Influence of ambient pressure on spatial–temporal evolution of local thermodynamic equilibrium for laser-induced plasma

Ke, Wei; Wang, Xiaohua; Chen, Minyuan; Yuan, Huan; Yang, Aijun; Chu, Jifeng; Liu, Dingxin; Rong, Mingzhe

doi:10.1039/d2ja00256f

Cited by 3 publications

(3 citation statements)

References 22 publications

(43 reference statements)

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“…Due to the strong ionic radiation and continuous background radiation at the earlier stage of LIP, the spectral intensity of the atomic line cannot be accurately obtained, and thus only the LIP in the middle and later times is analyzed: the delay time T d is from 300 ns to 3500 ns at 10 3 Pa, the delay time T d is from 400 ns to 6000 ns at 10 4 Pa, and the delay time T d is from 600 ns to 6000 ns at 10 5 Pa. One can see from figure 6(a) that the minimum electron density n e decreases against the delay time T d and is greater than the electron density n e obtained in the experiment within the measurement time when the air pressure is 10 3 Pa; this means that LIP in the present study at 10 3 Pa does not meet the McWhirter criterion when the delay time T d is from 300 ns to 3500 ns, and it has deviated from LTE. In our previous work [16], we also studied the time points at which the LIP deviated from LTE using the coefficient v; the results show that the time point is closer to the moment of the pulsed laser energy peak in a lower ambient pressure environment, which can be verified with the conclusion of the present work. At evaluate the LTE of LIP are the cumulative spectra obtained from r = −4 mm to r = 4 mm; the LIP core has stronger radiation, higher electron temperature, higher electron density, and longer LTE duration; therefore, the time point at which the LIP did not satisfy the McWhirter criterion in the previous work is later than that in the present work.…”

Section: Radial Distribution Of Lip Satisfying the Mcwhirter Criterionsupporting

confidence: 86%

“…In summary, air pressure can significantly affect the temporal evolution of LIP's radial distribution. In addition, the moment at which the LIP starts to not meet the McWhirter criterion with the increases in the delay time T d in a higher-pressure environment occurs later, which means that the lifetime of the LIP satisfying the McWhirter criterion is longer in a higher-pressure environment.In our previous work[16], we also studied the time points at which the LIP deviated from LTE using the coefficient v; the results show that the time point is closer to the moment of the pulsed laser energy peak in a lower ambient pressure environment, which can be verified with the conclusion of the present work. At10 5 Pa, the LIP starts to deviate from LTE and meets the McWhirter criterion at 1500 ns in both works.…”

supporting

confidence: 85%

“…Local thermo-dynamic equilibrium (LTE) is a very important characteristic of LIP. In our previous work [16], we used the coefficient v proposed by Liu et al [17] to study the deviation of LIP from LTE in the direction of laser incidence. This method does not need to calculate the electron density and electron temperature of LIP, but can only study the extent of LIP deviation from LTE.…”

Section: Introductionmentioning

confidence: 99%

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Radial characteristics of laser-induced plasma under the influence of air pressure

Yuan

Liu

et al. 2023

J. Phys. D: Appl. Phys.

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Air pressure is one of the key factors affecting laser induced breakdown spectroscopy (LIBS), and the mechanism of its influence on the spatial-temporal evolution of laser induced plasma (LIP) is still not fully understood due to the complex physical processes. In this study, the spatially and temporally resolved LIP’s spectra at different pressures were collected from the direction of laser incidence, and the radial distribution characteristics of LIP along the target surface under the influence of air pressure was studied. Furthermore, the spatial-temporal evolution of radial distribution of electron density ne and electron temperature Te were studied by the Stark broadening and Boltzmann plot. Finally, the radial distribution of LIP satisfying the McWhirter’s criterion, and the influence of air pressure on its spatial-temporal evolution were studied. It was found that air pressure has a significant effect on radial distribution of LIP. Spectral intensity, electron density ne, electron temperature Te of LIP decrease faster against distance r from LIP core and slower with delay time Td in a higher air pressure environment. What’s more, the LIP will gradually fail to satisfy the McWhirter’s criterion with the increase of radius r and delay time Td; and the lifetime of LIP which satisfies the McWhirter’s criterion is longer at higher-pressure. This study is helpful to clarify the influence of air pressure on the spatial-temporal evolution of LIP, optimize the experimental parameters of LIBS, and provide a reference for application of LIBS.

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Section: Radial Distribution Of Lip Satisfying the Mcwhirter Criterionsupporting

confidence: 86%

supporting

confidence: 85%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Radial characteristics of laser-induced plasma under the influence of air pressure

Yuan

Liu

et al. 2023

J. Phys. D: Appl. Phys.

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Investigation of thermodynamic properties in picosecond laser-produced plasmas on silicon

Liu,

Chen,

Huang

et al. 2023

AIP Advances

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The validity of local thermodynamic equilibrium (LTE) in plasma is a long-term concern for laser-induced breakdown spectroscopy applications. In this paper, the spatial and temporal dependence of LTE deviation in picosecond laser-induced plasmas has been proved. A picosecond (∼20 ps) laser operated at 532 nm was used to ablate a silicon target to produce plasma at a pressure of 10−5 mbar. A general electron energy distribution function was used to provide access to the insight into population ratios of different energy levels for the spatially and temporally resolved optical emission intensity of laser-induced plasma. A precise temporal and spatial LTE boundary of plasma generated in picosecond laser ablation was obtained, and the results showed that only at delay times of 180–300 ns, the plasma away from the surface (>4 mm) is in LTE.

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recent advances in machine learning methodologies for LIBS quantitative analysis

Liu,

Han,

Yang

et al. 2024

Pulsed Laser Processing Materials [Working Title]

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The mapping between LIBS spectral data to the quantitative results can become highly complicated and nonlinear due to experimental conditions, sample surface state, matrix effect, self-absorption, etc. Therefore, the accurate quantitative analysis is the longstanding dream of the LIBS community. The advantages of machine learning in dealing with high-dimensional and nonlinear problems have made it a cutting-edge hot topic in quantitative LIBS in recent years. This chapter introduces the current bottlenecks in quantitative LIBS, sorts out the data processing methods, and reviews the research status and progress of conventional machine learning methods such as PLS, SVM, LSSVM, Lasso, and artificial neural network-based methods. By comparing the results of different methods, the perspective of future developments on learning-based methods is discussed. This chapter aims to review the applications of the combination of quantitative LIBS and machine learning methods and demonstrate the performance of different machine learning methods based on experimental results.

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Influence of ambient pressure on spatial–temporal evolution of local thermodynamic equilibrium for laser-induced plasma

Abstract: Laser-induced breakdown spectroscopy (LIBS) is used for quantitative detection based on the fact that the laser-induced plasma (LIP) is in local thermodynamic equilibrium (LTE). But the radiation lifetime of the...

Cited by 3 publications

References 22 publications

Radial characteristics of laser-induced plasma under the influence of air pressure

Radial characteristics of laser-induced plasma under the influence of air pressure

Investigation of thermodynamic properties in picosecond laser-produced plasmas on silicon

recent advances in machine learning methodologies for LIBS quantitative analysis

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