A review of the current analytical approaches for evaluating, compensating and exploiting self-absorption in Laser Induced Breakdown Spectroscopy

Rezaei, Fatemeh; Cristoforetti, G.; Tognoni, E.; Legnaioli, Stefano; Palleschi, Vincenzo; Safi, Ali

doi:10.1016/j.sab.2020.105878

Cited by 83 publications

(49 citation statements)

References 119 publications

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“…If the plasma is not optically thin for the transition, the measured peak intensity of the line would be reduced by a factor SA , defined (assuming a Lorentzian profile of the line, with full width half-maximum (FWHM) Δλ 0 ) as 3 in which SA is the self-absorption parameter of the emission line and τ is the optical depth at the peak of the line, defined as 3 where l is the optical path length viewed by the detector, c is the speed of light, and E i is the energy of the lower level of the transition.…”

Section: Discussionmentioning

confidence: 99%

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Branching Ratio Method for Assessing Optically Thin Conditions in Laser-Induced Plasmas

et al. 2021

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In the study of laser-induced plasmas it is customary to use the branching ratio method for assessing the conditions of optically thin plasma, which are important for the application of analytical methods such Calibration-Free LIBS. In this communication, we warn on the possibility that in some circumstances, the branching-ratio method might give results close to the one characterizing optically thin plasma conditions, even in the presence of a substantial self-absorption for the transitions considered.

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Section: Discussionmentioning

confidence: 99%

“…If the plasma can be considered as optically thin, 3 one of the simplest methods for determining if two emission lines (of the same species) are self-absorbed is to calculate their intensity ratio I2I1 and compare it with what is expected, in local thermodynamic equilibrium (LTE) conditions, for an optically thin plasma: …”

Section: Introductionmentioning

confidence: 99%

Branching Ratio Method for Assessing Optically Thin Conditions in Laser-Induced Plasmas

et al. 2021

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“…However, their mathematical complexity limited the application. There are many more studies on how to suppress the effect of self-absorption in LIBS which cannot be mentioned one by one in this paper [29][30][31][32][33][34] , but one can nd the references that are mentioned in this paper.…”

Section: Introductionmentioning

confidence: 99%

Simple Defocus Laser Irradiation to Suppress Self-Absorption in Laser-Induced Breakdown Spectroscopy (LIBS)

Marpaung

Harefa

Pardede

et al. 2021

Preprint

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This study introduces a novel and extremely simple way for suppressing the self-absorption effect in laser-induced breakdown spectroscopy (LIBS) by utilizing a defocusing laser irradiation technique. It is claimed that defocusing laser irradiation produces more uniform laser plasma due to lower fluence than tight focus laser irradiation, hence greatly lowering the effect of self-absorption in the laser plasma. KCl and NaCl pellet samples were used to demonstrate this achievement. When the defocus position is adjusted to – 6 mm for KCl and NaCl samples, the self-reversal emission lines K I 766.4 nm, K I 769.9 nm, Na I 588.9 nm, and Na I 589.5 nm vanish. Meanwhile, the FWHM values of K I 766.4 and K I 769.9 nm are 0.29 nm and 0.23 nm, respectively, during -6 mm defocus laser irradiation, as opposed to 1.24 nm and 0.86 nm, under tight focus laser irradiation. Additionally, this work demonstrates that when the laser energy is changed in between 10 to 50 mJ, no self-reversal emission occurs when -6 mm defocus laser irradiation is applied. Finally, a linear calibration curve is generated using KCl at a high concentration ranging between K concentration from 16.6–29%. This simple change of defocus laser irradiation will undoubtedly contribute to the suppression of the self-absorption phenomenon, which disrupts LIBS analytical results.

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“…These approaches seem to be in opposition with the "golden rule" in plasma diagnostics, that recommends to use transitions of moderate optical thickness only (τ ≤ 1), for which accurate corrections of intensity or width measurements are guaranteed [10]. Despite investigations of calibration-free LIBS measurement errors [11], and the great recent interest in the role of self-absorption [12,13,14,15], accuracy lowering due to the effect has not been yet assessed, and the choice of the most appropriate analytical lines still remains arbitrary.…”

Section: Introductionmentioning

confidence: 99%

Measurement error due to self-absorption in calibration-free laser-induced breakdown spectroscopy

Taleb

Motto-Ros

Carru

et al. 2021

Analytica Chimica Acta

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Self-absorption of spectral lines is known to lower the performance of analytical measurements via calibration-free laser-induced breakdown spectroscopy. However, the error growth due to this effect is not clearly assessed.Here we propose a method to quantify the measurement error due to self-absorption based on the calculation of the spectral radiance of a plasma in local thermodynamic equilibrium. Validated through spectroscopic measurements for a binary alloy thin film of compositional gradient, the method evidences that measurement performance lowering due to self-absorption depends on the spectral shape of the analytical transition and on the intensity measurement method. Thus, line-integrated intensity measurements of Stark broadened lines enable accurate analysis, even at large optical thickness, if line width and plasma size are precisely known. The error growth due to self-absorption is significantly larger for line shapes dominated by Doppler broadening and for line-center intensity measurements. The findings present a significant advance in compositional measurements via calibration-free laser-induced breakdown spectroscopy, as they enable straightforward selection of most appropriate analytical lines.

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A review of the current analytical approaches for evaluating, compensating and exploiting self-absorption in Laser Induced Breakdown Spectroscopy

Cited by 83 publications

References 119 publications

Branching Ratio Method for Assessing Optically Thin Conditions in Laser-Induced Plasmas

Branching Ratio Method for Assessing Optically Thin Conditions in Laser-Induced Plasmas

Simple Defocus Laser Irradiation to Suppress Self-Absorption in Laser-Induced Breakdown Spectroscopy (LIBS)

Measurement error due to self-absorption in calibration-free laser-induced breakdown spectroscopy

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