laser-induced plasma temperature

��

Laser-induced plasma temperature

Shudi Zhang, Xiaohua Wang, Miaohong He, Yunbin Jiang, Bochao Zhang,Wei Hang, Benli Huang

PII: S0584-8547(14)00061-5DOI: doi: 10.1016/j.sab.2014.04.009Reference: SAB 4681

To appear in: Spectrochimica Acta Part B: Atomic Spectroscopy

Received date: 25 January 2014Accepted date: 23 April 2014

Please cite this article as: Shudi Zhang, Xiaohua Wang, Miaohong He, Yunbin Jiang,Bochao Zhang, Wei Hang, Benli Huang, Laser-induced plasma temperature, Spectrochim-ica Acta Part B: Atomic Spectroscopy (2014), doi: 10.1016/j.sab.2014.04.009

This is a PDF file of an unedited manuscript that has been accepted for publication.As a service to our customers we are providing this early version of the manuscript.The manuscript will undergo copyediting, typesetting, and review of the resulting proofbefore it is published in its final form. Please note that during the production processerrors may be discovered which could affect the content, and all legal disclaimers thatapply to the journal pertain.

ACCEPTED MANUSCRIPT

Laser-induced plasma temperature

Shudi Zhang1, Xiaohua Wang

1, Miaohong He

1, Yunbin Jiang

1, Bochao Zhang

1, Wei Hang*

1,2，Benli

1 Department of Chemistry, the MOE Key Lab of Spectrochemical Analysis & Instrumentation,

College of Chemistry and Chemical Engineering, Xiamen University, China

2 State Key Laboratory of Marine Environmental Science, Xiamen University, China

Correspondence to: Wei Hang, Department of Chemistry, Xiamen University, 422 Simingnan Ro

ad, China 361005. Phone: 86-592-2184618; Fax: 86-592-2185610; E-mail: weihang@xmu.edu.cn

ACCEPTED MANUSCRIPT

ABSTRACT

It is of great importance to explore the evolution of laser-induced plasma (LIP) properties,

especially plasma temperature, with regard to variations of experiment conditions in both theoretical

study and routine applications. By investigating the influence of various factors on plasma temperature,

one can gain knowledge about the processes in plasma and adjust experimental conditions to obtain

optimum analytical performance.

Herein the fundamental theories and calculation methods of LIP temperature via spectroscopic

approaches are briefly reviewed. Its temporal and spatial evolutions together with several influencing

factors are discussed, such as laser parameters, ambient surrounding, and physical & chemical

properties of the sample. The results summarized exhibits the general trend that LIP temperature

increases with increasing laser wavelength, pulse width, laser energy, background gas pressure, and

sample hardness. On the other hand, it decreases with time elapsing and distance from sample surface.

Moreover, plasma temperature generated in argon surrounding is higher than that in other gas species,

and the rank of temperature values generated from different samples exhibits a general tendency of Cu >

Fe > Ni ≈ Al ≈ glass ≈ rock. Additionally, LIP temperature tends to increase as lens focal point

approaches sample surface, and the plasma confinement effect in sample cavity is significant in altering

plasma temperature. Various explanations are given to interpret these temperature behaviors.

Keywords: laser-induced plasma, plasma temperature, spectroscopic approach, local thermodynamic

equilibrium, temporal-spatial evolution.

ACCEPTED MANUSCRIPT

1. Introduction

Laser-induced breakdown spectrometry (LIBS) is a convenient and versatile technique for

analyzing all kinds of samples. It refers to the analysis of spectroscopic data emitting from the

laser-induced plasma (LIP) when the irradiance of the laser focused on the material exceeds its

threshold. LIBS has found its broad applications in various of fields, such as metal analysis, material

processing, thin films deposition, biomedical research, art restoration, environmental monitoring,

explosive residues detection, and so forth [1, 2]. Extensive reviews have been worked out to elaborate

the fundamental physic-chemical processes, modeling, instrumentation, and applications of the

technique [3-16].

The LIBS technique has many advantages over conventional atomic emission spectroscopy

methods: only simple sample preparation procedures and tiny amount of sample are required, and it can

be applied to both conducting and non-conducting sample analysis [17]. Although LIBS owns such

merits, it suffers from several shortcomings. The detection limits and reproducibility of the technique

are often not satisfactory compared with other elemental analysis methods [18-20]. It is mainly caused

by the violent and complicated processes involved in the whole scene of LIBS, including laser-solid

interaction, plume expansion, plasma formation, and laser-plasma interaction [21-25]. Therefore, it is

an urged task to gain a better insight into the complex processes.

The light emitting from LIP is a valuable asset that provides both the qualification and

quantification information of the sample and the properties of the plasma itself. The main plasma

properties influencing light emitting are temperature, electron density, and the number densities of

emitting species [26]. The knowledge of LIP temperature is important to understand the processes

occurring in the entire complex processes, namely dissociation, atomization, ionization, and excitation

[27, 28], and improve the application of LIBS [29, 30]. Moreover, the knowledge of gas temperature of

the plasma is vital in many applications such as surface modification, material processing, thin film

deposition, and remediation of hazardous gases [31, 32], Hence, it is worthy to focus attention on the

temperature behavior of LIP, which is the main purpose of this work.

The temperature of LIP is greatly influenced by the complicated processes, as mentioned above.

The factors influencing LIP temperature include laser pulse characteristics (e.g., laser wavelength,

pulse frequency, laser energy, dual-laser mode), ambient surrounding, sample characteristics (e.g.,

matrix composition, sample homogeneity, physics properties) [17, 33, 34] and sampling geometry. It is

of great importance to clarify how LIP temperature changes with regard to the factors listed above and

why such variations take place. Moreover, the spatial and temporal variations of LIP temperature are of

great interest. Before the discussion of these aspects, it is necessary to gain the knowledge about the

fundamental theories of LIP temperature and the spectroscopic methods for measuring. Accordingly,

the rest of the work will be arranged as follows. The fundamental theories of LIP temperature will be

discussed in Section 2; the main spectroscopic methods measuring and calculating the temperature will

be briefly reviewed in Section 3; the influencing factors, including laser characteristics, ambient

surrounding, and sample characteristics, will be discussed in Section 4, 5, 6, respectively; the spatial &

temporal observation will be summarized in Section 7. Finally a conclusion will be drawn in Section 8.

As numerous experiments have been carried out to get a deeper understanding of the whole processes,

modeling is indispensible in localizing and minimizing the drawbacks of experiments as well as

verifying and quantifying the explanations made from experiments [23, 35]. Several reviews have

summarized the models dealing with each process in plasmas and the comparison between experiment

ACCEPTED MANUSCRIPT

results and modeling results [36, 37]. In this work, some modeling results will be shown in each section

for the purpose of comparison with experimental results and offering potential explanations for the

phenomena observed.

2. Fundamental theories of LIP temperature

Before investigating how the factors would influence LIP temperature, it is important to

understand the origin of the term and the criteria for spectroscopic calculation. Strictly speaking, the

term ‘temperature’ can only be valid when a certain fraction of plasma satisfies the local

thermodynamic equilibrium (LTE) conditions, which will be explicitly described in Subsection 2.1.

Since the method calculating the temperature is spectroscopic, the criteria for selection of spectroscopic

lines are concisely summarized in Subsection 2.2 and the approaches to judge whether the plasma is

optically thin in Subsection 2.3. At the end of this section, we will briefly illustrate the evaluation of

uncertainty of calculated LIP temperature.

2.1. The description of LTE and approaches to determine its existence

The processes taking place in LIP can be listed as follows: collision ionization, photo-ionization,

radiative and three-body recombination, radiative decay, collisional excitation and de-excitation

process, photo-excitation, and Bremsstrahlung process [38]. As long as a plasma is in thermodynamic

equilibrium (TE), the state of the entire system composed of all kinds of species can be described by a

series of equilibrium distribution laws [39]. Electron energy distribution function (EEDF) will have a

Maxwell distribution defined by Te (electronic temperature), and heavy particle energy distribution

function (HEDF) could be determined by another term TH [40]. TH is frequently applied to represent

plasma gas temperature and can be estimated through molecular vibrational temperature Tvib and

rotational temperature Trot owing to the effectiveness of the energy exchange between translational and

rotational-vibrational states of heavy particles [31, 40]. The Boltzmann distribution law can be applied

to describe the relative population of excited levels of an atom or ion [38]:

where Nn (cm-3

) stands for the population of certain quantum level n; gn (dimensionless) the degeneracy

of that; En (erg) the energy of that; N (cm-3

) the number density of the species; k (erg•K-1

Boltzmann constant; T (K) and U (T) the temperature and the partition function. The temperature in the

above equation is the so-called excitation temperature and is indicated as Texc. Moreover, the number

densities of the same species at different ionization stages can be described by the Saha-Eggert

equation [38]:

where ne (cm-3

) represents the electron number density; Nz (cm-3

) the number density of a certain

ionization stage; Nz+1 (cm-3

) the number density of next ionization stage; me (g) the mass of the electron;

(erg) the first ionization energy for an isolated system; the correction of for the

interactions in the plasma and can be calculated via

[32]; = (h/2 ) where h is

the Planck constant. In this case, the temperature appears in Equation 2 is interpreted as Tion (ionization

ACCEPTED MANUSCRIPT

temperature). At last, photon energy density (erg•cm-3

•Hz-1

) in vacuum can be depicted by the

Planck function [38]:

where c (cm•s-1

) is the speed of light and h (erg•s) is the Planck constant. Similarly, the temperature

determining W is assigned by the symbol of Tν. When a system is under TE, each process will be

balanced by its inverse process, and the distribution behaviors stated above can be characterized by an

unique temperature value, namely Te = TH = Texc= Tion = Tν.

Nevertheless, TE is an ideal thermodynamic state which can never be completely achieved in the

case of highly transient and inhomogeneous LIP. The radiative equilibrium under TE requires that

plasma is completely optically thick at all frequencies [41], but it is obviously not the case for LIP

where photons can be emitted out quite easily. Consequently, the photon energy distribution will no

longer obey the Planck function and the state of TE is violated which will inevitably disrupt the

balances of atoms, ions, and electrons to some extent [42]. However, if the energy loss induced by

photon emitting is considerably less than the energy involved in other processes, it is still applicable for

the Boltzmann distribution, Maxwell distribution, and Saha-Eggert equation to describe the state of the

plasma. Thus, the concept of LTE is derived. Accordingly, the relationship among different

temperatures is expressed as Te = TH = Texc= Tion ≠ Tν. The photon escaping from plasma is related with

the spatial and temporal behavior of plasma. It is necessary to clarify that the variations of space and

time are sufficiently small in order to achieve LTE [38]. LIP seems to satisfy the LTE conditions under

typical conditions (Ne > 1017

- 1018

, T > 1 - 2 eV) [43]. Most LIPs are electron excitation kinetic

(EEK) plasmas where the energy translation among different excited levels is manipulated by the

collision between electrons rather than heavy particles. The reason is that an ionization degree of the

order of 10-4

is enough to insure that the collision processes are dominated by electrons [40]. The time

to establish equilibrium between electrons and heavy particles can be estimated through the expression

[44, 45]:

where (J) stands for the ionization energy of hydrogen; NI (cm-3

) the number density of neutral

species; NII the number density of charged species; m (g) the atomic mass, whereas the time needed for

the Boltzmann distribution to be valid can be described as follows [45]:

where z is the state of ionization; f the oscillator strength; Ez-1,2 (J) the energy of the corresponding state.

The results of calculations indicate that both equilibriums require only several nanoseconds. From the

experimental perspective of view, most of the studies supposed that the LTE conditions will be

satisfied 1 – 2 microseconds after the formation of plasma [46, 47]. In fact, LTE can be hardly achieved

perfectly in some cases in that there are several factors violating the balance of the processes [43], and

it is difficult for all the excited states to be in Boltzmann equilibrium [41]. As described above, the

most important criterion of LTE is that collisional processes must be dominant over the radiative

process, and this could only be partly satisfied in a state deviating from complete LTE. In such a state,

there exists a certain energy level where the excitation and de-excitation rate through collisional

process is equal to that through radiative process, and this state is the so-called partial local

thermodynamic equilibrium (pLTE). Fujimoto et al. [48] extensively discussed pLTE and figured out

ACCEPTED MANUSCRIPT

the way to estimate the excited level n just stated above. Readers may refer to other well-written

studies dealing with the basic theories of LTE for a further understanding [38, 40, 41, 43, 49].

The utilization of the distribution laws to describe the plasma should have a prerequisite that the

LTE state is achieved, as is the case for the calibration-free procedure in LIBS [49, 50]. Meanwhile,

LTE is essential for getting reliable quantitative results [40]. Hence, it is crucial to assess that whether a

plasma region has achieved LTE. This naturally draws our attention to concisely evaluating the

approaches to LTE. The most frequently used methods to evaluate LTE are the EEDF Maxwell

distribution criterion [44, 45, 51, 52] and the McWhirter criterion [38, 44, 45, 49, 52]. The former

requires that Ne 1016

and kT 5eV. The latter requires that the rate of collisional process must

be ten times higher than that of radiative process, which can be expressed mathematically as [49]:

where T is the temperature of the plasma and is the largest energy gap between the upper and

lower energy state of the spectroscopic lines used; Ne, T, and are expressed in cm-3

, K, and eV,

respectively. Though widely used, the McWhirther criterion is criticized to be a necessary but

insufficient criterion. It assumes that the plasma is stationary and homogeneous, which is apparently

not the case in LIP, and doesn’t take the collisional equilibrium itself into consideration [41, 49]. With

regard to the transient and inhomogeneous feature of LIP, Cristoforetti et al. developed two criterions

[49] which were applied by a few studies [38, 53]. In the case of homogeneous and transient plasma,

the temporal evolution of plasma parameters must be sufficiently low so that the species have adequate

time to reach thermodynamic equilibrium. The criterion can be expressed as follows:

where is the relaxation time of the plasma which can be deduced [49]. The other criterion requires

that the species diffusion length is shorter than the variation length of electron number density and

plasma temperature during approximately the relaxation time to the equilibrium. It can be described as

follows:

where x is a certain position in the plasma; and = in which D stands for the diffusion

coefficient [49]. Another way to estimate LTE is the ‘Boltzmann plot’ method, which is a method to

calculate Texc and will be further elaborated in Section 3. If the data points in Boltzmann plot can be

fitted into a straight line, the exhibited good linearity is indicative of Boltzmann distribution of each

excited levels, thus a powerful evidence of LTE is obtained [21, 29, 41, 54]. Yet it has its own

shortcoming that the ground level population is unable to be measured: it has the longest relaxation

time and diffusion length and is more susceptible to radiative decay-induced non-LTE deviations [40].

A method assessing the establishment of ionization/recombination balance was utilized in many

studies [40, 41, 44, 52, 55-57]. In this method, the population ratios of two energy levels belonging to a

neutral atom and a charged ion are calculated by two different ways and compared with each other [40]:

one is by measuring the appropriate line intensities and the other is through applying the measured

excitation or ionization temperature to the Saha-Eggert equation. It is a proof of

ACCEPTED MANUSCRIPT

ionization/recombination equilibrium if the two ratios calculated resemble each other. Additionally,

Moon et al. [58] developed two novel means of assessing thermodynamic equilibrium in LIBS. Firstly,

the line-to-continuum ratio and Texc are applied to calculate Te assuming that Te and Texc are kept

distinct from each other [59]. The ratio can be expressed as:

where (Hz) is the spontaneous transition probability between an upper level and a lower level;

the statistical weight of the upper level; (J) the excitation energy of the upper level; (J) the

ionization potential; (J) the lowering correction term of ; (nm) the wavelength of the atomic

transition and the continuum; (nm) the monochromator spectral bandwidth; h (J s) the Planck

constant; k (J K-1

) the Boltzmann constant; c (m s-1

) the speed of light; Te (K) the electron temperature;

Texc (K) the excitation temperature; the free-bound continuum correction factor; the free-free

Gaunt factor. By applying the value of Texc and the line-to-continuum ratio to Equation 9, the value of

Te can be obtained. An accordance of the two temperature values is indicative of LTE. Secondly, the

ion-to-neutral ratio approach is derived and the working relation is given as:

where j indicates a species in the plasma; the degree of ionization; and the partition

function of the atoms and ions; the Saha constant; and the ionization potential. According to

Equation 10, by plotting the ion to neutral ratios (corrected by the partition function) versus the

ionization potentials of different elements into a straight line, the slope of the line is determined by Texc

and the intercept is correlated with both Texc and Ne. By comparing the theoretically plotted line and the

experimental data, the achievement of equilibrium state can be estimated. The authors employed these

two criteria and deemed that LTE is reached at least 5 microseconds after the onset of plasma generated

from copper-aluminum alloys [58].

It is an explicit way to assess LTE by comparing different temperature values calculated by

various approaches or species, and the procedure was widely utilized in many studies [38, 41, 44, 46,

52, 57, 60-69]. The different behaviors of two or more temperatures is claimed to be an evidence of

non-LTE state, whereas the accordance of them is indicative of LTE. For example, Gautier et al. [62]

calculated the ionization temperature of the aluminum plasma generated by a 532 nm laser (pulse width

9 ns) at an irradiance of 1 GW/cm2 by time-integrated spectral data. The different temperatures

calculated via iron, titanium, and nickel species correlated well with each other, exhibiting that LTE

was reached. Lei et al. [64] utilized a 266 nm laser, whose fluence lied between 6.4 105 J/cm

2.5 106 J/cm

2, to produce plasma on the skin of a potato. They found out that Texc and Tion calculated

from calcium species and Tvib derived from CN vibrational lines showed similar behaviors 600

nanoseconds after the generation of the plasma, which was thought to be a testimony of LTE.

Barthélemy et al. [41] applied two lasers (800 nm, 80 fs; 308 nm, 10 ns) both at 10 J/cm2 to generate

aluminum plasma. They plotted the temporal behaviors of Texc calculated through iron atomic lines and

Tion deduced via magnesium species. The two temperature values were distinguished in the first one

microsecond after the onset of plasma, which was explained to be a departure from LTE. In spite of the

viewpoints stated above, there are additional interpretations with respect to the differences between

various temperatures. Shaikh et al. [70] calculated Texc and Tion via cadmium species in a cadmium

plasma generated by a 1064 nm, 5 ns laser at 5 1010

W/cm2. These two values didn’t coincide with

each other at the time of 500 ns and the spatial region of 1 - 4 mm, which was supposed to be caused

ACCEPTED MANUSCRIPT

by the uncertainty of spontaneous transition probability and measurement accuracy rather than the

departure from LTE. The same conclusion was drawn by Simeonsson et al. [45] who observed the

different behavior of Texc and Tion in CO and CO2 plasma in the time window of 0.1 – 2 μs. Aguilera et

al. [68] calculated two Texc through iron atomic and ionic lines respectively and a Tion via the whole two

line sets in a Fe-Ni alloy plasma generated by a 1064 nm, 4.5 ns laser with an irradiance of 1.5 1010

W/cm2. The spectra were spatially resolved and the three temperatures reached a similar value at the

specific location. However, when the topic was switched to the spatial integrated manner, the two

apparent temperatures calculated by the iron atomic and ionic lines did not coincide with each other.

This phenomenon was attributed to the spatial inhomogeneity of the plasma where the atomic

distribution is distinct from the ionic distribution. Several other studies observed similar experimental

results and held the same viewpoint [29, 71-74]. There still exist other explanations why temperatures

deduced from different species are not the same. Park et al. [75] focused a 1064 nm, 8 ns laser on a

graphite sample at the fluence of 2.8 J/cm2 and obtained Tvib and Trot from CN spectra. The result

showed that Trot> Tvib, which indicated that the chemical reaction C2 + N2 CN had taken place in the

plasma. Patel et al. [76] compared the excitation temperatures calculated from copper and zinc atomic

lines in a brass plasma and found that the former was always higher than the latter within the time

period investigated, which was ascribed to the much higher vaporization temperature of copper than

that of zinc. Still other comparisons of different temperatures were made [26, 77-81].

2.2. The criteria of selecting spectroscopic lines

Now that the plasma characterization approach discussed in this study is spectroscopic, it is

significant to come up with the criteria to select appropriate lines for a better estimation of the

temperature [21, 39, 52, 82]:

(1) The lines must have reasonable line-to-background ratio.

(2) The spectral efficiency should be measured accurately.

(3) The greater the gap between the upper energy levels of selected lines, the better the accuracy

of temperature measurement.

(4) The accuracy of spontaneous transition probability is relatively high.

(5) Special care should be taken to avoid the lines of self-absorption resonance or having

low-lying energy levels.

Spectra are dominated by continuum emission in the first tens of nanoseconds after the onset of

plasma [57], which mainly results from radiative combination and bremsstrahlung [83]. In other words,

the line emissions can only emerge after that period of time and get a sufficient line-to-background

ratio. If the wavelengths of the lines are approximately the same, the relative radiance calibration

would be more accurate and much easier [21]. However, it is not possible in many case; consequently,

the spectral efficiency needs to be measured accurately. The result of temperature calculation would be

more reliable if the energy gap of upper levels is more remarkable, which will be further illustrated in

the Subsection 2.4. As will be illustrated in Section 3, some temperature calculation methods

necessitate the knowledge about the spontaneous transition probability A, therefore the accuracy of A is

of great importance. Finally, the lower levels have considerably higher population and larger oscillator

strengths which are susceptible to self-absorption, hence great efforts should be made to avoid the

self-absorption lines.

ACCEPTED MANUSCRIPT

2.3. The ways to verify the optically thin of plasma

It is crucial to testify that plasma is optically thin for the lines used for the sake of eliminating the

severe effect of intensity saturation and obtaining precise temperature results. Self-absorption effect

relies on the line parameters involving degeneracy, oscillator strength, level energies, as well as plasma

parameters such as temperature, electron density, and number densities of different species [39, 68].

The corresponding topic was discussed in the review work [4] and the criteria are concisely

summarized herein:

(1) For the multiplet lines of a species whose lower/upper terms have a single level, the intensity

ratio of them is in accordance with the statistical weight ratio [17, 44, 47, 84-86].

(2) The intensity ratio of two atomic lines having the same upper level energy should be within

the limit defined by a branching ratio, namely

[30, 87].

(3) The optical depth of the plasma should be much lower than 1, namely ,

where is the absorption coefficient, is the thickness of the plasma [70, 82, 88, 89].

(4) The value of self-absorption coefficient defined as

should be close to 1,

where stands for the experimental Stark width of the line; the half-width Stark broadening

parameter and = -0.54 [38, 90].

(5) The curve of growth of the line should be a straight line [92, 229].

Radziemski et al. [47] utilized the N I triplet, 414.3 nm, 414.5 nm, and 415.1 nm to verify that the

plasma was optically thin if their intensity ratio is close to their statistical weight ratio of 1:2:3. Hegazy

et al. [30] took the spontaneous transition probability A and wavelength into account on the basis of

the ratio of statistical weight g. The absorption coefficient (cm-1

) in the third criterion can be

referred as [70]:

where represents the oscillator strength; (cm-3

) the number density of the lower energy

level; the normalized line profile at the center of a Lorentzian profile line

in which

(cm) is the FWHM. The curve-of-growth method was first

introduced by Gornushkin et al. to plasma analyses [92] and was reviewed by Aragón et al [4]. Readers

may refer to the corresponding references for details.

2.4. The estimation of uncertainty of temperature measurement

It is widely believed that temperature determination error primarily comes from the systematic

errors regarding the uncertainties of transition probabilities and the statistical errors of line intensity

measurements [41, 52]. The influence of the uncertainty of spontaneous transition probability A on

temperature can be expressed as [93]:

where and are the mean values of the upper level energies for the two groups of lines in

Boltzmann plot therein. Similarly, the influence of errors coming from relative line intensity

measurements can be described as [45]:

ACCEPTED MANUSCRIPT

where R is the ratio of measured emission intensities ( ). On the other hand, Sattmann et al.

estimated the temperature uncertainty via the maximum and minimum slopes of Boltzmann plot lines

fitted by error-affected data dots [136].

3. The methods to calculate LIP temperature

In Subsection 2.1 we have discussed the relationships that the plasma parameters must obey when

plasma is in LTE. By applying the equations stated above, LIP temperature can be calculated through

different approaches which are partly summarized in this section. Readers may refer to the work done

by Hahn et al. [94] who listed comprehensively the methods utilized by different research groups.

mthods utilized in the studies involved in this article are summarized in Table 1.

Table 1

The samples, measured species, and utilized methods in temperature determination summarized in this article.

Sample Measured species Methods* Ref.

HCl solution Li I, Fe I BT [80]

Cu Cu I BT [19, 95, 96]

Al Al I BT [97, 98]

Al Al II BT [20]

aerosol Pb I BT [99]

Zn Zn I BT [100, 101]

Al O I BT [38]

boron nitride Hα/Hβ BT [102]

steel Fe I BT [103]

water Hβ/Hγ BT [86]

steel Fe II BT [85]

steel, glass Fe I BT [104]

YBCO Cu I, Y I, Ba II BT [72]

soil, sand Ca I, Fe I BT [105]

Fe Fe I BT [106, 107]

air O I BT [108]

brass N I/O I BT [109]

Al alloy Al I BP [110, 111]

Al alloy Fe I BP [17, 74, 83,

112-116]

Al Al I BP [88, 117, 118]

Al, Fe Al I, Fe I BP [119]

brass Cu I BP [120, 121]

Fe-Cr alloy Fe I BP [122, 123]

Cu Cu I BP [1, 27, 124-131]

CaO Fe I, Mn I BP [26]

soil Fe I BP [33, 132]

ACCEPTED MANUSCRIPT

steel Fe I BP [92, 93, 133-137]

Cd, Zn Zn I, Cd I BP [138]

ferrite aluminum Fe I, Li I BP [79]

Ni Ni I BP [139]

Cd Cd I BP [70]

silicon Si I BP [52]

Ti Ti II BP [30, 140]

Ti Ti I, Ti II, Ti III BP [78]

H2 Balmer Series BP [141]

bronze alloy Sn I BP [142]

Al O I BP [87, 143]

graphite Fe I, Pb I, CN BP [34]

Al, Cu Fe I BP [144]

Cd Cd II BP [145]

Pb Pb I BP [2, 21, 146-148]

Cu, Pb Cu I, Pb I BP [28]

borax Fe I BP [149]

Al Fe I BP [41, 54]

Al-Ti alloy Ti II BP [150]

ZnO Zn I BP [151]

Al Al I, Ni I, Cu I BP [77]

W W I BP [152]

Multi-elemental film Co II, Cr II BP [153]

Ta Ta I BP [154]

basaltic rock Fe I, Ti II BP [61]

Al, steel Fe I BP [155]

Al Al II BP [89, 156, 157]

Sr Sr I BP [158]

TiO2 Ti I BP [159]

graphite C2 BP [160]

HgCl Hg I BP [82]

Ti Ti I BP [161]

Al2O3 Al I BP [162]

Zn alloy Fe I BP [163]

Al, Cu Fe I BP [164]

aerosol Fe II BP [165]

PTFE C2, CN BP [166]

Ar Ar II BP [167]

Fe Fe I BP [168]

Al alloy Al I BP [169]

LiF Li I BP [170]

Sn Sn II BP [39, 171, 172]

brass Cu I, Zn I BP [76, 173]

Zn Zn I BP [84]

ACCEPTED MANUSCRIPT

Ca Ca I BP [174]

Al Cu I BP [175]

vanadium oxide V I BP [176]

Cu, Ni, Al Fe II BP [177]

steel S IV, S V BP [71]

Ar Ar I BP [178]

steel Fe I, Fe II BP [73]

graphite, polymer C2, CN BP [67]

lithium niobate Nb I/Nb II SBT [179]

Al Al I/Al II SBT [180]

graphite C III/C II SBT [181, 182]

Al Mg I/Mg II SBT [183]

water Ca I/Ca II SBT [184]

air He I/He II SBT [185]

Cu-Zn alloy Zn I/Zn II SBT [186]

YBCO Ba I/Ba II SBT [187]

Ni-Fe-Al alloy Fe I/Fe II SBP [188]

Al, glass, rock, steel Fe I/Fe II, Ti I/Ti II, Ni I/Ni II SBP [62]

Sn Sn I/Sn II SBP [189]

Cr solution Cr I/Cr II SBP [91]

Al Al I/Al II SBP [90]

aerosol N I/N II, Mg I/Mg II SBP [66]

Al Fe I/Fe II SBP [190]

Fe-Ni alloy Fe I/Fe II SBP [191]

air O I/O II SBP [192]

Al alloy Fe I/Fe II, Si I/Si II, Al I/Al II MSBP [53]

Cu-Fe-Ni-Mn alloy Fe I/Fe II, Ni I/Ni II, Mn I/Mn II MSBP [29]

silicon Si I (288.16nm) LTC [193-197]

bio-ceramic Si I (288.16nm) LTC [198]

silica glass Si I (288.16nm) LTC [199-201]

fused silica Si I (288.16nm) LTC [202]

air OH, N2+, O2 SS [31]

air N22+ (C-B) SS [65]

graphite CN SS [203]

CO C2, CN SS [204]

graphite C2, CN SS [69]

CO2/N2 mixture CN SS [205]

air N II SS [206]

graphite C2 SS [75, 207]

water Ca I/Ca II, Hβ/Hγ BT, SBT [81]

CO, CO2 O I, C I/C II BT, SBT [45]

CO2, CO, CH3OH, CHCl3 O I, Cl I, C I/C II, Cl I/Cl II BT, SBT [44]

graphite C I, C II, C I/C II, C III/C II BP, SBT [208, 209]

Al alloy Fe I, Mg I/Mg II BP, SBT [57]

ACCEPTED MANUSCRIPT

Al Al I, Mg I/Mg II BP, SBT [46]

graphite CN, C II/C III BP, SBT [32]

aerosol Be I, C I/C II, N I/N II, Be I/Be II BP, SBT [47]

Fe-Ni alloy Fe I, Fe II, Fe I/Fe II BP, SBP [68]

potato skin Ca I, Ca II, CN, Ca I/Ca II BP, SBP [64]

graphite CN BP, SS [63]

graphite C2, CN BT, BP, SS [60]

Al alloy, Cu Cu I, Cu I/ Cu II BP, SBP, LTC [58]

Al, Cu, steel, Fe, Al / [210]

graphite CN / [211]

* BT and BP stand for Boltzmann two-line and Boltzmann plot method; SBT and SBP stand for Saha-Boltzmann two-line and

Saha-Boltzmann plot method; MSBP stands for multi-element Saha-Boltzmann plot method; LTC stands for line-to-continuum

method; SS stands for synthetic spectra method.

3.1. Boltzmann method

As mentioned in Subsection 2.1, the populations of different excited levels obey the Boltzmann

distribution law (Equation 1). The emissivity of a particular transition of the species at a given position

of plasma can be expressed as:

where the subscript n and m represent the upper and lower excited level of a species; (W/cm3) the

emissivity; (m) the wavelength of the transition; h the Planck constant; (s-1

) the transition

possibility. Substituting for Equation 1 and we will get:

In experimental systems, the emissivity is replaced by the line intensity Inm, which is measured by

integrating the signal along the line-of-sight. Aguilera et al. suggested that the temperature worked out

is indicative of the whole source (apparent temperature) being integrated instead of local values [188].

By selecting two spectral lines and making the ratio of their intensities, we can get:

where ,

, , and

indicate the line intensity, statistical weight, transition possibility, and

upper level energy of another spectral line, respectively. The intensity and wavelength can be measured

and the other quantum values can be acquired via other studies, hence the temperature is obtained.

Based on the two-line method, Labutin et al. [79] found a way to circumvent the problem of

low-resolution spectra. They applied the integrated intensity of multiplets instead of single lines and

readers may refer to the details therein. When the case switches to molecular spectra, the Boltzmann

two-line method equation can be expressed as [60]:

where is the emission intensity decaying from a certain vibrational state of a upper

electronic level to another vibrational state of a lower electronic level; the transition

probability between the energy levels; the term value of the upper vibrational state ; and

ACCEPTED MANUSCRIPT

the molecular vibrational temperature to be calculated. Note that the intensity integrated over all

rotational fine structures should be used as in the equation theoretically.

While the Boltzmann two-line method only necessitates two spectral data points, another

approach utilizing Boltzmann distribution equation called ‘Boltzmann plot’ method takes more spectral

lines into consideration, which is advantageous over the former in temperature determination accuracy.

In the case of neutrals and ions, Equation 15 can be rewritten using the integrated intensity I:

By plotting the value of

in the left of the equation versus the upper level energy , the

slope of the fitted straight line is equal to

and thus T is worked out without knowing the value of

partition function . A typical atomic Boltzmann plot is shown in Fig. 1(A) using species of Fe I

and Fe II. By adding more data to Boltzmann plot, the upper level energies of the lines lie in a broader

range compared with two-line method, and the statistical error as well as the error induced by the

uncertainties of the transition probabilities is lower. As a result, the uncertainty of the measured

temperature is reduced. Nevertheless, the plotted lines are usually distributed in only two or three

groups of energy, therefore it’s difficult to estimate the departure from linearity [41]. Under the

circumstance of molecular spectra, the Boltzmann plot equation can be expressed as [32, 34, 160]:

where stands for the wavelength of each transition ( ). Similarly, the vibrational temperature

can be obtained from the slope of the Boltzmann plot by plotting to , as

shown in Fig.1(C).

ACCEPTED MANUSCRIPT

Fig. 1. Typical examples of Boltzmann Plot and Saha-Boltzmann Plot. (A) Boltzmann plot of Fe I and Fe II species of Fe-Ni

alloy plasma with the temperatures of 13 000 ± 400 K and 12 800 ± 500 K, respectively; (B) Saha-Boltzmann plot of the same

species in (A) with the temperature of 13 160 ± 65K; (C) Boltzmann Plot of CN vibrational bands obtained at a distance of 1 mm.

Both (A) and (B) are reproduced from Ref. 68 while (C) is from Ref. 32.

3.2. Saha-Boltzmann method

The population distribution of two successive ionization stages belonging to the same species can

be described by Saha-Eggert distribution law which has been expressed in Equation 2. Combining

Equation 2 and 15 and taking the neutral atoms and the first ionization stage into consideration, one can

get Saha-Boltzmann two-line equation [66, 81]:

where (J) is the ionization potential of atom; (J) the excitation energy of the ionic line;

(J) the excitation energy of the atomic line; the ionization temperature. Detalle et al. [113]

utilized dichotomy method to calculate the temperature by varying the value of until the

difference between the calculated and the experimental measured was lower than 1%. Same

ACCEPTED MANUSCRIPT

as the Boltzmann plot method, the Saha-Boltzmann plot equation can be acquired by combining

Equation 2 and 18 which results in a similar form [68]:

here the superscript 0 stands for neutral atoms. The new terms having the superscript “*” are expressed

as follows:

According to Equation 23, the ionization energy is added to the excitation energy, thus the term

has an even broader range in comparison with Boltzmann plot, which results in a more accurate

temperature determination. A typical Saha-Boltzmann plot is shown in Fig.1 (B). Since the newly

added term

depends on the temperature deduced from the plot, an iterative

procedure is supposed to be applied [68]: the data are plotted irrespective of the newly added term

initially and a start temperature value is obtained, then the value is introduced into the term and the new

plot provides a new temperature. The procedure goes on and on until the convergence provides the

ultimate temperature value. One may observe that all the above methods are related to just one kind of

species. To involve more than one kind of element in the calculation needs more procedures, as was

provided by Aguilera et al. [29] who worked out an approach called multi-element Saha-Boltzmann

and Boltzmann plots method. They claimed that one should take the ionization ratios of all the

elements and the elemental number densities into consideration. The ionization ratio depends on the

ionization energy and partition function of each element. Assuming that the ionic species above z = 1

can be neglected, the total number density of a species is:

where , , and

represents the total number density, number density of atoms and ions of a

certain species, respectively. The above equation can be rewritten as:

where stands for the number density ratio between ionic and neutral atoms for the species ,

which can be deduced from the Saha equation as well:

Assuming that the elemental concentration in the sample (%) is maintained for the species number

density in the plasma:

where N (cm-3

) stands for the total number density involving all the elements in the plasma. Combining

Equation 21 – 27, another correction term is added to the left term of Equation 21:

and the energy term is altered as:

ACCEPTED MANUSCRIPT

Similar to the Saha-Boltzmann plot method, Aguilera et al. used an iterative process to determine the

temperature [29]. Three species, Fe, Mn, and Ni, were applied to construct the plot and a fairly straight

line was obtained.

3.3. Line-to-continuum method

So far we have discussed the utilization of line spectra without applying the continuum emission.

However, the continuum spectra can offer another approach for calculating temperature, by either

combining the line spectra or not. Sasaki et al. [212] believed that the continuum emission is generated

from blackbody radiation and the temperature is determined using the Planck’s law of radiation. The

line-to-continuum method is worthy of emphasizing. According to Bastiaans et al. [213], the line

radiation can be described as:

where and are the partition function and number density of the first ionization stage,

respectively. The expression of continuum emission is semi-classical and multiplied by

correction factors generated from quantum mechanical considerations:

where is the factor correcting the semi-classical expression for free-bound continuum radiation;

the free-free Gaunt factor which improves the theoretical description of the free-free continuum.

Assuming that , and the product of / as well as the exponential term is insignificantly

small (either or is large), the ratio between and can be simplified as:

where . A Lorentzian curve must be fitted to each data set when applying the

method [195]. This method has the merit that no calibration is required due to the fact that .

Nevertheless, it has its own restrictions [193, 213]: the presence of impurities would affect the accuracy

of temperature determination because the number of gas ions is not the same as that of electrons.

Meanwhile, the plasma must be closer to LTE. At last, the plasma temperature shouldn’t exceed 2.5 eV;

otherwise the ionization stage would shift to a higher level and more contribution to continuum

radiation would be made via collisions between electrons and higher ionization level species. Ref. 58

and 195 also discussed the theories of line-to-continuum method.

3.4. Synthetic spectra method

Synthetic spectra method is mainly applied to determine the molecular temperature (Tvib, Trot)

which is supposed to be an indicator of gas temperature, namely heavy particle temperature TH (see

Subsection 2.1). Temperature value is introduced as a parameter of synthetic spectra and the value is

figured out by fitting experimental spectra to synthetic spectra. Readers may refer to some studies

dealing with this topic for details therein [31, 65, 203-205]. The work done by Moon et al. [31] is

illustrated here as an example.

The theoretical diatomic molecular spectrum intensity can be expressed as:

ACCEPTED MANUSCRIPT

where S represents the oscillator strength; k the wavenumber; a coefficient; the rotational

energy level. The expression of is:

where stands for the rotational partition function; a constant related to the change of dipole

moment and total number of molecules in the initial vibrational state; and the upper and lower

states, respectively. can be described as:

where represents a rotational constant of the vibrational quantum number . By comparing the

measured spectrum with synthetic spectrum via the chi-square method, the rotational temperatures of

the gas species of OH, , and were obtained. The method has a maximum deducible rotational

temperature for each of the species in that the overall shape of the spectrum becomes less sensitive to

the temperature above a certain threshold. Additionally, impure spectral lines begin to take place at

higher temperature and the simulation may turn difficult.

4. The influence of laser parameters on LIP temperature

The parameters of laser tremendously affect the performance of LIBS and the properties of plasma,

viz. laser wavelength, pulse width, and laser energy. In this section, we will give a brief review of the

works done by various groups coping with this theme and list out the viewpoints about the changing of

temperature according to the variation of each parameter. In the last subsection, the temperature

improvement effect of dual-pulse (DP) laser mode and the potential reasons of it will be discussed.

Plasma temperature discussed in the rest of this study is excitation temperature unless other indicated.

4.1. Laser wavelength

Many studies have been carried out investigating the influence of wavelength at a constant energy,

as summarized in Table 2. Most of them showed temperature increasing with increasing wavelength.

Shaikh et al. [138] applied 1064 nm, 532 nm, and 355 nm lasers all having a pulse width of 5 ns and a

irradiance of W/cm2 on zinc and cadmium samples within the background of He, Ne, and Ar.

They observed an increasing trend in temperature with increasing wavelength. It was suggested that the

main photon energy absorption mechanism in plasma is inverse bremsstrahlung (IB) by which

electrons gain kinetic energy and promote plume excitation and ionization via collisions with neutrals

and ions. The IB process is more significant in the case of longer wavelength. In this manner, the 1064

nm laser had the greatest IB absorption and thus generates the highest temperature [152, 173, 175, 208].

Hoffman et al. [208] constructed a model taking photo-ionization, neutral-electron IB, and ion-electron

IB into consideration and predicted that the plasma absorption coefficient ratio for 1064 nm, 532 nm,

and 355 nm is 9:2:1. Moreover, Abdellatif et al. [156] utilized the same three laser beams (7 ns) at a

irradiance in the same magnitude (~1010

W/cm2) and observed that the peak position of temperature

shifted away with respect to the surface of the sample with increasing wavelength.

Table 2

Selected plasma temperature behaviors with respect to increasing wavelength.

Wavelength Plasma temperature behavior Time and space region Ref.

ACCEPTED MANUSCRIPT

532 nm, 1064 nm increasing time-integrated/surface [170]

355 nm, 532 nm, 1064 nm increasing time-integrated [152]

355 nm, 532 nm, 1064 nm increasing 0 – 5 mm [174]

355 nm, 532 nm, 1064 nm increasing 0.3 mm [158]

532 nm, 1064 nm increasing time-integrated/0 – 2 mm [139]

355 nm, 532 nm, 1064 nm increasing 0.3 – 4 mm [208]

355 nm, 532 nm, 1064 nm increasing Time-integrated [207]

355 nm, 1064 nm increasing 40ns [209]

355 nm, 532 nm, 1064 nm increasing 1.5 – 4.5 mm [127]

532 nm, 1064 nm increasing time-integrated / 0.05 – 3.5 mm [162]

355 nm, 532 nm, 1064 nm increasing 0 – 5 mm [175]

355 nm, 532 nm, 1064 nm increasing 0 – 7.5 μs [138]

355 nm, 532 nm, 1064 nm increasing 500 ns/0.3 mm [173]

355 nm, 532 nm, 1064 nm increasing time-integrated / 0 – 4 mm [101]

355 nm, 532 nm, 1064 nm increasing 500 ns / 0 – 4 mm [70]

532 nm, 1064 nm decreasing 0.2 – 10 mm [27]

308 nm, 1064 nm decreasing 2 μs [34]

355 nm, 532 nm, 1064 nm decreasing / [2]

1064 nm, 10.6 μm decreasing 200 – 1100 ns / 0 – 5 mm [171]

266 nm, 532 nm, 1064 nm remaining constant 0.1 – 10 μs / spatial-integrated [115]

532 nm, 1064 nm remaining constant 0 – 7 μs [30]

Nevertheless, Shaikh’s group observed an inverse behavior that lead plasma temperature increased

with decreasing laser wavelength in another study utilizing 1064 nm, 532 nm, and 355 nm laser beams

at irradiances range from 3×1010

W/cm2 to 9.87×10

10 W/cm

2 [2]. The same phenomenon can also be

found in Ref. 27, 34, and 171. Compared with the temperature generated by 1064 nm laser, Shaikh et al.

ascribed the lower temperature generated by 10.6 μm laser to its smaller penetration depth into the Sn

sample which resulted in less ablation mass in the plasma [171]. Meanwhile, Bogaerts et al. [35] made

a potential explanation about the negative relationship by modeling. In plasma there exist

electron-neutral and electron-ion IB processes whose coefficients can be expressed as [35]:

where , , , , and stand for the number density of , , ,

and , respectively; the cross section of photon absorption. Though depends on

the term which has been cited by most of the research workers, one can observe in the above

equations that doesn’t have such a dependence and both of them contain the factor

which is inversely proportional to laser wavelength. According to their calculation, the

longer the wavelength, the lower the number density of electrons, neutrals, and ions, thus the impact of

the term further decreases.

ACCEPTED MANUSCRIPT

Yet Barthélemy et al. [115] compared the result of simulation with that of experiment conducted

in air using three wavelength beams (1064 nm, 532 nm, 266 nm, 6 ns) focused on an aluminum alloy at

10 J/cm2. They claimed that wavelength has little influence on the plasma temperature in the observed

time window of 0.1 μs – 10 μs. In their perspective of view, the temperature evolution is dominated by

the cooling mechanisms at later stage no matter what the initial condition is, hence the plasma

temperatures would get close to each other.

4.2. Laser pulse width

The studies dealing with laser pulse width are considerably less than other laser parameters (Table 3).

Most of the cases suggest that LIP temperature increases with increasing laser pulse width. Le Drogoff

et al. [57] compared the plasma temperatures generated from two lasers (800 nm, 100 fs; 1064 nm, 8 ns)

both at the fluence of 20 J/cm2 on an aluminum sample in air in spatial-integrated manner at the time

window of 200 ns – 25 μs. They found that the ns laser-induced plasma temperature was higher than

that of fs laser. They attributed the result to further plasma heating caused by the ns laser whereas the

endurance time of fs laser is not sufficient for it to interact with plasma. There are other studies in

which similar results were observed [26, 78, 83, 104, 115]. Elhassan et al. [142] and Laville et al. [214]

deemed that the temperatures generated under different pulse widths would become approximately the

same after a certain period of time (e.g., 1 μs). It is due to the fact that the plasma begins to stagnate at

that time and the radiation cooling dominates over the expansion cooling in plasma. According to Le

Drogoff et al. [83], the longer the pulse width, the longer time it will take for the spectral lines to

dominate over continuum emission and the longer lifetime the spectral lines hold. Therein, the authors

also compared the 100 fs and 500 fs generated plasma temperatures and didn’t observe significant

difference, indicating that the properties of plasmas induced by different lasers with pulse widths all

lower than 1 ps are reasonably the same. Bogaerts et al. [35] modeled the influence of different pulse

width (1 – 30 ns). At a fixed irradiance, the maximum temperature of the whole plasma increases with

increasing pulse width; while, at a fixed fluence, it remains almost constant at the time at 100 ns, which

leads to the conclusion that the total laser energy of the laser is the more important factor.

Table 3

Selected plasma temperature behaviors with respect to increasing pulse width

Laser pulse width Plasma temperature behavior Time and space region Ref.

80 fs, 3 ps, 270 ps increasing (2 μs, 10μs) / 0 – 2 mm [115]

250 fs, 7 ns increasing 0 – 1000 ns / 1.0 mm [78]

1.3 ps, /ns increasing 0.042 – 0.8 μs for ps

0.7 – 20 μs for ns

100 fs, 8 ns increasing 200 ns – 25 μs / spatial-integrated [57]

500 fs, 5 ps, 270 ps increasing 0 – 35μs / spatial-integrated [83]

35 ps, 5 ns increasing 100 – 2000 ns / spatial-integrated [26]

500 fs, 15 ns increasing 100 – 750 ns / spatial-integrated [142]

100 fs, 270 ps, 5 ns increasing (0.5 μs, 10 μs) / 0 – 1.7 mm [214]

10 ns, 150 ns decreasing 0 – 6000 ns [103]

4.3. Laser energy

ACCEPTED MANUSCRIPT

Among the parameters of laser, laser energy is the most widely investigated owning to its

technical facility. Note that the general term “laser energy” has three expressions, namely pulse energy,

fluence, and irradiance. When other experimental parameters (e.g. pulse width, sample spot size, and

laser-to-sample distance) are fixed, these three expressions can be transformed to each other within

each individual reference, therefore the general term “laser energy” is applied with respect to this topic

without being divided further. It’s easily observed in most of the cases that LIP temperature increases

with increasing laser energy, as is plotted in Fig. 2 in which all the data are excitation temperature

values. The process was modeled by Bogaerts et al. [35] who combined the effects of laser-solid and

laser-plasma interactions into their model and drew the same conclusion at the time of 100 ns. Sarkar et

al. [176] further observed that the temperature of the plasma (vanadium, air) generated by higher laser

energy (1064 nm, 7 ns, 625 J/cm2– 1187.5 J/cm

2) decreased much faster at the time window of 0.5 – 8

μs and it was supposed to be caused by the faster expansion cooling of the plasma.

Fig. 2. The increasing nature of plasma temperature regarding increasing laser irradiance. The data sets in the figure are

reproduced from various works: [128]; [175]; [173]; [83]; [161]; [176]; [71]; [160]; [2];

[159]; [152]; [102].

Frequently, when laser irradiance exceeds a certain threshold, LIP temperature will no longer

ascend rapidly and get saturated. Harilal et al. [187] investigated the influence of laser irradiance (15

GW/cm2– 70 GW/cm

2) on the YBCO plasma temperature generated by a 1064 nm, 9 ns laser in

vacuum at 3 mm above sample surface in the time-integrated manner. They found that the temperature

began to saturate at 54 GW/cm2. The saturation effect was supposed to be induced by plasma shielding,

i.e. reflection and absorption [32, 88, 97, 110, 160, 173, 175, 181, 187]. If the frequency of the laser

is lower than that of the plasma expressed as , the laser will be reflected out of

the plasma. In most cases, is much smaller than and the energy loss caused by reflection is

negligible. As irradiance increases, the plasma in front of the sample will absorb more energy via IB

and the sample will not receive the tailing part of the laser energy, thus the vaporization under high

irradiance is not as efficient as that under low irradiance. Based on the theory of plasma shielding,

ACCEPTED MANUSCRIPT

Harilal et al. [181, 187] came up with a concept of ‘self-regulating regime’ to account for the saturation

effect. At higher irradiance, the formed self-regulating regime absorbs more laser energy which results

in less vaporization from the target surface. Consequently, the electron number density in the plasma is

declined and the shielding effect of the plasma is less significant as well, which again introduces more

laser energy onto the target surface leading to more vaporization. The whole process goes on and on

and the concept of self-regulating regime is thus derived. For the assumption to be valid in the transient

plasma, it must be confirmed that the thermalization time is less than the plasma expansion time [187].

The energy exchange thermalization time between electrons and ions via collisions can be expressed as

follows:

where represents the atomic weight and equals to:

The term represents the Coulomb logarithm which contains the dynamic information of

ion-electron collisions. The calculated relaxation time in their study is on the magnitude of picoseconds

which is sufficiently lower than the pulse width and plasma expansion time. Russo et al. [196]

proposed two other reasons to explain the saturation effect. The first mechanism is self-focusing of the

laser beam resulted from density gradient in the plasma. They cited the criteria of the self-focusing

threshold power offered by Hora [215] which can be expressed as:

where P is the laser power in watts. In most cases the criterion is P/T 1.15×104. Under such

condition, the laser beam is further focused by the plasma in addition to lens focusing, thus the laser

irradiance casted onto the sample surface sharply increases and more material is removed into the

plasma. As a result, the given laser energy is shared by the newly ablated mass and the saturation effect

occurs. The other explanation might be that the sample surface reaches its critical point. When the

surface temperature is below the critical point, the energy required in phase transition of one mole of

mass equals to CpTs+Lv, where Cp is the heat capacity of the sample, Ts is the surface temperature, and

Lv is the latent heat. After the surface temperature surpasses the critical point, the densities of liquid and

vapor in their mixture become the same and the energy term Lv is no longer needed for transition.

Consequently, more mass will be ablated at given laser energy. Similarly, the additionally removed

mass will consume part of the laser energy which results in the saturation effect. In the case of

molecular temperature saturation effect, Harilal et al. [32, 160] further suggested that the ionization and

dissociation of excited molecules in high temperature generated by excessive laser energy as well as

the plasma shielding may be responsible for the effect. Finally, Laville et al. [214] conducted a model

with the help of one-dimensional fluid code and claimed that the additionally delivered laser energy

above the threshold is balanced by the increasing radiative cooling, thus the saturation effect emerges.

Still results from several studies exhibited that temperature remained relatively unchanged against

the variation of laser energy [66, 86, 157, 163, 165, 167, 191, 192] or showed a decreasing tendency in

a certain irradiance region [131]. St-Onge et al. [163] focused the laser (1064 nm, 6 ns) on an

aluminum alloy at 38.22 J/cm2 and 76.43 J/cm

2 in air with an observation time window of 0.5 – 50 μs,

and found that there was no significant temperature difference between the two fluences. They

supposed that larger plasma volume and more emitting species are generated rather than a denser and

ACCEPTED MANUSCRIPT

higher temperature-plasma with the aid of excessive laser energy. On the other hand, Wu et al. [131]

investigated the Cu plasma generated by a 532 nm, 15 ns laser whose fluence ranges from 45 J/cm2 to

120 J/cm2 and observed that electron temperature started to decrease at an irradiance of about 103

J/cm2 after a saturation region. They ascribed the result to the air plasma generated above the sample

surface which reflects and absorbs the incoming laser energy.

4.4. Dual-pulse laser mode

Since introduced, the dual-pulse (DP) laser configuration is well-known for its improvement in

spectral intensity, sensitivity, as well as detection limit of LIBS. Excellent reviews have been published

to discuss its instrumentation, sampling geometry, signal enhancement, and the possible explanations

[216, 217]. Herein we will focus on its influence on temperature compared with that of single-pulse

(SP) laser as well as the influence of different interval time between two lasers ( ). The majority of

the works confirmed that the temperature of DP plasma is higher than that of SP [54, 62, 74, 112, 117,

130, 133, 136, 147, 180, 186, 189, 190, 218]. Khalil et al. [189] compared the DP and SP Sn plasma

temperatures in air utilizing the laser (532 nm, 8 ns) at the irradiance from 1.19×1010

W/cm2 to 2.04×

W/cm2 within the time window of 0 – 6000 ns and found a significant temperature improvement in

DP mode. St-Onge et al. [74] investigated the DP mode composed of a UV laser (266 nm, 6 ns, 4

GW/cm2) and a NIR laser (1064 nm, 6 ns, 4 GW/cm

2) and drew the same conclusion, which was

explained that the second laser penetrates into the core of the plasma and the sample easily due to the

already rarefied plasma, viz. the plasma shielding effect is less significant compared to the SP mode.

Interestingly, the average temperature of DP mode firing UV laser prior to NIR laser was 400 K higher

than that firing NIR primarily. They ascribed this observation to the superior material ablation

efficiency of UV laser and high plasma absorption efficiency of NIR laser. On the other hand, it was

suggested that the DP plasma temperature vanishes much slower than the SP according to the result

obtained by Piñon et al. who investigated the Cu plasma produced by a 248 nm, 450 fs laser at the

fluence ranging from 0.57 J/cm2 to 5.66 J/cm

2 for both SP and DP mode ( : 200 ps) in air [130]. In

addition, Sattmann et al. [136] studied a steel plasma generated by the laser (1064 nm, 15 ns for SP,

and 25 ns for DP) firing at 80 mJ. They drew the conclusion that the threshold laser energy value of

temperature saturation in DP mode is evidently higher than that of SP based on the observation therein.

Nevertheless, there also exist observations that the temperature does not increase in DP mode.

Corsi et al. [109] observed no significant difference between the maximum temperature of DP and SP

brass plasma generated by a 1064 nm, 8 ns laser (200 mJ in both DP and SP; : 2 μs) in air at the

observation time window of 2 – 3 μs. Gehlen et al. [73] utilized a laser burst energy of 2 mJ (1064 nm,

7 ns, : 1 μs) to produce a steel plasma in air and didn’t observe palpable temperature variation

between DP and SP. They supposed that the reason of low burst energy used therein might account for

the result. Furthermore, Uebbing et al. [121] conducted a DP reheating mode (1064 nm, 8 ns, 2×1010

W/cm2 for ablation; 1064 nm, 5 ns, 2×10

11 W/cm

2 for reheating; : 40 μs) which generated a brass

plasma in the surrounding of Ar. They investigated the temporal variation of temperature at the

position of 1.5 mm and the time window of 5 – 80 μs, and observed that the second laser only heated

the plasma to a lower temperature of 10 000 K compared with the first laser (14 000 K), indicating that

ACCEPTED MANUSCRIPT

the second laser might be rarely absorbed by the plasma. Although it can be observed that DP

temperature (maximum temperature in the whole plasma) is slightly higher than SP within tens of

nanoseconds after the arrival of the second laser in the model set up by Bogaerts et al. [218], the

temperature improvement effect is closely related to the observation time which should be sufficiently

early therein. This might be the reason why many research workers didn’t observe the temperature

increment in DP mode.

The interval time between two lasers is another factor that influences the temperature.

Cristoforetti et al. [186] varied from 100 ns to 5 μs in pre-ablation DP mode (1064 nm, 8 ns, 120

mJ for pre-ablation, 240 mJ for ablation) in spatial-integrated manner at the time of 500 ns after the

onset of ablation laser. They found that the temperature didn’t change with when the distance

between the focal point of the lens and sample surface (named d) was less than 0.7 mm whereas it

reached a valley value at about 1000 – 3000 ns when d > 0.7 mm. Benedetti et al. [180] adjusted

from 0 μs to 50 μs to generate an aluminum plasma in spatial-integrated manner and got a maximum

temperature value for from 1 – 7 μs. Similar results were obtained by Gautier et al. [190] who

observed a maximum temperature at = 200 ns ( ) and Stratis et al. [133] who

changed from 0 μs to 300 μs and got a maximum temperature at approximately .

However, in another work done by Cristoforetti et al. [128], a Cu plasma was generated in air varying

from 0 – 8 μs (1064 nm, 10 ns, 80 mJ for each pulse) in spatial-integrated manner at an observation

time point of 0.2 μs and no significant variation of temperature was observed. Similarly, Sattmann et al.

[136] got the same result in which varied from 0 to (in this case the DP mode could be

regarded as two single shots) in a steel plasma in air (1064 nm, 25 ns, total energy 80 mJ). Mao et al.

[197] investigated the ranging from 0 ns to 10 (1064 nm, 4 ns, 10 mJ, silicon sample, air

atmosphere, spatial-integrated, observation time 600 ns) and observed that temperature decreased as

increased from 1 to 100 ns but showed a sharply increment at . The

decreasing behavior ( < 100 ns) was attributed to free expansion of the second generated plasma in

the pre-rarefied circumstance caused by the first laser shot, and the increasing nature at

was ascribed to absorption of the second laser at the sample surface.

5. The influence of ambient surrounding

The ambient surrounding is also a significant factor affecting the ablation process and the

properties of plasma. In order to optimize the ambient surrounding conditions for a better performance

of LIBS, it is of great importance to get insight into how and why these conditions would influence the

plasma temperature.

5.1. Gas species

Most of the results exhibited that the highest plasma temperature was obtained in the surrounding

of argon among differenct gas species, which are summarized in Table 4. Bashir et al. [145]

investigated Cd plasma temperature in Ar, Air, and He by applying a 1064 nm, 10 ns laser firing at

5200 J/cm2 in time-integrated manner and observed that TAr > TAir > THe. They proposed three reasons

accounting for the result. First of all, the essential condition which must be met for the development of

cascade-like growth can be expressed as [182, 219]:

ACCEPTED MANUSCRIPT

where stands for the energy of the free electrons; the radiation intensity; the effective

frequency of electron-neutral collisions; the cyclic frequency of radiation; the energy of the first

ionization stage of the gas; M the background gas neutral particle mass. The first term of the equation

remains the same for all gas species, and the second term indicates the maximum energy loss rate of

plasma by elastic and inelastic collisions with neutral gas particles which is substantially determined by

the value of E/M. The calculated E/M value for Ar, N2, O2, and He are 0.39, 0.52, 0.43, and 6.14,

respectively, which implies that the plasma generated in Ar is more absorptive due to its greater

cascade-like growth. Besides, the thermal properties of gas species should also be taken into

consideration. The thermal conductivity of Ar, Air, and He are 42.57, 62.40 (N2) and 360.36,

respectively, which apparently means that the plasma generated in He suffers from more energy loss

via faster cooling compared with Ar and Air. Finally, the elastic collision is chiefly responsible for the

rate of electron energy loss, as the elastic collision term is given as [220]:

where is the particle mass of background gas and is the elastic scattering cross section of the

electrons. It can be deduced that elastic collisional cooling is more efficient in lighter background gases

like He since it is inversely proportional to . Aguilera et al. [93] also observed that the steel plasma

temperature generated in Ar (1064 nm, 4.5 ns, 38 GW/cm2, spatial-integrated) not only surpassed those

in air and He, but also decreased the slowest within the time window of 0.7 – 46 μs, whereas the

temperature generated in He had a completely opposite behavior. In another experiment done by the

same group [106], it was observed in spatially-resolved manner that the gradient of iron plasma

temperature in Ar was lower than that in air as well (1064 nm, 4.5 ns, 100 mJ, time window: 2 – 3 ,

5 – 6 , 9 – 11 ). Bogaerts et al. [221] simulated the spatial distribution (0 – 0.7 mm) of Cu plasma

temperature generated by a 266 nm, 6 ns laser at 2.9 GW/cm2 in Ar and He within the investigated time

of 10 – 100 ns. The result showed that the temperature in Ar and He were almost the same near sample

surface, which was ascribed to the fact: in the early stage of plasma evolution (before 100 ns), plasma

is mainly composed of sample particles and not fully mixed with background gas , and cooling effect is

not significant [144, 221]. However, as the position moved away from the sample surface, the

temperature generated in Ar decreased slower than that in He. They suggested that more electrons are

produced in Ar surrounding due to its lower ionization potential; hence the plasma is able to absorb

more energy via IB which leads to a slower decreasing behavior of temperature.

Table 4

Selected studies on plasma temperature behaviors with respect to different surrounding gas species

Sample Plasma temperature behavior Time and space region Ref.

Fe Ar> air 2 – 11 μs [106]

Cu, Al Ar> air 0 – 10 μs / (0 mm, 0.5 mm) [144]

steel Ar> He 0.7 – 46 μs / space-integrated [93]

Cd, Zn Ar> Ne > He / [138]

brass Ar> Ne > He 500 ns / 0.5 mm [173]

Pb Ar> Ne > He / [2]

water Ar> air > N2 2 – 10 μs [86]

Cd Ar> air > He time-integrated [145]

Cu Ar> Ne > air > N2> He 2 – 42 μs / 1 mm [124, 125]

ACCEPTED MANUSCRIPT

graphite Ar> N2> He 500 ns / 5 mm [75]

Ta Ar> mixture (CO2, N2, He) >

O2> N2> He

Time-integrated [154]

graphite Ar> He > air 3 mm [182]

Al alloy He > air 0.5 μs [116]

Al alloy He > air 0.5 – 10 μs / space-integrated [114]

Al N2> He > air > O2 1 – 20 μs [118]

graphite air >Ar 500ns / 5mm [75]

lithium niobate O2>Ar time-integrated / 2 – 17 mm [179]

TiO2 O2>Ar / [159]

steel air ≠ Ar ≈ He 0.6 – 6 mm [134]

As opposite to the phenomenon observed above, Lee et al. [129] found that the Cu plasma

temperature (193 nm, 10 ns, 9.8×108 W/cm

2, time-integrated) generated in air was higher than that in

Ar. It was attributed to the exothermal effect happened in the reactions with O2. Detalle et al. [114]

found that the average temperature of aluminum alloy plasma (1064 nm, 6 ns, 0.37 GW/cm2) produced

in He was approximately 2500 K higher than that in air. They proposed that fewer electrons are

generated in He by which the IB process is less efficient and more laser energy can be delivered to the

sample, thus higher temperature-plasma is generated at early stage. However, the temperature in He

declined more rapidly due to its higher thermal conductivity.

5.2. gas pressure

Most of the studies for the influence of gas pressure exhibited that LIP temperature increased with

increasing ambient pressure [2, 69, 70, 75, 89, 97, 127, 129, 132, 134, 138, 150, 158, 159, 173, 174,

194, 195], some of which are plotted in Fig. 3.

ACCEPTED MANUSCRIPT

Fig.3. The increasing behavior of plasma temperature versus increasing surrounding gas pressure. The data sets are extracted as:

[129]; [127]; [194]; [97]; [138]; [2]; [173]; [132]; [70].

Grant et al. [134] investigated the steel plasma (308 nm, 28 ns, 1.6×106 W/cm

2) generated in

various of background gases at pressure ranging from 0.5 – 760 Torr and the position of 0.6 – 6.6 mm.

They observed the temperature decreased with decreasing pressure and deemed that low background

pressure could not confine the plasma very well, in other words the plasma would expand freely;

Consequently the plasma and energy spread over a large volume. Lee et al. [129], Lu et al. [97], and

Rashid et al. [127] got similar experimental results and held the same viewpoint. In a work carried out

by Shaikh et al. [70], a Cd plasma (1064 nm, 5 ns, 5×1010

W/cm2) was generated in air at pressure

ranging from 25 – 1000 mbar and the plasma temperature increased with increasing pressure at the

position of 0.5 mm and the time of 500 ns. Confinement is thought to be responsible for it, but the

authors proposed two other factors: firstly, as the pressure increases, gas species in air would take part

in the reaction with plasma species to release more energy and heat the plasma to a higher temperature;

secondly, since the plasma is confined in a rather small space, the mean free path of the particles in

plasma would decline and thus the collision heating effect would be more significant. Chen et al. [222]

conducted a model in which they found that the maximum temperature of the plasma in vacuum is

higher than that in He (5 atm) at the time of 10 ns whereas the situation turns inversely at 30 ns,

indicating that the decreasing rate of plasma temperature in high pressure is lower than that in low

pressure. The standpoint was confirmed by experimental results acquired by Liu et al. [150] who

investigated the temperature of Ti-Al alloy plasma (1064 nm, 10 ns, 10.04 GW/cm2) generated in air

and vacuum. They observed that the temperature in air was not only higher at the position of 1 mm and

time window of 200 – 1200 ns but also lasted longer.

Several studies found that LIP temperature was inversely proportional to gas pressure [27, 89, 126,

144, 160, 179, 207]. A few explanations were figured out to interpret the result. Gomes et al. [144]

observed that the temperature of Cu plasma (1064 nm, 8 ns, 109 W/cm

2) generated in 5×10

5 Pa of He

was lower than that in 105 Pa at sample surface and the time window of 0.5 – 9 , which was ascribed

to the severer shielding effect at higher pressure. Hafez et al. [126] and Harilal et al. [160] held the

same standpoint that the energy transfer between electrons/excited species and background gas via

collisions (collisional cooling) becomes more remarkable with increasing gas pressure. Bogaerts et al.

made a comparison of the Cu plasma temperatures (266 nm, 10 ns, 4×108 W/cm

2) generated in 1 atm

He and vacuum by means of modeling [227]. The result exhibited that the latter is higher than the

former. The primary reason is the direct cooling effect of background gas whose temperature is near to

room temperature initially. Moreover, the ionization degree of the plume in He is lower than that in

vacuum, thus the laser-plasma interaction effect is not notable. Finally, there exists a Knudsen layer

above the surface of the sample in the case of 1 atm He where the temperature jump effect takes place.

In terms of temperature decreasing rate with time, Vivien et al. [69] found that the temperature of

graphite plasma generated in 0.1 Torr N2 decreased faster than that in 0.05 Torr, which showed that a

higher temperature gradient was established in 0.1 Torr N2.

Some researchers observed a maximum [32, 128, 145, 154] or minimum [100] temperature value

within the pressure range investigated instead of monotonical changing. For example, Smijesh et al.

[100] got the lowest temperature of Zn plasma (796 nm, 100 fs, 1.6×1014

W/cm2) at the air pressure of

0.1 – 0.5 Torr (0.05 – 10 Torr investigated) at the position of 2 mm, 4 mm, and 6 mm. Khan et al. [154]

observed the maximum temperature of Ta plasma (1064 nm, 10 ns, 700 J/cm2) at 300 Torr (5 – 760

ACCEPTED MANUSCRIPT

Torr investigated) in time-integrated manner. It was supposed that, under the low pressure, the mean

free path of the electrons is small, thus the plasma expands freely and the IB process is not significant,

which is responsible for the low plasma temperature. As pressure ascends, the gas content acts as a

buffer region which assists energy transferring from laser to sample and more material can be ablated

into the plasma [145, 154]. Meanwhile, plasma is confined to a smaller region which promotes the IB

and momentum transfer process as well as accelerates the recombination process which releases energy

back into the plasma [182], thus the plasma temperature is elevated. By further increasing the pressure,

plasma shielding effect greatly hinders the energy transferring to sample. At the same time, more

energy is lost via collisions between electrons and surrounding species [128] which obstructs the

growth rate of free electrons energy via IB [145, 182].

Nonetheless, in the research by Kurnawan et al. [95], the temperature of Cu plasma (1064 nm, 750

mJ) generated in N2 kept relatively constant versus the variation of gas pressure (200 – 50 000 Pa) in

spatial- and time-integrated manner. Analogously, Li et al. [120] observed the same conservative

behavior of the temperature of brass plasma (1064 nm, 15 ns, 1.75×109 W/cm

2), whose pressure lied

between 10-3

Pa and 500 Pa of air, at the position of 0 – 1.35 mm and time of 300 ns. No explanation

was given to interpret the result.

6. The influence of sample characteristics and sampling geometry

The properties of sample play an important role in plasma formation and plasma processes. Since

the physical and chemical characteristics of atoms and molecules inside the sample could vary

significantly, it is worthy to investigate the influence of samples with different chemical compositions

and physical features/morphologies on plasma temperature. Meanwhile, one could adjust sampling

geometry for LIBS to get optimum analytical result, which is set aside to the last subsection.

6.1. Sample composition

The samples investigated in the studies summarized here include Cu, Al, Fe, Ni, glass, rock, sand,

soil, oxides, and solutions, which are summarized in Table 5. According to the majority of the

experimental results, the comparison of plasma temperature generated in various solid samples can be

revealed as Cu> Fe> Ni ≈ Al ≈ glass ≈ rock (herein this simplified form is used to compare the

temperature generated in different samples), except for the result obtained by Sabsabi et al. [164] in

which Al> Cu (1064 nm, 8 ns, 2.5×109 W/cm

2) in spatial-integrated manner at the time window of 1 –

40 . Bulatov et al. [105] investigated the temperature of plasma (1064 nm, 7 ns, 3.55×109 W/cm

generated in sand-soil-mixed samples with different ratios and observed that the plasma temperature

for the sample with more fraction of sand was higher than that of soil. In the work carried out by

Dadras et al. [119], Fe plasma temperature was higher than that of Al (1064 nm, 240 ns, 38.2 J/cm2) in

time-integrated manner, which was ascribed to the fact that the absorption coefficient of Fe for 1064

nm is 0.1 while it is 0.06 for Al. In this case more energy is absorbed for Fe for melting and

vaporization. According to Gomes et al. [144] Cu plasma temperature generated in Ar, air, and N2 was

approximately 3000 K higher than that of Al plasma temperature (1064 nm, 8 ns, 109 W/cm

2) at sample

surface and the observation window of 0.2 – 4.7 . They supposed that the lower fusion temperature

ACCEPTED MANUSCRIPT

of Al might be responsible for the plasma temperature behavior by which more particles would be

ablated and the given laser energy is further shared by these additional material; hence lower plasma

temperature is produced. In the result acquired by Lee et al. [28] the temperature of Cu plasma

generated by a 193 nm, 10 ns, 1.54×109 W/cm

2 laser in air surpassed that of Pb in time-integrated

manner at the position of 0 – 3.6 mm, which was supposed to result from the higher thermal

conductivity and boiling temperature of Cu by which a more compact plasma would be generated.

Ismail et al. [155] compared the plasma temperatures generated in Al and steel in air (1064 nm, 7 ns,

70 mJ), and found that steel> Al at the time window of 0 – 40 , which was attributed to the higher

ionization potential of the main composition of the sample matrix (Fe in this case). Bleiner et al. [223]

constructed a model considering the heat capacity, thermal conductivity and diffusivity, optical

absorption coefficient, surface reflectivity, melting and boiling point, heat of fusion and evaporation,

and first and second ionization potential of various metal elements. They obtained the simulation result

that Cu> Zn> Mn> Fe> Mo> Al regarding the maximum temperature in the plasma (266 ns, 5 ns, 1

GW/cm2) at the time of 100 ns. Nevertheless, Sarkar et al. [176] investigated the temperature of plasma

(1064 nm, 7 ns, 875 J/cm2) generated in different forms of vanadium oxides (VO, V2O3, VO2, V2O5)

and didn’t observe any diversity among them at the time window of 0.5 – 8 μs.

Table 5

Selected plasma temperature behaviors with respect to different sample compositions

Surrounding gas Plasma temperature behavior Time and space region Ref.

air Al> Cu 1 – 40 μs [164]

Ar, air, N2 Cu> Al 0.2 – 4.7μs / 0 mm [144]

air Cu> Al Time-integrated / 0 – 3.6 mm [28]

air Cu> Ni≈ Al 3 μs [177]

Ar Cu> Fe> Al 2 – 30 μs [210]

/ Fe> Al time-integrated [119]

air Fe> Al 0 – 40 μs [155]

Ar Fe> Al 6 – 30 μs / space-integrated [123]

air Fe> Al≈ glass≈ rock time-integrated [62]

/ sand> soil 0 – 30 μs / (0.5 mm, 3.5 mm) [105]

air VO≈ V2O3≈ VO2≈ V2O5 0.5 – 8 μs [176]

Apart from the composition of samples, the species concentration is another vital aspect of sample

characteristics. In a study done by Aguilera et al. [177], the plasma temperature (1064 nm, 4.5 ns, 40

GW/cm2) for different Ni-based alloys (Ni concentrations ranged from 65% - 99%) kept constant at the

observation time of 3 . Similar conservative behavior of temperature was observed by Lo et al. [80]

who compared the temperatures of plasmas (193 nm, 15 ns, 10 J/cm2) for hydrochloric acid solutions

with different concentrations of lithium chloride (20 M, 98 M, 1 M) at the time window of 1 – 6 .

On the other hand, Leis et al. [122] observed a negative relationship between the Fe-Cr alloy plasma

temperature (1064 nm, 8 ns, 8×109 W/cm

2) and the concentration of Cr in the sample (0 – 90%) due to

the extra material ablated with the increase of Cr concentration. Similarly, Rai et al. [91] found that the

plasma temperature (532 nm, 7×1012

W/cm2) for diverse Cr solutions decreased with increasing Cr

concentration in the liquid matrix (0 - 2×104 ppm). They claimed that as analyte concentration ascends,

ACCEPTED MANUSCRIPT

laser-target interaction volume will increase as well, consequently a greater part of the laser energy will

be consumed to heat the sample volume, and the plasma temperature will decrease.

6.2. Physical features/morphology

Cowpe et al. [198] investigated the influence of hardness of bio-ceramic sample on plasma

temperature (532 nm, 4 – 6 ns, 200 mJ) in spatial-integrated manner at the time of 4 and observed

that the temperature increased with increasing sample hardness (Vickers Hardness Number: 400 - 600).

The result was further confirmed by the study conducted by Labutin et al. [79] in which the

temperature of Li-Al alloy plasma (532 nm, 15 ns, 4 GW/cm2) was proportional to the micro-hardness

(50 – 120 kg/cm2) of the alloy samples. At the same time, they observed that the temperature of

annealed lithium ferrite plasma was higher than that of the non-annealed. They supposed that less

material is ablated with higher hardness of the sample, thus the plasma is featured by a higher

temperature value. Besides, as the samples of higher hardness having lower thermal conductivity, the

plasma would be heated to a higher degree.

Several researches have investigated the influence of confinement on plasma temperature. Russo’s

group has carried out plenty of studies dealing with the influence of cavity confinement [199-202]. In

their work, the greater the cavity aspect ratio (depth/diameter values of 1, 3, 6) against the flat silica

surface, the higher the plasma temperature (266 nm, 3 ns, 6.95 GW/cm2) at positions ranging -0.5 – 1

mm (the negative value indicates the distance from a certain position inside the cavity to the bulk

sample surface). It was also found that plasma expansion was restricted and electron number density

was higher than that produced on the sample surface due to the confinement effect of sample cavity. As

a consequence, the IB process was enhanced and more energy was absorbed to be converted into

internal energy of the plasma. Meanwhile, they compared the temporal behaviors of plasma

temperature (50 – 400 ns, 7.67 GW/cm2) in the cavity and sample surface at the position of 0.2 mm

with respect to the bottom of the cavity and the sample surface respectively, and observed that the

former was higher at early stage but declined more rapidly than the latter. The result was ascribed to

four mechanisms of energy transferring from plasma to cavity wall [200, 202]:

(1) normal electron heat conduction;

(2) electron-ion recombination on cavity walls (exothermic);

(3) short-wavelength thermal plasma radiation;

(4) condensation of the vapor moves to the sample surface due to plasma expansion.

Besides, they studied the temperature behavior of silica plasma versus increasing irradiance (2 – 40

GW/cm2) at flat surface and in cavities of different aspect ratios at the positions of 0.2 mm and 0.7 mm

(to the sample surface and the bottom of the cavity, respectively) and the time of 30 ns [201].

According to their result, there exists an irradiance threshold above which temperature increases much

more rapidly compared with the irradiance below the threshold. The greater the aspect ratio is, the

lower the threshold value is. It might due to the fact that self-focusing effect is more significant in the

cavity of higher aspect ratio in that its electron number density is higher, thus even stronger energy

density is generated and phase explosion threshold is surpassed at lower laser irradiance accordingly.

Corsi et al. [96] carried out similar experiments and observed a temperature rise of Cu plasma (1064

nm, 6 ns, 7.9 GW/cm2) generated in a 1 mm deep cavity compared with that on the sample surface, but

no elevation effect was observed in the 1.5 mm deep cavity. They claimed that the energy loss

mechanism dominated over the confinement enhancement effect in the 1.5 mm deep cavity. Shannon et

ACCEPTED MANUSCRIPT

al. [224] established a model dealing with the relationship between cavity aspect ratio and laser energy

absorption efficiency and got the result that the higher the aspect ratio, the more efficient the laser

absorption. Jeong et al. [225] investigated the laser-cavity interaction by means of photo-thermal

deflection and observed that: (1) the reflected laser in the cavity could enhance laser-cavity interaction;

(2) the greater the thermal conductivity of the metal samples, the more significant the laser-cavity

interaction. Wu et al. [131] investigated the influence of substrate confinement on Cu plasma generated

in air (532 nm, 15 ns, 6.4×109 W/cm

2) at the time window of 100 – 5500 ns. They found that the

plasma temperature with confinement was higher than that without confinement at sample surface.

6.3. Sampling geometry

Focusing position is easily adjusted simply by moving the position of lens or samples. With

regards to this topic, the term is introduced here representing the difference between the focusing

length and the sample-to-lens length, a positive value indicates the focal point is under the sample

surface and a negative value is above. The majority of the studies revealed the tendency that the lower

the absolute value of the higher the plasma temperature. Aguilera et al. [168] varied from 5 to

15.5 mm and found that the iron plasma temperature (1064 nm, 4.5 ns, 100 mJ) generated in air and Ar

reached the highest value at of 5 mm within the time scale of 5 – 6 . In the work done by Khalil

et al. [147] the temperature of Pb plasma (532 nm, 1.36×1010

W/cm2) generated in air found its

maximum at = 0 mm within the time scale of 0 – 600 ns. In another study done by the same group

[189] was varied from -2.54 to 4.7 mm and the Sn plasma temperature (532 nm, 8 ns, 40 mJ)

produced in air reached a maximum value at = 1.74 mm at the time window of 0 – 6000 ns.

Furthermore, Sattmann et al. [136] observed the maximum temperature of steel plasma (1064 nm, 15

ns, 80 mJ) generated in air at = 2 mm (-19 < < 25 mm). From a general point of view, as

approaches 0, the spot size gets smaller, the irradiance becomes greater and the temperature is elevated.

Nevertheless, different results were obtained by several groups. Diao et al. [146] compared the

temperatures of Pb plasma (1064 nm, 10 ns, 30 mJ) generated in air at of -0.4 and -0.2 mm and

observed that the former was higher than the latter. Multari et al. [33] investigated the influence of

(from -15 to 2 mm) on the temperature of soil plasma (1064 nm, 10 ns, 186 mJ) and got valley values

at -2 < < 2 mm. In their opinion, as becomes more and more negative, air plasma will be

produced in front of the sample which is bound to absorb lots of laser energy. They also estimated the

influence of laser incidence angle on plasma temperature and acquired the result that temperature

decreased from 8000 K to 7200 K as the sample rotated from 0° to 40° but again rose to 8700 K as the

sample went on rotating to 80°.

7. The temporal and spatial evolution of LIP temperature

It is well-known that LIP is a transient and inhomogeneous system in which plasma properties

vary with the time and space. The temporal variation of plasma temperature is a vital parameter since

many kinetic reaction rates are directly or indirectly related to it [167]. Besides, it is of prime

importance to choose the time delay in order to ensure that LTE is reached within the plasma region

investigated and get reliable quantitative results [81]. On the other hand, after the onset of ablation, the

plume expands away from ablation point both axially and laterally, thus the plasma energy is

ACCEPTED MANUSCRIPT

distributed over the whole plasma region. The investigation of spatial distribution of plasma

temperature can shed light on the study of plasma expansion mechanism and plasma-surrounding

interaction. Hence in this section, the different temporal and spatial evolutions of LIP temperature

studied by various groups are reviewed and some explanations will be listed to interpret the results.

7.1. Temporal evolution

According to the simulation work carried out by Amoruso et al. [226], electron temperature rises

rapidly at the very beginning of the plasma evolution (0 – 6 ns) and stops climbing as the laser duration

ends (6 ns), as well as the electrons reach an equilibrium with heavy particles. Subsequently, the

plasma temperature features a decreasing trend as time elapses, since many energy loss mechanisms

exist in the whole process, i.e., thermal conduction to the background gas and target, the cooling of

plasma expansion against ambient pressure, and radiative cooling [83]. In most cases, plasma

temperature decreases rapidly (sometimes exponentially) at early stage of plasma expansion and keeps

relatively constant subsequently until the end of spectral emission, as plotted in Fig.4. In the studies

done by Harilal et al. [181, 187] the variation of graphite plasma temperature (1064 nm, 50 GW/cm2)

against time showed a t -2

dependence within 100 – 300 ns which was consistent with the modeling

result established by Rumsby at al. [220] who assumed that the plasma expands adiabatically. As time

goes on to 2000 ns, plasma temperature declines much slower and keeps approximately constant near 2

eV (20 000 K), which is ascribed to the mechanism that the energy loss induced by expansion cooling

is partly compensated by the energy released in recombination process.

Fig.4. The decreasing trend of LIP temperature as time elapses. The data sets are regenerated from various studies: [167];

[146]; [75]; [61]; [195]; [171]; [184]; [140].

Apart from the monotonically decreasing behavior of plasma temperature illustrated above,

several studies found a maximum [32, 97, 131, 160, 189] or minimum [39, 61, 118] temperature value

at a certain time of plasma evolution. Harilal et al.[160] calculated C2 vibrational temperature in

ACCEPTED MANUSCRIPT

graphite plasma (1064 nm, 9 ns, 7.3×1010

W/cm2) generated in He surrounding and observed a

maximum value at 2 μs (observation time: 0 – 40 μs) and the position of 5 mm. They proposed that, at

early stage of the plasma (less than 2 μs), the overall energy of the plasma is extremely excessive,

hence the species are dissociated as well as excited to higher vibrational levels. According to the work

done by Khalil et al. [189] the temperature of Sn plasma (532 nm, 8 ns, 40 mJ) generated in air

remained increasing before 500 ns both in SP and DP mode which was attributed to the result of

laser-plasma interaction. The same conclusion was drawn by Lu et al. [97] who observed an increasing

trend of Al plasma temperature (248 nm, 23 ns, 4.63 J/cm2) within the time scale of pulse duration.

Nevertheless, in another study done by Harilal et al. [39] the temperature of Sn plasma (1064 nm, 8 ns,

2 GW/cm2) generated in vacuum again ascended at the time of 400 – 500 ns after reaching a valley

value. They claimed that the three-body recombination might be responsible for the increasing in later

stage by which the energy loss is compensated by the energy released in recombination process. In

addition, Colao et al. [61] investigated the temporal evolution of temperature of basaltic rock plasma

(355 nm, 8 ns, 300 J/cm2) and found that the temperature calculated using higher excited levels of Fe

neutrals increased after 1 μs (observation time: 0 – 3 μs). The explanation was that the intermediate

excited levels are under-populated during recombination but it is not always the case for the low

excited levels, thus LTE state may be violated accordingly.

There exist several studies in which the temperature stayed constant with respect to time evolution.

Knudtson et al. [157] observed that the temperature of Al plasma (583 nm, 2 μs, 5.3×107 W/cm

generated in vacuum kept approximately at 8000 K within the time window of 0.2 – 3 μs at the position

of 1.27 mm. Milan et al. [52] also found that the Si excitation temperature of silicon plasma (532 nm, 5

ns, 53 J/cm2) generated in air kept nearly unchanged within 200 – 2200 ns which was ascribed to the

difficulty in selecting satisfactory spectral lines of Si.

7.2. Spatial evolution

Most of the studies dealing with spatial evolution summarized here exhibited a decreasing trend of

plasma temperature with increasing distance [1, 71, 82, 101, 120, 127, 134, 139, 151, 157-159, 161,

162, 170, 171, 174, 175, 181, 187] and somewhat a conservative feature above a certain distance, as is

plotted in Fig.5. The laser energies utilized in these studies were different from each other.

ACCEPTED MANUSCRIPT

Fig.5. Axial distribution of LIP temperature. Data are extracted from various studies: [134]; [127]; [174]; [1];

[139]; [159]; [82]; [171]; [175]; [187]; [161]; [157]; [151]; [101]; [162];

[170].

For example, Harilal et al. [187] investigated the spatial evolution of the temperature of YBCO

plasma (1064 nm, 9 ns, 42 GW/cm2) generated in vacuum in time-integrated manner and observed that

the temperature deceased rapidly from 1.12 eV (11 200 K) to 0.18 eV (1800 K) before the distance of 5

mm and kept relatively constant in the region of 5 – 11 mm. It is widely believed that the higher

temperature near sample surface is attributed to the IB process by which plasma takes in more energy

in its inner part, while the lower temperature lying away from the surface results from the conversion

of thermal energy into kinetic energy to obtain maximum expansion velocity [1, 82, 101, 127, 139, 161,

162, 170]. The conservative behavior of temperature in the outer region of plasma is attributed to the

recombination process by which extra energy is released [159, 187]. However, contrary temperature

evolution behavior was also observed in several works [39, 63, 69]. According to the study done by

Harilal et al. [39], the temperature of Sn plasma (1064 nm, 8 ns, 2 GW/cm2) generated in vacuum

evenly distributed over 1 – 5 mm and increased in the spatial region of 5 – 15 mm. They claimed that it

should be ascribed to the effect of three-body recombination in the outer region of plasma. Besides, a

deviation from LTE is supposed to take place far away from sample surface in that: (1) various species

of different moving velocities separate themselves from each other in later time, and the time required

to establish equilibrium via collisions becomes greater; (2) the number density of electrons decreases to

a relatively low value in the outer region of plasma. Vivien et al. [69] found that the C2 rotational

temperature of graphite plasma (248 ns, 25 ns, 6 J/cm2) generated in N2 increased with increasing

distance (2 – 8 mm) within the time window of 200 – 2000 ns, which was attributed to the collisional

heating effect of background gas species. Yet in a study done by Gordillo et al. [179] the plasma

temperature generated from lithium niobate sample (193 nm, 20 ns, 0.06 GW/cm2) kept constant over a

long range of distance (2 – 17 mm) in vacuum and 1 torr Ar. They deemed that the low laser irradiance

utilized (thus low-energy electrons didn’t further dissipate) might be responsible for it. As the species

separated from each other due to their different velocities, the collisional cooling between atoms and

ACCEPTED MANUSCRIPT

electrons might be not likely to take place, thus the plasma temperature would keep approximately

unchanged.

On the other hand, several studies obtained their maximum [28, 32, 53, 110, 115, 126, 156, 167,

169, 211, 212] or minimum [38, 183] temperature values at a certain region of the plasma. For example,

in the work done by Barthélemy et al. [115], the temperature of Al plasma (1064 nm, 6 ns, 10 J/cm2)

was calculated at the positions ranging from 0 mm to 2 mm and different delay times (2 – 30 μs). It

reached its maximum value within 1 – 1.5 mm. It is commonly accepted that the lower temperature

above sample surface is attributed to the thermal conduction from plasma to target [53, 115, 169]

considering the equilibrium time of energy transfer from electrons to ions (10-10

– 10-11

s) [110], while

the IB process is responsible for the maximum temperature occurring in the middle of plasma [126,

169]. The decreasing feature at the outer region of the plasma is attributed to the three cooling

mechanisms mentioned in the beginning of subsection 7.1, viz. thermal conduction [169], expansion

cooling [110, 126, 169], and radiative cooling [52, 110, 115, 169]. In the case of molecular temperature,

Harilal et al. [32, 211] got the maximum CN vibrational temperature of graphite plasma (1064 nm, 9 ns,

3.54×1010

W/cm2, air atmosphere) at the position of 8 mm (0 – 20 mm). It’s believed that the

collisional dissociation of CN species happens frequently above the sample surface due to the extreme

high overall temperature there, thus the vibrational temperature is declined. The decreasing feature at

the outer region was ascribed to the decreased overall plasma temperature. As for the case of

minimum temperature, Cristoforetti et al. [38] got the minimum Al plasma temperature (1064 nm, 20

ns, 8×109 W/cm

2, air atmosphere) in the middle of plasma at the time of 1 μs. Giacomo et al. [183] also

observed the minimum temperature of Al plasma (1064 nm, 7 ns, 5×109 W/cm

2, air atmosphere)

between 0.5 mm to 1 mm within the observation region of 0.25 – 2 mm and time window of 0.5 – 4 μs.

They attributed the minimum temperature to the effect of pressure equalization within the contact wall.

Two-dimensional distribution of plasma temperature is either line-of-sight integrated or spatially

resolved. The routinely obtained spectral intensity I (W m-2 nm

-1) stands for the integrated spectral

emission along the line-of-sight [168]. Since the plasma is an inhomogeneous system, the integrated

intensity is derived from different plasma regions featured by different properties. The spatially

resolved data can be obtained by applying a deconvolution procedure called Abel inversion through

which local temperature values could be calculated [68]. In the procedure, the plasma is assumed to be

optically thin and features a cylindrical symmetry, thus the intensity can be expressed as [228]:

where y stands for the lateral position; the radius of the source; r the distance from the axis of

symmetry; the emissivity per wavelength (W m-3 nm

-1). By applying Abel inversion, one can

obtain the value of by:

The method has two shortcomings: firstly, the derivative term could not be precisely determined

by the experiment data with random errors; secondly, there exists the divergence of integrals in the

above two equations for y = r [106]. Several works were carried out to improve the performance of

Abel inversion [85, 106, 109] which will not be elaborated here. It is believed that the temperature

calculated via Abel inversion procedure will be higher than that without it, since the integrated

experimental data involves the outer region where cooling effect becomes significant. Yalçin et al. [66]

compared the air plasma temperature (532 nm, 10 – 13 ns, 40 – 150 mJ) calculated with and without

ACCEPTED MANUSCRIPT

Abel inversion and found that the former was higher than the latter by 5%. Cristoforetti et al. [38] also

found that the two temperatures (1064 nm, 20 ns, 8×109 W/cm

2, Al sample, air atmosphere) equaled to

each other at outer region but Abel inversion-temperature surpassed the other by 3% in the inner

plasma region. However, some authors found that the difference between the two temperatures was

equal to experimental error [137] and calculated temperature without utilizing Abel inversion [144]. In

general, the lateral distribution of temperature frequently exhibits a ‘plateau’ like behavior around the

axis of the plasma, as shown in Fig. 6. For example, in the research done by Aguilera et al. [68], the

temperature of Fe-Ni alloy plasma (1064 nm, 4.5 ns, 15 GW/cm2) reached its maximum value of 12

000 K at the radiation position of 0 mm (axial position 2 mm, at the time of 3 μs) and decreased

monotonically to about 5500K at both lateral directions. Readers may refer to more studies [53, 107,

109, 125, 137, 168] for a further understanding of two-dimensional distribution of plasma temperature.

Fig.6. Lateral distributions of plasma temperatures in different studies. Data are extracted from the references below with

corresponding axial positions: [53], z = 1.6 mm, 10 GW/cm2; [137], z = 1 mm, 45 GW/cm2; [68], z = 2 mm, 15

GW/cm2; [125], z = 1 mm, 12 mJ.

8. Conclusion

This study has reviewed the fundamental theories and calculation methods of LIP temperature, as

well as its dependence on various experimental conditions including laser parameters, ambient

surrounding, sample characteristics and sampling geometry, and temporal and spatial evolution. For the

term ‘plasma temperature’ to be valid, the plasma investigated should be close to the state of LTE.

Under such a circumstance, a unique temperature value can be applied to various distribution laws. The

criteria for selecting proper spectral lines, judging the optically thin state, and estimating the

uncertainty of temperature have also been briefly reviewed. As to the temperature dependence on laser

parameters, most of the studies summarized exhibit that plasma temperature increases with increasing

laser wavelength, pulse width, and laser energy by fixing other parameters. Meanwhile, the temperature

of plasma generated in dual-laser pulse mode frequently surpassed that in single-laser pulse mode. In

general, most of the studies dealing with the influence of the background gas species and pressure

ACCEPTED MANUSCRIPT

reveal that the plasma generated in argon features a maximum temperature compared with other

surrounding gas species, and the temperature is proportional to the background pressure, while contrary

results were also observed in a few works. With regard to the sample characteristics, the greater the

sample hardness is, the higher the plasma temperature is. The influence of plasma confinement (cavity

or substrate) is significant for plasma temperature and its decreasing rate. It tends to reach maximum

when the sample to lens distance is approaching the focal length of the lens. Finally, LIP temperature

appears to decline monotonically as the time elapses and distance increases due to various plasma

cooling mechanisms, yet maximum or minimum values were also acquired at certain time periods and

plasma regions according to some studies.

The investigation of the factors influencing LIP temperature is of great importance both in

theoretical researches and applications. By gaining the knowledge of how and why such factors would

affect plasma temperature, one can get further insight into the whole processes happening within the

plasma and opt for appropriate operating conditions to achieve optimum analytical performance.

Various applications, such as surface modification, material processing, thin film deposition, and

remediation of hazardous gases, urgently necessitates the knowledge about plasma temperature

evolution, thus again underline the importance of investigating the variation of temperature with

respects to various factors. It should be emphasized that it is difficult to directly compare the results

obtained by different authors in that the parameters could hardly be kept the same in different

laboratories, thus more research works should be carried out in the future to further validate the

conclusions reached.

Acknowledgement

We gratefully acknowledge the financial support from the Natural Science Foundation of

China Financial (No. 21027011) and Program for Changjiang Scholars and Innovative Research

Team in University (IRT13036). This work has also been supported by NFFTBS (No. J1310024).

References

[1] M.A. Naeem, M. Iqbal, N. Amin, M. Musadiq, Y. Jamil, F. Cecil, Measurement of Electron Density

and Temperature of Laser-Induced Copper Plasma, Asian J. Chem. 25 (2013) 2192-2198.

[2] N.M. Shaikh, M.S. Kalhoro, A. Hussain, M.A. Baig, Spectroscopic study of a lead plasma produced

by the 1064nm, 532nm and 355nm of a Nd: YAG laser, Spectrochim. Acta Part B: At. Spectrosc. 88

(2013) 198-202.

[3] A.A. Lushnikov, A.E. Negin, Aerosols in strong laser beams, J. Aero. Sci. 24 (1993) 707-735.

[4] C. Aragón, J.A. Aguilera, Characterization of laser induced plasmas by optical emission

spectroscopy: A review of experiments and methods, Spectrochim. Acta Part B: At. Spectrosc. 63

(2008) 893-916.

[5] 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, J. Anal. At. Spectrom. 19 (2004) 1061-1083.

[6] R.E. Russo, Laser ablation, Appl. Spectrosc. 49 (1995) 14A-28A.

[7] D. Günther, S.E. Jackson, H.P. Longerich, Laser ablation and arc/spark solid sample introduction

into inductively coupled plasma mass spectrometers, Spectrochimica Acta Part B: At. Spectrosc. 54

(1999) 381-409.

ACCEPTED MANUSCRIPT

[8] R.E. Russo, X.L. Mao, H.C. Liu, J. Gonzalez, S.S. Mao, Laser ablation in analytical chemistry—a

review, Talanta 57 (2002) 425-451.

[9] C.C. Garcia, H. Lindner, K. Niemax, Laser ablation inductively coupled plasma mass

spectrometry—current shortcomings, practical suggestions for improving performance, and

experiments to guide future development, J. Anal. At. Spectrom. 24 (2009) 14-26.

[10] R.E. Russo, X.L. Mao, C. Liu, J. Gonzalez, Laser assisted plasma spectrochemistry: laser ablation,

J. Anal. At. Spectrom. 19 (2004) 1084-1089.

[11] L. Moenke-Blankenburg, Laser Microanalysis, John Wiley and Sons Ltd. ,1989.

[12] R.S. Adrain, J. Watson, Laser microspectral analysis: a review of principles and applications, J.

Phys. D: Appl. Phys. 17 (1984) 1915-1940.

[13] C.G. Morgan, Laser-induced breakdown of gases, Rep. Prog. Phys. 38 (1975) 621-665.

[14] 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,

Appl. Spectrosc. 66 (2012) 347-419.

[15] A. Vogel, V. Venugopalan, Mechanisms of pulsed laser ablation of biological tissues, Chem. Rev.

103 (2003) 577-644.

[16] I.B. Gornushkin, U. Panne, Radiative models of laser-induced plasma and pump-probe diagnostics

relevant to laser-induced breakdown spectroscopy, Spectrochim. Acta Part B: At. Spectrosc. 65 (2010)

345-359.

[17] M. Sabsabi, P. Cielo, Quantitative analysis of aluminum alloys by laser-induced breakdown

spectroscopy and plasma characterization, Appl. Spectrosc. 49 (1995) 499-507.

[18] 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' J. Anal. Chem. 369 (2001) 320-327.

[19] X.L. Mao, M.A. Shannon, A.J. Fernandez, R.E. Russo, Temperature and emission spatial profiles

of laser-induced plasmas during ablation using time-integrated emission spectroscopy, Appl. Spectrosc.

49 (1995) 1054-1062.

[20] F. Colao, V. Lazic, R. Fantoni, S. Pershin, A comparison of single and double pulse laser-induced

breakdown spectroscopy of aluminum samples, Spectrochim. Acta Part B: At. Spectrosc. 57 (2002)

1167-1179.

[21] B. Castle, K. Visser, B.W. Smith, J.D. Winefordner, Level populations in a laser-induced plasma

on a lead target, Spectrochim. Acta Part B: At. Spectrosc. 52 (1997) 1995-2009.

[22] S. Amoruso, R. Bruzzese, N. Spinelli, R. Velotta, Characterization of laser-ablation plasmas, J.

Phys. B: At. Mol. Opt. Phys. 32 (1999) R131-R172.

[23] A. Bogaerts, Z.Y. Chen, R. Gijbels, A. Vertes, Laser ablation for analytical sampling: what can we

learn from modeling?, Spectrochim. Acta Part B: At. Spectrosc. 58 (2003) 1867-1893.

[24] R.E. Russo, X.L. Mao, S.S. Mao, The physics of laser ablation in microchemical analysis, Anal.

Chem. 74 (2002) 70A-77A.

[25] P. Gibbon, E. Förster, Short-pulse laser-plasma interactions, Plasma Phys. Controlled Fusion 38

(1996) 769-793.

[26] P. Stavropoulos, C. Palagas, G.N. Angelopoulos, D.N. Papamantellos, S. Couris, Calibration

Measurements in laser-induced breakdown spectroscopy using nanosecond and picosecond lasers,

Spectrochim. Acta Part B: At. Spectrosc. 59 (2004) 1885-1892.

[27] Y.-I. Lee, K. Song, H.-K. Cha, J.-M. Lee, M.-C. Park, G.-H. Lee, J. Sneddon, Influence of

atmosphere and irradiation wavelength on copper plasma emission induced by excimer and Q-switched

ACCEPTED MANUSCRIPT

Nd: YAG laser ablation, Appl. Spectrosc. 51 (1997) 959-964.

[28] Y.-I. Lee, S.P. Sawan, T.L. Thiem, Y.-Y. Teng, J. Sneddon, Interaction of a laser beam with

metals. Part II: Space-resolved studies of laser-ablated plasma emission, Appl. Spectrosc. 46 (1992)

436-441.

[29] J.A. Aguilera, C. Aragón, Multi-element Saha–Boltzmann and Boltzmann plots in laser-induced

plasmas, Spectrochim. Acta Part B: At. Spectrosc. 62 (2007) 378-385.

[30] H. Hegazy, H.A. Abd El-Ghany, S.H. Allam, T.M. El-Sherbini, Spectral evolution of nano-second

laser interaction with Ti target in Air, Appl. Phys. B 110 (2013) 509-518.

[31] S.Y. Moon, W. Choe, A comparative study of rotational temperatures using diatomic OH, O2 and

N2+ molecular spectra emitted from atmospheric plasmas, Spectrochim. Acta Part B: At. Spectrosc. 58

(2003) 249-257.

[32] S.S. Harilal, R.C. Issac, C.V. Bindhu, P. Gopinath, V.P.N. Nampoori, C.P.G. Vallabhan, Time

resolved study of CN band emission from plasma generated by laser irradiation of graphite,

Spectrochim. Acta Part A: Mol. Spectrosc. 53 (1997) 1527-1536.

[33] R.A. Multari, L.E. Foster, D.A. Cremers, M.J. Ferris, Effect of sampling geometry on elemental

emissions in laser-induced breakdown spectroscopy, Appl. Spectrosc. 50 (1996) 1483-1499.

[34] D.A. Rusak, B.C. Castle, B.W. Smith, J.D. Winefordner, Excitational, vibrational, and rotational

temperatures in Nd: YAG and XeCl laser-induced plasmas, Spectrochim. Acta Part B: At. Spectrosc.

52 (1997) 1929-1935.

[35] A. Bogaerts, Z.Y. Chen, Effect of laser parameters on laser ablation and laser-induced plasma

formation: A numerical modeling investigation, Spectrochim. Acta Part B: At. Spectrosc. 60 (2005)

1280-1307.

[36] M. Capitelli, A. Casavola, G. Colonna, A. De Giacomo, Laser-induced plasma expansion:

theoretical and experimental aspects, Spectrochim. Acta Part B: At. Spectrosc. 59 (2004) 271-289.

[37] J. Van Dijk, G.M.W. Kroesen, A. Bogaerts, Plasma modelling and numerical simulation, J. Phys.

D: Appl. Phys. 42 (2009) 190301.

[38] G. Cristoforetti, G. Lorenzetti, S. Legnaioli, V. Palleschi, Investigation on the role of air in the

dynamical evolution and thermodynamic state of a laser-induced aluminium plasma by spatial- and

time-resolved spectroscopy, Spectrochim. Acta Part B: At. Spectrosc. 65 (2010) 787-796.

[39] S.S. Harilal, B. O'Shay, M.S. Tillack, M.V. Mathew, Spectroscopic characterization of

laser-induced tin plasma, J. Appl. Phys. 98 (2005) 013306.

[40] G. Cristoforetti, E. Tognoni, L.A. Gizzi, Thermodynamic equilibrium states in laser-induced

plasmas: From the general case to laser-induced breakdown spectroscopy plasmas, Spectrochim. Acta

Part B: At. Spectrosc. 90 (2013) 1-22.

[41] O. Barthélemy, J. Margot, S. Laville, F. Vidal, M. Chaker, B. Le Drogoff, T.W. Johnston, M.

Sabsabi, Investigation of the state of local thermodynamic equilibrium of a laser-produced aluminum

plasma, Appl. Spectrosc. 59 (2005) 529-536.

[42] J.A.M. Van Der Mullen, On the atomic state distribution function in inductively coupled

plasmas—II: The stage of local thermal equilibrium and its validity region, Spectrochim. Acta Part B:

At. Spectrosc. 45 (1990) 1-13.

[43] M. Capitelli, F. Capitelli, A. Eletskii, Non-equilibrium and equilibrium problems in laser-induced

plasmas, Spectrochim. Acta Part B: At. Spectrosc. 55 (2000) 559-574.

[44] J.B. Simeonsson, A.W. Miziolek, Time-resolved emission studies of ArF-laser-produced

microplasmas, Appl. Opt. 32 (1993) 939-947.

ACCEPTED MANUSCRIPT

[45] J.B. Simeonsson, A.W. Miziolek, Spectroscopic studies of laser-produced plasmas formed in CO

and CO2 using 193, 266, 355, 532 and 1064 nm laser radiation, Appl. Phys. B 59 (1994) 1-9.

[46] A.H. Galmed, M.A. Harith, Temporal follow up of the LTE conditions in aluminum laser induced

plasma at different laser energies, Appl. Phys. B 91 (2008) 651-660.

[47] L.J. Radziemski, T.R. Loree, D.A. Cremers, N.M. Hoffman, Time-resolved laser-induced

breakdown spectrometry of aerosols, Anal. Chem. 55 (1983) 1246-1252.

[48] T. Fujimoto, R.W.P. McWhirter, Validity criteria for local thermodynamic equilibrium in plasma

spectroscopy, Phys. Rev. A 42 (1990) 6588-6601.

[49] G. Cristoforetti, A. De Giacomo, M. Dell'Aglio, S. Legnaioli, E. Tognoni, V. Palleschi, N.

Omenetto, Local thermodynamic equilibrium in laser-induced breakdown spectroscopy: beyond the

McWhirter criterion, Spectrochim. Acta Part B: At. Spectrosc. 65 (2010) 86-95.

[50] A. Ciucci, M. Corsi, V. Palleschi, S. Rastelli, A. Salvetti, E. Tognoni, New procedure for

quantitative elemental analysis by laser-induced plasma spectroscopy, Appl. Spectrosc. 53 (1999)

960-964.

[51] H.R. Griem, Validity of local thermal equilibrium in plasma spectroscopy, Phys. Rev. 131 (1963)

1170-1176.

[52] M. Milan, J.J. Laserna, Diagnostics of silicon plasmas produced by visible nanosecond laser

ablation, Spectrochim. Acta Part B: At. Spectrosc. 56 (2001) 275-288.

[53] Q.L. Ma, V. Motto-Ros, W.Q. Lei, M. Boueri, X.S. Bai, L.J. Zheng, H.P. Zeng, J. Yu, Temporal

and spatial dynamics of laser-induced aluminum plasma in argon background at atmospheric pressure:

Interplay with the ambient gas, Spectrochim. Acta Part B: At. Spectrosc. 65 (2010) 896-907.

[54] 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, Spectrochim. Acta

[55] A. Alonso-Medina, Measured Stark widths of several spectral lines of Pb III, Spectrochim. Acta

[56] A. De Giacomo, M. Dell’Aglio, R. Gaudiuso, A. Santagata, G.S. Senesi, M. Rossi, M.R. Ghiara, F.

Capitelli, O. De Pascale, A Laser Induced Breakdown Spectroscopy application based on Local

Thermodynamic Equilibrium assumption for the elemental analysis of alexandrite gemstone and

copper-based alloys, Chem. Phys. 398 (2012) 233-238.

[57] B. Le Drogoff, J. Margot, M. Chaker, M. Sabsabi, O. Barthelemy, T.W. Johnston, S. Laville, F.

Vidal, Y. Von Kaenel, Temporal characterization of femtosecond laser pulses induced plasma for

spectrochemical analysis of aluminum alloys, Spectrochim. Acta Part B: At. Spectrosc. 56 (2001)

987-1002.

[58] H.-Y. Moon, B.W. Smith, N. Omenetto, Temporal behavior of line-to-continuum ratios and ion

fractions as a means of assessing thermodynamic equilibrium in laser-induced breakdown spectroscopy,

Chem. Phys. 398 (2012) 221-227.

[59] A. Sola, M.D. Calzada, A. Gamero, On the use of the line-to-continuum intensity ratio for

determining the electron temperature in a high-pressure argon surface-microwave discharge, J. Phys. D:

Appl. Phys. 28 (1995) 1099-1110.

[60] X. Chen, J. Mazumder, A. Purohit, Optical emission diagnostics of laser-induced plasma for

diamond-like film deposition, Appl. Phys. A 52 (1991) 328-334.

[61] F. Colao, R. Fantoni, V. Lazic, A. Paolini, LIBS application for analyses of martian crust

analogues: search for the optimal experimental parameters in air and CO2 atmosphere, Appl. Phys. A

ACCEPTED MANUSCRIPT

79 (2004) 143-152.

[62] C. Gautier, P. Fichet, D. Menut, J. Dubessy, Applications of the double-pulse laser-induced

breakdown spectroscopy (LIBS) in the collinear beam geometry to the elemental analysis of different

materials, Spectrochim. Acta Part B: At. Spectrosc. 61 (2006) 210-219.

[63] G. Hatem, C. Colon, J. Campos, Study of CN emission from a laser induced plasma of graphite in

air, Spectrochim. Acta Part A: Mol. Spectrosc. 49 (1993) 509-516.

[64] W.Q. Lei, V. Motto-Ros, M. Boueri, Q.L. Ma, D.C. Zhang, L.J. Zheng, H.P. Zeng, J. Yu,

Time-resolved characterization of laser-induced plasma from fresh potatoes, Spectrochim. Acta Part B:

At. Spectrosc. 64 (2009) 891-898.

[65] M. Thiyagarajan, J. Scharer, Experimental investigation of ultraviolet laser induced plasma

density and temperature evolution in air, J. Appl. Phys. 104 (2008) 013303.

[66] Ş. Yalçin, D.R. Crosley, G.P. Smith, G.W. Faris, Influence of ambient conditions on the laser air

spark, Appl. Phys. B: Lasers Opt. 68 (1999) 121-130.

[67] B. Német, K. Musiol, I. Sánta, J. Zachorowski, Time-resolved vibrational and rotational emission

analysis of laser-produced plasma of carbon and polymers, J. Mol. Struct. 511–512 (1999) 259-270.

[68] J.A. Aguilera, C. Aragón, Characterization of a laser-induced plasma by spatially resolved

spectroscopy of neutral atom and ion emissions.: Comparison of local and spatially integrated

measurements, Spectrochim. Acta Part B: At. Spectrosc. 59 (2004) 1861-1876.

[69] C. Vivien, J. Hermann, A. Perrone, C. Boulmer-Leborgne, A. Luches, A study of molecule

formation during laser ablation of graphite in low-pressure nitrogen, J. Phys. D: Appl. Phys. 31 (1998)

1263-1272.

[70] N.M. Shaikh, B. Rashid, S. Hafeez, S. Mahmood, M.A. Saleem, M. Baig, Diagnostics of cadmium

plasma produced by laser ablation, J. Appl. Phys. 100 (2006) 073102.

[71] J. Bengoechea, E.T. Kennedy, Time-integrated, spatially resolved plasma characterization of steel

samples in the VUV, J. Anal. At. Spectrom. 19 (2004) 468-473.

[72] A.H. El‐Astal, S. Ikram, T. Morrow, W.G. Graham, D.G. Walmsley, A quantitative investigation

of emission from low temperature laser-induced YBa2Cu3Ox plasma plumes, J. Appl. Phys. 77 (1995)

6572-6580.

[73] C.D. Gehlen, P. Roth, Ü. Aydin, E. Wiens, R. Noll, Time-resolved investigations of laser-induced

plasmas generated by nanosecond bursts in the millijoule burst energy regime, Spectrochim. Acta Part

B: At. Spectrosc. 63 (2008) 1072-1076.

[74] L. St-Onge, V. Detalle, M. Sabsabi, Enhanced laser-induced breakdown spectroscopy using the

combination of fourth-harmonic and fundamental Nd: YAG laser pulses, Spectrochim. Acta Part B: At.

Spectrosc. 57 (2002) 121-135.

[75] H.S. Park, S.H. Nam, S.M. Park, Time-resolved optical emission studies on the laser ablation of a

graphite target: The effects of ambient gases, J. Appl. Phys. 97 (2005) 113103.

[76] D.N. Patel, P.K. Pandey, R.K. Thareja, Stoichiometric investigations of laser-ablated brass plasma,

Appl. Opt. 51 (2012) B192-B200.

[77] H.E. Bauer, F. Leis, K. Niemax, Laser induced breakdown spectrometry with an echelle

spectrometer and intensified charge coupled device detection, Spectrochim. Acta Part B: At. Spectrosc.

53 (1998) 1815-1825.

[78] A. De Giacomo, M. Dell'Aglio, A. Santagata, R. Teghil, Early stage emission spectroscopy study

of metallic titanium plasma induced in air by femtosecond- and nanosecond-laser pulses, Spectrochim.

ACCEPTED MANUSCRIPT

Acta Part B: At. Spectrosc. 60 (2005) 935-947.

[79] T.A. Labutin, A.M. Popov, V.N. Lednev, N.B. Zorov, Correlation between properties of a solid

sample and laser-induced plasma parameters, Spectrochim. Acta Part B: At. Spectrosc. 64 (2009)

938-949.

[80] K.M. Lo, N.H. Cheung, ArF laser-induced plasma spectroscopy for part-per-billion analysis of

metal ions in aqueous solutions, Appl. Spectrosc. 56 (2002) 682-688.

[81] O. Samek, D.C. Beddows, J. Kaiser, S.V. Kukhlevsky, M. Liska, H.H. Telle, J. Young,

Application of laser-induced breakdown spectroscopy to in situ analysis of liquid samples, Opt. Eng.

39 (2000) 2248-2262.

[82] N.M. Shaikh, S. Hafeez, B. Rashid, S. Mahmood, M.A. Baig, Optical emission studies of the

mercury plasma generated by the fundamental, second and third harmonics of a Nd: YAG laser, J. Phys.

D: Appl. Phys. 39 (2006) 4377-4385.

[83] B. Le Drogoff, J. Margot, F. Vidal, S. Laville, M. Chaker, M. Sabsabi, T.W. Johnston, O.

Barthelemy, Influence of the laser pulse duration on laser-produced plasma properties, Plasma Sources

Sci. Technol. 13 (2004) 223-230.

[84] R. Qindeel, M.S. Dimitrijević, N.M. Shaikh, N. Bidin, Y.M. Daud, Spectroscopic estimation of

electron temperature and density of zinc plasma open air induced by Nd:YAG laser, Eur. Phys. J. Appl.

Phys. 50 (2010) 30701.

[85] G.Y. Chen, M.J. Zhang, Z. Zhao, Y. Zhang, S.C. Li, Measurements of laser-induced plasma

temperature field in deep penetration laser welding, Opt. Laser Technol. (2012) 551-557.

[86] M. Adamson, A. Padmanabhan, G.J. Godfrey, S.J. Rehse, Laser-induced breakdown spectroscopy

at a water/gas interface: A study of bath gas-dependent molecular species, Spectrochim. Acta Part B:

At. Spectrosc. 62 (2007) 1348-1360.

[87] H. Hegazy, Oxygen spectral lines for diagnostics of atmospheric laser-induced plasmas, Appl.

Phys. B 98 (2010) 601-606.

[88] W.F. Luo, Q.B. Sun, C.X. Gao, J. Tang, H.J. Wang, W. Zhao, Plasma properties of 532 nm

laser-ablated aluminum E414d target with different power densities, Plasma Sci. Technol. 12 (2010)

385-390.

[89] C. Colón, G. Hatem, E. Verdugo, P. Ruiz, J. Campos, Measurement of the Stark broadening and

shift parameters for several ultraviolet lines of singly ionized aluminum, J. Appl. Phys. 73 (1993)

4752-4758.

[90] A.M. El Sherbini, T.M. El Sherbini, H. Hegazy, G. Cristoforetti, S. Legnaioli, V. Palleschi, L.

Pardini, A. Salvetti, E. Tognoni, Evaluation of self-absorption coefficients of aluminum emission lines

in laser-induced breakdown spectroscopy measurements, Spectrochim. Acta Part B: At. Spectrosc. 60

(2005) 1573-1579.

[91] N.K. Rai, S. Pandhija, S. Rai, A.K. Pathak, A.K. Rai, Effect of Analyte Concentration on the

Laser-Induced Plasma Temperature and Electron Density in Liquid Matrix, Spectrosc. Lett. 46 (2013)

218-226.

[92] I.B. Gornushkin, J.M. Anzano, L.A. King, B.W. Smith, N. Omenetto, J.D. Winefordner, Curve of

growth methodology applied to laser-induced plasma emission spectroscopy, Spectrochim. Acta Part B:

At. Spectrosc. 54 (1999) 491-503.

[93] J.A. Aguilera, C. Aragón, A comparison of the temperatures and electron densities of

laser-produced plasmas obtained in air, argon, and helium at atmospheric pressure, Appl. Phys. A 69

(1999) S475-S478.

ACCEPTED MANUSCRIPT

[94] 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, Appl. Spectrosc. 64 (2010) 335A-366A.

[95] H. Kurniawan, W.S. Budi, M.M. Suliyanti, A.M. Marpaung, K. Kagawa, Characteristics of a laser

plasma induced by irradiation of a normal-oscillation YAG laser at low pressures, J. Phys. D: Appl.

Phys. 30 (1997) 3335-3345.

[96] M. Corsi, G. Cristoforetti, M. Hidalgo, D. Iriarte, S. Legnaioli, V. Palleschi, A. Salvetti, E.

Tognoni, Effect of laser-induced crater depth in laser-induced breakdown spectroscopy emission

features, Appl. Spectrosc. 59 (2005) 853-860.

[97] Y.-F. Lu, Z.-B. Tao, M.-H. Hong, Characteristics of excimer laser induced plasma from an

aluminum target by spectroscopic study, J. Appl. Phys. 38 (1999) 2958-2963.

[98] M. Stafe, C. Negutu, Real-Time Monitoring of the Pulsed Laser Ablation of Metals Using

Ablation Plasma Spectroscopy, Plasma Chem. Plasma Process. 32 (2012) 643-653.

[99] M. Essien, L.J. Radziemski, J. Sneddon, Detection of cadmium, lead and zinc in aerosols by

laser-induced breakdown spectrometry, J. Anal. At. Spectrom. 3 (1988) 985-988.

[100] N. Smijesh, R. Philip, Emission dynamics of an expanding ultrafast-laser produced Zn plasma

under different ambient pressures, J. Appl. Phys. 114 (2013) 093301.

[101] N.M. Shaikh, B. Rashid, S. Hafeez, Y. Jamil, M.A. Baig, Measurement of electron density and

temperature of a laser-induced zinc plasma, J. Phys. D: Appl. Phys. 39 (2006) 1384-1391.

[102] T. Atwee, L. Aschke, H.J. Kunze, Investigations of laser-produced plasmas from boron nitride

targets, J. Phys. D: Appl. Phys. 33 (2000) 2263-2267.

[103] K.Y. Yamamoto, D.A. Cremers, L.E. Foster, M.P. Davies, R.D. Harris, Laser-induced

breakdown spectroscopy analysis of solids using a long-pulse (150 ns) Q-switched Nd: YAG laser,

Appl. Spectrosc. 59 (2005) 1082-1097.

[104] K.L. Eland, D.N. Stratis, T. Lai, M.A. Berg, S.R. Goode, S.M. Angel, Some comparisons of

LIBS measurements using nanosecond and picosecond laser pulses, Appl. Spectrosc. 55 (2001)

279-285.

[105] V. Bulatov, R. Krasniker, I. Schechter, Study of matrix effects in laser plasma spectroscopy by

combined multifiber spatial and temporal resolutions, Anal. Chem. 70 (1998) 5302-5311.

[106] J.A. Aguilera, C. Aragón, J. Bengoechea, Spatial characterization of laser-induced plasmas by

deconvolution of spatially resolved spectra, Appl. Opt. 42 (2003) 5938-5946.

[107] J.A. Aguilera, C. Aragón, Temperature and electron density distributions of laser-induced

plasmas generated with an iron sample at different ambient gas pressures, Appl. Surf. Sci. 197 (2002)

273-280.

[108] N. Kawahara, J.L. Beduneau, T. Nakayama, E. Tomita, Y. Ikeda, Spatially, temporally, and

spectrally resolved measurement of laser-induced plasma in air, Appl. Phys. B 86 (2007) 605-614.

[109] M. Corsi, G. Cristoforetti, M. Giuffrida, M. Hidalgo, S. Legnaioli, V. Palleschi, A. Salvetti, E.

Tognoni, C. Vallebona, Three-dimensional analysis of laser induced plasmas in single and double pulse

configuration, Spectrochim. Acta Part B: At. Spectrosc. 59 (2004) 723-735.

[110] W.F. Luo, X.X. Zhao, Q.B. Sun, C.X. Gao, J. Tang, H.J. Wang, W. Zhao, Characteristics of the

aluminum alloy plasma produced by a 1064 nm Nd: YAG laser with different irradiances, Pramana 74

(2010) 945-959.

[111] M.A. Baig, M.A. Fareed, B. Rashid, R. Ali, On the Rydberg transitions and elemental

compositions in the laser produced Al (6063) plasma, Phys. Plasma 18 (2011) 083303.

ACCEPTED MANUSCRIPT

[112] L. St-Onge, M. Sabsabi, P. Cielo, Analysis of solids using laser-induced plasma spectroscopy in

double-pulse mode, Spectrochim. Acta Part B: At. Spectrosc. 53 (1998) 407-415.

[113] V. Detalle, R. Héon, M. Sabsabi, L. St-Onge, An evaluation of a commercial Échelle

spectrometer with intensified charge-coupled device detector for materials analysis by laser-induced

plasma spectroscopy, Spectrochim. Acta Part B: At. Spectrosc. 56 (2001) 1011-1025.

[114] V. Detalle, M. Sabsabi, L. St-Onge, A. Hamel, R. Héon, Influence of Er: YAG and Nd: YAG

wavelengths on laser-induced breakdown spectroscopy measurements under air or helium atmosphere,

Appl. Opt. 42 (2003) 5971-5977.

[115] O. Barthélemy, J. Margot, M. Chaker, M. Sabsabi, F. Vidal, T.W. Johnston, S. Laville, B. Le

Drogoff, Influence of the laser parameters on the space and time characteristics of an aluminum

laser-induced plasma, Spectrochim. Acta Part B: At. Spectrosc. 60 (2005) 905-914.

[116] V. Detalle, M. Sabsabi, L. St-Onge, A. Hamel, R. Héon, Study of the influence of Er: YAG and

Nd: YAG wavelengths upon LIBS measurements under air or helium atmosphere, Trends Opt.

photonics 81 (2002) 87-89.

[117] R. Ahmed, M.A. Baig, A comparative study of single and double pulse laser induced breakdown

spectroscopy, J. Appl. Phys. 106 (2009) 033307.

[118] T.N. Piehler, F.C. DeLucia Jr, C.A. Munson, B.E. Homan, A.W. Miziolek, K.L. McNesby,

Temporal evolution of the laser-induced breakdown spectroscopy spectrum of aluminum metal in

different bath gases, Appl. Opt. 44 (2005) 3654-3660.

[119] S. Dadras, M.J. Torkamany, J. Sabbaghzadeh, Characterization and comparison of iron and

aluminium laser ablation with time-integrated emission spectroscopy of induced plasma, J. Phys. D:

Appl. Phys. 41 (2008) 225202.

[120] X.W. Li, W.F. Wei, J. Wu, S.L. Jia, A.C. Qiu, Comparison of nanosecond laser produced brass

plasmas under low and moderate pressure air, J. Phys. D: Appl. Phys. 46 (2013) 475207.

[121] J. Uebbing, J. Brust, W. Sdorra, F. Leis, K. Niemax, Reheating of a laser-produced plasma by a

second pulse laser, Appl. Spectrosc. 45 (1991) 1419-1423.

[122] F. Leis, W. Sdorra, J.B. Ko, K. Niemax, Basic investigations for laser microanalysis: I. Optical

emission spectrometry of laser-produced sample plumes, Microchim. Acta 98 (1989) 185-199.

[123] J. Vrenegor, R. Noll, V. Sturm, Investigation of matrix effects in laser-induced breakdown

spectroscopy plasmas of high-alloy steel for matrix and minor elements, Spectrochim. Acta Part B: At.

Spectrosc. 60 (2005) 1083-1091.

[124] W. Sdorra, K. Niemax, Basic investigations for laser microanalysis: III. Application of different

buffer gases for laser-produced sample plumes, Microchim. Acta 107 (1992) 319-327.

[125] W. Sdorra, K. Niemax, Basic investigations for laser microanalysis: IV. The dependence on the

laser wavelength in laser ablation, Microchim. Acta 108 (1992) 1-10.

[126] M.A. Hafez, M.A. Khedr, F.F. Elaksher, Y.E. Gamal, Characteristics of Cu plasma produced by

a laser interaction with a solid target, Plasma Sources Sci. Technol. 12 (2003) 185-198.

[127] B. Rashid, S. Hafeez, N.M. Shaikh, M. Saleem, R. Ali, M.A. Baig, Diagnostics of copper plasma

produced by the fundamental, second and third harmonics of a Nd: Yag laser, Int. J. Mod. Phys. B 21

(2007) 2697-2710.

[128] 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,

[129] Y.-I. Lee, T.L. Thiem, G.-H. Kim, Y.-Y. Teng, J. Sneddon, Interaction of an excimer-laser beam

ACCEPTED MANUSCRIPT

with metals. Part III: The effect of a controlled atmosphere in laser-ablated plasma emission, Appl.

Spectrosc. 46 (1992) 1597-1604.

[130] V. Piñon, D. Anglos, Optical emission studies of plasma induced by single and double

femtosecond laser pulses, Spectrochim. Acta Part B: At. Spectrosc. 64 (2009) 950-960.

[131] L.Z. Wu, R.Q. Shen, J. Xu, Y.H. Ye, Y. Hu, Spectroscopic study of laser-induced cu plasma with

and without the confinement of a substrate, IEEE Trans. Plasma Sci. 38 (2010) 174-180.

[132] A.K. Knight, N.L. Scherbarth, D.A. Cremers, M.J. Ferris, Characterization of laser-induced

breakdown spectroscopy (LIBS) for application to space exploration, Appl. Spectrosc. 54 (2000)

331-340.

[133] D.N. Stratis, K.L. Eland, S.M. Angel, Effect of pulse delay time on a pre-ablation dual-pulse

LIBS plasma, Appl. Spectrosc. 55 (2001) 1297-1303.

[134] K.J. Grant, G.L. Paul, Electron temperature and density profiles of excimer laser-induced

plasmas, Appl. Spectrosc. 44 (1990) 1349-1354.

[135] K.L. Eland, D.N. Stratis, D.M. Gold, S.R. Goode, S.M. Angel, Energy dependence of emission

intensity and temperature in a LIBS plasma using femtosecond excitation, Appl. Spectrosc. 55 (2001)

286-291.

[136] R. Sattmann, V. Sturm, R. Noll, Laser-induced breakdown spectroscopy of steel samples using

multiple Q-switch Nd: YAG laser pulses, J. Phys. D: Appl. Phys. 28 (1995) 2181-2187.

[137] E.M. Monge, C. Aragón, J.A. Aguilera, Space-and time-resolved measurements of temperatures

and electron densities of plasmas formed during laser ablation of metallic samples, Appl. Phys. A 69

(1999) S691-S694.

[138] N.M. Shaikh, S. Hafeez, M.A. Baig, Comparison of zinc and cadmium plasma parameters

produced by laser-ablation, Spectrochim. Acta Part B: At. Spectrosc. 62 (2007) 1311-1320.

[139] M. Hanif, M. Salik, M.A. Baig, Diagnostic Study of Nickel Plasma Produced by Fundamental

(1064 nm) and Second Harmonics (532 nm) of an Nd: YAG Laser, J. Mod. Phys. 3 (2012) 1663-1669.

[140] J. Hermann, C. Boulmer-Leborgne, D. Hong, Diagnostics of the early phase of an ultraviolet

laser induced plasma by spectral line analysis considering self-absorption, J. Appl. Phys. 83 (1998)

691-696.

[141] C. Parigger, J.W.L. Lewis, D. Plemmons, Electron number density and temperature measurement

in a laser-induced hydrogen plasma, J. Quant. Spectrosc. Radiat. Transfer 53 (1995) 249-255.

[142] A. Elhassan, A. Giakoumaki, D. Anglos, G.M. Ingo, L. Robbiola, M.A. Harith, Nanosecond and

femtosecond laser induced breakdown spectroscopic analysis of bronze alloys, Spectrochim. Acta Part

B: At. Spectrosc. 63 (2008) 504-511.

[143] H. Hegazy, F.M. Abdel-Rahim, S.H. Allam, Evolution of Al plasma generated by Nd–YAG laser

radiation at the fundamental wavelength, Appl. Phys. B 108 (2012) 665-673.

[144] A. Gomes, A. Aubreton, J.J. Gonzalez, S. Vacquié, Experimental and theoretical study of the

expansion of a metallic vapour plasma produced by laser, J. Phys. D: Appl. Phys. 37 (2004) 689-696.

[145] S. Bashir, N. Farid, K. Mahmood, M.S. Rafique, Influence of ambient gas and its pressure on the

laser-induced breakdown spectroscopy and the surface morphology of laser-ablated Cd, Appl. Phys. A

107 (2012) 203-212.

[146] C.Y. Diao, C.S. Chen, B.Y. Man, C. Wang, H.B. Fu, Influence of distances between the lens and

the target on the characteristic of laser induced lead plasma, Eur. Phys. J. D 63 (2011) 123-128.

[147] A. Khalil, Spectroscopic studies of UV lead plasmas produced by single and double-pulse laser

excitation, Laser Phys. 23 (2013) 015701.

ACCEPTED MANUSCRIPT

[148] H.L. Xu, J. Bernhardt, P. Mathieu, G. Roy, S.L. Chin, Understanding the advantage of remote

femtosecond laser-induced breakdown spectroscopy of metallic targets, J. Appl. Phys. 101 (2007)

033124.

[149] V. Detalle, J.L. Lacour, P. Mauchien, A. Semerok, Investigation of laser plasma for solid element

composition microanalysis, Appl. Surf. Sci. 138 (1999) 299-301.

[150] Y.H. Liu, X.D. Liu, M. Chen, M.W. Zhao, Laser Ablation of Ti-Al Alloy in Vacuum and Air

Environments, Appl. Mechan. Mater. 217 (2012) 2257-2264.

[151] M. Hanif, M. Salik, M.A. Baig, Laser Based Optical Emission Studies of Zinc Oxide (ZnO)

Plasma, Plasma Chem. Plasma Process. 33 (2013) 1167-1178.

[152] N. Farid, C. Li, H.B. Wang, H.B. Ding, Laser-induced breakdown spectroscopic characterization

of tungsten plasma using the first, second, and third harmonics of an Nd: YAG laser, J. Nucl. Mater.

433 (2013) 80-85.

[153] S. Acquaviva, E. D'Anna, M.L. De Giorgi, F. Moro, Laser-induced breakdown spectroscopy for

compositional analysis of multielemental thin films, Spectrochim. Acta Part B: At. Spectrosc. 61 (2006)

810-816.

[154] S. Khan, S. Bashir, A. Hayat, M. Khaleeq-ur-Rahman, Laser-induced breakdown spectroscopy of

tantalum plasma, Phys. Plasma 20 (2013) 073104.

[155] M.A. Ismail, H. Imam, A. Elhassan, W.T. Youniss, M.A. Harith, LIBS limit of detection and

plasma parameters of some elements in two different metallic matrices, J. Anal. At. Spectrom. 19

(2004) 489-494.

[156] G. Abdellatif, H. Imam, A study of the laser plasma parameters at different laser wavelengths,

[157] J.T. Knudtson, W.B. Green, D.G. Sutton, The UV‐visible spectroscopy of laser‐produced

aluminum plasmas, J. Appl. Phys. 61 (1987) 4771-4780.

[158] S. Hafeez, N.M. Shaikh, B. Rashid, M.A. Baig, Plasma properties of laser-ablated strontium

target, J. Appl. Phys. 103 (2008) 083117.

[159] G. Shukla, A. Khare, Optical emission spectroscopic studies on laser ablated TiO2 plasma, Appl.

Surf. Sci. 255 (2009) 8730-8737.

[160] S.S. Harilal, R.C. Issac, C.V. Bindhu, V.P.N. Nampoori, C.P.G. Vallabhan, Optical emission

studies of species in laser-produced plasma from carbon, J. Phys. D: Appl. Phys. 30 (1997) 1703-1709.

[161] M. Hanif, M. Salik, M.A. Baig, Optical spectroscopic studies of titanium plasma produced by an

Nd: YAG laser, Opt. Spectrosc. 114 (2013) 7-14.

[162] M. Salik, M. Hanif, M.A. Baig, Plasma Diagnostic Study of Alumina (Al2O3) Generated by the

Fundamental and Second Harmonics of a Nd:YAG laser, IEEE Trans. Plasma Sci. 39 (2011)

1861-1867.

[163] L. St-Onge, M. Sabsabi, P. Cielo, Quantitative analysis of additives in solid zinc alloys by

laser-induced plasma spectrometry, J. Anal. At. Spectrom. 12 (1997) 997-1004.

[164] M. Sabsabi, P. Cielo, Quantitative analysis of copper alloys by laser-produced plasma

spectrometry, J. Anal. At. Spectrom. 10 (1995) 643-647.

[165] J.E. Carranza, D.W. Hahn, Sampling statistics and considerations for single-shot analysis using

laser-induced breakdown spectroscopy, Spectrochim. Acta Part B: At. Spectrosc. 57 (2002) 779-790.

[166] G. Padmaja, A.V. Ravi Kumar, P. Radhakrishnan, V.P.N. Nampoori, C.P.G. Vallabhan, Spatial

and temporal analysis of laser induced plasma from a polymer sample, J. Phys. D: Appl. Phys. 26

ACCEPTED MANUSCRIPT

(1993) 35-41.

[167] S.S. Harilal, Spatial and temporal evolution of argon sparks, Appl. Opt. 43 (2004) 3931-3937.

[168] J.A. Aguilera, J. Bengoechea, C. Aragón, Spatial characterization of laser induced plasmas

obtained in air and argon with different laser focusing distances, Spectrochim. Acta Part B: At.

Spectrosc. 59 (2004) 461-469.

[169] W.F. Luo, X.X. Zhao, Q.B. Sun, C.X. Gao, J. Tang, W. Zhao, Spatial diagnostics of 532-nm

laser-induced aluminum plasma, Nucl. Instrum. Methods Phys. Res., Sect. A 637 (2011) S158-S160.

[170] M.A. Baig, A. Qamar, M.A. Fareed, M. Anwar-ul-Haq, R. Ali, Spatial diagnostics of the laser

induced lithium fluoride plasma, Phys. Plasma 19 (2012) 063304.

[171] N.M. Shaikh, Y. Tao, R.A. Burdt, S. Yuspeh, N. Amin, M.S. Tillack, Spectroscopic analysis of

temperature and density of Sn plasma produced by a CO2 laser, J. Appl. Phys. 108 (2010) 083109.

[172] N.M. Shaikh, Y. Tao, R.A. Burdt, S. Yuspeh, N. Amin, M.S. Tillack, Spectroscopic studies of tin

plasma using laser induced breakdown spectroscopy, J. Phys.:Conf. Ser. 244 (2010) 042005.

[173] N.M. Shaikh, S. Hafeez, M.A. Kalyar, R. Ali, M.A. Baig, Spectroscopic characterization of laser

ablation brass plasma, J. Appl. Phys. 104 (2008) 103108.

[174] S. Hafeez, N.M. Shaikh, M.A. Baig, Spectroscopic studies of Ca plasma generated by the

fundamental, second, and third harmonics of a Nd: YAG laser, Laser Part. Beams 26 (2008) 41-50.

[175] N.M. Shaikh, S. Hafeez, B. Rashid, M.A. Baig, Spectroscopic studies of laser induced aluminum

plasma using fundamental, second and third harmonics of a Nd: YAG laser, Eur. Phys. J. D 44 (2007)

371-379.

[176] A. Sarkar, R.V. Shah, D. Alamelu, S.K. Aggarwal, Studies on the ns-IR-Laser-Induced Plasma

Parameters in the Vanadium Oxide, J. At. Mol. Phys. 2011 (2011) 504764.

[177] J.A. Aguilera, C. Aragón, V. Madurga, J. Manrique, Study of matrix effects in laser induced

breakdown spectroscopy on metallic samples using plasma characterization by emission spectroscopy,

[178] L. Cadwell, L. Hüwel, Time-resolved emission spectroscopy in laser-generated argon

plasmas—determination of Stark broadening parameters, J. Quant. Spectrosc. Radiat. Transfer 83

(2004) 579-598.

[179] F.J. Gordillo-Vázquez, A. Perea, C.N. Afonso, Effect of Ar and O2 Atmospheres on the

Fundamental Properties of the Plasma Produced by Laser Ablation of Lithium Niobate, Appl.

Spectrosc. 56 (2002) 381-385.

[180] P.A. 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,

[181] S.S. Harilal, C.V. Bindhu, R.C. Issac, V.P.N. Nampoori, C.P.G. Vallabhan, Electron density and

temperature measurements in a laser produced carbon plasma, J. Appl. Phys. 82 (1997) 2140-2146.

[182] S.S. Harilal, C.V. Bindhu, V.P.N. Nampoori, C.P.G. Vallabhan, Influence of ambient gas on the

temperature and density of laser produced carbon plasma, Appl. Phys. Lett. 72 (1998) 167-169.

[183] A. De Giacomo, M. Dell'Aglio, R. Gaudiuso, G. Cristoforetti, S. Legnaioli, V. Palleschi, E.

Tognoni, Spatial distribution of hydrogen and other emitters in aluminum laser-induced plasma in air

and consequences on spatially integrated Laser-Induced Breakdown Spectroscopy measurements,

[184] D.A. Cremers, L.J. Radziemski, T.R. Loree, Spectrochemical analysis of liquids using the laser

spark, Appl. Spectrosc. 38 (1984) 721-729.

ACCEPTED MANUSCRIPT

[185] J. Hermann, S. Bruneau, M. Sentis, Spectroscopic analysis of femtosecond laser-induced gas

breakdown, Thin solid films 453 (2004) 377-382.

[186] G. Cristoforetti, S. Legnaioli, L. Pardini, V. Palleschi, A. Salvetti, E. Tognoni, Spectroscopic and

shadowgraphic analysis of laser induced plasmas in the orthogonal double pulse pre-ablation

configuration, Spectrochim. Acta Part B: At. Spectrosc. 61 (2006) 340-350.

[187] S.S. Harilal, C.V. Bindhu, V.P.N. Nampoori, C.P.G. Vallabhan, Temporal and spatial behavior of

electron density and temperature in a laser-produced plasma from YBa2Cu3O7, Appl. Spectrosc. 52

(1998) 449-455.

[188] J.A. Aguilera, C. Aragón, Apparent excitation temperature in laser-induced plasmas, J. Phys. C:

Conf. Ser. 59 (2007) 210-217.

[189] A.A. Khalil, A comparative spectroscopic study of single and dual pulse laser produced UV tin

plasmas, Opt. Laser Techol. (2012) 443-452.

[190] 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, Spectrochim. Acta Part B: At. Spectrosc. 60 (2005) 265-276.

[191] C. Aragón, J.A. Aguilera, Spatial and temporal scaling and common apparent excitation

temperature of laser-induced plasmas generated at constant irradiance with different pulse energies, J.

Appl. Phys. 103 (2008) 013310.

[192] Ş. Yalçin, D.R. Crosley, G.P. Smith, G.W. Faris, Spectroscopic characterization of

laser-produced plasmas for in situ toxic metal monitoring, Hazard. waste Hazard. Mater. 13 (1996)

51-61.

[193] H.C. Liu, X.L. Mao, J.H. Yoo, R.E. Russo, Early phase laser induced plasma diagnostics and

mass removal during single-pulse laser ablation of silicon, Spectrochim. Acta Part B: At. Spectrosc. 54

(1999) 1607-1624.

[194] J.S. Cowpe, R.D. Pilkington, J.S. Astin, A.E. Hill, The effect of ambient pressure on

laser-induced silicon plasma temperature, density and morphology, J. Phys. D: Appl. Phys. 42 (2009)

165202.

[195] J.S. Cowpe, J.S. Astin, R.D. Pilkington, A.E. Hill, Temporally resolved laser induced plasma

diagnostics of single crystal silicon—Effects of ambient pressure, Spectrochim. Acta Part B: At.

Spectrosc. 63 (2008) 1066-1071.

[196] R.E. Russo, X.L. Mao, H.C. Liu, J.H. Yoo, S.S. Mao, Time-resolved plasma diagnostics and

mass removal during single-pulse laser ablation, Appl. Phys. A 69 (1999) S887-S894.

[197] X.L. Mao, X.Z. Zeng, S.-B. Wen, R.E. Russo, Time-resolved plasma properties for double

pulsed laser-induced breakdown spectroscopy of silicon, Spectrochim. Acta Part B: At. Spectrosc. 60

(2005) 960-967.

[198] J.S. Cowpe, R.D. Moorehead, D. Moser, J.S. Astin, S. Karthikeyan, S.H. Kilcoyne, G. Crofts,

R.D. Pilkington, Hardness determination of bio-ceramics using Laser-Induced Breakdown

Spectroscopy, Spectrochim. Acta Part B: At. Spectrosc. 66 (2011) 290-294.

[199] S.S. Mao, X.Z. Zeng, X.L. Mao, R.E. Russo, Laser-induced breakdown spectroscopy: flat surface

vs. cavity structures, J. Anal. At. Spectrom. 19 (2004) 495-498.

[200] X.Z. Zeng, S.S. Mao, C.Y. Liu, X.L. Mao, R. Greif, R.E. Russo, Laser-induced plasmas in

micromachined fused silica cavities, Appl. Phys. Lett. 83 (2003) 240-242.

[201] X.Z. Zeng, X.L. Mao, S.S. Mao, J.H. Yoo, R. Greif, R.E. Russo, Laser–plasma interactions in

fused silica cavities, J. Appl. Phys. 95 (2004) 816-822.

ACCEPTED MANUSCRIPT

[202] X.Z. Zeng, S.S. Mao, C.Y. Liu, X.L. Mao, R. Greif, R.E. Russo, Plasma diagnostics during laser

ablation in a cavity, Spectrochim. Acta Part B: At. Spectrosc. 58 (2003) 867-877.

[203] E. Aldea, A.P. Caricato, G. Dinescu, A. Luches, A. Perrone, Optical emission diagnostic of

laser-induced plasma during CNx film deposition, J. Appl. Phys. 36 (1997) 4686-4689.

[204] C. Parigger, D.H. Plemmons, J.O. Hornkohl, J.W.L. Lewis, Spectroscopic temperature

measurements in a decaying laser-induced plasma using the C2 Swan system, J. Quant. Spectrosc.

Radiat. Transfer 52 (1994) 707-711.

[205] J.O. Hornkohl, C. Parigger, J.W.L. Lewis, Temperature measurements from CN spectra in a

laser-induced plasma, J. Quant. Spectrosc. Radiat. Transfer 46 (1991) 405-411.

[206] N.G. Glumac, G.S. Elliott, M. Boguszko, Temporal and spatial evolution of a laser spark in air,

AIAA J. 43 (2005) 1984-1994.

[207] A.M. Keszler, L. Nemes, Time averaged emission spectra of Nd: YAG laser induced carbon

plasmas, J. Mol. Struct. 695 (2004) 211-218.

[208] J. Hoffman, T. Moscicki, Z. Szymanski, The effect of laser wavelength on heating of ablated

carbon plume, Appl. Phys. A 104 (2011) 815-819.

[209] T. Moscicki, J. Hoffman, Z. Szymanski, The effect of laser wavelength on laser-induced carbon

plasma, J. Appl. Phys. 114 (2013) 083306.

[210] A. Quentmeier, W. Sdorra, K. Niemax, Internal standardization in laser induced fluorescence

spectrometry of microplasmas produced by laser ablation of solid samples, Spectrochim. Acta Part B:

At. Spectrosc. 45 (1990) 537-546.

[211] S.S. Harilal, R.C. Issac, C.V. Bindhu, G.K. Varier, V.P.N. Nampoori, C.P.G. Vallabhan, Spatial

and time resolved analysis of CN bands in the laser induced plasma from graphite, Pramana 46 (1996)

145-151.

[212] K. Sasaki, S. Yasuda, N. Takada, Temporal and Spatial Variations in Electron Density and

Blackbody Temperature in the Initial Phase of a Laser Ablation BN Plasma, Plasma Fusion Res. 3

(2008) 023.

[213] G.J. Bastiaans, R.A. Mangold, The calculation of electron density and temperature in Ar

spectroscopic plasmas from continuum and line spectra, Spectrochim. Acta Part B: At. Spectrosc. 40

(1985) 885-892.

[214] S. Laville, F. Vidal, T.W. Johnston, M. Chaker, B. Le Drogoff, O. Barthélemy, J. Margot, M.

Sabsabi, Modeling the time evolution of laser-induced plasmas for various pulse durations and fluences,

Phys. Plasma 11 (2004) 2182-2190.

[215] H. Hora, Plasmas at High Temperature and Density: Applications and Implications of Laser

Plasma Interaction, Springer, 1991.

[216] V.I. Babushok, F.C. DeLucia Jr, J.L. Gottfried, C.A. Munson, A.W. Miziolek, Double pulse laser

ablation and plasma: Laser induced breakdown spectroscopy signal enhancement, Spectrochim. Acta

[217] J. Scaffidi, S.M. Angel, D.A. Cremers, Emission enhancement mechanisms in dual-pulse LIBS,

Anal. Chem. 78 (2006) 24-32.

[218] A. Bogaerts, Z.Y. Chen, D. Autrique, Double pulse laser ablation and laser induced breakdown

spectroscopy: a modeling investigation, Spectrochim. Acta Part B: At. Spectrosc. 63 (2008) 746-754.

[219] Y. Iida, Effects of atmosphere on laser vaporization and excitation processes of solid samples,

[220] P.T. Rumsby, J.W.M. Paul, Temperature and density of an expanding laser produced plasma,

ACCEPTED MANUSCRIPT

Plasma Phys. 16 (1974) 247.

[221] A. Bogaerts, Z.Y. Chen, D. Bleiner, Laser ablation of copper in different background gases:

comparative study by numerical modeling and experiments, J. Anal. At. Spectrom. 21 (2006) 384-395.

[222] Z.Y. Chen, D. Bleiner, A. Bogaerts, Effect of ambient pressure on laser ablation and plume

expansion dynamics: A numerical simulation, J. Appl. Phys. 99 (2006) 063304.

[223] D. Bleiner, Z. Chen, D. Autrique, A. Bogaerts, Role of laser-induced melting and vaporization of

metals during ICP-MS and LIBS analysis, investigated with computer simulations and experiments, J.

Anal. At. Spectrom. 21 (2006) 910-921.

[224] M.A. Shannon, A simplified cavity analysis for estimating energy coupling during laser ablation

and drilling of solids–theory, Appl. Surf. Sci. 127 (1998) 218-225.

[225] S.H. Jeong, R. Greif, R.E. Russo, Laser heating of a cavity versus a plane surface for metal

targets utilizing photothermal deflection measurements, J. Appl. Phys. 80 (1996) 1996-2002.

[226] S. Amoruso, Modeling of UV pulsed-laser ablation of metallic targets, Appl. Phys. A 69 (1999)

323-332.

[227] A. Bogaerts, Z.Y. Chen, Nanosecond laser ablation of Cu: modeling of the expansion in He

background gas, and comparison with expansion in vacuum, J. Anal. At. Spectrom. 19 (2004)

1169-1176.

[228] H.R. Griem, Plasma spectroscopy, McGraw-Hill, New York, 1964.

[229] C. Aragón, F. Peñalba, J.A. Aguilera, Curves of growth of neutral atom and ion lines emitted by a

laser induced plasma, Spectrochimica Acta Part B: At. Spectrosc. 60 (2005) 879-887.

ACCEPTED MANUSCRIPT

Highlights

•Fundamental theories and calculation methods of LIP temperature are reviewed

•Influences of various factors on LIP temperature are discussed

•Various explanations are given to interpret the temperature behaviors

laser-induced plasma temperature

Documents

laser-plasma-accelerator’s potential to radically...

2. experimental procedure for laser-induced plasma …

laser induced breakdown spectroscopy (libs) · laser...

thomson scattering from laser induced plasma in air

laser-induced plasma image velocimetry - spiral: home ·...

picosecond optical phenomena of laser induced electron...

temporal evolution of the laser-induced plasma...

relativistic laser–plasma interactions.pdf

laser-induced breakdown spectroscopy and its … laser spark...

0 relativistic induced transparency and laser propagation in...

table-top soft x-ray microscope using laser- induced plasma...

plasma induced catalytic removal ofnitric oxide froid...

laser-induced fluorescence spectroscopy · 2018-02-27 ·...

-ray emission from ultrafast laser induced plasma in...

relativistic laser propagation through underdense and...

11 applications of planar laser induced ﬂuorescence in...

laser induced breakdown spectroscopy · icp-aes inductively...

laser based plasma

time resolved spectroscopy of laser induced air...

libs 2004, 3rd international conference on laser induced ......