Laser-induced Breakdown Spectroscopy Method Research Articles

Characteristics of laser induced plasma near a flat gas-liquid interface and its effect on the performance of laser induced breakdown spectroscopy (LIBS) detection

Moving the laser focus to the vicinity of the gas-liquid interface is the key point for many new enhanced and new methods to improve the quality of spectral signals in water Laser induced breakdown spectroscopy (LIBS) detection. Understanding the generation and evolution characteristics of the plasma induced by pulsed laser near the gas–liquid interface is of great significance for the establishment of evolution models and improvement of these new LIBS methods. In this paper, a set of slow horizontal flow auxiliary system is established to provide an ideal flat gas–liquid two-phase interface experimental condition. Experimental research on vertical incidence flat system was conducted using techniques such as time-resolved imaging, plasma characterization diagnosis, and spectral analysis. And the detection capabilities of the system were also tested. The characteristics and mechanisms of LIBS near the gas-liquid two-phase interface were investigated with the laser incident on the sample along the vertical direction. Simulation of the laser beam focusing process and observation of laser beam spot images show that the shift of plasma generation position relative to the focal point results from the refraction of the laser beam entering the solution from the air and the ‘interface effect’ of propagation on the vertical direction. Moreover, the plasma forms only the optical power density surpasses the breakdown threshold. In this work, plasma with smaller size, rounder shape, stronger radiation, higher temperature, and higher density can be produced when the focus position is in the liquid column 0.3 mm away from the upper interface. Simultaneously, for example, the Mg ion line at 285.213 nm, the obtained spectral intensity to signal-to-background ratio reaches the maximum value, and a better spectral signal can be obtained, which is 2–4 times of other positions, and the detection limits of the elements Na, Mg, and Ca also reach the lowest level, with 1.6–2.4 times of the detection limit of other focusing positions for Mg and 1.4–1.7 times for Ca, respectively.

Real-time in situ detection of petroleum hydrocarbon pollution in soils via a novel optical methodology

Petroleum hydrocarbon (PHC) contamination in soils is considered one of the most serious problems currently, of which the detection and identification is a fairly significant but challenging work. Conventional methods to do such work usually need complex sample pretreatment, consume much time and fail to do the in-situ detection. This paper set out to create a novel systematic methodology to realize the goals accurately and efficiently. Based on laser-induced breakdown spectroscopy (LIBS) and self-improved machine learning methods, the innovative methodology only uses extremely simple devices to do the real-time in situ detection and identification work and even realize the quantitative analysis of pollution level accurately. In the study, clean soils mixed with petroleum were served as polluted samples, clean soils to be the blank group for comparison. Based on the elemental information from the spectra obtained by LIBS, machine learning methods were improved and helped optimized the algorithm to identify the PHC polluted soil samples for the first time. Furthermore, a novel model was designed to perform the quantitative analysis of the concentration of PHC pollution in soils, which can be applied to detect the degree of PHC contamination in soils accurately. Finally, the harmful volatile component of the PHC polluted soils was also successfully and identified despite its extremely minimal content in the air. The newly-designed methodology is novel and efficient, which has extensive application prospect in the real-time in situ detection of petroleum hydrocarbon pollution.

Laser-induced breakdown spectroscopy for helium detection in beryllium coatings

Laser Induced Breakdown Spectroscopy (LIBS) method is considered to be a promising tool for analyzing the retention of hydrogen isotopes (D and T) and helium (He) on the first walls and divertor regions of future fusion reactors. Helium will be produced in DT reactions but could also be used in the initial non-nuclear phases of DEMO concepts. The present study investigates the He detection by LIBS method in the Be coatings simulating the deposits on the divertor plasma-facing components of JET while the results are also relevant for He detection in the deposits of other wall materials. The study was carried out in a vacuum vessel filled with 2–40 mbar argon background gas. It was shown that 2.8 at. % of He was confidently detectable by LIBS at optimized measurement conditions and the estimated limit of detection at used experimental conditions is approximately 0.7 at. %. The intensity of the He emission line at 587.56 nm was the strongest at the center of the laser-induced plasma plume. The He line intensity increased with the pressure of Ar gas but the broadening of the He line and the increase of the background emission and noise set an upper limit to the Ar background pressure usable for He detection. The application of the calibration-free LIBS procedure resulted in the overestimation of the He/Be ratio by several orders of magnitude. The overestimation can be explained by the deviation of LIBS plasma from the local thermodynamic equilibrium, which is caused by the very high excitation energy of He atoms.

Classification of diverse plastic samples by LIBS and Raman data fusion

The plastic production and usage in the world is steadily increasing. This leads to increased amounts of plastic waste. Most of the waste could be potentially recycled, but only 14 % of plastic waste is recycled. In order to increase the share of recycling in plastic waste management, the recycling process should be completely automated. The problematic part of sorting is being solved by either manual (labor-intensive) or spectroscopy-based (still in development) methods. In this work, we propose the data fusion of Laser-Induced Breakdown Spectroscopy (LIBS) and Raman spectroscopy as a fast, robust, and reliable way to sort/classify any potential polymer material. The sample set of this work consists of several types of polymers in clear, colored, and even mixture versions. So far, no LIBS/Raman classification works involved all these categories in one experiment. Additionally, the low and medium level of data fusion is discussed, and the performance is compared. By using LIBS and Raman data fusion method and both linear and nonlinear chemometric techniques, increased accuracy reaching more than 98 % in the classification of investigated plastic samples was achieved, which was a significant improvement when compared with singular methods classification accuracy.

Comparison of laser-induced breakdown spectroscopy (LIBS) and ICP analysis results for measuring Pb and Zn in soil

Context Laser-induced breakdown spectroscopy (LIBS) is a rapid, multielement analytical technique. It is particularly suitable for the qualitative and quantitative analyses of heavy metals in solid samples. Aims To validate the technique, the LIBS data were compared with the data obtained via conventional inductively coupled plasma (ICP) spectroscopy for the same soil samples. Methods In this study, standard and unknown soil samples from contaminated areas were prepared and fixed to an adhesive tape for LIBS analysis. The soils were also digested with acids for ICP analysis. The emission intensity of one selected line for each of the two analytes, i.e. lead (Pb) and zinc (Zn), was normalised to the background signal and plotted as a function of the concentration values previously determined via ICP analysis. Key results The data demonstrated good linearity for the calibration lines drawn, and the correlation between the ICP and LIBS data was confirmed by the satisfactory agreement between the corresponding values. Conclusions The concentration coefficient of determination (R2) between LIBS and ICP-aqua regia digestion analysis or ICP-total digestion analysis were >0.86 and >0.89 for Pb and Zn, respectively. The total analysis time for the LIBS method was 310 min, which was 54.40% shorter than that for the ICP method (680 min). Implications Consequently, LIBS can be used to measure Pb and Zn in soils without any chemical preparation.

Rapid detection and recognition of phosphors using laser-induced breakdown spectroscopy and principal component analysis method—back propagation neural network algorithm

Rapid detection and quality monitoring of phosphor materials have always been a difficult problem in phosphor materials market. In this work, an independently proposed method based on principal component analysis method—error back propagation neural network algorithm—laser induced breakdown spectroscopy (PCA-BPNN-LIBS) was used for the detection and recognition of phosphors. Firstly, spectroscopic study was carried out on phosphor material samples, and the composition of phosphor elements was analyzed according to the full emission spectrum. Spectral data with different element characteristics detected by LIBS were used as training data sets for further identification. Then PCA method and BPNN algorithm were applied to identify 4 types phosphor samples (P11, P20, P43, P46). A very clear distinction graph was obtained, and the classification accuracy of 99.93% was verified. Allresults show that the proposed PCA-BPNN-LIBS method is an effective method for rapid analysis and recognition of phosphors.

The detection of elemental content changes in electrode coating using laser-induced breakdown spectroscopy

The elemental content of battery electrode coating is prone to change due to the production technology and ambient factors. To ensure the consistent performance and safety of a lithium battery, the elemental content of the electrode coating needs to be kept strictly consistent. This study proposes an internal mixed matrix method that combines laser-induced breakdown spectroscopy and chemometric method to achieve rapid and accurate detection of elemental content changes in electrode coating. The stoichiometric ratios of analytical elements are calculated by using the spectra of laser-induced breakdown spectroscopy. The relationships between that stoichiometric ratios and the actual content of analytical elements are studied and show that they are linear. Thus, the content change of the analytical element can be determined by calculating the change of the stoichiometric ratio. The average relative errors for content changes of iron, lithium, and phosphorus are 6.43%, 2.96%, and 4.12%, respectively, and the lowest detection limits are 278.2 mg/kg, 20.5 mg/kg, and 105.4 mg/kg, respectively. Furthermore, the internal reference method is proposed to correct the effect of ambient gases and improve detection accuracy. The results are that when Fe I 372.751 nm and Fe I 373.485 nm are used as analytical lines, after correcting for the effect of ambient gases, the average relative errors of Fe content changes are reduced by 62% and 72%, respectively, and the lowest detection limits are increased by 67% and 71%, respectively.

Rare earth elements and radioactive elements in black sands from the Konkan and Malabar coasts of India

ABSTRACT The objective of the present work is to demonstrate the ability of the laser-induced breakdown spectroscopy (LIBS) technique for quick detection and quantification of rare earth elements (REEs) and radioactive elements in the black sands at selected locations of the Konkan coast (Goa) and Malabar coast (Kerala) in India. Several REEs such as Ce, Nd, Sm, Dy, Ho, Tm, Gd, and Th have been detected in the LIBS spectra. Calibration-free LIBS method has been used to calculate the concentration of REEs and radioactive elements. The experimental result shows that the concentration of REEs such as Sm, Dy, Ho, and radioactive element Th is maximum in the sands collected from Thiruvananthapuram (Kerala) beach and minimum in the Baga (Goa) beach. The reliability of the results (qualitative and quantitative) obtained by the LIBS method has been examined by other spectroscopic techniques like XRF and Inductively Coupled Plasma Mass Spectrometry (ICP-MS) and found to be in close agreement. The multivariate approach (principal component analysis) has been applied to discern the samples based on their spectral data. Photoacoustic spectroscopy and XRD technique are used to detect compounds/minerals of REEs. The relative hardness, degree of crystallinity (DOC), and crystallite size have been calculated.

Investigation of Laser-Induced Cavity and Plasma Formation in Water Using Double-Pulse LIBS

This paper deals with double-pulse laser-induced breakdown spectroscopy (LIBS) underwater, which is a promising analytical method for elemental analysis in the deep sea up to a water depth of 6000 m. A double-pulse laser with a wavelength of 1064 nm is used, which provides a pulse energy of up to 266 mJ for each laser pulse (in single pulse mode), a pulse width of 5–7 ns and a pulse delay in the range of 0.5 to 20 µs. In the double-pulse LIBS method, the first laser pulse creates a cavity on the material surface, and then the second laser pulse forms the plasma in this cavity. It is expected that the plasma is affected by the cavity’s size and lifetime. For this reason, the influence of focus position, pulse energy and pulse delay on the cavity and plasma formation at shallow water depth has been investigated.

Quantitative analysis method of laser-induced breakdown spectroscopy based on temperature iterative correction of self-absorption effect

Laser-induced breakdown spectroscopy (LIBS) is an ideal real-time on-line method of detecting minor elements in alloys. However, in the case of laser-produced high-density plasma, the self-absorption is usually an undesired effect because it not only reduces the true line intensity, leading the line intensity to become nonlinear with the increase of emitting species content, but also affects the characterization parameters of the plasma, and finally affects the accuracy of quantitative analysis. Since the plasma electron temperature (<i>T</i>), radiation particle number density and absorption path length (<i>Nl</i>) determine the degree of self-absorption and affect the corrected spectral line intensity, a new self-absorption correction method is proposed based on temperature iteration. The initial <i>T</i> is obtained by using this method through spectral line intensity, and the self-absorption coefficient SA is calculated based on the initial <i>Nl</i> parameter to correct the spectral line intensity. Then a new <i>T</i> is obtained from the new spectral line intensity and the new SA is calculated to further correct the spectral line intensity. Through continuous calculation and correction of these two parameters, self-absorption correction is finally achieved. The experimental results of alloy steel samples show that the linearity of Boltzmann plot is increased from 0.867 without self-absorption correction to 0.974 with self-absorption correction, and the linear correlation coefficient <i>R</i><sup>2</sup> of the single variable calibration curve for Mn element increases from 0.971 to 0.997. The relative error of elemental content measurement is improved from 4.32% without self-absorption correction to 1.23% with self-absorption correction. Compared with the commonly applied self-absorption correction methods, this method has obvious advantages of simpler programming, higher computation efficiency, and its independence of the availability or accuracy of Stark broadening coefficients. Moreover, this method can directly obtain the radiation particle number density and absorption path length, which is beneficial to the diagnosis and quantitative analysis of plasma.

Identification and Analysis of Meat Species Using Laser Induced Breakdown Spectroscopy (LIBS): A Review

The high price of beef and its processed products has led to many cases of adulteration with pork, resulting in issues related to halal food assurance. Therefore, it is crucial to conduct identification and analysis of the types of meat used in order to maintain food halalness. One of the methods currently advancing in the identification and analysis of meat types is Laser-Induced Breakdown Spectroscopy (LIBS). The aim of this study is to determine the capability of Laser-Induced Breakdown Spectroscopy (LIBS) in identifying and analyzing various types of meat. The study results indicate that the Laser-Induced Breakdown Spectroscopy (LIBS) method is capable of identifying and analyzing meat types with simple sample preparation and accurate outcomes compared to other methods such as Real Time-PCR, Enzyme-Linked Immunosorbent Assay (ELISA), Electronic Nose System, Fourier-transform infrared spectroscopy (FTIR), and Raman spectroscopy. The Laser-Induced Breakdown Spectroscopy (LIBS) method can be combined with various chemometric methods such as PCA, PLS, and MSC. Laser-Induced Breakdown Spectroscopy (LIBS) can identify and analyze various types of meat with an accuracy of up to 100% in shrimp and clams mixed sample. In conclusion, the combination of LIBS and chemometric methods demonstrates promising results in identifying and analyzing meat types.

Improving the Laser-Induced Breakdown Spectroscopy for Highly Efficient Trace Measurement of Hazardous Components in Waste Oils.

Improper disposal of waste oils containing hazardous components damages the environment and the ecosystem, posing a significant threat to human life and health. Here, we present a method of discharge-assisted laser-induced breakdown spectroscopy combined with filter paper sampling (DA-LIBS-FPS) to detect hazardous components and trace the source of polluting elements. DA-LIBS-FPS significantly enhances spectral intensity by 1-2 orders of magnitude due to the discharge energy deposition into the laser-induced plasma and the highly efficient laser-sample interaction on the filter paper, when compared to single-pulse LIBS with silica wafer sampling (SP-LIBS-SWS). Additionally, the signal-to-noise ratio and the signal-to-background ratio are both significantly increased. Resultantly, indiscernible lines, such as CN and Cr I, are well distinguished. In contrast with DA-LIBS combined with silica wafer sampling (DA-LIBS-SWS), the spectral signal fluctuations in DA-LIBS-FPS are reduced by up to 33%, because of the homogeneous distribution of the oil layer on the filter paper in FPS. Further examination indicates that the limit of detection for Ba is reduced from a several parts per million level in SP-LIBS-SWS to a dozens of parts per billion level in DA-LIBS-FPS, i.e., nearly 2 orders of magnitude enhancement in analysis sensitivity. This improvement is attributed to the extended plasma lifespan in DA-LIBS and the increasing electron density and plasma temperature in FPS. DA-LIBS-FPS provides a low-cost, handy, rapid, and highly sensitive avenue to analyze the hazardous components in waste oils with great potential in environmental and ecological monitoring.

Characterization of impurity distribution and composition on the shutter plate for an optical diagnosis in EAST tokamak using laser-induced breakdown spectroscopy

The quantification of impurities in tokamak devices is of great significance as it allows for a better understanding of the plasma performance and the lifetime of plasma-facing components (PFCs). This study focuses on the characterization of the impurity distribution and composition on the surface of a shutter plate for an optical diagnosis in the Experimental Advanced Superconducting Tokamak (EAST) by Laser-Induced Breakdown Spectroscopy (LIBS). The primary impurity elements, including copper (Cu), tungsten (W), molybdenum (Mo), lithium (Li), and Sodium(Na), were identified by analyzing the LIBS spectra obtained from the surface of the shutter plate. The spatial distribution of these impurities on both sides of the plate was investigated. The analysis results indicate an increase in impurity content on the outer surface of the shutter plate as proximity to Last Closed Flux Surface (LCFS), followed by a near-linear decrease with the distance from the LCFS. The results of the inner ring on the inner side facing the glass window show fewer metal impurities than the outer rings on the edge for the inner side of the plate. Moreover, the thickness of the deposition layer was determined by estimating the Average Ablation Rate (AAR) through the measurement by confocal microscopy. In addition, Calibration-Free LIBS method were performed to determine the relative content of impurities. The results of this study provide valuable references for studying the migration and transportation of impurities.

A Simple Laser-Induced Breakdown Spectroscopy Method for Quantification and Classification of Edible Sea Salts Assisted by Surface-Hydrophilicity-Enhanced Silicon Wafer Substrates.

Salt, one of the most commonly consumed food additives worldwide, is produced in many countries. The chemical composition of edible salts is essential information for quality assessment and origin distinction. In this work, a simple laser-induced breakdown spectroscopy instrument was assembled with a diode-pumped solid-state laser and a miniature spectrometer. Its performances in analyzing Mg and Ca in six popular edible sea salts consumed in South Korea and classification of the products were investigated. Each salt was dissolved in water and a tiny amount of the solution was dropped and dried on the hydrophilicity-enhanced silicon wafer substrate, providing homogeneous distribution of salt crystals. Strong Mg II and Ca II emissions were chosen for both quantification and classification. Calibration curves could be constructed with limits-of-detection of 87 mg/kg for Mg and 45 mg/kg for Ca. Also, the Mg II and Ca II emission peak intensities were used in a k-nearest neighbors model providing 98.6% classification accuracy. In both quantification and classification, intensity normalization using a Na I emission line as a reference signal was effective. A concept of interclass distance was introduced, and the increase in the classification accuracy due to the intensity normalization was rationalized based on it. Our methodology will be useful for analyzing major mineral nutrients in various food materials in liquid phase or soluble in water, including salts.

Laser-induced breakdown spectroscopy for rapid and accurate qualitative analysis of elemental composition in fertilizers

Through elemental analysis, laser-induced breakdown spectroscopy (LIBS), a quick and effective analytical method, has enormous potential to advance agriculture. In this context, our study intends to better the fertilizer sector by utilizing LIBS’s capabilities. The main objective is to make it possible to rapidly and accurately analyze the elements in frequently used fertilizers such as nitrophos (NP), diammonium phosphate (DAP), and single super phosphate (SSP). We identify all elements contained in the fertilizers using qualitative and semi-quantitative analysis utilizing a single LIBS shot by noting their matching spectral lines and peak positions. This identification is validated more thoroughly by matching peak positions to the National Institute of Standards and Technology (NIST) database. Phosphorus (P), potassium (K), iron (Fe), calcium (Ca), nickel (Ni), and aluminum (Al) are effectively recognized due to their distinct spectral fingerprints. Our findings highlight the vital need to precisely characterize fertilizer content in order to maximize agricultural yield. Furthermore, our approach presents an efficient means for rapid and precise analysis of fertilizers, offering the advantage of minimal sample requirements.

Applying laser induced breakdown spectroscopy (LIBS) and elemental imaging on marine shells for archaeological and environmental research.

Using LIBS for the analysis of archaeological and geological marine mollusc shells is a growing research area that relies on customised instrumentation and specific workflows that can accommodate the variety and precision of the required sampling parameters. However, the increased efficiency offered by LIBS, which enables the study of a larger quantity of shell samples for temperature variation, ecological parameters, and human consumption practices, outweighs the initial efforts required to develop customised instrumentation and workflows. In this work, we present detailed specifications and parameters for the development of a LIBS system capable of generating Mg/Ca images on marine shells that directly correlate with seasonal sea temperatures. Our main objective was to develop specifications that enable easy adaptation of LIBS systems to existing laboratories for studying hard-tissue samples. These specifications were used to develop a customised micro-LIBS system and apply it to a real-world example of an archaeological study to better understand its efficiency on the marine mollusc shells and demonstrate its potential for broader applications in interdisciplinary research. In total 101 shell specimens have been analysed within a time frame of approximately 71h of machine time, producing 234 images (100µm resolution: 100 images, 30µm resolution: 134 images). SEM analysis of the irradiated sections of the shell revealed a primary ablated area of 10-15µm in diameter, while a secondary affected area of the shell's crystal fabric extended to 30-50µm after repeated shots. Overall, this new customised system reliably and efficiently analysed marine mollusc specimens without major destructive effects, enabling additional analyses for other proxies to be carried out. This study highlights the potential of the LIBS method for interdisciplinary research, encompassing applications in paleoclimatology, marine ecology, and archaeology.

Compositional analysis of copper and iron-based alloys using LIBS coupled with chemometric method.

The present manuscript deals with the utility of the calibration-free LIBS and calibration curve methods for the compositional study of different alloys using laser-induced breakdown spectroscopy (LIBS). In the process of alloying in the smelting industry, metal concentration in different alloys affects the physical and chemical properties of the final products. Therefore, LIBS can be used as an efficient quantitative analysis tool for online monitoring of the quality of the products. This is because LIBS can be performed online, in situ, without any pre-processing, and need no sample preparation for the compositional analysis of any type of materials present in any phase (solid, liquid, gas or even molten alloys in the industries). In the present study, four alloys (three copper and one iron-based alloy) consisting of Cu, Al, Zn, Ni, Fe, Cr and Mn as major and Sn and Si as minor elements were selected for the study using calibration-free laser-induced breakdown spectroscopy (CF-LIBS) and calibration curve method i.e. partial least square regression (PLSR). For the CF-LIBS method, the temporal delay has been optimized in order to satisfy the optically thin and local thermal equilibrium (LTE) condition of the plasma. For the PLSR method, different regions of the strongest emission lines of constituents have been selected for quantitative analysis. The study of time-resolved LIBS spectra and the variation of plasma parameters with respect to the delay time is also discussed. The utility of the combined technique of CF-LIBS with the PLSR method for rapid monitoring and quality assessment of desired material/products without any sample pretreatment, thus reducing the cost of the analysis, is presented in this paper.

Two-dimensional elemental mapping of simulated fuel debris using laser-induced breakdown spectroscopy

ABSTRACT In this experimental study, two-dimensional elemental mapping of simulated fuel debris was conducted by laser-induced breakdown spectroscopy (LIBS). Since the real fuel debris was unavailable as a sample, simulated fuel debris was prepared from predicted materials including compounds and metals. An Nd:YAG laser at the second harmonic was used to generate plasma on the sample surface, and the optical emission from plasma was detected using an echelle spectrometer in the visible wavelength range from 435 to 650 nm. Due to the size and complexity of the collected dataset, the conventional data analysis method was ineffective; consequently, there arose a need to design a new data analysis method for study purposes. Therefore, in the present study, a method that is based on label-free chemometric methods, such as Principal Component Analysis and Multivariate Curve Resolution-Alternative Least Square methods, were implemented to obtain the spatial and spectral information regarding each constituent within the simulated sample. The study results demonstrated that the integration of LIBS and chemometric methods is a highly effective tool to obtain qualitative information regarding samples (e.g. fuel debris) with little or no prior knowledge.

Multi-Spectroscopic Characterization of MgO/Nylon (6/6) Polymer: Evaluating the Potential of LIBS and Statistical Methods.

The potential of using laser-induced breakdown spectroscopy (LIBS) in combination with various other spectroscopic and statistical methods was assessed for characterizing pure and MgO-doped nylon (6/6) organic polymer samples. The pure samples, obtained through a polycondensation chemical technique, were artificially doped with MgO prior to analysis for comparative purposes. These artificially doped samples served as crucial reference materials for comparative analysis and reference purposes. The LIBS studies were performed under local thermodynamic equilibrium (LTE) and optically thin plasma conditions. To assess the structural crystallinity of the nylon (6/6) polymer samples, X-ray diffraction (XRD) analysis, and Fourier transform infrared (FTIR) spectroscopy were employed to detect functional groups such as N-H, C-H, and C-N in the adsorbent polyamide nylon sample. Additionally, diffuse reflectance spectroscopy (DRS) analysis was conducted to investigate the effects of doping and temperature on the band gap and material reflectance across different sample temperatures. Chemical compositional analysis was performed using X-ray photoelectron spectroscopy (XPS) with the carbon C1s peak at 248.8 eV serving as a reference for spectrum calibration, along with energy-dispersive X-ray (EDX) analysis, which demonstrated good agreement between the techniques. To validate the different methodologies, the results obtained from CF-LIBS and EDX were compared with those from the standard inductively coupled plasma mass spectrometry (ICP-MS) technique. Finally, for classification analysis, principal component analysis (PCA) was applied to the LIBS spectral data at different sample temperatures (25 °C, 125 °C, 225 °C, and 325 °C). The analyses demonstrated that the combination of LIBS with PCA, along with other methods, presents a robust technique for polymer characterization.

An approach for measurement of the magnetic field near the surface of plasma-facing components in tokamak by laser induced breakdown spectroscopy based on Zeeman effect

Laser-induced breakdown spectroscopy (LIBS) has been demonstrated to diagnose the surface element distribution of plasma-facing components (PFCS) in fusion devices. However, the magnetic field intensity and polarity near the wall surface change frequently and cannot be measured in real time, which will affect the analytical accuracy of LIBS results. The determination of the strength and polarity direction of the magnetic field near the surface will be conducive to the quantitative analysis of LIBS and provide valuable information for the distribution of the magnetic field near the surface of PFCs. In this work, the effects of magnetic fields on the characteristics of laser-induced Mo plasma, such as the ablation depth and mass, the spatio-temporal evolution behavior of spectrum and the plasma parameters, were first systematically investigated. The different phenomenon of continuum radiation, Mo I line and Mo II line under the magnetic field were mutually verified by optical emission spectroscopy and fast plasma imaging methods. Meanwhile, an approach for measurement of the magnetic field intensity and polarity near the surface of PFCS by LIBS method has been proposed and investigated. When the magnetic field polarity is changed, the spatial distribution profile of Mo spectrum will drift in the opposite direction affected by of the Lorentz force, which realizes the measurement of magnetic field polarity. Moreover, the splitting distance of Mo I line caused by Zeeman effect with the variable magnetic fields were preliminarily calculated. The experimental values of splitting distance agree well with the theoretical values that calculated by the known magnetic field strength. These results confirm the feasibility of measuring the magnetic field intensity and polarity of PFCs surface by LIBS approach.