It has the capability of multielement measurements. Its self-absorption and auto- reversal effects are negligible. It has detection limits up to 10 ppb or low and accuracy 1-5 % which is higher than AAS. A number of elements that remain difficult to be analyzed via AAS can be analyzed easily. However, it needs complex sample preparation which is further needed to be dissolved or solid samples need to be fused [64-66]. Signal fluctuation is a critical problem that leads to generating error results. Additionally, this technique doesn’t have enough authenticated methods for impurities detection and calculation which is the most vital drawback [67]. In addition, the sampling rate may exceeds from minutes to hours and remote analysis is also not possible [68](Table 1). 2.3. X-Ray Florescence (XRF) It is applied to those solids in which emission of secondary X-rays is possible. X-ray ejects inner shell electrons from an atom. The outer electrons jump to fill the deficiency

9

of inner electrons. In doing so it emits fluorescence radiation having an energy equal to the energy difference of corresponding levels The energy dispersive detector measures the energy distribution of fluorescence radiation. A multi-stage electronics circuit processes the measurement signals. The spectrum displays peaks which are characteristic for the specific elements in the sample. X-rays produces high energetic electrons which interact with sample under examination, it is one of best techniques where X-rays are detected with greater precision. X-rays are detected mostly by using crystal spectrometer adjusted by a crystal which diffracts it to select suitable wavelength, or by using energy-dispersive (ED) spectrometers, which have capability to separate X-rays produced because of transition between different energy levels. These techniques are called wavelength-dispersive spectroscopy (WDS) and energy-dispersive spectroscopy (EDX). X-ray fluorescence is a non-destructive and in-situ technique which has been widely used for elemental analysis [55-57]. XRF requires no sample preparation and sample pretreatment. It provides very fast detection within few minutes (Table 1). By using µ-XRF and PIXE techniques sensitivity, detection speed and detection efficiency can be increased [69-72]. Disadvantages of this technique are: lower limit of detection (ppm-%), accuracy (3-23 %), higher cost and non-portability. Quantitative analysis using XRF can only be made for thick homogeneous surfaces [73, 74]. Fluorescence amount depends upon sample type and quantitative analysis using XRF involves calibration curves with similar matrix. It cannot be applied to light elements. All these drawbacks make this technique limited to only few applications [58]. 2.4. Energy Dispersive X-ray Spectroscopy (EDX) EDX has become a popular analytical technique of microanalysis in research community. Energy-dispersive X-ray spectroscopy (EDX) is a powerful but an easy technique . Chief-

10

ly, EDX works by detecting characteristic X-rays produced by elements present in a sample when it is exposed to high energetic electrons. X-ray mapping is then used to get magnified image of sample for examination. In EDX the amount of X-rays emitted by a particular element have a direct connection with the concentration of that element this property makes EDX suitable for microanalysis. By obtaining this magnified image Xray spectrum can be obtained which is then used to find concentrations of different chemical species existing in a sample. The images formed by electrons diffracted from sample provide surface topography or average atomic number variances depending on the mode being selected. EDX has subsequent advantages over other analytical techniques [60]. Energy resolution of EDX is about 130 eV (FWHM) at Mn Kα, Limit of detection (LOD) for EDX ranges 1000 to 3000 ppm, the sample preparation for EDX analysis is not so complex, The experimentation can also be done easily. A computer software provides data sheet for atomic and weight percentages, there is no need of any theoretical treatment, EDX coupled with SEM provides the resolved image of sample which can be used for the estimation of spatial and matrix effects. Precision of EDX approaching ±0.1%. Although EDX is a better technique of microanalysis yet it has some disadvantages: EDX necessitates a high voltage to accelerate electrons, to resolve the spatial and matrix problems SEM is also mandatory, bremsstrahlung effect is also present due to continuous xray spectrum. Secondary electrons may cause additional excitation and emission of spectral lines. Secondary fluorescence may also appear in the spectrum. Spectral lines emitted due to X-rays and additional rays produced due to secondary events may overlap. 2.5. Laser Induced Break down Spectroscopy (LIBS) Laser induced breakdown spectroscopy has numerous advantages over other specroscopic analytical techniques. In LIBS, a high energy laser beam is focused on to the sample which ablates a small amount of material of sample as a result a luminous plasma is gen11

erated. Light generated in plasma is collected and guided by using a collecting optics to spectrometer which displays resulting spectrum. Wavelengths found in spectrum are characteristics of particular elements existing in the material under examination. These wavelengths are then used for the elemental identification and quantification of elements [75-77]. It also provides temporal and spatial resolved measurements [78]. It requires a minor quantity of sample with no or very little sample preparation. Multi-element detection is also possible with this technique. It can be used for remote measurements [32, 79], and is feasible at a distance up to 130 m [79]. However, LOD (ppm-%) and accuracy ( 5 – 20 %) of LIBS as compare to other spectroscopic analytical techniques is not so promising but its ability to direct analyzing and without sample preparation make it feasible to use it in analytical field. LIBS provides physical response and multi-element recognition. It is easy to implement, cost-effective and can be performed by non-experts [80]. 2.5.1

Merits of LIBS

LIBS has the following merits over other techniques [33, 54, 81]. LIBS provides analysis free from sample preparation unlike AAS, ICP-AES and XRF. LIBS measurements are done without sample pre-treatment. A small amount of material is utilized which makes it minimally destructive. It is very fast analytical technique. Measurements are performed within a fraction of a second. This technique is equally useful for all states of matter. It is especially sensitive to light elements which is not possible with other techniques. No direct access to the sample is required.

12

It could be joint with other analytical techniques such as Raman spectroscopy etc. for multielement and molecular surface analysis. 2.5.2

Demerits of LIBS

Despite being one of the best analytical technique LIBS has some limitations as given below. •

Accuracy

Limit of detection (LOD) using laser-induced breakdown spectroscopy falls in the range of part per million (ppm) [20] while other well-known techniques have precision of the order of part per billion (ppb) [82]. •

Self-Absorption

Emissions from hotter regions are absorbed by the colder atoms surrounding the plasma which reduced the spectral intensity therefore affect the quantitative analysis. •

Matrix Effect

The physical and chemical properties of the sample can affect the ablation, composition of plasma, plasma temperature and signal this effect is referred as matrix effect. These difficulties has been overcome by using advanced LIBS methods and instrumentations. 2.6

Quantitative and Qualitative Analysis algorithms

Ability of LIBS to detect emission lines of all species present in a sample allows a precise qualitative analysis. Yet, there are some applications wherever such kind of analysis is not required, for instance, if two different materials are to be distinguished and classified. In such cases, spectra offered by LIBS can be treated by using classification algorithms to distinguish between different samples. Algorithms including artificial neural networks (ANN), support vector machines (SVM), machine learning (ML) or K nearest neighbors

13

(Knn) belong to this set. Above mentioned algorithms need a substantial training data-sets to acquire an accurate classifier and require long period to train (SVM and ANN), need time to organize but not needed to train (Knn), however the results are frequently outstanding. These algorithms offer “chemometric” analysis, powerful statistical signal processing methods to attain automatic identification of chemical information. One of the major aspect of spectral data offered by LIBS and other Spectro-analytical methods is that, each spectrum comprises a lot of redundant information. Particularly in LIBS only a limited emission lines at specific wavelengths can be used to perform the required calculation. Redundancy can decrease the accuracy of classifiers and should be avoided in many cases. There are two main kind of algorithms that abandon redundant information. The first group comprises of algorithms which choice most discriminating features. Algorithms, for example Sequential Floating Forward Selection (SFFS) and Linear Discriminant Analysis (LDA) select the top features of input data-set to enhance the classification ratio, in LIBS, the best wavelengths. The second group contains algorithms such as principal component analysis (PCA). These algorithms associate features of input data-set and create new features. Both groups, conveniently improve capability of the classifiers. 3. LIBS EXPERIMENTAL SETUP A typical LIBS experimental setup is shown in Fig. 1. It consists a pulsed laser, focusing optics, light collection optics, a spectrometer and a sample chamber [83-85]. An overview of LIBS devices is given in Table. 2. Laser pulse interacts with sample, ablates a minute amount of material of sample, a luminous plasma is generated and each specie in plasma cloud become excited and then de-excited, expansion and condensation of plasma plume occur which causes to produce electromagnetic radiations containing information

14

about each specie present in the sample. Fiber optics then transmits the emitted light to spectrometer, finally spectral fingerprint is developed by system software. Collimating lens bends these radiation towards diffraction grating placed 0-45 field of view and orthogonal to plasma expansion. Radiations emitted by plasma are collected as pixels which develop intensity data.

Fig. 1. Graphical illustration of the LIBS setup [83].

3.1. Laser and Focusing Optics Q-switched (pulsed) Nd:YAG lasers are commonly employed in LIBS analysis. Qswitched mode allows pulse width of about 5-100 ns. Pulse duration of Pico and femto seconds are also available. Fluence and Laser irradiance are parameters related to laser pulse energy. These parameters depend upon the spot size [86]. A minimum spot size

15

produces a maximum irradiance. In most studies pulse energy varies between 1-500 mJ [87]. A summary of LIBS devices is given in Table 2. Table. 2. Overview of LIBS devices. Laser: (wavelength, pulse width, repetition rate and pulse energy)

Spectrometer: (spectral range, resolution, gate widths, gate Delays and detectors)

Laser-focusing op- References tics (LFO): (beam size, Plasma collimated optics (PCO))

(Quantel-Brillant), Qswitched Nd:YAG laser. (355 nm, 5 ns, 10 Hz and 50 mJ)

(Mechelle-Andor Technology) Echelle spectrometer. (240-820 nm, R = 5000, Gate width 1-4µs and ICCD.)

[88]

(Quantel-Brilliant) Qswitched Nd:YAG laser. (532 nm, 5 ns, 10 Hz and 7.5 mJ)

(2300i-Acton) CzernyTurner spectrometer. (Gate width: 10µs Gate delay: 0.1ns ICCD camera) (Mechelle750,Multichanell) Machelle spectrometer. (200 To 700 nm, Gate width 2µs, Gate delay 2µs ICCD (PCO, computer optics)) (Aryelle200Lasertechnik) Echell spectrometer. (200 -800 nm, Gate delay: 3µs, CCD detector (Andor)

LFO: (quartz lens, f = 5 cm, beam size ~500µm) PCO: (pair of parabolic mirrors and optical fiber of 50µm core diameter) LFO: (lens f = 3.6 cm. beam size~ 240µm) PCO: (two lenses f = 3.5 cm(front) and f = 6 cm (back), optical fiber) LFO: (planoconvex quartz lens F = 10 cm) PCO: (optical fibre)

LFO: (lens f = 15 cm; Beam size~ 0.7 mm) PCO: (lens f = 5 cm)

[91]

(BRIO-Quantel) Qswitched Nd:YAG laser. (1064 nm, 5 ns and 1 Hz, 100 mJ)

(Quantel-Bozeman CFR400) frequency doubled Nd:YAG laser. (532 nm, 9 ns and 230 mJ)

[89]

[90]

(Quantel-Brio) Nd:YAG laser. (1064 nm, 4 ns, 20 Hz and 10 mJ)

(LTB-Aryelle Butterfly) Echelle spectrometer. (R= 1×104 , Gate width: 5µs Gate delay: 1µs ICCD (Andor, iStar))

LFO: (plano-convex lanes F = 15 cm; Beam size~ 120µm) PCO: (Two lenses f= 15- and 3.5 cm and optical fibre 600µm)

[92]

(Surelite-II-10, Contunuum) Q-switched Nd-YAG laser. (1064 nm, 7 ns, 10 Hz and 80-140 mJ)

(Ocean-Optics) LIBS 2000 + Broadband Spectrometer. (200-980 nm; R = 0.1 nm)

LFO: (plano-convex lanes F= 9 cm)

[93]

(Beamtech-Optronics Ltd.) Dawa-200 Q-switched Nd:YAG laser. (1064 nm, 3~5 ns, 20 Hz and 50 mJ)

(Ocean-Optics) HR 2000+ Spectrometer. (200-1100 nm; R = 0.2 nm, Gate width: 2000µs and Gate delay: 2µs)

Beam size~ 100 µm; PCO: optical fibre.

[94]

16

Majority of studies showed that lasers with 1064 nm, 532 nm, 355 nm and 266 nm have shorter wavelength which results in lower influence. It is usually operated at repetition rate of 10 Hz (Table 2). A higher repetition rate provides more order of spectra and increases measurement speed [86]. Mostly an assemblage of focused silica convex lens of suitable wavelength are used to concentrate the laser beam on the sample (Table 2). For field applications (FO-LIBS), optical fiber is used instead of lens [95, 96]. 3.2. Light Collection Optics and Spectrometer Light collection is done by lenses and mirrors. Light from plasma is collected through fiber optics [97]. A spectrometer consists of a spectrograph and a detector. The spectrograph forms spectrum while detector is used to measure the intensities of various lines. Performance of a spectrometer is determined by its spectral range, resolution and attainment time [86]. Varies LIBS spectrometers with different spectral range are available in Table 2. Spectral resolution of most spectrometers lies in microsecond range. A spectrometer with wide spectral range is used for multi-element detection. Commonly used an Echelle spectrometer couple with CCD provides a maximum resolution range of 200- 780 nm. LIBS 2000+ spectrometers coupled with CCD are also common. CCD and ICCD detectors employed in LIBS setup consist of pixels. Photoelectrons are produced by laser interaction with pixels. The number of photoelectrons thus produced is a measure of intensity [98]. 3.3 Echelle Spectrometer Detalle et al. have introduced the principle of this spectrometer [99]. It has a focal length of 25 cm and provides spectral resolution ranges from 200 to 780 nm. It has a detector consisting of an ICCD camera and CCD arrangement (of 1024 × 1024 pixels). Different Echelle spectrometers and their specifications are given in Table.2.

17

3.4 Multi- spectrometer The LIBS-2000+ spectrometer comprises of five HR-2000 spectrometers of high resolution (up to 0.065 nm). As a result, it covers a wide range of wavelengths. The spectrometers are linked to computer via USB port. Luminous micro-level plasma is generated by the interaction of laser beam with the sample. Various atomic processes such as de-excitation, recombination and optical emission also happened within the plasma continuously. Light emitted from these processing is directed to LIBS 2000+ spectrometer using optical fiber. The detectors are used for collection of optical signals. A specially designed system software produces spectrum and data-logging competences [100]. 3.5 Sample Chamber Specially designed sample chambers are installed in LIBS setup to accommodate the sample. Sample is fixated on the chamber. It protects the optics and lenses from any damage. Most of the chambers has the facility to rotate so as to provide fresh surface of sample for each incoming laser shot. 3.6 Advancement and Innovations in LIBS Instrumentation During recent years, important developments have been brought in applications of laser induced breakdown spectroscopy (LIBS) for elemental imaging. In the following section some recent advancements like double-pulse LIBS, multi-pulse LIBS and hand held LIBS setup will be discussed. •

Double-Pulse LIBS

Double-pulse LIBS (DP-LIBS) is a method used to improve analytical performance of LIBS for recognition of emission lines. It depend on accumulation of a second time re-

18

solved laser pulse to a single pulse LIBS setup. DP-LIBS method has chiefly designed either in orthogonal or in collinear geometry. A survey of literature shows, a widespread variability in experimental conditions applied for double-pulse experimentations which can be highlighted in connection with laser energy, laser wavelength, and collection conditions. Recently, work has been reported about optimization of the delay between two laser pulses in collinear geometry for aluminum and brass samples. Two optima of delays between laser pulses have been determined dependent on excitation energy levels of emission lines. Some neutral lines having excitation-energy levels lower than 6 eV experiences emission boosts at a smaller inter-pulse delays (>1µs), whereas for lines with excitation energy levels higher than 6 eV. The mechanism elaborates the double-pulse experiments which might be the gas rarefaction of ambient atmosphere. The mass ablation is caused by the second laser pulse, which contributes to enhance emission intensities. On survey of literature, it has been found that the collinear geometry is most appropriate and practical arrangement for DP-LIBS to rise sensitivity of emission lines [101-104]. •

Multi-pulse LIBS

In double pulse LIBS setup two successive laser pulses are made to incident on the sample under various configuration. An extension of DP-LIBS technique is a multi-pulse LIBS [10], which makes use of passive Q-switches. It is more compact and have longer lifetime than cavity switching systems used to produce short pulses in double-pulse LIBS setup. It is found that using more than one laser pulse to generate plasma improves signal intensities of the LIBS spectrum. This in turn improves the detection limits [105]. •

Hand Held LIBS

Handheld LIBS (HH-LIBS) devices have been developed recently. HH-LIBS units are commercially offered by many companies. All these units offer elemental study of mate-

19

rials under examination and some of the units have capability of chemometric analysis by means of proprietary software. Some HH-LIBS units provide video targeting, material rastering, and an argon purge of atmosphere neighboring the target to increase detection limits. Analysis requires introduction of analyzing tip on the target and firing the laser. Results are displayed on a compact screen. HH-LIBS units are specified for several applications including scrap metal categorization, forensics, fiery materials recognition, mineral investigation, and medicinal administering [106]. 4. LIBS SPECTRA LIBS spectrum contains a many spectral lines. Some examples of LIBS spectra are shown in Fig. 2 [83]. An online database is provided by “National institute of standards and technology (NIST)” which is used for the identification of emission lines present in the spectrum. The Emission lines can be characterized by wavelength, intensity and shape of spec

20

tral lines which depends upon atomic structure, plasma temperature and electron number

densities of plasma [98]. Fig. 2. Samples of LIBS spectra: (a) powder milk, (b) lamb meat, (c) Baby formula (d) Oregano [83].

5. PRINCIPLE OF LIBS AND OVERALL PROCESS In LIBS, a nano-second pulse of Q switched Nd:YAG laser is used. This high energy pulse inters into sample and deposit energy. So a small mass of sample is evaporated and a plasma vapor plume is generated near the surface which on further absorption of energy 21

from incident pulse and produces plasma. Light emitted from plasma is dispersed with the help of a spectrometer which results into a spectrum which is then used for elemental recognition and quantification of atoms present in the sample. Overall processes occurring in nanosecond LIBS are as follow. •

A short pulse of laser is focused on to the sample.

•

Energy from the beam is absorbed by atoms and molecules of the specimen that vaporized small amount of material of the sample. A vapors plume will be formed near the surface of the material. The succeeding laser pulses interact with cloud to generate plasma.

•

The light originated from spontaneous emission by atoms and ions is guided and collected by an optical fiber system, a prism or spectrometer disperse this light.

•

Resulting spectral signature is analyzed for the elemental detection and quantitative analysis [24].

5.1 Ablation Process Initially a highly energetic laser pulse is fixated (smallest possible spot size) on to the sample (i.e. sage). The pulse interval is of the order of Nano-second. Heat produces due to absorption of energy from the beam evaporates a small amount of sample results into creation of a vaporous plume over the surface of sample. This process is called ablation [107, 108]. The ablated mass will produce a plume on the surface of the sample. The incident laser light will illuminate this cloud. Absorption of energy by the plume from incident laser beam generates a plasma. This plasma will stop the beam from entering into the sample. This effect is known as ‘plasma shielding’. This decoupling of laser beam from the sample stops further ablation and causes strong heating and ionizes the plasma. As a result, a high luminous plasma is generated. Depending upon the number density and plume temperature excited levels become populated. Plasma in response of laser irradi22

ance expands first isothermally and then adiabatically on the expense of its internal energy. By the end of these expansion phenomena, plasma condensation begins and temperature of ionized species falls. During condensation excited atoms emit electromagnetic radiation. An optical fiber system guides these electromagnetic radiation to the spectrometer which disperse light and provides spectrum having spatial and temporal variation. The spectrum carry information about the atoms of the sample. 5.2 Plasma Breakdown Two process are responsible for plasma break down in the plume. •

Presence of free electrons in focal volume of laser that may be due to cosmic rays [98].

•

Electron cascade in the focal region.

A typical laser irradiance for production of cascade is of the order of 108 to 1010 Wcm-2 [109]. An atom becomes ionized by absorbing photons from the laser [110]. This is possible only when radiation intensity is sufficiently high and energy of photons is less than work function of material. There is another possibility that atom may absorb numerous photons and stimulate a bound-free transition. Consequently, a free electron will be liberated but maximum electron production occurs via electron cascade. After the production of electron cascade plasma expands at supersonic speed and shock waves are generated in the surroundings. Plasma becomes opaque when “plasma frequency” becomes equal to the frequency of laser till a stage reaches when the “plasma frequency” exceeds laser frequency. Now the laser pulse will be reflected back by the plasma and plasma cooling begins [111] and light will be collected by the plasma for LIBS analysis.

23

5.3 Light Emission and Spectrum Formation When plasma is cooled down light from plasma is collected and sent to a spectrometer which is couple with a computer for spectrum formation. Three type of spectrums are formed. •

Continuous spectrum.

•

Band spectrum.

•

Line spectrum

In line spectrum each line has its own characteristic wavelength which is the property of emitting atom. Each spectral line results from a single transition. Spectrum used in the present work is a line spectrum. Characteristics of a line is determined by broadening mechanism. Two broadening mechanisms are commonly used. 5.3.1

Doppler broadening

It is because of thermal motions of electrons and after broadening emission line looks like Gaussian profile. 5.3.2

Stark broadening

It is due to generated electric field and line profile looks like Lorentzian after broadening. 5.4 PROCESS IN PLASMA There are many events occurring in the plasma. LIBS plasmas are weakly ionized plasmas with electron to other species ratio less than 10%. Common events occurring in the LIBS plasmas are. 5.4.1

Radiative or Emissive Processes

Laser induced plasmas (LIP) emit light consisting of continuum, band and discrete emission. The spectrum from ablated material’s plasma grows rapidly with time. Initially 24

number density and plasma temperature are very high. At early stages of emission a broad emission spectrum is observed due to free-free and free-bound transitions of the electrons. This effect of continuum emission is called bremsstrahlung. Following radiative processes take please in plasma. 5.4.1.1 Free-Free radiation It causes as a result of acceleration or declaration of electrons in the ionic field. These radiation having wavelengths in x-ray region are considered to be x-rays. 5.4.1.2 Free-Bound radiation When atoms are ionized and recombined course of recombination. During condensation process recombination are dominant, and excess energy which is captured by the atoms releases in the form of photons. 5.4.1.3 Bound-Bound radiation It occurs due to transition of electrons between bound levels. These emitted discrete lines have three features, wavelength (λ), intensity (I) and shape, these features of discrete line spectrum are employed for elemental detection and quantification. 5.4.2

Collisional Process in Plasma

As plasma contains ions and electrons moving randomly with large kinetic energy (K.E), during their course of random motion they collide with each other and with the atoms of ambient gas thereby giving rise to several collisional process. Some of these collisional events are described below. 5.4.2.1 Collisional Ionization and Recombination When an electron having large K.E collides with an atom it ejects electrons from the atom if it transfers sufficient energy (greater than or equal to threshold of ionization) this process is known as collisional ionization. It is represented as: = 25

+

, here

“M” represents neutral atoms and “

” represents ions. Reverse process of ionization is

recombination. When an electron recombines with an ion it causes the emission of photons.

+

=

+ ℎν, where “hν” is the energy of emitted photons. The overall

ionization and recombination phenomena is given by ‘Saha’ equation [112]. 5.4.2.2 Collisional Excitation and De-Excitation Whenever an electron with sufficient energy makes a collision with an atom of energy less than ionization energy of the atom, then energy of electron is taken by the atom and it goes to a higher energy state. The excitation process could be expressed as:

+

+

→

. In reverse process the atom or ion de-excites by emitting photon. If forward

and reverse processes are exactly balanced and entropy of the system is constant then energy distribution function is Boltzmann distribution and direct measurement of distribution can be carried out by the measurement of peak intensities of the specie and by Boltzmann plot method [18]. This allows to find excitation temperature and partition function, from slope of Boltzmann plot electron number density can be calculated. 5.4.2.3 Three Body Recombination Due to high plasma density sometimes two electrons make collision with an ion simultaneously, one is being captured and other moves by gaining energy imparted by the first one such a collisional process is termed as three body recombination. 6. MEASUREMENT OF PLASMA TEMPERATURE Light emitted by the plasma is used for elemental analysis and quantitative study of sample as well as plasma properties. Fundamental plasma parameters are plasma temperature and electron number density. Determination of plasma parameters is critical for LIBS quantitative analysis [113]. These parameters are also necessary for knowing LTE conditions, if plasma does not satisfy LTE criteria then there will be self- absorption and concentration measurement will not be accurate. Temperature measurement is also important 26

to understand the processes occurring in plasma. A survey of literature showed that usually three methods are employed for the determination of temperature which are explained as below. 6.1. Boltzmann Plot Method Intensity of a spectral line corresponding to transition between any two energy levels Ek and Ei is given as =



…………………………. 1

Where Ns is the number density, Aki is transition probability, gk is statistical and Us (T) is partition function. By rearranging this equation and taking natural logarithm: !" #

$

% & '

(=

+ ) … … … … … … … … … … . . 2)

This is equation of straight line. Plotting relative intensities of several lines against Ek and

Fig. 3. Examples of Boltzmann plots taken from the literature [114].

fitting it linearly result in to a straight. Reciprocal of slope gives plasma excitation temperature [114]. Some examples of Boltzmann plot are shown in Fig. 3. In majority of re27

search works, Boltzmann plot method has been used for calculating plasma temperature (as shown in Table 3). Table. 3. Comparison of different methods used for temperature measurement. Method

Sample

Elements detected

Laser used

Temperature

Reference

Ratio method

Ar plasma YaBaCuO

-

9024 K 3921.9

[115] [116]

SahaBoltzmann plot

Iron sample

Ar Ya, Ba, Cu and O Fe, Si and H

Q-switched Nd:YAG 1.06 µm, 600 mJ

14500 K

[117]

Nd:YAG, 1064 nm, 100 mJ, 4.5 ns Q-switched Nd-YAG 1.06 µm, 670 mJ.

9600 K

[118]

12992 K

[119]

Boltzmann Plot

Cu alloy

Fe, Mn, Ni and Cu

Al plasma

Al, Mg and H

Brass alloy

Cu, Zn and Pb

Nd:YAG Qswitched, 1064 nm,5mJ,250 ns repetition rate of 1 Hz.

7500 K ± 1500 K

[120]

Potato

C, Ca, Cl, Fe, H, K, Li, Mg, N, Na and O,

Nd:YAG laser at 1064 nm, ≈10ns and repetition rate of 30 Hz

6770 K

[121]

Soil sample

Al, Ca, Cr, Cu, Fe, Mg, Mn, Pb, Si, Ti, V and Zn

Nd:YAG repetition rate of 10 Hz, 6 ns

7800 K

[33]

Alloy

Al, Cu, Mn and Mg

Pulsed Nd:YAG laser, λ = 532 nm, t = 8ns, E = 83 mJ

11000 K

[122]

28

6.2. Saha-Boltzmann plot Temperature estimated by Saha-Boltzmann method is “ionization temperature” which under LTE is considered to be plasma temperature. It utilizes spectral lines of the same species. Saha- Boltzmann equation is given as + +

6.04 × 100 = "3

12 0



4,6

4,678

96

………………………………… 3

Where I is intensity, E is energy of upper level, ; is ionization energy and scripts z and z+1 show neutral and ionized lines [123]. An example of Saha-Boltzmann plot is shown in Fig. 4 [118]. Saha-Boltzmann plot method has been used in many research studies to calculate plasma temperature (as can be seen in Table 3). One disadvantage of this method is electron number density which should be known.

29

Fig. 4. Example of Saha-Boltzmann plot [118].

6.3. Ratio Method A survey of the literature showed that the temperature has also been calculated using a simple technique known as ratio method (Table 3). Excitation temperature is calculated by using the following equation

0

=

0

<0 0<

8

8

………………………………….. 4

Here I is intensity, A is transition probability, g is level degeneracy and scripts 1 and 2 refers to the selected line [124-127]. 7. CALCULATION OF ELECTRON NUMBER DENSITY Electron number density is another parameter which is used for quantitative analysis and to verify LTE condition. The emission lines in LIBS spectra are accompanied by certain

30

level of broadening. Major broadening mechanisms are Doppler, pressure and stark broadenings. Among these, stark broadening is the most significant mechanism. Coulomb interaction of charged species is responsible for this broadening. Stark broadening profile of an atomic or ionic line is commonly used for calculation of electron number density (Ne). It can be calculated by using FWHM of stark broadening profile as:

3

3

= =

∆>8 ?

0@

∆>8 ?

0@

× 10 A )B

1

… … … … … … … … … … … … . 5 (for atomic lines)

× 10 D )B

1

… … … … … … … … … … … … . 6 (for ionic lines)

Where ωelectron is impact parameter and ∆<8 is FWHM of stark broadening line [50, ?

128, 129]. An example of stark-broadening profile is shown in Fig. 5 [130]. Ne can also be calculated by means of FWHM of hydrogen Balmer (H-α) line as below ∆<8 = 0.549 × # ?

FG

H8I

(

H.ADJAK

………………………… 7

[129]

Fig. 5. Example of a Stark-broadening profile [130].

31

8. QUANTITATIVE ANALYSIS The study of LIBS showed that commonly two approaches are used for quantitative analysis. Both of these are discussed as below: 8.1. Calibration Approach Many calibration methods have been practiced to many research fields and physical samples of LIBS quantitative study. These include partial least squares regression (PLSR), univariate regression, multivariate regression, principal component regression (PCR) and so on. We cannot include detail description of these methods in this article due to lack of space, detail of these methods can be found in reference [131]. In this approach, calibration curves are to be constructed for the quantification of each element. A calibration curve comprises of a plot (intensity versus concentration) of emission line. It provides a mean to calculate concentration of an element in any sample [130, 132]. There are only a few techniques to build calibration curves. It is found that a standardization sample with a matrix comprising parallel physical and chemical properties to that of target is required but it is difficult to obtain standard samples [37, 97, 133]. Most common method is either using standard reference material (having classified concentration as that of element of interest) or a non-classified material earlier analyzed by using reference method [134]. Trevizan el al. (2009) studied composition of beam leaves by using reference material with different elemental composition to build calibration curves [135]. Ferreira et al. (2010) used seven specimen of commercial breakfast having different calcium (Ca) concentrations as calibration standard [136]. Kim et al. (2012) by using certified spinach leaves and rice samples formulated calibration sets and obtained a range of concentrations of neutral species [93]. Advantages of this technique is the calibration curves offer a

32

reliable way to calculate uncertainty in calculated concentration also these curves provide data on empirical relationship. The disadvantage of this method is that, the samples with composition similar to the unknown samples are required which is not possible in each case. Many authors indicated that calibration approach is inefficient, lack of capability and lack of standards for developing calibration model [88, 92]. 8.2. Calibration Free Approach Calibration free Laser induced break down spectroscopy (CF-LIBS) approach offers quantitative study free from sample matrix. CF-LIBS provides quantitative results without using calibration data sets [137]. This technique has been widely applied for quantification after its introduction in 1999 [42]. This method has been utilized for the quantitative study of alloys [43-46, 138]. Recently a numerous applications of CF-LIBS for quantitative analysis has been reported [88, 92]. CF-LIBS method depend on the following assumptions Laser produced plasma should be in local thermodynamic equilibrium (LTE). Plasma should be optically thin [137]. 8.2.1

One Point CF-LIBS Method

In CF-LIBS method neutral and ionized number densities NI and NII are calculated by using Saha equation [17]. The total number density is given by =

$

+

$$

… … … … … … … … … … … … … … … …(8)

Finally mass concentration of each specie is given by using equation NF

M = ∑ NFO … … … … … … … … … … … … … … … … … … 9 O

33

8.2.2

Boltzmann Intercepts Method

According to this method the elemental composition is carried by using the value of intercept. By taking the natural logarithm of Boltzmann equation and rearranging. !" #

$

&Q % Q

(=−

+ !" #

ST 6

U6

( … … … … … … 10

Equation.10 can be used to draw Boltzmann plot, where in general linear form is: V = WX + Y Where ‘a’ represents the slope and ‘b’ represents the intercept. The slope W = − 1⁄Z and intercept Y = !" \M + ⁄

+

. From the value of intercept the relation for M + de-

rived as. M + =

1 \

+

]

… … … … … … … … … … … … … . . 11

By normalizing the equation “F” can be calculated as: ∑ M + = ∑ #S

+

]

( = 1 … … … … … … … … … . 12

For concentration of ionized species the Saha-Boltzmann equation is used M+

T 6

= #F ( ^ G

0NG

_⁄?

`_

a

0U678 U6

exp #

'ef

( … … … … 13

The total concentration of both elements are calculated as M = M+ + M+ The elemental percentage composition is calculated as T h ×i h

M % = #∑f

fj8 T

h ×i h

( × 100 … … … … … … … … . . 14

34

9. LOCAL THERMODYNAMIC EQUILIBRIUM (LTE) To determine plasma temperature using Boltzmann plot method for quantitative analysis demands plasma to be optically thin and obey LTE condition. Strict thermodynamic equilibrium requires unbounded, spatially and temporally homogeneous plasma. In LTE, excitation or de-excitation processes are dominant [139]. The validity of LTE is critical to guarantee CFLIBS accuracy in quantitative results. To ensure LTE in time-dependent and inhomogeneous plasmas with thermal spatial gradients, further conditions need to be placed on the electron density. The most popular criterion used in the literature to evaluate validity of LTE is McWhirter criteria based upon electron number density for plasma to be in LTE [140]. 3

≥ 1.4 × 10

l

m ∆n 1 … … … … … … … … … … … .. (15)

In LTE all the temperatures are equal. A survey showed that LTE conditions are satisfied in most cases (Table 4). If LTE are not present then temperature of each specie has to be determined separately, but review of literature presented in Table 4 shows that LTE conditions are satisfied in most of the studies. So, only one temperature is sufficient for the determination of plasma temperature.

Table 4. Verification of LTE conditions. Sample

Temperature

Electron Ne calcula- LTE con- Reference number densi- tion method dition ty

Wheat seeds

7000 K

2.28×1016 cm-3

FWHM of stark broadening line

verified

[141]

Steel sample

10000 K

2.5×1017 cm-3

FWHM of stark broadening line of carbon

Verified

[142]

Textile dyes

7985 K

5.4×1017cm−3

FWHM of stark broaden-

verified

[143]

35

ing line of Ca Gum Arabic

10812±510 K

3.81×1017 cm−3

Fe-Ni loy

8200±100 K

2.6×1016cm−3

Human nails

17181 K

1.83×1018 cm−3

Betel leaves

7584 ±200 K

Kidney stone

12500 ± 450 K

al-

FWHM of stark broadening line of Ca FWHM of stark broadening line Fe

verified

[144]

Verified

[145]

Using FWHM of stark broadening line of Mg

Verified

[146]

1.5×1018cm−3

Using FWHM of stark broadening line of Ca

Verified

[147]

6.8×1016 cm-3

Using FWHM of stark broadening line of Ca

Verified

[148]

10. OPTICALLY THIN CONDITION For the estimation of plasma parameters and to use CF-LIBS technique for quantitative analysis there should be no self- absorption because an optically thick line could imply selfabsorption and saturation in line profile leading to a distorted or irregular peak in the spectrum and causes incorrect measurements of electron number density and temperature. In opti-

cally thin plasma intensity ratio of two lines with same upper level energy should be equal to ratio

&% >

for same two lines [124]. To verify optical thinness, the following

equation has been commonly employed: $8 $?

& % >

= &8 %8 >? exp[ ? ? 8

?

8

] … … … … … … … … … … … .. (16)

Left hand side contain experimentally determined values and right hand side has theoretically predicted values. Thus, for plasma to be optically thin, the ratio of experimentally determined quantities must be equal to the ratio of theoretically predicted quantities

36

[149]. Another method to check whether plasma is optically thin or not is by inspecting the linearity of the Boltzmann plot. Data point showing great deviation from the linear relationship implies that corresponding lines are optically thick. We can also check the exist-

ence of self-absorption by recording emission spectra at various laser energies at a constant delay time but keeping detector at a fixed distance. In second case by keeping the laser pulse energy and delay time constant but moving the detector along plume expansion. The line intensities increases in the first case when pulse energy increases but decreases in the second case when detector is moving along the plume expansion. The recaptivation of light emitted by plasma effects the emission line profile, however, if no distortion in the line shape or dip in middle of the profile for the strongest lines is observed in both cases, then there will be negligible self-absorption [150]. 11. EFFECT OF VARIATION IN LASER PARAMETERS ON PLASMA PARAMETERS Plasma parameters are affected by laser parameters like pulse energy, distance from sample and time delay. Zhang et al., [151] reported the impact of laser parameters on plasma temperature. Their results predicted that laser produced plasma (LPP) temperature increases by increasing pulse energy. In the following section, the main is the influence of laser parameters like pulse energies, distance from target, delay time on plasma parameters (plasma temperature and electron number density). 11.1. Influence of Variation in Pulse Energy on Plasma Temperature and Electron Number Density Several studies found in literature where effect of laser pulse energy has been discussed. Iqbal et al., [150] presented the effect of laser pulse energy on plasma temperature and electron number density by using Q-switched Nd :YAG laser. They reported that by increasing laser pulse energy from (160-230) mJ, increases the plasma temperature from 37

(8500-10200) K and number density about (1-6) ×1017 cm-3. Arnab Sarkar and Manjeet Sing while analyzing pigs Skelton, studied the effect of laser pulse energies on plasma temperature and concluded that an increase in pulse energy causes plasma temperature to increase [152]. Asamoah et al. investigated effect of pulse energy on Mg plasma, they presented a similar trend of temperature [153]. Shuang et al. studied the effect of increase in laser pulse energy on plasma temperature as well as on electron number density by using femto-second laser pulse. It was found that both parameters are increased by increasing pulse energy [154]. Hanif et al. also studied the consequence of laser energy on plasma parameters using 1064 nm and 532 nm laser. They showed that, by incrreasing laser pulse energy from 90 -160 mJ, plasma temperature rises from 14192- 15765 K and number density increase from 1.83×1015-1.51×1016 cm-3 [155]. Peng et al. also reported the effect of laser pulse energy on plasma parameters [156]. A brief comparison of effects of laser pulse energy on plasma temperature and electron number density is given in Table 5.

Table. 5. Influence of variation in laser pulse energy on plasma parameters. Sample

Laser pa- Laser rameters Energy

Effect on Effect on References temperature number density

Naturally occurring crystals

Q-switched Nd:YAG. 5 ns pulse duration, 10 Hz repetition rate, E= 400 mJ at 1064 nm and 200 mJ at 532 nm.

Laser energy increases from 160 mJ to 230 mJ)

Te increases from 8500 to10,200 K

Ne increases from 1.0×1017 to 6.0×1017 −3 cm

[150]

Nickel alloy

Q-switched Nd:YAG pulse duration 5 ns and 10 Hz repetition rate E= 400 mJ at 1064

Laser energy increases (90 to 116) mJ for fundamental and (58 to 79) mJ for second harmonic

Te rises from (14192 to 15765) K for fundamental and (13170 to 14800) K for second harmon-

Ne increases from 1.83×1015 to 1.54×1016 −3 cm for fundamental and to 9.6×1015 1.2× 1016 cm−3

[155]

38

nm and 200 mJ at 532 nm.

ic.

for second harmonic

A frequencydoubled Nd:YAG laser, 10 Hz repetition rate and pulse duration 5 ns.

Laser energy increases from 130 mJ to 150 mJ

increases Te from 9500 K to 15000 K

Ne increases from 1016 cm-3 to 1017 cm-3

[157]

Rice leaves

Nd:YAG laser 532 nm and 1064 nm pulse duration 8 ns

Laser energy increases from 20–130 mJ

increases Te from 5250 to 7500 K

Ne increases from 7.7×1016 3.8×1017cm-3

[156]

Magnesium plasma

1064-nm Qswitched Nd:YAG laser,10 ns 1-Hz pulse repetition rate

Laser energies of 100, 200 and 300 mJ

the electron temperatures were found to be 8810, 9303 and 9724K, respectively

-

[153]

Zn and Nanoparticles

Sn

It has found that, increasing the pulse energy causes plasma temperature and electron number density to show an increasing trend. It could be due to availability of more energy which increases the mass ablation and hence causes an increase in plasma parameters [158-160]. An example of a graph of Laser energy versus corresponding plasma temperature and electron number density is presented in Fig. 6.

Fig. 6. Effects of laser energy on temperature and number density [155].

39

11.2. Influence of Distance (from Target) on Plasma Temperature (T) and Electron Number Density (Ne) Many authors presented the influence of increase of axial distance from the sample on plasma parameters. It has found that the increase in axial distance of laser from sample, T and Ne shows a decrease [161-163]. It could be due to plume expansion and cooling. An example of graph between distance from the target versus plasma temperature and electron number density is shown in Fig. 7.

Fig. 7. Influence of distance from sample on plasma parameters [155].

Liu et al., investigated effect of distance variation from the target on plasma constraints, they showed that plasma temperature (T) and electron number density (Ne) both are initially high and then declined by increasing distance of pulse from the target [164]. Yao et al., also presented the same trend for plasma parameters when distance from increases [154]. Amer et al., using Nd:YAG laser (1064 nm and 532 nm) showed that when distance has been increased from 0 to 2 mm, “T” decreased from (13700 to 10270) K and “Ne” decreased from (2.81×1016 to 9.81×1015 ) cm-3 [165]. Rehan et al., observed a decrease in the temperature (from 6770- 4266) K and number density (from 3×1016 to

40

2×1016 ) cm-3 by variation of distance from 0 to 3mm [121]. A summary of effects of spatial variation of pulse from target on plasma parameters is given in Table 6. Table 6. Influence of distance from the target on plasma parameters. Sample

Laser pa- Distance rameters from sample

Effect on Effect on elec- References Plasma tron Number temperature density

Titanium dioxide

Nd:YAG laser 1064 nm

Distance increases from 0 to 7 mm

decreases Te from 18792 K to 15312 K

1.6×1016cm−3 at 1 mm decreases to 1.2×1016cm−3 at 9 mm

[166]

Nickel alloy

Q-switched Nd: YAG, 5 ns duration, 10 Hz repetition rate and energy = 400 mJ at 1064 nm, and 200 mJ at 532 nm

Increases from 0.05mm to 2 mm

Decreases from 13700 to 10270 K

varies from to 2.81×1016 9.81×1015 cm−3

[155]

Iron sample

Q-switched Nd: YAG, 5 ns pulse duration and 10 Hz repetition rate

Increases from (0.05 to 2) mm

Rises from (6980 to 6500) K

Decrease from (1.38 ×1015 to 3.75×1015 ) cm-3

[167]

Al plasma

Nd:YAG laser, 5-ns, 40 mJ, wavelength of 266 nm, 10 Hz

Increases from 0 mm to 1 mm

Decreases from 17500 K to 6500 K

1.68×1023m-3. The electron density decreases slightly for r > 0.3 mm

[168]

Copper based alloy

Nd:YAG laser wavelength 1064 nm, energy 100 mJ, pulse width 4.5 ns

Increases from 0.2 mm to 2 mm

Decreases from 10930 K to 6090 K

Varies from 9×1016 cm-3 to 6×1014 cm-3

[118]

Aluminum plasma

Q-switched Nd: 5 ns and 10 Hz repetition rate.

Increases from 0 mm to 5 mm

(9630K, 8590 K and 8160 K) decreases to (7660K, 7065 K and 6525 K)

[169]

Copper and Nano copper sample

Q-switched Nd:YAG laser: 10 ns, 80 mJ at 532 nm and the repetition rate is 10 Hz

Increase in target distance from (1 to 6) mm

Decreases from 20000 K to 8000 K

(1.3×1018cm−3, 1.7×1018cm−3and 2.7×1018cm−3) decreases to (4.2×1017cm−3, 5.1×1017cm−3 and 9.3×1017cm−3) Decreases from 1×1017 cm-3 to 3×1017 cm-3

Potato

Nd:YAG laser at 1064 nm with pulse du-

Distance increases from (0 to

Temperature rises from 6770 K to 4266 K

Number density decreases from 3.0 × 1016cm−3 to 2.0×

[121]

41

[170]

1016cm−3

ration ≈10 ns and repetition rate 30 Hz

3) mm

Ti alloy

1.06mm, 10 ns Nd: YAG pulsed-laser

Distance decreases (0 mm to 2 mm)

For (1064 nm) wavelength, temperature varies (13700 – 10270) K and for (532 nm) mode of laser it varies (132709660) K

For first harmonic varies from 2.81x1016cm-3 to 9.81×1015 cm-3 and for second harmonic varies from 3.67×1016 cm-3 to 1.48×1016 cm-3

[165]

Marble

Q-switched Nd:YAG, 5 ns and 10 Hz, 400 mJ energy at 1064 nm and 200 mJ energy at 532 nm

0 mm to 2 mm

8500-6500 K

(4.4±0.4)×1016 cm−3 to (3.5±0.3)×1016 −3 cm and (4.7±0.4)×1016 cm−3 to (3.8±0.3) ×1016 cm−3for first and second harmonic respectively.

[171]

11.3.

Influence of Delay Time on Plasma Parameters

Interval between laser pulse and acquisition of spectra is called delay time. It has been found that increasing delay time emission decreases emission intensity, plasma temperature and electron number density this is because e of convers of ion thermal energy into kinetic energy with plasma expansion [172-175].

Fig. 8. Effects of delay time on plasma parameters(T and Ne) [153, 154].

42

DANN et al., examined influence of time delay on plasma temperature and electron number density. It was found that the increasing delay time from 0 – 200 ns causes a decrease in plasma temperature (from 1.3 eV to 1.1 eV) and number density (from 5.5 x 1016 and 4.4 x 1016 cm-3 ) [166]. Rezk et al., (using Nd: YAG laser delivering 96 mJ, at 1064 nm and repetition rate 10 Hz) reported the effect of delay time on plasma parameters (temperature and electron number density), a decrease in temperature (from 0.9-0.5) eV and number density (from 2.23 x 1017 to 4 x 1016 )cm-3 has been reported with increase in delay time (500-3000) nm [176]. Alsherbini et al., also observed the effect of time delay on plasma parameters and showed that both T and Ne decreases by increasing delay time [177]. Liu et al., found that both T and N are initially high but decline with increase in delay time [164]. Arnab Sarkar and Manjeet Sing also presented the same trend [152]. Yao Hongbin showed that electron temperature reached to the highest value of 10164 K at 100 ns and then decreases to 8833 K at about 500 ns. He also observed effect of delay time on spectral intensities and found it to be decreasing with delay time [153]. Unnikrishnan et al., investigated variation of temperature and number density by increasing delay time and found that temperature decreases from 0.78 eV to 0.69 eV and number density decreases from 1.2x1015 and 4.10x1013 cm-3 by increasing delay time from 500900 ns [125]. Aragon and Aguilera also presented the same effect on plasma parameters by increasing delay time [178]. Several other studies [117, 119, 154, 165, 170, 179-183], have also reported the variation of plasma parameters caused by rise in delay time. A comparison on effects of pulse delay on plasma parameters is shown in Table 7 and a plot of delay time versus plasma temperature and electron number density is shown in Fig. 8.

43

Table 7. Influence of delay time on plasma parameters.

Sample

LASER parameters

Delay time

Effect on Effect on Plasma electron temperanumber ture density.

Trend of Referrelative ences intensities of emitted spectral lines

Titanium dioxide

Nd:YAG laser 1064 nm

delay time increases from (0 to 200) ns

Decreases from 15080 K to 12260 K

Reductions from (5.5× 10164.4×1016) cm-3

-

[166]

Fish bones

Nd: YAG: E= 96 mJ at 1064, nm with repetition rate up to 10 Hz and pulse duration 5 ns.

delay time increases from 5003000 ns

Decreases from (10440 to 5800) K

decreases 2.23×1017 to 4 ×1016 cm-3

-

[176]

pure aluminum

Nd-YAG Laser), 1064 nm, 80 mJ and 12ns

Delay time increases from 100 to 600 ns

Decreases from (13920 to 10440) K

Decreases with increasing delay time (6.1×1017 to 1.2×1017 ) cm-3

-

[138]

Magnesium plasma

Q-switched Nd:YAG laser: 1064 nm, pulse duration 10 ns and pulse repetition rate 10 Hz

Delay time increases from 100 to 500 ns

Decreases from (10164 to 8833.6) K

-

Decreases with increase in delay time

[153]

Copper plasma

Q-switched Nd:YAG laser, third harmonic wavelength 355 nm, pulse duration 6 ns and repetition rate 10 Hz.

Delay time increases from 300 to 2000 ns

Decreases from (9048 to 8004) K

Decreases from 2.0×1014 to 4.5×1013 cm-

-

[125]

Nd:YAG laser 1064 nm, pulse energy

Delay time increases

Temperature drops from 7400 to 7200 K

-

[178]

Fused glass sample

3

44

decreases from (0.87 to 0.05)×1017

cm-3

300 mJ, pulse width 4.5 ns, and repetition rate 20 Hz)

from 0.4 µs to 3.4 µs

Soil sample

The femtosecond laser with center wavelength of 800 nm, repetition rates of 1 kHz, maximum pulsed energy of 4 mJ

Delay time increases from 150 ns to 800 ns

Temperature drops from 18000 to 16000 K

Decreases from 12×1015 cm-3 to 8×1015 -3 cm

decreases from 16000 to 2000 for delay time increases from 100 to 800 ns

[154]

Copper and iron

1064 nm, 9 ns Nd: YAG laser

Increases from 0 to 8 µs

Temperature drops from 18000 to 8000K

-

[179]

Iron ple

Q-switched Nd:YAG laser 1.06 µm and 600 mJ

Increases from 1 to 5 µs

From 14500 K down to 11020 K

decreases from 2.2×1017 cm-3 to 6×1016 cm-3 From 2×1018 cm–3 down to 4×1017 –3 cm

-

[117]

Hydrogen calcium sulphate

Nd:YAG laser: 4 ns pulse duration, E= 40 mJ at wavelength 266 nm

Increases from 200 to 6000 ns

Temperature reduces from about (14,000 to 6,000 K)

From 5×1017 cm−3 down to 3×1015cm−3

-

[180]

Titanium plasma

Nd: YAG, 248 nm, 30 ns

Increases from 300 to 2000 ns

Temperature diminishes from about 19720 to 4640 K.

From 3.3×1017 cm−3 down to 1.2×1017cm−

-

[181]

sam-

3

Titanium

KrF excimer laser fixed at 5J cm-1 with a rectangular spot 2.00×2.42 mm2 and a repetition rate of 5 Hz

Increases from 50 to 200 ns

Temperature decreases from about 11800 K to 9600 K.

Decreases from 2.8× 1018 down to 8× 1017 cm-3

-

[112]

Alloy

Pulsed Nd:YAG laser λ =532 nm, τ = 8 ns, E = 83 mJ/pulse

Increases from 500 to 2000 ns

Temperature decreases from about 11000 K to 7000 K.

Decreases from 5×1017 down to 2× 1017 cm-3

-

[122]

45

Kidney stone

Fluid sample

(Nd:YAG) laser source 266 nm 50, 8 ns, 20 Hz repetition rate

in the delay time changes (0-10 µs)

15200 to 6000 K

Nd: YAG laser with 266 nm wavelength 8 ns pulse duration and 20 Hz pulse repetition rate

Increases from 600 ns to 1500 ns

Decreases 4700- 3000K

From 6.8x1016 down to 3.2×1015 cm-

-

[148]

-

[184]

3

6.1x1016 to 5.3x1016 cm3

11.4 Ambient Environment Ambient condition comprises a set of parameters including temperature, pressure and humidity of environment of experiment. LIBS can be performed under specific ambient circumstances in open air. Sample ablation is performed several times in the presence of ambient gas, commonly argon is used as ambient gas. Electron number density and plasma temperature are two parameters essentially used for laser produced plasma analysis. Ambient conditions could be varied by changing gas concentration. Pressure of ambient gas when initially increases causes both plasma temperature and electron number density to increase any more increase of pressure causes to decrease both parameters, this is because of reduction in shielding effect of plasma. When shielding effect becomes less, laser energy reaching surface of sample causes greater mass ablation. Further rise in pressure initiates confinement effect of plasma which decrease rate of mass ablation, thereby causing a decrease in plasma temperature and electron number density. Spectral emission of laser produced plasma can also be affected by changing temperature, and thermal properties of ambient gas [185].

46

11.5

Laser Irradiance

Any change in radiant flux density strongly affects laser induced plasmas. A survey of literature has revealed that spectral intensities rise with increase in laser irradiance, it is due to the fact that by increasing laser irradiance, rate of mass ablation rises, which increase number density and plasma temperature. T and Ne both become saturated on higher laser irradiance [186]. 11.6 Laser Spot Size Laser produced plasmas (LPP) strongly rely on “laser spot size” and its focal position to target lenses. Laser beam has negligible divergence this is why it subtends a small solid or cone angle at point of coincidence. Spot size is the function of cone angle, smaller cone angle provides a minimum spot size and plasma absorption becomes strong about central axis. This is done by focusing lenses which converges incident laser beam at minimum solid angle about few milli-radian. Reducing solid angle or laser spot size, density gradient of plasma also rises [187].

11.7 Laser Wavelength Wavelength of laser beam also affects ablation process and absorption in laser induced plasmas. The shortest laser wavelength (highest energy) can penetrate more in plasma and it has ability to ablate more matter from sample so plasma temperature and number density will increase, while longest wavelength has fewer optical penetration, it cannot ablate more mass so temperature and density of plasma will decrease. Due to different energy per photon. electron temperature and number density are different for two modes of Nd:YAG lasers[188].

47

11.8Nature of Material Laser produced plasmas (LPP) critically depend on nature of target. The geometrical shape, mass distributions, type of bonding, physical and chemical properties, crater size, amount of ablation and cavities in the sample specifies plasma temperature and number density of plasma. 12. APPLICATION OF LIBS Laser induced breakdown spectroscopy is an analytical technique used for elemental analysis and quantitative measurement of wide diversity of materials in all form of matter. In the following section we will review some applications of LIBS in different fields. 12.1.

LIBS in Solid Analysis

LIBS has been employed for quantitative analysis of naturally occurring crystals in Pakistan (using Nd: YAG laser). Plasma temperature has been estimated by Boltzmann plot method utilizing Si lines. Effect of laser pulse energy on plasma parameters has also been studied [150]. The concentrations of Cu, Zn and Pb were determined in long (ns) pulse with and without correction for non-stoichiometric ablation of brass alloy [120]. Labutin et al., detected carbon in steel sample by using LIBS and compared the accuracy of LIBS with other techniques [142]. A. M El Sherbini et al., studied pure aluminum sample by the application of LIBS [138]. Luo et al., employed LIBS technique to study percentage composition of elements in aluminum alloy. LOD of LIBS have also been studied [177]. Hanif et al., deployed LIBS (1064 nm and 532 nm Nd: YAG laser) for diagnostic study of Nickel alloys. In addition, they also examined variation of plasma parameters caused by variation in laser parameters [155]. Nasar Ahmed et al., [189] and Aguilera et al., [118] quantitatively analyzed brass and copper based alloys by using CF-LIBS method. Hanif et al., studied composition of nick48

el alloys, effect of variation in pulse energy and spatial variation of laser pulse on plasma parameters [190]. Titanium samples have also been analyzed qualitatively and quantitatively by many researchers via LIBS technique [112, 165, 181, 182, 191, 192]. Some applications of LIBS for qualitative and quantitative analysis of solids is summarized in Table 8. Table. 8. Application of LIBS for solid analysis. Sample

Laser pa- Elements Plasma Number rameters detected temperature density

Naturally occurring crystals

Q-switched Nd:YAG laser: pulse duration 5 ns, repition rate 10 Hz, E = 400 mJ at 1064 nm and 200 mJ at 532 nm.

Fe, Si,

9500±500 K

Brass alloy

1064 nm Nd:YAG Qswitched 5 mJ, 250 ns and 1 Hz

Cu, Zn and Pb

Carbon detection in steel

Nd:YAG (λ = 540 nm, fixed energy of 15 mJ/pulse, τ=0.5 - 20 ns, 5 Hz, second pulse (λ = 532 nm, 60 mJ/pulse, τ= 8 ns, 5 Hz

Pure aluminum

AL alloy

Silicon target

Parametric study

References

(4.2±0.4)×1017 cm-3

Effect of pulse energy on plasma parameters

[150]

7500±1500 K

(2.79 ± 0.41) × 1016 cm−3

-

[120]

C, Mn, Cr, Si, Ni and Fe

10000 K

2.5 × 1017 cm-

-

[142]

Nd-YAG: emitting two pulses at 1064 nm with 80 mJ/pulse and 12-ns FWHM

Al

11000 K

1017cm-3

Variation in delay time on plasma parameters.

[138]

Q-switched Nd:YAG laser: (1064 nm, 19.7 1 Hz, 81±5 mJ/pulse)

Al, Si, Fe, Cu, Mn, Mg, Ni, Zn and Ti

10766 K

1.6 × 1017 cm-

-

[177]

Nd:YAG laser with energies of 20–72 mJ and durations in the range 9–

Si

22040 K

Temporal and spatial effects of pulse

[164]

3

3

49

<1023 m-3

20 ns Nickel alloy

Iron sample

Q-switched Nd: YAG 5 ns and 10 Hz, 400 mJ at 1064 nm, and 200 mJ at 532 nm Q-switched Nd: YAG laser: 5 ns and 10 Hz repetition rate

Fe and Ni

13720±100 K

2.8×1016 cm-3

Effect of pulse energy and distance from target on plasma parameters

[155]

Fe

6960 K

1.12×1016 cm-3

[167]

1.68×1023m-3

Effect of laser irradiance and distance from target on plasma parameters Effect of distance from target on plasma parameters

2.79×1016 cm-3

-

[120]

Aluminum plasma

Nd:YAG laser, 5-ns duration and 40-mJ, 266 nm with the repetition rate of 10 Hz

Al, Fe

11900 K

Brass alloy

1064 nm Nd:YAG Qswitched laser 5 mJ pulse of duration 250 nm and repetition rate 10 Hz. Q-switched Nd:YAG laser: 5 ns, 10 Hz repetition rate, 850 mJ pulse energy at 1064 nm and 500 mJ at 532 nm. Nd: YAG laser: wavelength 1064 nm, energy 100 mJ, pulse width 4.5 ns Q-switched Nd:YAG laser: 1064 nm wavelength, 4.5-ns width at 20-Hz repetition rate

Cu, Zn and Pb

(7500± K

Cu and Zn

(10000±1000) K

(2.0±0.5)× 1017 cm−3

-

[118, 189]

Fe, Mn, Ni and Cu

9600 K

3.9×1016cm−3

Effect of distance from target on plasma parameters

[118]

Fe

(8200±100) K

2.6 × cm−3

-

[145]

Brass alloy

Copper based alloy

Fe-Ni loy

al-

12.2.

1500)

1016

[168]

LIBS for Food Analysis

Some applications of LIBS for analysis of food materials are summarized in Table 9. In 2011 Lei et al., utilized LIBS technique for finding Ca, Mg and K in seven varieties of milk powder, results were compared with ICP-AES technique [88]. Liu et al., assessed 50

the capability of LIBS to determined moisture contents in chees [89]. Abdeslam et al., reported quantitative analysis of mineral composition in motherly milk [90]. Zheng Peichao et al., studied the composition of tea samples and detected Ca, Na, Al, K, Fe, Mg and Mn as well as organic elements O, C and H by using LIBS. Tea samples were also analyzed by Gondal et al., via LIBS and the results were compared with ICP-MS technique [130]. Rehan et al., employed LIBS for spatial characterization of red and white skin potato [121]. Beldjilali et al., studied minor element’s concentration in potato via LIBS [92]. Hasan Murat et al., studied identification of offal adulteration of beef by using LIBS [193]. Elemental compositions of coffee samples were studied via LIBS by Ahmed Asadi et al.,[194]. Table. 9. Applications of LIBS for food analysis. Sample

Laser param- Eleeters ments detected

Tea samples

Nd:YAG laser fundamental wavelength of 1064 nm, 8 ns, a repetition rate of 20 Hz and pulse energy 100 mJ

Tea samples

quadrupled Qswitch Nd: YAG (wavelength 266 nm), repetition rate of 20 Hz, maximum energy 30 mJ and 8 ns pulse. (Nd:YAG) laser: 2 Hz, 7 ns FWHM, 6 mm diameter, and 235 mJ energy. Nd:YAG laser at 1064 nm, repetition rate, 8 Hz and 36 mJ/s Nd:YAG pulsed laser (1064 nm)

Powder milk

Beaf

Rock and sea

Plasma temperature

Parametric study

References

1017cm−3

-

[195]

-

[130]

Ca, Na, Al, K, Fe, Mg and Mn, the organic elements C, H, O and N Xe, Hg, Cr, Fe, K, Si, Ca, Cu and Br

10892 11736 K

Ca, K, Na, and Mg

N/A

N/A

-

[196]

Na, Mg, Ca, K and Fe

N/A

N/A

-

[193]

Cu, N,

7849 ± 620 K

1016cm−3

-

[157]

Cd, Fe,

to

Number density

6864 K 1.2×1017 cm-3 and 1.03×101 7 cm-3

51

salts

Tea sample

C0ffee

Dates

with a pulse width of 5 ns and repetition rate 10 Hz. Q-switch Nd: YAG laser: wavelength 266 nm, repetition rate 20 Hz, energy 30 mJ and 8 ns pulses Nd:YAG laser beam running at 266 nm pulse repetition rate of both lasers at 20 Hz and the pulse duration of both lasers at 6 ns Nd: YAG laser: having 8 ns pulse width, 10 Hz pulse repetition rate and pulse energy range 15–18 mJ

12.3.

Ca, Co, Mg, Mn, S, and Zn Hg, Xe, Cr, Cu, Si and Br

6864-7514 K

-

[130]

1.2×1017 cm-3 and 1.03× 1017cm-3

Mg, Ca, Na, K, Al, Pb, Zn, and Cr

(6785±425) K

0.90× 1017cm−3

-

[194]

Mg, Ti, Fe, K, Ca, and Cr

5660 K

3.47× 1016cm-3

-

[197]

Applications of LIBS for Soil, Minerals and Sediments

LIBS technique has been widely used for soil, minerals and sediment analysis. Luo et al., employed LIBS technique for spectral examination of Quinling mountain rocks. They observed Fe, C, Si, Mg, Cu, Na and Ti by using Q-switched Nd: YAG laser having wavelength 1064 nm [198]. Walid and Abeer Askar [142] studied matrix effect on plasma characterization by using LIBS with portable Echelle spectrometer. Xu et al., employed LIBS technique for soil analysis and parametric study of soil [199]. Under water sediments were analyzed by Lazic et al., via LIBS. They detected trace elements (Mg, Fe, Ti, Sr and S) with major elements (Ba and Mn), and compared LIBS limit of detection [200]. Fahad et al., employed LIBS for elemental analysis of lime stone [201]. Marble has been examined by using LIBS method [171]. Diaz et al., utilized LIBS for mineral analysis. They also considered the influence of laser irradiance and laser wavelength on plasma parameters [202]. Mahmood et al., performed elemental analysis of different stones by 52

using Nd: YAG laser coupled with LIBS 2000+ spectrometer. They detected Ca, Fe, Sr, Li and Mg [203]. Zuhaib Haider et al., utilized LIBS for Pb determination in soil [204]. A summary of application of LIBS for soil, rock and mineral analysis is presented in Table 10. Table. 10. Applications of LIBS for Soil, minerals and rocks. Sample

Laser parame- Elements Plasma Number ters detected tempera- density ture

Rock sample

Q-switched Nd:YAG laser (SGR, Beamtech Optronics), which delivers 135 mJ per pulse at 1064 nm with 19.7 ns pulse duration, 10 mm beam diameter and a frequency of 1 Hz Q-switched Nd: YAG laser at 1064 nm having pulse duration of 7 ns Q-switched Nd:YAG at 1064 nm, E = 100 mJ/ pulse and time delay 0.4 µs

Soil sediments

Shilajit

Parametric study

References

Fe, C, Si, Mg, Si, Ca, Na and Ti

15,587 K to 16,825 K

1.49×1018 cm−3

-

[198]

Pb, Co, V and Mn

8000 K

3×1017cm−3

-

[142]

Al, C, Ca, Fe, K, Li, Mg, Mn, Na, Ni, P, S and Si

7750 K

5.8 ± 0.09 × 1017 cm−3

-

[205]

Effect of pulse energy, distance from target and delay time on plasma parameters -

[154]

-

[200]

Soil

The femtosecond laser 800 nm, repetition rates of 1 kHz, maximum pulsed energy of 4 mJ

Fe

18500 K

6.48×1015 cm−3

Soil

(pulse energy 325 mJ, pulse width 80 µs) and a Q-switched (pulse energy 67.6 mJ, pulse width 18 ns) Nd:YAG lasers (λ = 1064 nm)

Fe, Cr, Si and S

2.988×1017 and 2.412×1017 cm–3 for the longpulse and Q-switched laser confi guration.

Underwater sedi-

Q-Switched Nd:YAG laser:

Ti, Ba, Mn Li, Si, Ca,

15795.907 K in the long-pulse laser configuration and 9040.792 K in the Qswitched laser confi guration. 9000 K and 11800 K

53

-

[199]

ment

Copper ores

1064 nm, E = 310 mJ and repetition rate 10 Hz Q-switched Nd: YAG Laser capable of delivering 450 mJ at 532 nm, 5 ns pulse duration, and 10 Hz repetition rate

Al, C, Fe, Na and K Li, Mn, Na, Mg, Al, Si, K, Ca, Ti, Fe, Cu, Zn, Ag, Sr and Ba

for sample S-1, S-2 and S-3 are (8000±500) K, (9500± 500) K and (9000± 500) K, respectively (81277225) K

(2.5± 0.5)× 1016 and (1.6± 0.5)× 1016 cm−3

-

[206]

1.5×1018 cm−3

-

[147]

(0.90± 0.02) eV

(1.9 ± 0.1) x 1017cm-3

-

[207]

For the 1064 and 532 nm lasers, the electron temper tures ~8500 ±850 K and ~6800± 680 K 7211± 1943 K and 6312± 1226 K

(4.4 ± 0.4) × 1016 cm−3 and (4.7 ± 0.4) × 1016 −3 cm For the 1064 and 532 nm lasers 9.86±1.38× 1017 cm-3

Effect of distance from target

[171]

-

[202]

Ca, Fe, Sr, Li, Mg

N/A

N/A

-

[203]

major elements (Ca, Na, Mg, K, Fe, Zn, Cl and Cu) and toxic elements (Cd, Ni, Cr, Pb and Hg) C, Mg, Pb and N

17200 K.

3×1018 cm-

Effect of delay time on plasma parameters

[130]

-

[204]

Drilling fueled soil

Q-switched Nd:YAG laser: wavelength 1064 nm, 100 mJ/pulse, and repetition rate 10 Hz

Al, Pb, Fe, Si, Mg, Mn, Ca,

Waste Foundry sand

Nd:YAG: wavelength 1064 nm, energy 80 mJ per pulse, FWHM 10 ns andrepetition rate 10 Hz. Q-switched Nd:YAG laser: pulse duration 5 ns, 10 Hz repetition rate and 400 mJ energy (1064 nm) and 200 mJ energy (532 nm)

Si, Fe, C, Mn, Mg, Ti, Al, Ca, Sr, Ba, Na, Li, K, H, O, N, Zr, and Pb calcium (Ca), magnesium (Mg), aluminum (Al), strontium (Sr), and sodium (Na)

Q-switched Nd:YAG lasers: 5 Hz repetition rate and 1064 nm and 355 nm wavelengths Nd:YAG laser: Qswitch, pulse duration 5 ns and repetition rate 10 Hz Nd:YAG laser: 266 nm, pulse width 8 ns, 20 Hz and energy 12.5 and 35 mJ

Au, Ag, Fe and C

Marble

Minerals

Stones

Gallstone

Soil

Nd:YAG laser (1064 nm, 10 ns,

3

24,870 K

54

1.4×1018 cm-3

100 mJ)

12.4 LIBS in industry Laser induced breakdown spectroscopy (LIBS) has been utilized for many industrial processes, for example detection of explosives even at trace level has been made using LIBS [208, 209]. This technique has been helpful for recognition of toxic heavy metals in industrial wastes [210]. Recently solar cells are analyzed for the detection of impurities [211] this helps to improve the manufacturing process and to increase efficiency. 12.5 LIBS in biomaterials and biomedicine Bio material analysis is of potential interest in research on human for identification of diseases, nutritional deficiencies, occurrence of poisonous elements and animal remains. Quantitative identification of traces of aluminum, strontium and lead in human skeletons and teeth were studied using laser induced breakdown spectroscopy [212]. Fresh and old corals and shells analysis has achieved using LIBS, this technique can also be used to examine chemical structure of human bones, tissues and body liquids [213]. Laser breakdown spectroscopy has also been used to detect surplus or shortage of minerals contents in tissues, teeth, nails and bone detection of toxic elements has also been studied by this technique [214-216]. LIBS has also been used for cancer detection in human body as well as for detection and destruction of tumor. 12.6 LIBS in environmental applications Applications of LIBS starts from mid 1990s with the detection of toxic and trace metal pollutants in atmosphere. Buckley utilized LIBS to made a immediate measurement of Be, Cd, Hg and Pb in emission from waste furnace [217]. Presence of metallic elements in crude oil residue have been examined by Gondal et al. [218, 219]. Fortes identified the crude oil and fuel residue by a portable LIBS system [220]. The profusion of toxic metals 55

present in waste water by a paint manufacturing unit were determined utilizing 1064 nm Nd: YAG. LIBS system. Pandhija and Rai using CF-LIBS technique determined the concentration of different elements in coral sample by producing plasma on the surface without any pretreatment [221]. A low weight rucksack LIBS unit was assembled that uses a 50 mj/pulse Qswitched 1064 nm Nd:YAG. laser coupled with a high HR spectrometer having 2048element linear CCD array detector. Its volume enables it to use in inaccessible places such as caves etc. [222-224]. Another study [79] developed an alteration procedure for LIBS signal and applied this for the study of major and trace element’s concentrations in linearly censored slice of “stalagmite” from Baradla cave (hungry). 12.4.

Miscellaneous Applications of LIBS

LIBS has been employed in different fields for elemental recognition and quantitative analysis. It has been found that almost every sample can be analyzed via LIBS. Durgesh et al., studied wheat seeds by using LIBS [225] and detected Mg, Si, Cr, Ca, K and Na in the seed sample. Fish bones has been analyzed by Rezk et al. They carried out quantitative examination of copper and cobalt absorbed in fish skeletons. Plasma temperature has been calculated by “Boltzmann plot method”, electron number density by using “stark broadening” profile of hydrogen alpha line[176]. Quantitative analysis of Shilajit found at different altitudes has been reported by Rehan et al., results were compared with ICPAES [205]. Proher et al., studied oxide materials by using Nd: YAG laser (1064 nm). Quantitative analysis has been performed via CF-LIBS technique [226]. Similarly, metal detection in textile dye has been done by LIBS, result for the detected elements (AL, Co, Cr, Fe, K, Mg, Mg, Na, Ni and Zn) were compared with ICP-AES [143]. Gondal et al., [144] performed spectral analysis of Gum Arabic via LIBS. Boltzmann plot has been used

56

for estimation of plasma temperature while electron number density was calculated by stark broadening line of Ca. Elemental analysis of plants and compost used for soil remediation were carried out by Sensi et al., via laser induced plasma breakdown spectroscopy [227]. Cristina et al., employed LIBS for determination of macronutrients present in plants [228]. Qualitative and quantitative investigation of human nail has been achieved by LIBS and ICP-AES techniques [146]. Nasar Ahmed et al., deployed LIBS for analysis of different karate of gold [229]. LIBS coupled with ICP-OES has been used by Rehan et al., for finding Pb contents in drilling fueled soil [230]. Kidney stone has been analyzed via LIBS by Ahmed Asaadi et al., [148] for carcinogenic metal detection. Shuai et al., used CF-LIBS technique for elemental analysis of carbides [231]. metal alloys for metallurgy and jewelry [29, 30], cultural heritage materials analysis [31, 32] CONCLUSIONS In this article various steps and approaches of laser induced breakdown spectroscopy for analytical study, quantitative analysis and its applications has been reviewed. It has been tried to summarize the current state of literature pointing out the relevant concepts of LIBS. LIBS is compared with other well established analytical techniques. It is found that some established analytical techniques are more sensitive and accurate than LIBS but certain features of LIBS make it more appealing for elemental analysis. LIBS is a spectrochemical analytical technique with a wide range of applications. It has unique capability of analyzing trace, major and minor elements in all type of materials. Elemental analysis with LIBS is simple, fast and minimally destructive. LIBS is an attractive candidate for its peculiar capabilities such as no sample preparation, remote detection and compact instrumentation. Based on this review, it is recommended that some new instruments and

57

techniques are to be employed such as double pulsed LIBS, magnetic confined LIBS and spark discharge LIBS in order to enhance LIBS sensitivity and accuracy. It is believed that with further developments in methods and instruments, LIBS would be the best analytical technique for qualitative and quantitative analysis. Acknowledgement This Research work is supported by Higher Education Commission (HEC) of PAKISTAN under SRGP # 1400 and University of Malaya, 50603 Kuala Lumpur Malaysia.

REFERENCE [1] F. Brech, L. Cross, Abstracts of Xth Colloquium Spectroscopicum Internationale and First Meeting of the Society for Applied Spectroscopy, Appl. Spectrosc., 16 (1962) 59. [2] D. Rusak, B. Castle, B. Smith, J. Winefordner, Recent trends and the future of laserinduced plasma spectroscopy, TrAC Trends in Analytical Chemistry, 17 (1998) 453-461. [3] M. Díaz, C.E. Díaz, R.G. Álvarez, A. González, L. Castillo, A. González-Coloma, G. Seoane, C. Rossini, Differential anti-insect activity of natural products isolated from Dodonaea viscosa Jacq.(Sapindaceae), Journal of plant protection research, 55 (2015) 172-178. [4] Y.-I. Lee, K. Song, J. Sneddon, Laser-induced breakdown spectrometry, Nova Publishers2000. [5] J. Sneddon, Y.-I. Lee, Laser-induced breakdown spectrometry, Current Topics in Analytical Chemistry, 4 (2004) 111-118. [6] C. Latkoczy, T. Ghislain, Simultaneous LIBS and LA-ICP-MS analysis of industrial samples, Journal of analytical atomic spectrometry, 21 (2006) 1152-1160.

58

[7] L.J. Radziemski, From LASER to LIBS, the path of technology development, Spectrochimica Acta Part B: Atomic Spectroscopy, 57 (2002) 1109-1113. [8] F. Weritz, D. Schaurich, G. Wilsch, J. Wöstmann, H. Wiggenhauser, Laser induced breakdown spectroscopy as a tool for the characterization and sorting of concrete waste material in view of high-order re-use, International Symposium Non-Destructive Testing in Civil Engineering (NDT-CE) in Berlin, Germany, 2003. [9] T. Gunaratne, M. Kangas, S. Singh, A. Gross, M. Dantus, Influence of bandwidth and phase shaping on laser induced breakdown spectroscopy with ultrashort laser pulses, Chemical Physics Letters, 423 (2006) 197-201. [10] B. Le Drogoff, J. Margot, F. Vidal, S. Laville, M. Chaker, M. Sabsabi, T. Johnston, O. Barthélemy, Influence of the laser pulse duration on laser-produced plasma properties, Plasma Sources Science and Technology, 13 (2004) 223. [11] B. Le Drogoff, M. Chaker, J. Margot, M. Sabsabi, O. Barthélemy, T. Johnston, S. Laville, F. Vidal, Influence of the laser pulse duration on spectrochemical analysis of solids by laser-induced plasma spectroscopy, Applied spectroscopy, 58 (2004) 122-129. [12] S.M. Angel, D.N. Stratis, K.L. Eland, T. Lai, M.A. Berg, D.M. Gold, LIBS using dual-and ultra-short laser pulses, Fresenius' journal of analytical chemistry, 369 (2001) 320-327. [13] A. Lenk, T. Witke, G. Granse, Density and electron temperature of laser induced plasma—a comparison of different investigation methods, Applied surface science, 96 (1996) 195-198. [14] K. Song, Y.-I. Lee, J. Sneddon, Recent developments in instrumentation for laser induced breakdown spectroscopy, Applied Spectroscopy Reviews, 37 (2002) 89-117.

59

[15] W.B. Lee, J. Wu, Y.I. Lee, J. Sneddon, Recent applications of laser‐induced breakdown spectrometry: a review of material approaches, Applied Spectroscopy Reviews, 39 (2004) 27-97. [16] R. Goodacre, S. Vaidyanathan, G. Bianchi, D.B. Kell, Metabolic profiling using direct infusion electrospray ionisation mass spectrometry for the characterisation of olive oils, Analyst, 127 (2002) 1457-1462. [17] D.W. Hahn, N. Omenetto, Laser-induced breakdown spectroscopy (LIBS), part I: review of basic diagnostics and plasma–particle interactions: still-challenging issues within the analytical plasma community, Applied spectroscopy, 64 (2010) 335A-366A. [18] D.W. Hahn, N. Omenetto, Laser-induced breakdown spectroscopy (LIBS), part II: review of instrumental and methodological approaches to material analysis and applications to different fields, Applied spectroscopy, 66 (2012) 347-419. [19] B. Kearton, Y. Mattley, Laser-induced breakdown spectroscopy: Sparking new applications, Nature photonics, 2 (2008) 537. [20] D.A. Cremers, F.Y. Yueh, J.P. Singh, H. Zhang, Laser‐induced breakdown spectroscopy, elemental analysis, Encyclopedia of Analytical Chemistry: Applications, Theory and Instrumentation, DOI (2006). [21] R. Gaudiuso, M. Dell’Aglio, O.D. Pascale, G.S. Senesi, A.D. Giacomo, Laser induced breakdown spectroscopy for elemental analysis in environmental, cultural heritage and space applications: a review of methods and results, Sensors, 10 (2010) 7434-7468. [22] D. Bulajic, M. Corsi, G. Cristoforetti, S. Legnaioli, V. Palleschi, A. Salvetti, E. Tognoni, A procedure for correcting self-absorption in calibration free-laser induced breakdown spectroscopy, Spectrochimica Acta Part B: Atomic Spectroscopy, 57 (2002) 339-353.

60

[23] J.M. Anzano, M.A. Villoria, A. Ruíz-Medina, R.J. Lasheras, Laser-induced breakdown spectroscopy for quantitative spectrochemical analysis of geological materials: Effects of the matrix and simultaneous determination, Analytica chimica acta, 575 (2006) 230-235. [24] A.W. Miziolek, V. Palleschi, I. Schechter, Laser induced breakdown spectroscopy, Cambridge university press2006. [25] T.H. Maiman, Optical maser action in ruby, Advances in Quantum Electronics, 1961, pp. 91. [26] K. Giroux, Étude critique de la densité électronique et des températures (excitation et ionisation) d'un plasma d'aluminium induit par laser, DOI (2010). [27] H. Moenke, L. Moenke-Blankenburg, Laser micro-spectrochemical analysis, Crane, Russak1973. [28] K.Y. Yamamoto, D.A. Cremers, M.J. Ferris, L.E. Foster, Detection of metals in the environment using a portable laser-induced breakdown spectroscopy instrument, Applied Spectroscopy, 50 (1996) 222-233. [29] A. Jurado-López, M.L. De Castro, Rank correlation of laser-induced breakdown spectroscopic data for the identification of alloys used in jewelry manufacture, Spectrochimica Acta Part B: Atomic Spectroscopy, 58 (2003) 1291-1299. [30] J. Gruber, J. Heitz, H. Strasser, D. Bäuerle, N. Ramaseder, Rapid in-situ analysis of liquid steel by laser-induced breakdown spectroscopy, Spectrochimica Acta Part B: Atomic Spectroscopy, 56 (2001) 685-693. [31] A. De Giacomo, M. Dell’Aglio, O. De Pascale, R. Gaudiuso, R. Teghil, A. Santagata, G. Parisi, ns-and fs-LIBS of copper-based-alloys: A different approach, Applied surface science, 253 (2007) 7677-7681.

61

[32] A. Giakoumaki, K. Melessanaki, D. Anglos, Laser-induced breakdown spectroscopy (LIBS) in archaeological science—applications and prospects, Analytical and bioanalytical chemistry, 387 (2007) 749-760. [33] G. Senesi, M. Dell’Aglio, R. Gaudiuso, A. De Giacomo, C. Zaccone, O. De Pascale, T. Miano, M. Capitelli, Heavy metal concentrations in soils as determined by laserinduced breakdown spectroscopy (LIBS), with special emphasis on chromium, Environmental research, 109 (2009) 413-420. [34] M.E. Asgill, D.W. Hahn, Particle size limits for quantitative aerosol analysis using laser-induced breakdown spectroscopy: Temporal considerations, Spectrochimica Acta Part B: Atomic Spectroscopy, 64 (2009) 1153-1158. [35] L. Zimmer, S. Tachibana, Laser induced plasma spectroscopy for local equivalence ratio measurements in an oscillating combustion environment, Proceedings of the combustion institute, 31 (2007) 737-745. [36] M. Lawrence-Snyder, J. Scaffidi, S.M. Angel, A.P. Michel, A.D. Chave, Sequentialpulse laser-induced breakdown spectroscopy of high-pressure bulk aqueous solutions, Applied spectroscopy, 61 (2007) 171-176. [37] W. Lei, V. Motto-Ros, M. Boueri, Q. Ma, D. Zhang, L. Zheng, H. Zeng, J. Yu, Time-resolved

characterization

of

laser-induced

plasma

from

fresh

potatoes,

Spectrochimica Acta Part B: Atomic Spectroscopy, 64 (2009) 891-898. [38] A. Segnini, A.A.P. Xavier, P.L. Otaviani-Junior, E.C. Ferreira, A.M. Watanabe, M.A. Sperança, G. Nicolodelli, P.R. Villas-Boas, P.P.A. Oliveira, D.M.B.P. Milori, Physical and chemical matrix effects in soil carbon quantification using laser-induced breakdown spectroscopy, American Journal of Analytical Chemistry, DOI (2014) 722729.

62

[39] G.G.A. de Carvalho, D. Santos Jr, M. da Silva Gomes, L.C. Nunes, M.B.B. Guerra, F.J. Krug, Influence of particle size distribution on the analysis of pellets of plant materials by laser-induced breakdown spectroscopy, Spectrochimica Acta Part B: Atomic Spectroscopy, 105 (2015) 130-135. [40] A. Khumaeni, Z.S. Lie, H. Niki, K.H. Kurniawan, E. Tjoeng, Y.I. Lee, K. Kurihara, Y. Deguchi, K. Kagawa, Direct analysis of powder samples using transversely excited atmospheric CO2 laser-induced gas plasma at 1 atm, Analytical and bioanalytical chemistry, 400 (2011) 3279-3287. [41] E.J. Judge, J.E. Barefield II, J.M. Berg, S.M. Clegg, G.J. Havrilla, V.M. Montoya, L.A. Le, L.N. Lopez, Laser-induced breakdown spectroscopy measurements of uranium and thorium powders and uranium ore, Spectrochimica Acta Part B: Atomic Spectroscopy, 83 (2013) 28-36. [42] A. Ciucci, M. Corsi, V. Palleschi, S. Rastelli, A. Salvetti, E. Tognoni, New procedure for quantitative elemental analysis by laser-induced plasma spectroscopy, Applied spectroscopy, 53 (1999) 960-964. [43] K.K. Herrera, E. Tognoni, I.B. Gornushkin, N. Omenetto, B.W. Smith, J. Winefordner, Comparative study of two standard-free approaches in laser-induced breakdown spectroscopy as applied to the quantitative analysis of aluminum alloy standards under vacuum conditions, Journal of Analytical Atomic Spectrometry, 24 (2009) 426-438. [44] M. Shah, A. Pulhani, G. Gupta, B. Suri, Quantitative elemental analysis of steel using calibration-free laser-induced breakdown spectroscopy, Applied optics, 51 (2012) 4612-4621.

63

[45] Q. WANG, Y.-x. LIANG, Y. YANG, B. WU, Quantitative analysis of slag by calibration-free laser-induced breakdown spectroscopy, Spectroscopy and Spectral Analysis, 31 (2011) 3289-3293. [46] G. Cristoforetti, S. Legnaioli, V. Palleschi, A. Salvetti, E. Tognoni, Effect of target composition on the emission enhancement observed in Double-Pulse Laser-Induced Breakdown Spectroscopy, Spectrochimica Acta Part B: Atomic Spectroscopy, 63 (2008) 312-323. [47] B. Piccolo, R.T. O’Connor, Atomic absorption spectroscopy, Journal of the American Oil Chemists' Society, 45 (1968) 789-792. [48] R. García, A. Báez, Atomic absorption spectrometry (AAS), Atomic absorption spectroscopy, IntechOpen2012. [49] E.Z. Jahromi, A. Bidari, Y. Assadi, M.R.M. Hosseini, M.R. Jamali, Dispersive liquid–liquid microextraction combined with graphite furnace atomic absorption spectrometry: Ultra trace determination of cadmium in water samples, Analytica Chimica Acta, 585 (2007) 305-311. [50] G.D. Christian, F.J. Feldman, A comparison study of detection limits using flameemission spectroscopy with the nitrous oxide–acetylene flame and atomic-absorption spectroscopy, Applied Spectroscopy, 25 (1971) 660-663. [51] G. Bekefi, Principles of laser plasmas, New York, Wiley-Interscience, 1976. 712 p, DOI (1976). [52] J.D. Winefordner, I.B. Gornushkin, T. Correll, E. Gibb, B.W. Smith, N. Omenetto, Comparing several atomic spectrometric methods to the super stars: special emphasis on laser induced breakdown spectrometry, LIBS, a future super star, Journal of Analytical Atomic Spectrometry, 19 (2004) 1061-1083.

64

[53] A. Seubert, On-line coupling of ion chromatography with ICP–AES and ICP–MS, TrAC Trends in Analytical Chemistry, 20 (2001) 274-287. [54] F.Y. Yueh, J.P. Singh, H. Zhang, Laser‐Induced Breakdown Spectroscopy, Elemental Analysis, Encyclopedia of analytical chemistry, DOI (2000). [55] M. Mantler, M. Schreiner, X‐ray fluorescence spectrometry in art and archaeology, X‐Ray Spectrometry: An International Journal, 29 (2000) 3-17. [56] S. Ridolfi, Portable X-ray Fluorescence Spectrometry for the analyses of Cultural Heritage, IOP Conference Series: Materials Science and Engineering, IOP Publishing, 2012, pp. 012001. [57] B. Liss, S. Stout, Materials Characterization for Cultural Heritage: XRF Case Studies in Archaeology and Art, Heritage and Archaeology in the DigitalAge, Springer2017, pp. 49-65. [58] N. Carmona, I. Ortega-Feliu, B. Gomez-Tubio, M. Villegas, Advantages and disadvantages of PIXE/PIGE, XRF and EDX spectrometries applied to archaeometric characterisation of glasses, Materials Characterization, 61 (2010) 257-267. [59] M.C. Schlegel, U. Mueller, K. Malaga, U. Panne, F. Emmerling, Spatially resolved investigation of complex multi-phase systems using µXRF, SEM-EDX and high resolution SyXRD, Cement and Concrete Composites, 37 (2013) 241-245. [60] P. Echlin, C. Fiori, J. Goldstein, D.C. Joy, D.E. Newbury, Advanced scanning electron microscopy and X-ray microanalysis, Springer Science & Business Media2013. [61] C. Davies, H. Telle, D. Montgomery, R. Corbett, Quantitative analysis using remote laser-induced breakdown spectroscopy (LIBS), Spectrochimica Acta Part B: Atomic Spectroscopy, 50 (1995) 1059-1075.

65

[62] R. Murray, D.J. Miller, K. Kryc, Analysis of major and trace elements in rocks, sediments, and interstitial waters by inductively coupled plasma–atomic emission spectrometry (ICP-AES), DOI (2000). [63] X. Hou, B.T. Jones, Inductively coupled plasma/optical emission spectrometry, Encyclopedia of analytical chemistry, 11 (2000) 9468-9485. [64] R. Kägi, A. Ulrich, B. Sinnet, R. Vonbank, A. Wichser, S. Zuleeg, H. Simmler, S. Brunner, H. Vonmont, M. Burkhardt, Synthetic TiO 2 nanoparticle emission from exterior facades into the aquatic environment, Environmental pollution, 156 (2008) 233239. [65] M. Murillo, J. Chirinos, Use of emulsion systems for the determination of sulfur, nickel and vanadium in heavy crude oil samples by inductively coupled plasma atomic emission spectrometry, Journal of Analytical Atomic Spectrometry, 9 (1994) 237-240. [66] S.A. Darke, S.E. Long, C.J. Pickford, J.F. Tyson, Laser ablation system for solid sample analysis by inductively coupled plasma atomic emission spectrometry, Journal of Analytical Atomic Spectrometry, 4 (1989) 715-719. [67] K.F. Khan, Application, principle and operation of ICP-OES in pharmaceutical analysis, DOI (2019). [68] A. Montaser, D.W. Golightly, Inductively coupled plasmas in analytical atomic spectrometry, DOI (1987). [69] K. Janssens, G. Vittiglio, I. Deraedt, A. Aerts, B. Vekemans, L. Vincze, F. Wei, I. De Ryck, O. Schalm, F. Adams, Use of microscopic XRF for non‐destructive analysis in art and archaeometry, X‐Ray Spectrometry: An International Journal, 29 (2000) 73-91. [70] G. Paternoster, R. Rinzivillo, F. Nunziata, E.M. Castellucci, C. Lofrumento, A. Zoppi, A.C. Felici, G. Fronterotta, C. Nicolais, M. Piacentini, Study on the technique of

66

the Roman age mural paintings by micro-XRF with polycapillary conic collimator and micro-Raman analyses, Journal of Cultural Heritage, 6 (2005) 21-28. [71] M.A. Denecke, A. Somogyi, K. Janssens, R. Simon, K. Dardenne, U. Noseck, Microanalysis (micro-XRF, micro-XANES, and micro-XRD) of a tertiary sediment using microfocused synchrotron radiation, Microscopy and Microanalysis, 13 (2007) 165-172. [72] J. Dik, K. Janssens, G. Van Der Snickt, L. van der Loeff, K. Rickers, M. Cotte, Visualization of a lost painting by Vincent van Gogh using synchrotron radiation based X-ray fluorescence elemental mapping, Analytical chemistry, 80 (2008) 6436-6442. [73] M. Alfeld, J.V. Pedroso, M. van Eikema Hommes, G. Van der Snickt, G. Tauber, J. Blaas, M. Haschke, K. Erler, J. Dik, K. Janssens, A mobile instrument for in situ scanning macro-XRF investigation of historical paintings, Journal of Analytical Atomic Spectrometry, 28 (2013) 760-767. [74] C. Ruberto, A. Mazzinghi, M. Massi, L. Castelli, C. Czelusniak, L. Palla, N. Gelli, M. Betuzzi, A. Impallaria, R. Brancaccio, Imaging study of Raffaello's “La Muta” by a portable XRF spectrometer, Microchemical Journal, 126 (2016) 63-69. [75] S. Buckley, LIBS Basics, Part I: Measurement Physics and Implementation, Spectroscopy, 29 (2014) 22-29. [76] D. Cremers, L. Radziemski, Basics of the LIBS Plasma, Laser-Induced Breakdown Spectroscopy (LIBS): Fundamentals and Applications, DOI (2006) 23-50. [77] S. Abdulmadjid, M. Suliyanti, K. Kurniawan, T. Lie, M. Pardede, R. Hedwig, K. Kagawa, M. Tjia, An improved approach for hydrogen analysis in metal samples using single laser-induced gas plasma and target plasma at helium atmospheric pressure, Applied Physics B, 82 (2006) 161-166. [78] L.J. Radziemski, T.R. Loree, D.A. Cremers, N.M. Hoffman, Time-resolved laserinduced breakdown spectrometry of aerosols, Analytical chemistry, 55 (1983) 1246-1252.

67

[79] S. Palanco, C. López-Moreno, J.J. Laserna, Design, construction and assessment of a field-deployable laser-induced breakdown spectrometer for remote elemental sensing, Spectrochimica Acta Part B: Atomic Spectroscopy, 61 (2006) 88-95. [80] V.K. Singh, A.K. Rai, Prospects for laser-induced breakdown spectroscopy for biomedical applications: a review, Lasers in medical science, 26 (2011) 673-687. [81] R.C. Wiens, S.K. Sharma, J. Thompson, A. Misra, P.G. Lucey, Joint analyses by laser-induced breakdown spectroscopy (LIBS) and Raman spectroscopy at stand-off distances, Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, 61 (2005) 2324-2334. [82] K. Meissner, T. Lippert, A. Wokaun, D. Guenther, Analysis of trace metals in comparison of laser-induced breakdown spectroscopy with LA-ICP-MS, Thin Solid Films, 453 (2004) 316-322. [83] M. Markiewicz-Keszycka, X. Cama-Moncunill, M.P. Casado-Gavalda, Y. Dixit, R. Cama-Moncunill, P.J. Cullen, C. Sullivan, Laser-induced breakdown spectroscopy (LIBS) for food analysis: a review, Trends in Food Science & Technology, 65 (2017) 8093. [84] M. Simileanu, R. Radvan, N. Puscas, Underwater LIBS investigations setup for metals' identification, University Politehnica Of Bucharest Scientific Bulletin-Series AApplied Mathematics And Physics, 72 (2010) 209-216. [85] R. Noll, Laser-induced breakdown spectroscopy,

Laser-Induced Breakdown

Spectroscopy, Springer2012, pp. 7-15. [86] J. Rakovský, P. Čermák, O. Musset, P. Veis, A review of the development of portable laser induced breakdown spectroscopy and its applications, Spectrochimica Acta Part B: Atomic Spectroscopy, 101 (2014) 269-287.

68

[87] J. Sneddon, Y.-I. Lee, Laser-induced breakdown spectrometry, The Chemical Educator, 3 (1998) 1-7. [88] W. Lei, J. El Haddad, V. Motto-Ros, N. Gilon-Delepine, A. Stankova, Q. Ma, X. Bai, L. Zheng, H. Zeng, J. Yu, Comparative measurements of mineral elements in milk powders with laser-induced breakdown spectroscopy and inductively coupled plasma atomic emission spectroscopy, Analytical and bioanalytical chemistry, 400 (2011) 33033313. [89] Y. Liu, L. Gigant, M. Baudelet, M. Richardson, Correlation between laser-induced breakdown spectroscopy signal and moisture content, Spectrochimica Acta Part B: Atomic Spectroscopy, 73 (2012) 71-74. [90] Z. Abdel-Salam, J. Al Sharnoubi, M. Harith, Qualitative evaluation of maternal milk and commercial infant formulas via LIBS, Talanta, 115 (2013) 422-426. [91] M.-B.S. Andersen, J. Frydenvang, P. Henckel, Å. Rinnan, The potential of laserinduced breakdown spectroscopy for industrial at-line monitoring of calcium content in comminuted poultry meat, Food Control, 64 (2016) 226-233. [92] S. Beldjilali, D. Borivent, L. Mercadier, E. Mothe, G. Clair, J. Hermann, Evaluation of minor element concentrations in potatoes using laser-induced breakdown spectroscopy, Spectrochimica Acta Part B: Atomic Spectroscopy, 65 (2010) 727-733. [93] G. Kim, J. Kwak, J. Choi, K. Park, Detection of nutrient elements and contamination by pesticides in spinach and rice samples using laser-induced breakdown spectroscopy (LIBS), Journal of agricultural and food chemistry, 60 (2012) 718-724. [94] F. Ma, D. Dong, A measurement method on pesticide residues of apple surface based on laser-induced breakdown spectroscopy, Food analytical methods, 7 (2014) 1858-1865. [95] G. Galbács, A critical review of recent progress in analytical laser-induced breakdown spectroscopy, Analytical and bioanalytical chemistry, 407 (2015) 7537-7562.

69

[96] L. St-Onge, V. Detalle, M. Sabsabi, Enhanced laser-induced breakdown spectroscopy using the combination of fourth-harmonic and fundamental Nd: YAG laser pulses, Spectrochimica Acta Part B: Atomic Spectroscopy, 57 (2002) 121-135. [97] D. Santos Jr, L.C. Nunes, G.G.A. de Carvalho, M. da Silva Gomes, P.F. de Souza, F. de Oliveira Leme, L.G.C. dos Santos, F.J. Krug, Laser-induced breakdown spectroscopy for analysis of plant materials: a review, Spectrochimica Acta Part B: Atomic Spectroscopy, 71 (2012) 3-13. [98] J.P. Singh, S.N. Thakur, Laser-induced breakdown spectroscopy, Elsevier2007. [99] V. Detalle, R. Héon, M. Sabsabi, L. St-Onge, An evaluation of a commercial Echelle spectrometer with intensified charge-coupled device detector for materials analysis by laser-induced plasma spectroscopy, Spectrochimica Acta Part B: Atomic Spectroscopy, 56 (2001) 1011-1025. [100] V. Rai, Laser-induced breakdown spectroscopy: A versatile technique of elemental analysis and its applications, arXiv preprint arXiv:1407.0132, DOI (2014). [101] C. Gautier, P. Fichet, D. Menut, J.-L. Lacour, D. L'Hermite, J. Dubessy, Quantification of the intensity enhancements for the double-pulse laser-induced breakdown spectroscopy in the orthogonal beam geometry, Spectrochimica Acta Part B: Atomic Spectroscopy, 60 (2005) 265-276. [102] C. Gautier, P. Fichet, D. Menut, J.-L. Lacour, D. L'Hermite, J. Dubessy, Main parameters influencing the double-pulse laser-induced breakdown spectroscopy in the collinear beam geometry, Spectrochimica Acta Part B: Atomic Spectroscopy, 60 (2005) 792-804. [103] C. Gautier, P. Fichet, D. Menut, J.-L. Lacour, D. L'Hermite, J. Dubessy, Study of the double-pulse setup with an orthogonal beam geometry for laser-induced breakdown spectroscopy, Spectrochimica Acta Part B: Atomic Spectroscopy, 59 (2004) 975-986.

70

[104] J. Uebbing, J. Brust, W. Sdorra, F. Leis, K. Niemax, Reheating of a laser-produced plasma by a second pulse laser, Applied spectroscopy, 45 (1991) 1419-1423. [105] K. Elsayed, H. Imam, A. Harfoosh, Y. Hassebo, Y. Elbaz, M. Aziz, M. Mansour, Design and construction of Q-switched Nd: YAG laser system for LIBS measurements, Optics & Laser Technology, 44 (2012) 130-135. [106] D. Day, B. Connors, M. Jennings, J. Egan, K. Derman, P. Soucy, S. Moller, D. Sackett, A full featured handheld LIBS analyzer with early results for defense and security, Next-Generation Spectroscopic Technologies VIII, International Society for Optics and Photonics, 2015, pp. 948206. [107] R. Stoian, D. Ashkenasi, A. Rosenfeld, E. Campbell, Coulomb explosion in ultrashort pulsed laser ablation of Al 2 O 3, Physical review B, 62 (2000) 13167. [108] P. Lorazo, L.J. Lewis, M. Meunier, Short-pulse laser ablation of solids: from phase explosion to fragmentation, Physical review letters, 91 (2003) 225502. [109] L.J. Radziemski, D.A. Cremers, Handbook of laser induced breakdown spectroscopy, John Wiley & Sons, 1 (2006) 1-4. [110] D. Batani, C.J. Joachain, S. Martellucci, A.N. Chester, Atoms, solids, and plasmas in super-intense laser fields, Springer Science & Business Media2012. [111] C. Pasquini, J. Cortez, L. Silva, F.B. Gonzaga, Laser induced breakdown spectroscopy, Journal of the Brazilian Chemical Society, 18 (2007) 463-512. [112] A. De Giacomo, Experimental characterization of metallic titanium-laser induced plasma by time and space resolved optical emission spectroscopy, Spectrochimica Acta Part B: Atomic Spectroscopy, 58 (2003) 71-83. [113] M. Gondal, Y. Maganda, M. Dastageer, F. Al Adel, A. Naqvi, T. Qahtan, Detection of carcinogenic chromium in synthetic hair dyes using laser induced breakdown spectroscopy, Applied optics, 53 (2014) 1636-1643.

71

[114] I. Borgia, L.M. Burgio, M. Corsi, R. Fantoni, V. Palleschi, A. Salvetti, M.C. Squarcialupi, E. Tognoni, Self-calibrated quantitative elemental analysis by laser-induced plasma spectroscopy: application to pigment analysis, Journal of Cultural Heritage, 1 (2000) S281-S286. [115] H.-H. Ley, Analytical methods in plasma diagnostic by optical emission spectroscopy: A tutorial review, Journal of Science and Technology, 6 (2014). [116] D. Devia, L. Rodriguez-Restrepo, E. Restrepo-Parra, Methods employed in optical emission spectroscopy analysis: a review, Ingeniería y Ciencia, 11 (2015). [117] A.M. El Sherbini, A.A.S. Al Aamer, Measurement of plasma parameters in laserinduced breakdown spectroscopy using Si-lines, World Journal of Nano Science and Engineering, 2 (2012) 206. [118] J.A. Aguilera, C. Aragón, G. Cristoforetti, E. Tognoni, Application of calibrationfree laser-induced breakdown spectroscopy to radially resolved spectra from a copperbased alloy laser-induced plasma, Spectrochimica Acta Part B: Atomic Spectroscopy, 64 (2009) 685-689. [119] A.M. El Sherbini, A.A.S. Al Aamer, A.T. Hassan, T.M. El Sherbini, Measurements of plasma electron temperature utilizing magnesium lines appeared in laser produced aluminum plasma in air, Optics and Photonics Journal, 2 (2012) 278. [120] T. Takahashi, B. Thornton, K. Ohki, T. Sakka, Calibration-free analysis of immersed

brass

alloys using long-ns-duration pulse laser-induced breakdown

spectroscopy with and without correction for nonstoichiometric ablation, Spectrochimica Acta Part B: Atomic Spectroscopy, 111 (2015) 8-14. [121] I. Rehan, K. Rehan, S. Sultana, M.O. ul Haq, M.Z.K. Niazi, R. Muhammad, Spatial characterization of red and white skin potatoes using nano-second laser induced breakdown in air, The European Physical Journal Applied Physics, 73 (2016) 10701.

72

[122] A. Popov, T. Labutin, S. Zaytsev, N. Zorov, Experimental Stark parameters of Mn I lines in the y6P°→ a6S multiplet under conditions of “long” laser plasma, Optics and Spectroscopy, 123 (2017) 521-525. [123] E. Tognoni, G. Cristoforetti, S. Legnaioli, V. Palleschi, A. Salvetti, M. Müller, U. Panne, I. Gornushkin, A numerical study of expected accuracy and precision in calibration-free laser-induced breakdown spectroscopy in the assumption of ideal analytical plasma, Spectrochimica Acta Part B: Atomic Spectroscopy, 62 (2007) 12871302. [124] C. Aragón, J.A. Aguilera, Characterization of laser induced plasmas by optical emission spectroscopy: A review of experiments and methods, Spectrochimica Acta Part B: Atomic Spectroscopy, 63 (2008) 893-916. [125] V. Unnikrishnan, K. Alti, V. Kartha, C. Santhosh, G. Gupta, B. Suri, Measurements of plasma temperature and electron density in laser-induced copper plasma by timeresolved spectroscopy of neutral atom and ion emissions, Pramana, 74 (2010) 983-993. [126] G. Abdellatif, H. Imam, A study of the laser plasma parameters at different laser wavelengths, Spectrochimica Acta Part B: Atomic Spectroscopy, 57 (2002) 1155-1165. [127] N.M. Shaikh, B. Rashid, S. Hafeez, Y. Jamil, M. Baig, Measurement of electron density and temperature of a laser-induced zinc plasma, Journal of Physics D: Applied Physics, 39 (2006) 1384. [128] D. Cremers, L. Radziemski, Handbook of Laser-Induced Breakdown Spectroscopy. eBookMall, Inc, 2007. [129] M.A. Gigosos, M.Á. González, V.n. Cardeñoso, Computer simulated Balmeralpha,-beta and-gamma Stark line profiles for non-equilibrium plasmas diagnostics, Spectrochimica Acta Part B: Atomic Spectroscopy, 58 (2003) 1489-1504.

73

[130] M.A. Gondal, M.A. Shemis, A.A. Khalil, M.M. Nasr, B. Gondal, Laser produced plasma diagnosis of carcinogenic heavy metals in gallstones, Journal of Analytical Atomic Spectrometry, 31 (2016) 506-514. [131] H. Fu, J. Jia, H. Wang, Z. Ni, F. Dong, Calibration Methods of Laser-Induced Breakdown Spectroscopy, Calibration and Validation of Analytical Methods-A Sampling of Current Approaches, IntechOpen2017. [132] G. Bilge, B. Sezer, K.E. Eseller, H. Berberoğlu, H. Köksel, İ.H. Boyacı, Determination of Ca addition to the wheat flour by using laser-induced breakdown spectroscopy (LIBS), European Food Research and Technology, 242 (2016) 1685-1692. [133] M. da Silva Gomes, G.G.A. de Carvalho, D.S. Junior, F.J. Krug, A novel strategy for preparing calibration standards for the analysis of plant materials by laser-induced breakdown spectroscopy: A case study with pellets of sugar cane leaves, Spectrochimica Acta Part B: Atomic Spectroscopy, 86 (2013) 137-141. [134] S.-J. Choi, K.-J. Lee, J.J. Yoh, Quantitative laser-induced breakdown spectroscopy of standard reference materials of various categories, Applied Physics B, 113 (2013) 379388. [135] L.C. Trevizan, D. Santos Jr, R.E. Samad, N.D. Vieira Jr, L.C. Nunes, I.A. Rufini, F.J. Krug, Evaluation of laser induced breakdown spectroscopy for the determination of micronutrients in plant materials, Spectrochimica Acta Part B: Atomic Spectroscopy, 64 (2009) 369-377. [136] E.C. Ferreira, E.A. Menezes, W.O. Matos, D.M. Milori, A.R.A. Nogueira, L. Martin-Neto, Determination of Ca in breakfast cereals by laser induced breakdown spectroscopy, Food Control, 21 (2010) 1327-1330.

74

[137] G. Bilge, B. Sezer, K.E. Eseller, H. Berberoglu, A. Topcu, I.H. Boyaci, Determination of whey adulteration in milk powder by using laser induced breakdown spectroscopy, Food chemistry, 212 (2016) 183-188. [138] A. El Sherbini, T. El Sherbini, H. Hegazy, G. Cristoforetti, S. Legnaioli, L. Pardini, V. Palleschi, A. Salvetti, E. Tognoni, Measurement of the Stark Broadening of Atomic Emission Lines in Non–Optically Thin Plasmas by Laser‐Induced Breakdown Spectroscopy, Spectroscopy Letters, 40 (2007) 643-658. [139] C. Colon, G. Hatem, E. Verdugo, P. Ruiz, J. Campos, Measurement of the Stark broadening and shift parameters for several ultraviolet lines of singly ionized aluminum, Journal of applied physics, 73 (1993) 4752-4758. [140] J.B. Simeonsson, A.W. Miziolek, Time-resolved emission studies of ArF-laserproduced microplasmas, Applied optics, 32 (1993) 939-947. [141] D.K. Tripathi, V.P. Singh, S.M. Prasad, D.K. Chauhan, N.K. Dubey, A.K. Rai, Silicon-mediated alleviation of Cr (VI) toxicity in wheat seedlings as evidenced by chlorophyll florescence, laser induced breakdown spectroscopy and anatomical changes, Ecotoxicology and environmental safety, 113 (2015) 133-144. [142] T.A. Labutin, S.M. Zaytsev, A.M. Popov, N.B. Zorov, Carbon determination in carbon-manganese steels under atmospheric conditions by Laser-Induced Breakdown Spectroscopy, Optics express, 22 (2014) 22382-22387. [143] K. Rehan, I. Rehan, S. Sultana, M.Z. Khan, Z. Farooq, A. Mateen, M. Humayun, Determination of metals present in textile dyes using laser-induced breakdown spectroscopy and cross-validation using inductively coupled plasma/atomic emission spectroscopy, International Journal of Spectroscopy, 2017 (2017).

75

[144] M. Nasr, M. Gondal, M. Ahmed, M. Yousif, N. Al-Muslet, Direct spectral analysis of different gum Arabic samples using laser induced breakdown spectroscopy, AIP Conference Proceedings, AIP Publishing, 2018, pp. 020025. [145] C. Aragon, J. Bengoechea, J. Aguilera, Influence of the optical depth on spectral line emission from laser-induced plasmas, Spectrochimica Acta Part B: Atomic Spectroscopy, 56 (2001) 619-628. [146] M. Almessiere, R. Altuwiriqi, M. Gondal, R. AlDakheel, H. Alotaibi, Qualitative and quantitative analysis of human nails to find correlation between nutrients and vitamin D deficiency using LIBS and ICP-AES, Talanta, 185 (2018) 61-70. [147] I. Rehan, M. Gondal, K. Rehan, Determination of lead content in drilling fueled soil using laser induced spectral analysis and its cross validation using ICP/OES method, Talanta, 182 (2018) 443-449. [148] A.A.I. Khalil, M.A. Gondal, M. Shemis, I.S. Khan, Detection of carcinogenic metals in kidney stones using ultraviolet laser-induced breakdown spectroscopy, Applied optics, 54 (2015) 2123-2131. [149] H.-J. Kunze, Introduction to plasma spectroscopy, Springer Science & Business Media2009. [150] J. Iqbal, S. Mahmood, I. Tufail, H. Asghar, R. Ahmed, M. Baig, On the use of laser induced breakdown spectroscopy to characterize the naturally existing crystal in Pakistan and its optical emission spectrum, Spectrochimica Acta Part B: Atomic Spectroscopy, 111 (2015) 80-86. [151] S. Zhang, X. Wang, M. He, Y. Jiang, B. Zhang, W. Hang, B. Huang, Laser-induced plasma temperature, Spectrochimica Acta Part B: Atomic Spectroscopy, 97 (2014) 13-33.

76

[152] A. Sarkar, M. Singh, Laser-induced plasma electron number density: Stark broadening method versus the Saha–Boltzmann equation, Plasma Science and Technology, 19 (2017) 025403. [153] E. Asamoah, Y. Hongbing, Influence of laser energy on the electron temperature of a laser-induced Mg plasma, Applied Physics B, 123 (2017) 22. [154] S. Yao, J. Zhang, X. Gao, S. Zhao, J. Lin, The effect of pulse energy on plasma characteristics of femtosecondfilament assistedablation of soil, Optics Communications, 425 (2018) 152-156. [155] M. Hanif, M. Salik, M. Baig, Diagnostic Study of Nickel Plasma Produced by Fundamental (1064 nm) and Second Harmonics (532 nm) of an Nd: YAG Laser, Journal of Modern Physics, 3 (2012) 1663. [156] J. Peng, F. Liu, T. Shen, L. Ye, W. Kong, W. Wang, X. Liu, Y. He, Comparative Study of the Detection of Chromium Content in Rice Leaves by 532 nm and 1064 nm Laser-Induced Breakdown Spectroscopy, Sensors, 18 (2018) 621. [157] I. Rehan, M.Z. Khan, K. Rehan, A. Mateen, M.A. Farooque, S. Sultana, Z. Farooq, Determination of toxic and essential metals in rock and sea salts using pulsed nanosecond laser-induced breakdown spectroscopy, Applied optics, 57 (2018) 295-301. [158] J. Aguilera, C. Aragon, F. Penalba, Plasma shielding effect in laser ablation of metallic samples and its influence on LIBS analysis, Applied surface science, 127 (1998) 309-314. [159] G. Cristoforetti, S. Legnaioli, V. Palleschi, A. Salvetti, E. Tognoni, Influence of ambient gas pressure on laser-induced breakdown spectroscopy technique in the parallel double-pulse configuration, Spectrochimica Acta Part B: Atomic Spectroscopy, 59 (2004) 1907-1917.

77

[160] P. Benedetti, G. Cristoforetti, S. Legnaioli, V. Palleschi, L. Pardini, A. Salvetti, E. Tognoni, Effect of laser pulse energies in laser induced breakdown spectroscopy in double-pulse configuration, Spectrochimica Acta Part B: Atomic Spectroscopy, 60 (2005) 1392-1401. [161] B. Castle, K. Visser, B. Smith, J. Winefordner, Spatial and temporal dependence of lead emission in laser-induced breakdown spectroscopy, Applied spectroscopy, 51 (1997) 1017-1024. [162] I.V. Cravetchi, M.T. Taschuk, Y.Y. Tsui, R. Fedosejevs, Evaluation of femtosecond LIBS for spectrochemical microanalysis of aluminium alloys, Analytical and bioanalytical chemistry, 385 (2006) 287-294. [163] S. Grégoire, V. Motto-Ros, Q. Ma, W. Lei, X. Wang, F. Pelascini, F. Surma, V. Detalle, J. Yu, Correlation between native bonds in a polymeric material and molecular emissions from the laser-induced plasma observed with space and time resolved imaging, Spectrochimica Acta Part B: Atomic Spectroscopy, 74 (2012) 31-37. [164] H. Liu, B.S. Truscott, M.N. Ashfold, Position-and time-resolved Stark broadening diagnostics of a non-thermal laser-induced plasma, Plasma Sources Science and Technology, 25 (2015) 015006. [165] X. Wang, B. Man, G. Wang, Z. Zhao, Y. Liao, B. Xu, Y. Xia, L. Mei, X. Hu, Optical spectroscopy of plasma produced by laser ablation of Ti alloy in air, Journal of applied physics, 80 (1996) 1783-1786. [166] V. Dann, M. Mathew, V. Nampoori, C. Vallabhan, V. Nandakumaran, P. Radhakrishnan, Spectral characterization of laser induced plasma from titanium dioxide, Plasma Science and Technology, 9 (2007) 456. [167] M. Salik, M. Hanif, J. Wang, X. Zhang, Plasma properties of nano-second laser ablated iron target in air, International Journal of Physical Sciences, 8 (2013) 1738-1745.

78

[168] M. Cirisan, M. Cvejić, M. Gavrilović, S. Jovićević, N. Konjević, J. Hermann, Stark broadening measurement of Al II lines in a laser-induced plasma, Journal of Quantitative Spectroscopy And Radiative Transfer, 133 (2014) 652-662. [169] N. Shaikh, S. Hafeez, B. Rashid, M. Baig, Spectroscopic studies of laser induced aluminum plasma using fundamental, second and third harmonics of a Nd: YAG laser, The European Physical Journal D, 44 (2007) 371-379. [170] A. Chen, Y. Jiang, T. Wang, J. Shao, M. Jin, Comparison of plasma temperature and electron density on nanosecond laser ablation of Cu and nano-Cu, Physics of Plasmas, 22 (2015) 033301. [171] M. Fahad, M. Abrar, Laser-induced breakdown spectroscopic studies of calcite (CaCO3) marble using the fundamental (1064 nm) and second (532 nm) harmonic of a Nd: YAG laser, Laser Physics, 28 (2018) 085701. [172] M. Hanif, M. Salik, M. Baig, Quantitative studies of copper plasma using laser induced breakdown spectroscopy, Optics and Lasers in Engineering, 49 (2011) 14561461. [173] R. Barbini, F. Colao, R. Fantoni, A. Palucci, S. Ribezzo, H. Van der Steen, M. Angelone, Semi-quantitative time resolved LIBS measurements, Applied Physics B: Lasers and Optics, 65 (1997) 101-107. [174] X. Mao, X. Zeng, S.-B. Wen, R.E. Russo, Time-resolved plasma properties for double pulsed laser-induced breakdown spectroscopy of silicon, Spectrochimica Acta Part B: Atomic Spectroscopy, 60 (2005) 960-967. [175] R. Viskup, B. Praher, T. Linsmeyer, H. Scherndl, J. Pedarnig, J. Heitz, Influence of pulse-to-pulse delay for 532 nm double-pulse laser-induced breakdown spectroscopy of technical polymers, Spectrochimica Acta Part B: Atomic Spectroscopy, 65 (2010) 935942.

79

[176] R. Rezk, A. Galmed, M. Abdelkreem, N.A. Ghany, M. Harith, Quantitative analysis of Cu and Co adsorbed on fish bones via laser-induced breakdown spectroscopy, Optics & Laser Technology, 83 (2016) 131-139. [177] W. Luo, J. Tang, C. Gao, H. Wang, W. Zhao, Spectroscopic analysis of element concentrations in aluminum alloy using nanosecond laser-induced breakdown spectroscopy, Physica Scripta, 81 (2010) 065302. [178] C. Aragón, J. Aguilera, J. Manrique, Measurement of Stark broadening parameters of Fe II and Ni II spectral lines by laser induced breakdown spectroscopy using fused glass samples, Journal of Quantitative Spectroscopy and Radiative Transfer, 134 (2014) 39-45. [179] J. Becker, P. Skrodzki, P. Diwakar, A. Hassanein, Double-pulse neodymium YAG/Carbon dioxide laser-induced breakdown spectroscopy for excitation of bulk and trace analytes, Spectroscopy Letters, 49 (2016) 276-284. [180] M. Burger, J. Hermann, Stark broadening measurements in plasmas produced by laser ablation of hydrogen containing compounds, Spectrochimica Acta Part B: Atomic Spectroscopy, 122 (2016) 118-126. [181] S. Amor, T. Kerdja, S. Abdelli, S. Lafane, S. Messaoud-Aberkane, Electron Density and Temperature Diagnostic of Laser Created Titanium Plasma, CENTRE DE DEVELOPPEMENT DES TECHNIQUES AVANCEES ALGIERS (ALGERIA), 2003. [182] A. Khalil, M. Richardson, L. Johnson, M. Gondal, Titanium plasma spectroscopy studies under double pulse laser excitation, Laser physics, 19 (2009) 1981. [183] P. Radhakrishnan, V. Nampoori, C. Girijavallabhan, V. Nandakumaran, V. Dann, M. Mathew, Spectral Characterization of Laser Induced Plasma from Titanium Dioxide, DOI (2007).

80

[184] M. Gondal, Y. Maganda, M. Dastageer, F. Al-Adel, A. Naqvi, Study of temporal evolution of electron density and temperature for atmospheric plasma generated from fluid samples using laser induced breakdown spectroscopy, Electronics, Communications and Photonics Conference (SIECPC), 2013 Saudi International, IEEE, 2013, pp. 1-4. [185] S. Harilal, B. O’Shay, Y. Tao, M.S. Tillack, Ambient gas effects on the dynamics of laser-produced tin plume expansion, Journal of Applied Physics, 99 (2006) 083303. [186] A. Bogaerts, Z. Chen, Effect of laser parameters on laser ablation and laser-induced plasma formation: A numerical modeling investigation, Spectrochimica Acta Part B: Atomic Spectroscopy, 60 (2005) 1280-1307. [187] J. Green, V. Ovchinnikov, R. Evans, K. Akli, H. Azechi, F. Beg, C. Bellei, R. Freeman, H. Habara, R. Heathcote, Effect of laser intensity on fast-electron-beam divergence in solid-density plasmas, Physical review letters, 100 (2008) 015003. [188] J. White, P. Dunne, P. Hayden, F. O’Reilly, G. O’sullivan, Optimizing 13.5 nm laser-produced tin plasma emission as a function of laser wavelength, Applied physics letters, 90 (2007) 181502. [189] N. Ahmed, M. Abdullah, R. Ahmed, N.K. Piracha, M.A. Baig, Quantitative analysis of a brass alloy using CF-LIBS and a laser ablation time-of-flight mass spectrometer, Laser Physics, 28 (2017) 016002. [190] M. Hanif, M. Salik, M. Baig, Plasma diagnostic study of nickel alloy generated by fundamental and second harmonics of a ND: YAG laser, Plasma Science (ICOPS), 2012 Abstracts IEEE International Conference on, IEEE, 2012, pp. 2P-122-122P-122. [191] A. HAYAT, S. BAsHIR, K. VAHMOOD, PRESSURE GRADIENT EFFECTS ON LASER-LLLLaLLL LLL GGGGGGGG LL GGG LLLLLLGGG GG GG PLASMA, DOI.

81

[192] C.G. Parigger, A.C. Woods, D.M. Surmick, L.D. Swafford, M.J. Witte, Measurements of ultra-violet titanium lines in laser-ablation plasma, Spectrochimica Acta Part B: Atomic Spectroscopy, 99 (2014) 15-19. [193] H.M. Velioglu, B. Sezer, G. Bilge, S.E. Baytur, I.H. Boyaci, Identification of offal adulteration in beef by laser induced breakdown spectroscopy (LIBS), Meat science, 138 (2018) 28-33. [194] A.A.I. Khalil, O.A. Labib, Detection of micro-toxic elements in commercial coffee brands using optimized dual-pulsed laser-induced spectral analysis spectrometry, Applied optics, 57 (2018) 6729-6741. [195] Z. Peichao, S. Minjie, W. Jinmei, L. Hongdi, The spectral emission characteristics of laser induced plasma on tea samples, Plasma Science and Technology, 17 (2015) 664. [196] B.A. Alfarraj, H.K. Sanghapi, C.R. Bhatt, F.Y. Yueh, J.P. Singh, Qualitative Analysis of Dairy and Powder Milk Using Laser-Induced Breakdown Spectroscopy (LIBS), Applied spectroscopy, 72 (2018) 89-101. [197] A. Mehder, Y. Habibullah, M. Gondal, U. Baig, Qualitative and quantitative spectro-chemical analysis of dates using UV-pulsed laser induced breakdown spectroscopy and inductively coupled plasma mass spectrometry, Talanta, 155 (2016) 124-132. [198] W. Luo, X. Zhao, H. Zhu, D. Xie, J. Liu, P. Jin, Spectral analysis of Qinling Mountain rock using laser induced breakdown spectroscopy, Journal of Modern Optics, 60 (2013) 1905-1909. [199] S. Xu, W. Duan, R. Ning, Q. Li, R. Jiang, Laser-Induced Breakdown Spectroscopy and Plasma Characterization Generated by Long-Pulse Laser on Soil Samples, Journal of Applied Spectroscopy, 84 (2017) 35-39.

82

[200] V. Lazic, F. Colao, R. Fantoni, V. Spizzichino, S. Jovićević, Underwater sediment analyses by laser induced breakdown spectroscopy and calibration procedure for fluctuating plasma parameters, Spectrochimica Acta Part B: Atomic Spectroscopy, 62 (2007) 30-39. [201] M. Fahad, Z. Farooq, M. Abrar, K.H. Shah, T. Iqbal, S. Saeed, Elemental analysis of limestone by laser-induced breakdown spectroscopy, scanning electron microscopy coupled with energy dispersive x-ray spectroscopy and electron probe microanalysis, Laser Physics, 28 (2018) 125701. [202] D. Díaz, A. Molina, D. Hahn, Effect of laser irradiance and wavelength on the analysis of gold-and silver-bearing minerals with laser-induced breakdown spectroscopy, Spectrochimica Acta Part B: Atomic Spectroscopy, 145 (2018) 86-95. [203] S. Mahmood, M. Akhtar, A. Jabbar, J. Iqbal, M. Baig, Elemental analysis of stones using laser-induced breakdown spectroscopy, IEEE Transactions on Plasma Science, 43 (2015) 2636-2641. [204] Z. Haider, J. Ali, M. Arab, Y.b. Munajat, S. Roslan, R. Kamarulzman, N. Bidin, Plasma diagnostics and determination of lead in soil and phaleria macrocarpa leaves by ungated laser induced breakdown spectroscopy, Analytical Letters, 49 (2016) 808-817. [205] I. Rehan, R. Muhammad, K. Rehan, K. Karim, S. Sultana, Quantitative analysis of Shilajit using laser-induced breakdown spectroscopy and inductively coupled plasma/optical emission spectroscopy, J Nutr Food Sci, 7 (2017) 2. [206] N. Ahmad, R. Ahmed, Z.A. Umar, U. Liaqat, U. Manzoor, M.A. Baig, Qualitative and quantitative analyses of copper ores collected from Baluchistan, Pakistan using LIBS and LA-TOF-MS, Applied Physics B, 124 (2018) 160. [207] D.D. Pace, R.E. Miguel, H.O. Di Rocco, F.A. García, L. Pardini, S. Legnaioli, G. Lorenzetti, V. Palleschi, Quantitative analysis of metals in waste foundry sands by

83

calibration free-laser induced breakdown spectroscopy, Spectrochimica Acta Part B: Atomic Spectroscopy, 131 (2017) 58-65. [208] R. González, P. Lucena, L. Tobaria, J. Laserna, Standoff LIBS detection of explosive residues behind a barrier, Journal of Analytical Atomic Spectrometry, 24 (2009) 1123-1126. [209] V. Lazic, A. Palucci, S. Jovicevic, M. Carapanese, C. Poggi, E. Buono, Detection of explosives at trace levels by laser-induced breakdown spectroscopy (LIBS), Chemical, Biological, Radiological, Nuclear, and Explosives (CBRNE) Sensing XI, International Society for Optics and Photonics, 2010, pp. 76650V. [210] N.K. Rai, A. Rai, LIBS—an efficient approach for the determination of Cr in industrial wastewater, Journal of hazardous materials, 150 (2008) 835-838. [211] J.M. Kowalczyk, J. Perkins, J. Kaneshiro, N. Gaillard, Y. Chang, A. DeAngelis, S.A. Mallory, D. Bates, E. Miller, Measurement of the sodium concentration in CIGS solar cells via laser induced breakdown spectroscopy,

Photovoltaic Specialists

Conference (PVSC), 2010 35th IEEE, IEEE, 2010, pp. 001742-001744. [212] O. Samek, D. Beddows, H. Telle, J. Kaiser, M. Liška, J. Caceres, A.G. Urena, Quantitative laser-induced breakdown spectroscopy analysis of calcified tissue samples, Spectrochimica Acta Part B: Atomic Spectroscopy, 56 (2001) 865-875. [213] X.-Y. Liu, W.-J. Zhang, Recent developments in biomedicine fields for laser induced breakdown spectroscopy, Journal of Biomedical Science and Engineering, 1 (2008) 147. [214] L. Torrisi, F. Caridi, L. Giuffrida, A. Torrisi, G. Mondio, T. Serafino, M. Caltabiano, E. Castrizio, E. Paniz, A. Salici, LAMQS analysis applied to ancient Egyptian bronze coins, Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 268 (2010) 1657-1664.

84

[215] I. Osticioli, N. Mendes, S. Porcinai, A. Cagnini, E. Castellucci, Spectroscopic analysis of works of art using a single LIBS and pulsed Raman setup, Analytical and bioanalytical chemistry, 394 (2009) 1033-1041. [216] M. Alberghina, R. Barraco, M. Brai, T. Schillaci, L. Tranchina, Comparison of LIBS and µ-XRF measurements on bronze alloys for monitoring plasma effects, Journal of Physics: Conference Series, IOP Publishing, 2011, pp. 012017. [217] S.G. Buckley, H.A. Johnsen, K.R. Hencken, D.W. Hahn, Implementation of laserinduced breakdown spectroscopy as a continuous emissions monitor for toxic metals, Waste Management, 20 (2000) 455-462. [218] D. Hahn, W. Flower, K. Hencken, Discrete particle detection and metal emissions monitoring using laser-induced breakdown spectroscopy, Applied spectroscopy, 51 (1997) 1836-1844. [219] M. Gondal, T. Hussain, Z. Yamani, M. Baig, Detection of heavy metals in Arabian crude oil residue using laser induced breakdown spectroscopy, Talanta, 69 (2006) 10721078. [220] F. Fortes, T. Ctvrtnícková, M. Mateo, L. Cabalín, G. Nicolas, J. Laserna, Spectrochemical study for the in situ detection of oil spill residues using laser-induced breakdown spectroscopy, Analytica chimica acta, 683 (2010) 52-57. [221] S. Pandhija, A. Rai, In situ multielemental monitoring in coral skeleton by CFLIBS, Applied Physics B, 94 (2009) 545-552. [222] J. Cuñat, F. Fortes, L. Cabalín, F. Carrasco, M. Simón, J. Laserna, Man-portable laser-induced breakdown spectroscopy system for in situ characterization of karstic formations, Applied spectroscopy, 62 (2008) 1250-1255.

85

[223] J. Cunat, F. Fortes, J. Laserna, Real time and in situ determination of lead in road sediments using a man-portable laser-induced breakdown spectroscopy analyzer, Analytica Chimica Acta, 633 (2009) 38-42. [224] J. Cunat, S. Palanco, F. Carrasco, M. Simon, J. Laserna, Portable instrument and analytical

method

using

laser-induced

breakdown

spectrometry

for

in

situ

characterization of speleothems in karstic caves, Journal of Analytical Atomic Spectrometry, 20 (2005) 295-300. [225] D.K. Tripathi, R. Kumar, A.K. Pathak, D.K. Chauhan, A.K. Rai, Laser-induced breakdown spectroscopy and phytolith analysis: an approach to study the deposition and distribution pattern of silicon in different parts of wheat (Triticum aestivum L.) plant, Agricultural Research, 1 (2012) 352-361. [226] B. Praher, V. Palleschi, R. Viskup, J. Heitz, J. Pedarnig, Calibration free laserinduced breakdown spectroscopy of oxide materials, Spectrochimica Acta Part B: Atomic Spectroscopy, 65 (2010) 671-679. [227] G.S. Senesi, M. Dell'Aglio, A. De Giacomo, O. De Pascale, Z.A. Chami, T.M. Miano, C. Zaccone, Elemental Composition Analysis of Plants and Composts Used for Soil Remediation by Laser‐Induced Breakdown Spectroscopy, Clean–Soil, Air, Water, 42 (2014) 791-798. [228] L.C. Trevizan, D. Santos Jr, R.E. Samad, N.D. Vieira Jr, C.S. Nomura, L.C. Nunes, I.A. Rufini, F.J. Krug, Evaluation of laser induced breakdown spectroscopy for the determination of macronutrients in plant materials, Spectrochimica Acta Part B: Atomic Spectroscopy, 63 (2008) 1151-1158. [229] N. Ahmed, R. Ahmed, M.A. Baig, Analytical analysis of different karats of gold using laser induced breakdown spectroscopy (LIBS) and laser ablation time of flight mass

86

spectrometer (LA-TOF-MS), Plasma Chemistry and Plasma Processing, 38 (2018) 207222. [230] I. Rehan, K. Rehan, S. Sultana, M. Khan, R. Muhammad, LIBS coupled with ICP/OES for the spectral analysis of betel leaves, Applied Physics B, 124 (2018) 76. [231] S. Wang, D. Tian, M. Xu, Q. Lin, J. Wang, G. Guo, G. Yang, Y. Duan, Elemental analysis of cemented carbides by calibration-free portable laser-induced breakdown spectroscopy, Instrumentation Science & Technology, 46 (2018) 277-291.

87

Highlights 1. This study is a comprehensive review on the “laser induced breakdown spectroscopy methods and applications. 2. Laser induced breakdown spectroscopy (LIBS) has become an established analytical atomic emission spectroscopic technique. 3. It has analytical and technical advantages over other existing techniques. 4. The aim of the current study is to provide a critical review of LIBS in several aspects.

Conflicts of Interest

We wish to confirm that there are no known conflicts of interest associated with this publication and there has been no significant financial support for this work that could have influenced its outcome. We confirm that the manuscript has been read and approved by all named authors and that there are no other persons who satisfied the criteria for authorship but are not listed. We further confirm that the order of authors listed in the manuscript has been approved by all of us. We confirm that we have given due consideration to the protection of intellectual property associated with this work and that there are no impediments to publication, including the timing of publication, with respect to intellectual property. In so doing we confirm that we have followed the regulations of our institutions concerning intellectual property. We further confirm that any aspect of the work covered in this manuscript that has involved either experimental animals or human patients has been conducted with the ethical approval of all relevant bodies and that such approvals are acknowledged within the manuscript. We understand that the Corresponding Author is the sole contact for the Editorial process (including Editorial Manager and direct communications with the office). He is responsible for communicating with the other authors about progress, submissions of revisions and final approval of proofs. We confirm that we have provided a current, correct email address which is accessible by the Corresponding Author and which has been configured to accept email from ([email protected]) Signed by all authors as follows: [Corresponding author on behalf of all co-author: Dr. Pervaiz Ahmad ]