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Chlorine and sulfur determination in water using indirect laser-induced breakdown spectroscopy
摘要： The detection sensitivity of chlorine (Cl) and sulfur (S) elements is poor using direct laser-induced breakdown spectroscopy (LIBS) because of the high ionization energy of Cl and S. Therefore, a new technique, namely indirect laser-induced breakdown spectroscopy (ID-LIBS), was proposed to improve the detection sensitivity of Cl and S elements. The method detected Cl in water by indirectly detecting the excess silver (Ag) after the precipitation reaction of Ag and chloride. Similarly, the method indirectly detected S in water by detecting the excess barium (Ba) after the precipitation reaction of Ba and sulfate, due to Ag and Ba with low ionization energy and easy excitation. The lines of Ag I 546.5 nm and Ba I 553.5 nm were detected. The R2 values of 0.999 and 0.997 were obtained for Cl and S, respectively. The limit of quantitation (LoQ) was 2 mg/L for Cl and 5 mg/L for S. The detection sensitivity was improved by about three orders of magnitude compared to using Cl I 822.17 nm and S I 921.28 nm. The results showed that the technique of indirect LIBS can achieve the sensitive detection of Cl and S in water indicating that the technique has tremendous potential for element analysis of water.
关键词： Indirect LIBS,Water analysis,Laser-induced breakdown spectroscopy,Determination
更新于2025-09-19 17:13:59
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Laser-stimulated birefringence of Ga2O3-La2S2.95Se0.05 glasses for optical recording of information
摘要： We show an opportunity to change the birefringence of Ga2O3 – La2S2.95Se0.05 glasses doped by Er3+ and La3+ ions at λ = 1150 nm wavelength of cw He-Ne laser under illumination of the femtosecond laser. The variation of the refractive indices was found during illumination by 180 fs laser with frequency about 65 MHz (at wavelength λ = 1045 nm). The laser-stimulated birefringence has been explored versus temperature. The observed laser induced and temperature dependences of the birefringence con?rm a huge contribution of anharmonic phonon subsystems which is typical for chalcogenide glasses. Due to an occurrence of local space charge density asymmetry, the e?ciency of birefringence is enhanced. The anisotropy e?ect exists only during the illumination and is diminished during 10…12 s after switching o? of the photo-inducing laser treatment. There is observed also a correlation between the occurred grating patterns and the values of the birefringence.
关键词： Chalcogenide glasses,Optoelectronic materials,Laser-induced e?ects,Birefringence,Electronic and electrical engineering
更新于2025-09-19 17:13:59
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A singularity free and derivative free approach for Abel integral equation in analyzing the laser-induced breakdown spectroscopy
摘要： In order to make a detailed analysis of the laser-induced breakdown spectroscopy (LIBS), we present a new approach which has advantages of singularity free and derivative free for solving the Abel integral equation. After presenting the model describing the LIBS, a collocation method is applied and two main steps are introduced. First, the Abel integral equation is transformed to a singularity free and derivative free integral equation. Then, by expanding the solution of the integral equation to a polynomial of degree n, the solution can be approximated by a linear system established by the collocation method. Our approach is suitable for dealing with LIBS problem for any form of the measured intensity. In particular, the method is insensitive to the noisy intensity data. A convergence analysis is also given to show the validity of the method and numerical examples are provided to show its efficiency and accuracy.
关键词： spectrum,laser-induced breakdown spectroscopy (LIBS),Abel integral equation,plasma
更新于2025-09-19 17:13:59
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Effect of two-step post-treatment on optical properties, microstructure, and nanosecond laser damage threshold of HfO <sub/>2</sub> /TiO <sub/>2</sub> /SiO <sub/>2</sub> multilayer high reflection films
摘要： HfO2/TiO2/SiO2 periodic multilayer high reflection films deposited by an electron beam are post-treated by two-step post-treatment and thermal annealing post-treatment, respectively. The optical properties, microstructures, surface morphologies, and laser-induced damage threshold (LIDT) of the films are studied comparatively. The results show that the two-step post-treatment enhances the high reflection films’ density and reduces the film surface roughness and the defects of the film. The test results show that the LIDT of HfO2/TiO2/SiO2 high reflection films treated by two-step post-treatment reaches 32.8 J/cm2, which is 110.26% higher than that of the untreated film. Compared with the HfO2/TiO2/SiO2 high reflection films after thermal annealing post-treatment, the LIDT increased nearly 27.6% after two-step post-treatment. Two-step post-treatment of high reflection films can effectively remove the defects on the surface of the film, reduce the oxygen vacancies inside the film, and further increase the laser damage threshold of the high reflection films.
关键词： laser-induced damage threshold,HfO2/TiO2/SiO2,two-step post-treatment,thermal annealing,multilayer high reflection films
更新于2025-09-19 17:13:59
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Laser-Induced Breakdown Spectroscopy and Principal Component Analysis for Classification of Spectra from Gold-Bearing Ores
摘要： Laser-induced breakdown spectroscopy (LIBS) and principal component analysis (PCA) were applied to the classification of LIBS spectra from gold ores prepared as pressed pellets from pulverized bulk samples. Obtained for each sample were 5000 single-shot LIBS spectra. Although the gold concentrations in the samples were as high as 7.7 μg/g, Au emission lines were not observed in most single-shot LIBS spectra, rendering infeasible the application of the usual ensemble-averaging approach for spectral processing. Instead, a PCA approach was utilized to analyze the collection of single-shot LIBS spectra. Two spectral ranges of 21 nm and 0.15 nm wide were considered, and LIBS variables (i.e., wavelengths) reduced to no more than three principal components. Single-shot spectra containing Au emission lines (positive spectra) were discriminated by PCA from those without the spectral feature (negative spectra) in a spectral range of less than 1 nm wide around the Au(I) 267.59 nm emission line. Assuming a discrete gold distribution at very low concentration, LIBS sampling of gold particles seemed unlikely, therefore, positive spectra were considered as data outliers. Detection of data outliers was possible using two PCA statistical parameters, i.e., sample residual and Mahalanobis distance. Results from such a classification were compared with a standard database created with positive spectra identified with a filtering algorithm that rejected spectra with an Au intensity below the smallest detectable analytical LIBS signal (i.e., below the LIBS limit of detection). The PCA approach successfully identified 100% of the data outliers when compared with the standard database. False identifications in the multivariate approach were attributed to variations in shot-to-shot intensity and the presence of interfering emission lines.
关键词： gold ores analysis,Laser-induced breakdown spectroscopy,PCA,data outliers,principal component analysis,LIBS
更新于2025-09-19 17:13:59
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EXPRESS: Evaluation of a Thermoelectric Cooler as a Sample Pre-Treatment Method for Laser Induced Breakdown Spectroscopy (LIBS) Analysis of Liquid Samples
摘要： In this study, the performance of a thermoelectric cooler (TEC) as a simple and easy-to-assemble freezing instrument has been evaluated. Experiments were carried out using samples with different viscosity ranging from 44.07 to 16,965.80 mPas. The analysis on sodium component of the samples by direct laser irradiation of frozen samples showed emission enhancement and higher signal-to-noise ratio (SNR) compared to that of liquids. This work also focused on using chemometrics methods such as principal component analysis (PCA) to compare the PC score separation and clustering pattern between frozen and liquid samples. The PCA was constructed by dividing the samples into two different categories: (i) type (paste, cream, gel and oil); and (ii) viscosity (more than and less than 10000 mPas). The frozen samples showed a more established separation and clustering compared to that acquired from the liquid samples. However, poorer clustering pattern of some frozen samples could be due to the heat transfer during laser–sample interaction inducing surface melting and splashing. The average LIBS spectra were taken at as many different surface areas as possible to ensure the sample surface always maintain similar freezing temperature. This work showed that the TEC pre-treatment method had improved the LIBS measurement of the liquid samples.
关键词： viscosity,liquid sample,LIBS,Laser induced breakdown spectroscopy,thermoelectric cooler
更新于2025-09-19 17:13:59
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Laser-induced breakdown spectroscopy as a tool for homogeneity measurements in medicine tablets
摘要： In this work, we have used laser-induced breakdown spectroscopy (LIBS) in the analysis of commercial tablets. The samples were mainly composed of dipyrone, an analgesic and fever reliever consumed worldwide. At first, the physical parameters, temperature and electronic density of the plasma were calculated throughout the Boltzmann plot and Saha equation respectively, and the McWhirter criterion was achieved, which allows us to assert that the minimum criterion for local thermodynamic equilibrium is presented in the plasma generated. After that, the tablets’ homogeneity was assessed using the whole LIBS spectra combined to correlation statistic methods, such as principal components analysis (PCA) and hyperspectral images. The results show high homogeneity, R > 0.996, at the surface and some heterogeneity in the bulk. LIBS was also applied for major active pharmaceutical ingredients C, Na and Mg identification.
关键词： dipyrone tablets,homogeneity,laser-induced breakdown spectroscopy (LIBS)
更新于2025-09-19 17:13:59
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Improved measurement on quantitative analysis of coal properties using laser induced breakdown spectroscopy
摘要： It is of great significance to realize the rapid or online analysis of coal properties for combustion optimization of thermal power plants. In this work, a set of calibration schemes based on laser-induced breakdown spectroscopy (LIBS) was determined to improve the measurement on quantitative analysis of coal properties, including proximate analysis (calorific value, ash, volatile content) and ultimate analysis (carbon and hydrogen). Firstly, different normalization methods (channel normalization and normalization with the whole spectral area) combined with two regression algorithms (partial least-squares regression [PLSR] and support vector regression [SVR]) were compared to initially select the appropriate calibration method for each indicator. Then, the influence of de-noising by the wavelet threshold de-noising (WTD) on quantitative analysis was further studied, thereby the final analysis schemes for each indicator were determined. The results showed that WTD coupled SVR can be well estimated calorific value and ash, the root mean square error of prediction (RMSEP) were 0.80 MJ kg?1 and 0.60%. Coupling WTD and PLSR performed best for the measurement of volatile content, the RMSEP was 0.76%. For the quantitative analysis of carbon and hydrogen, normalization with the whole spectral area combined with SVR can get better measurement results, the RMSEP of the measurements were 1.08% and 0.21%, respectively. The corresponding average standard deviation (RSD) for calorific value, ash, volatile content, carbon and hydrogen of validation sets were 0.26 MJ kg?1, 0.57%, 0.79%, 0.47% and 0.08%, respectively. The results demonstrated that the selection of appropriate spectral pre-processing coupled with calibration strategies for each indicator can effectively improve the accuracy and precision of the measurement on coal properties.
关键词： partial least-squares regression (PLSR),quantitative analysis,normalization,Laser-induced breakdown spectroscopy (LIBS),coal properties,support vector regression (SVR),wavelet threshold de-noising (WTD)
更新于2025-09-19 17:13:59
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Formation of thioglucoside single crystals by coherent molecular vibrational excitation using a 10-fs laser pulse
摘要： Compound crystallization is typically achieved from supersaturated solutions over time, through melting, or via sublimation. Here a new method to generate a single crystal of thioglucoside using a sub-10-fs pulse laser is presented. By focusing the laser pulse on a solution in a glass cell, a single crystal is deposited at the edge of the ceiling of the glass cell. This finding contrasts other non-photochemical laser-induced nucleation studies, which report that the nucleation sites are in the solution or at the air-solution interface, implying the present crystallization mechanism is different. Irradiation with the sub-10-fs laser pulse does not heat the solution but excites coherent molecular vibrations that evaporate the solution. Then, the evaporated solution is thought to be deposited on the glass wall. This method can form crystals even from unsaturated solutions, and the formed crystal does not include any solvent, allowing the formation of a pure crystal suitable for structural analysis, even from a minute amount of sample solution.
关键词： crystallization,coherent molecular vibrations,single crystal,thioglucoside,laser-induced nucleation
更新于2025-09-19 17:13:59
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Diagnostics of laser induced plasmas at late delay times
摘要： The study of the diagnostics of plasmas produced by laser is not always possible without enough of data, usually a precise record of several lines meeting certain spectroscopic conditions is needed. In this work, a method of diagnosing plasmas was implemented in sufficiently late postbreakdown times, where it is no longer possible to apply known methods (e.g. Boltzmann plot for the estimation of kT). Through an iterative algorithm that uses the parameters obtained by traditional methods at early times (LIBS typical delay time), and a minimum number of lines visible in the later times. Using the late times that are typical to the plasma’s final life stage, an evolution of the temperature and electronic density of the plasma is studied. The LTE condition was also verified by McWhirter's criterion.
关键词： temperature,Laser Induced Breakdown Spectroscopy,density electronic,Plasma diagnostic,molecular emission.
更新于2025-09-19 17:13:59