Multivariate data analysis (MVDA) is getting popular across the spectroscopic community. To assess accurate results, the obtained data should be preprocessed prior to utilization of any MVDA algorithm. The process of data normalization or “internal standardization” is widely used across a broad range of applications. In this manuscript we investigate the utilization of Laser-Induced Breakdown Spectroscopy (LIBS) coupled with MVDA. However, many articles regarding the use of MVDA on data from LIBS do not provide any information about the data pretreatment. This work describes the impact of LIBS data normalization approaches on MVDA classification accuracy. Also, the impact of classical data preprocessing (mean centering and scaling) exploiting the prior utilization of MVDA was studied. This issue was investigated exploiting simple soft independent modelling of class analogies algorithm. The findings were generalized for three sample matrices (steel, Al alloys, and sedimentary ores). Furthermore, the selection of an appropriate normalization algorithm is not trivial since the spectrum of each sample matrix is composed of a different number of elements and corresponding elemental lines.

MACHINE REGRESSION-MODEL; CONVEX-OPTIMIZATION; COEFFICIENTS; LIBS

In quantitative laser-induced breakdown spectroscopy analysis, spectral signals are usually represented by the linear combination of characteristic peaks with useful spectral information and unwanted noise components. All of the existing regression analysis methods are related to a spectral data matrix, which is composed of certified samples with different spectral intensity. Therefore, spectral data matrix processing is critical for quantitative LIBS analysis. A prevalent assumption when constructing a matrix approximation is that the partially observed matrix is of low-rank. Moreover, the low-rank structure always reflects the useful information and is regarded as a powerful data preprocessing method. In this paper, a novel and quantitative LIBS analysis method based on a sparse low-rank matrix approximation via convex optimization is proposed. Based on the sparsity of the spectral signals, we present a convex objective function consisting of a data-fidelity term and two parameterized penalty terms. To improve the accuracy of the quantitative analysis, a new non-convex and non-separable penalty based on the Moreau envelope is proposed. Then, the alternating direction method of multipliers algorithm was utilized to solve the optimization problem. The proposed method was applied to the quantitative analysis of 23 high alloy steel samples. Both of the performances of the Partial Least Squares and Support Vector Machine regression models are improved by using the low-rank matrix approximation scheme, which proves the effectiveness of the proposed method.

SPECTRAL-LINE; EMISSION-LINES; INDUCED FLUORESCENCE; RESONANCE LINES; INDUCED PLASMAS; COEFFICIENTS; PRESSURE; ALUMINUM; CALIBRATION; LIBS

Reducing self-absorption is one of the most important steps in achieving accurate analyses in laser-induced breakdown spectroscopy . In this work, LIBSassisted with laser-stimulated absorption was used to reduce self-absorption effects in LIBS. A wavelength-tunable laser was used to resonantly excite cold atoms and reduce their amount in laser-induced plasmas, and thus fewer cold atoms at the plasma periphery re-absorb light from the plasma center. Accordingly, the self-absorption effect was reduced. Copper and chromium elements in steels were taken as examples to evaluate and compare the self-absorption effects in LIBS and LSA-LIBS. The results of calculated self-absorption coefficients supported the effectiveness in reducing self-absorption and improving analytical linearity using LSA-LIBS.

INDUCED BREAKDOWN SPECTROSCOPY; SUPPORT VECTOR MACHINES; PARTIAL LEAST-SQUARES; DISCRIMINANT-ANALYSIS; SUBSET-SELECTION; LASER; CLASSIFICATION; SAMPLES; IDENTIFICATION; ALGORITHM

In recent years, LIBS quantitative analysis based on multivariate regression has received considerable attention, and variable selection is critical for improving accuracy of multivariate regression analysis of LIBS. In the present study, sequential backward selection combined with random forest was proposed to improve detection accuracy of sulfur and phosphorus in steel. First, LIBS spectrum line of S and P was identified by the NIST database. Second, input variables for RF calibration model were selected and optimized by SBS, and RF model parameters and m) were optimized by out-of-bag estimation. Finally, optimized input variables and model parameters were employed to build an SBS-RF calibration model for quantitative analysis of P and S in steel. Results showed that the SBS-RF model provided good predictions for S and P compared with those provided by the univariate method, PLS model and traditional RF model. Thus, LIBS coupled with SBS-RF is an effective method for quality supervision and control of steel products.

Laser-induced breakdown spectrometry; X-ray fluorescence spectrometry; Chromium; Surface layer; Steel sheets;DEPTH PROFILE ANALYSIS; GALVANIZED STEEL; COATED STEEL; ABLATION; SPECTROSCOPY; COPPER

A method was proposed for the determination of Cr in a thin surface nanolayer deposited on top of a micrometrical Zn-based anticorrosive coating of steel sheets using laser-induced breakdown spectrometry . Optimization of the LIBS parameters was performed with respect to the statistical parameters of regression, these being the coefficient of determination , akaike information criterion and mean-squared prediction error. These were calculated for curves describing the relationship between the Cr surface concentration and the intensity of LIBS signal. The most critical parameter of analysis appears to be the focal spot diameter. When its value was 200 mu m and corresponding energy density had value of 413.8 J/cm, the intensity-concentration relationship revealed a negative slope. This phenomenon was caused by the difference in total ablated volume for samples with a different content of Cr in the surface layer. This phenomenon was not observed for higher values of the focal spot diameter and lower values of fluence ). A range of calibration obtained under optimal conditions was 11-21 mg/m and the limit of detection was 0.7 mg/m. The recovery values calculated from the results of the proposed LIBS method and the standard ED XRF method ranged from 99.2 to 101%.

INDUCED BREAKDOWN SPECTROMETRY; INDUCED PLASMA SPECTROMETRY; JEWELRY INDUSTRY; SPECTROSCOPY; METALS; STEEL

In this study, galvanic coatings of Cu and Ni, typically applied in industrial standard routines, were investigated. Ablation experiments were carried out using the first two harmonic wavelengths of a pulsed Nd: YAG laser and the resulting plasma spectra were analysed using a linear Pearson correlation method. For both wavelengths the absorption/ablation behaviour as well as laser-induced breakdown spectroscopy (LIBS) depth profiles were studied varying laserfluences between 4.3-17.2 J/cm(2) at 532 nm and 2.9-11.7 J/cm(2) at 1064 nm. The LIBS-stratigrams were compared with energy-dispersive X-ray spectroscopy of cross-sections. The ablation rates were calculated and compared to theoretical values originating from a thermal ablation model. Generally, higher ablation rates were obtained with 532 nm light for both materials. The light-plasma interaction is suggested as possible cause of the lower ablation rates in the infrared regime. Neither clear evidence of the pure thermal ablation, nor correlation with optical properties of investigated materials was obtained.

INDUCED BREAKDOWN SPECTROSCOPY; DENSITY; GAS; TEMPERATURE; HYDROGEN; SPECTRA; LIBS

Laboratory plasmas inherently exhibit temperature and density gradients leading to complex investigations. We show that plasmas generated by laser ablation can constitute a robust exception to this. Supported by emission features not observed with other sources, we achieve plasmas of various compositions which are both uniform and in local thermodynamic equilibrium. These properties characterize an ideal radiation source opening multiple perspectives in plasma spectroscopy. The finding also constitutes a breakthrough in the analytical field as fast analyses of complex materials become possible.

INDUCED BREAKDOWN SPECTROSCOPY; SPECTRUM STANDARDIZATION METHOD; PARTIAL LEAST-SQUARES; MICROCHIP LASER; CARBON ANALYSIS; MN; SPECTROMETRY; CONFINEMENT; IMPROVEMENT; REGRESSION

Laser-induced breakdown spectroscopy (LIBS) was named a future superstar. Nevertheless, in the last couple of years, several commercial instruments of LIBS and its different variants have become available on a limited scale due to the confinement of quantitative analysis. In this paper, quantitative analysis of various steel samples using a specially designed handheld mu-LIBS instrument and dominant factor based partial-least squares (PLS) regression with spectral standardization is presented. Average absolute measurement errors of 0.019, 0.039, 0.013 and 0.001% for the elements of Si, Cr, Mn and Ni, respectively, were achieved. The average relative standard deviation (RSD) for these elements was less than 5%. A linear calibration response was obtained for C which is difficult to achieve using traditional PLS and for Cu whose concentration in the samples is very low. The results are better than the results of previous LIBS studies using mu J lasers or portable handheld devices, comparable to those obtained using conventional benchtop LIBS systems and better than those of commercial handheld XRF instruments. The present work presents the best results for steel analysis using portable LIBS systems so far and shows the feasibility of the technology for real industrial applications.

IN-SITU; LIBS; STEELS; CLASSIFICATION; EXPLORATION; ELEMENTS; SPECTRA; SAMPLES; SOIL; MN

Stand-off laser-induced breakdown spectroscopy (ST-LIBS) has attracted increasing attention as a valuable method for the remote analysis of materials. In this work, a multi-collector (MC) system combining low cost small lenses imitating the structure and shape of an artificial optical compound eye (AOCE) is presented to enhance the spectral intensity of ST-LIBS. The volume of the MC system is one eighteenth smaller than that of a telescope system and the number of collectors can be flexibly changed according to the requirements. The mechanisms of spectral enhancement are also discussed. In order to illustrate the performance of the MC system, the spectral intensities and the limits of detection (LoDs) of Mn and Cr elements acquired by the telescope system and the MC system were compared at a distance of 2 meters. The results showed that the spectral intensity acquired from the MC system was enhanced by 2.2 times, and the LoDs of Mn and Cr were decreased to 294 mu g g(-1) and 49 mu g g(-1). These results indicate that the MC system has great potential in providing a portable, flexible and effective collection method for remote detection.

LIBS; Steel analysis; Material identification; Rolling mill; Production control;QUANTITATIVE-ANALYSIS; HIGH-TEMPERATURE; SAMPLES; SPECTROMETRY; LIBS

Laser-induced breakdown spectroscopy (LIBS) is applied for the elemental analysis of steel blooms in a rolling mill. The 2-3 tons steel blooms with superficial scale are transported in a sequence on a roller table to successive processing steps. Laser ablation of the scale and the analysis of the subsurface bulk steel is carried out using the same laser in <50 s during scheduled stop times of the roller table. Up to 14 elements such as Ni, Cr, and Mo are measured for several hundreds of blooms of low and high alloy steel during routine production. The comparison of the measured with the nominal compositions, results in root mean square errors of prediction in the range of 0.01-0.2 m.-%. The rolling sequence is clearly reflected by the LIBS measurement of the individual blooms demonstrating the feasibility for material identification. Identification rates are estimated from computer simulations by permutation of the LIBS measured values and the reference values from the rolling sequence. (C) 2017 The Authors. Published by Elsevier B.V.

LIBS stratigraphy; Galvanic coatings; Ablation rate; Plasma shielding; Light-plasma interaction; Depth profiling;INDUCED BREAKDOWN SPECTROMETRY; ION-BEAM ANALYSIS; PULSED-LASER DEPOSITION; REDUCED PRESSURE; JEWELRY INDUSTRY; PURE METALS; ABLATION; SPECTROSCOPY; FILMS; THICKNESS

Laser-induced depth profiling was applied to the investigation of galvanised steel sheets as a typical modern multi-layer coating system for environmental corrosion protection. The samples were ablated stepwise by the use of two different wavelengths of a frequency-converted Nd:YAG-laser, 266nm and 532nm, with a pulse duration of tau = 4ns at fluences ranging from F=50 to 250 J cm(-2). The emission light of the resulting plasma was analysed as a function of both penetration depth and elemental spectrum in terms of linear correlation analysis. Elemental depth profiles were calculated and compared to EDX-cross sections of the cut sample. A proven mathematical algorithm designed for the reconstruction of layer structures from distorted emission traces caused by the Gaussian ablation profile can even resolve thin intermediate layers in terms of depth and thickness. The obtained results were compared to a purely thermally controlled ablation model. Thereby light-plasma coupling is suggested to be a possible cause of deviations in the ablation behaviour of Al. The average ablation rate h as a function of fluence F for Ni ranges from 1 to 3.5 mu m/pulse for lambda = 266nm as well as for lambda =532nm. In contrast, the range of h for Al differs from 2 to 4 mu m/pulse for lambda = 532 nm and 4 to 8 mu m/pulse for lambda = 266 nm in the exact same fluence range on the exact same sample. (C) 2016 Elsevier B.V. All rights reserved.

Wear resistant coatings; Tungsten carbide; Elemental profiling; Laser induced breakdown spectroscopy; Energy dispersive X-ray spectroscopy; Laser cladded coating;TUNGSTEN CARBIDE; MICROSTRUCTURAL CHARACTERIZATION; COMPOSITE COATINGS; ABLATION; STEEL; LIBS; WEAR; EXCITATION; PLASMA; PULSES

Multilayer tungsten carbide wear resistant coatings were analyzed by laser induced breakdown spectroscopy (LIBS) and energy dispersive X-ray (EDX) spectroscopy. Coaxial laser cladding technique was utilized to produce tungsten carbide coating deposited on low alloy steel substrate with additional inconel 625 interlayer. EDX and LIBS techniques were used for elemental profiling of major components (Ni, W, C, Fe, etc.) in the coating. A good correlation between EDX and LIBS data was observed while LIBS provided additional information on light element distribution (carbon). A non-uniform distribution of tungsten carbide grains along coating depth was detected by both LIBS and EDX. In contrast, horizontal elemental profiling showed a uniform tungsten carbide particles distribution. Depth elemental profiling by layer by-layer LIBS analysis was demonstrated to be an effective method for studying tungsten carbide grains distribution in wear resistant coating without any sample preparation. (C) 2017 Published by Elsevier B.V.

LIBS quantitative analysis; reduction of matrix effect; internal standard calibration; normalization; correction of self-absorption;PART II; SAMPLES; PARAMETERS

A procedure for matrix effect reduction is proposed to enhance the precision of quantitative analysis of metal alloys using laser-induced breakdownspectroscopy (LIBS). This procedure is based on a number of successive steps in order to correct the signal fluctuations caused by plasma interaction and the matrix effect. The first step is the selection of optimum parameter settings of the detection system, such as laser power, delay time, and focal distance. The second step is the estimation of the absolute or relative values of impurities on the basis of the internal standard calibration. The third step is the analysis of the metal basis of the alloy used as an internal standard, which requires spectrum averaging, whole integral spectrum normalization, and self-absorption correction. Three sets of metal-based alloys (aluminum, steel, and copper) are used in this investigation as reference standards for calibration and validation. Successive improvements of the quality of calibration curves are observed during the proposed procedure.

Long pulse; dual-pulse laser-induced breakdown spectroscopy; DP-LIBS; enhancement; plasma temperature stabilization; underwater measurement;CO2-LASER PULSE; AMBIENT GAS; ABLATION; ENHANCEMENT; PRESSURES; FEASIBILITY; MAGNESIUM; DISCHARGE; SPECTRUM; LIQUIDS

Collinear long and short dual-pulse laser-induced breakdown spectroscopy (DP-LIBS) was employed to clarify the emission characteristics from laser-inducedplasma. The plasma was sustained and became stable by the long pulse-width laser with the pulse width of 60s under free running (FR) conditions as an external energy source. Comparing the measurement results of stainless steel in air using single-pulse LIBS (SP-LIBS) and DP-LIBS, the emission intensity was markedly enhanced using DP-LIBS. The temperature of plasma induced by DP-LIBS was maintained at a higher temperature under different gate delay time and short pulse-width laser power conditions compared with those measured using short SP-LIBS. Moreover, the variation rates of plasma temperatures measured using DP-LIBS were also lower. The superior detection ability was verified by the measurement of aluminum sample in water. The spectra were clearly detected using DP-LIBS, whereas it cannot be identified using SP-LIBS of short and long pulse widths. The effects of gate delay time and short pulse-width laser power were also discussed. These results demonstrate the feasibility and enhanced detection ability of the proposed collinear long and short DP-LIBS method.

INDUCED BREAKDOWN SPECTROSCOPY; LASER-INDUCED FLUORESCENCE; EXCITED ATOMIC FLUORESCENCE; ELEMENTAL ANALYSIS; ABLATION; LIBS; SPECTROMETRY; MECHANISM; METALS; WASTE

Coupling laser-induced fluorescence to laser ablation can reduce detection limits relative to LIBS. The wing of the broadband similar to 193.3 nm emission from unmodified argon fluoride lasers can excite arsenic fluorescence via its 193.76 nm ground state transition for a simple fluorescence scheme. We present argon fluoride-excited laser-ablation laser-excited atomic fluorescence (LA-LEAF) measurements in steel and copper under argon and helium atmospheres. Because the ArF laser saturates the absorption transition and the steel samples show substantial nonspecific iron fluorescence, it is necessary to optimize the laser energy in addition to interpulse delay. LODs are slightly lower under helium (1.0 ppm in steel, 0.15 ppm in copper). These detection limits represent a modest improvement over previous LODs with LIBS, but suggest potential for improvement with line narrowing of the ArF laser.

DUAL-PULSE LIBS; INDUCED PLASMA; ABLATION EFFICIENCY; SENSITIVE ANALYSIS; HELIUM PLASMA; FEMTOSECOND; ENHANCEMENT; NANOSECOND; MICROANALYSIS; DEUTERIUM

A time-resolved spectroscopic study is performed by using 125-500 micro-Joule (mu J) ps laser focused directly without the aid of microscope on a Cu plate sample in a variety of low-pressure ambient gases including air, helium and argon. It is shown that the ultrashort mu J laser-induced low-pressure plasma in Ar ambient gas exhibits the typical characteristics of shock wave plasma responsible for the thermal excitation and sharp emission of the analyte atoms. It is found that the highest signal to background (S/B) ratio of about 100 is achieved in 1.3 kPa argon ambient gas and detected with optical multichannel analyzer (OMA) gate delay of 1 ns and gate width of 50 mu s. The emission spectra obtained from pure Zn sample show the effective suppression of the ionic emission with ablation energy around and below 500 mu J. The experimental setup is successfully applied to Cr analysis with low detection limit in steel. In particular, its application to C analysis in steel is demonstrated to resolve the long standing problem of overlapping contributions from the neutral and ionic Fe emission. It is further found that an element of high excitation energy such as fluorine (F) can be clearly detected from a non metal teflon sample. Further, its application to alluminum sample containing various concentrations of Mg, Ca, Fe, and Si impurity elements clearly displays the existence of linear calibration lines promising for quantitative analyses in certain dynamical ranges. Finally, in view of the tiny crater sizes of less than 10 mu m diameter created by the very low ps laserenergy, this technique is promising for micrometer resolution mapping of elemental distribution on the sample surface and its depth profiling. (C) 2017 The Japan Society of Applied Physics

Laser-induced breakdown spectroscopy; Baseline correction; Asymmetric penalty; Convex optimization;PARTIAL LEAST-SQUARES; WAVELET-TRANSFORM; MODEL; LIBS; COAL

For laser-induced breakdown spectroscopy (LIBS) quantitative analysis technique, baseline correction is an essential part for the LIBS data preprocessing. As the widely existing cases, the phenomenon of baseline drift is generated by the fluctuation of laser energy, inhomogeneity of sample surfaces and the background noise, which has aroused the interest of many researchers. Most of the prevalent algorithms usually need to preset some key parameters, such as the suitable spline function and the fitting order, thus do not have adaptability. Based on the characteristics of LIBS, such as the sparsity of spectral peaks and the low-pass filtered feature of baseline, a novel baseline correction and spectral data denoising method is studied in this paper. The improved technology utilizes convex optimization scheme to form a non-parametric baseline correction model. Meanwhile, asymmetric punish function is conducted to enhance signal-noise ratio (SNR) of the LIBS signal and improve reconstruction precision. Furthermore, an efficient iterative algorithm is applied to the optimization process, so as to ensure the convergence of this algorithm. To validate the proposed method, the concentration analysis of Chromium (Cr),Manganese (Mn) and Nickel (Ni) contained in 23 certified high alloy steel samples is assessed by using quantitative models with Partial Least Squares (PLS) and Support Vector Machine (SVM). Because there is no prior knowledge of sample composition and mathematical hypothesis, compared with other methods, the method proposed in this paper has better accuracy in quantitative analysis, and fully reflects its adaptive ability. (C) 2017 Elsevier B.V. All rights reserved.

VACUUM-ULTRAVIOLET; INDUCED PLASMA; SPECTROMETRY; OPTIMIZATION; COAL; IMPROVEMENTS; ABSORPTION

Carbon is a key element for steel properties but (a) hard to be determined by laser-induced breakdown spectroscopy (LIBS). Utilizing the combination of carbon in analytes and nitrogen in ambient gas to generate carbon nitrogen (CN) radicals, LIBS assisted with laser-induced radical fluorescence (LIBS-LIRF) was proposed to resonantly excite radicals instead of atoms in plasmas. The CN radicals in the B-2 Sigma-A(2)II band were stimulated by a 421.60 nm laserwavelength and emitted 388.34 nm fluorescence. The results show that the spectral intensity of the CN radicals was enhanced by 2 orders of magnitude using LIBS-LIRF. Then carbon content in steels was accurately and sensitively determined without spectral interference. The limits of detection (LoDs) were 0.039 and 0.013 wt % in air and nitrogen gas, respectively. The limits of quantification (LoQs) were 0.130 and 0.043 wt % in air and nitrogen gas, respectively. This work demonstrated the feasibility of LIES to realize reliable carbon determination in steel industry.

INDUCED PLASMA SPECTROMETRY; IN-SITU ANALYSIS; HIGH-TEMPERATURE; ELEMENTAL ANALYSIS; GRADE TRANSITION; MOLECULAR BANDS; REAL-TIME; MOLD; LIBS; SAMPLES

Among the several controlling routines utilized in the steelmaking process, analytical operations during continuous casting are especially demanding due to the extreme environment of steel plants and the crude conditions of the steel surface at the exit of the casting system. This report presents how dual-pulse laser-induced breakdown spectroscopy (LIBS) can be used for the real-time monitoring of continuous casting sequences in a steel plant and the operations needed for detecting the separation between grades of close chemical compositions. Diverse dual-pulse laser conditions have been tested in order to improve the LIBS system performance. Apart from the scale layer formed by the oxidation of steel by the surrounding air, the presence of residues of mould powder on the steel surface tends to complicate the LIBS analysis as elements present in the powder such as manganese interfere with the steel components. LIBS data processing by discriminant function analysis has been demonstrated to be beneficial for the identification of steel transitions. Changes in steel composition as low as 0.20 percentage points Cr in a stainless steel sample containing above 17% of this element are detected by corresponding changes in Wilks' lambda values from 1.0 to 0.75 during the transition. Changes in the concentration of nickel are of minor relevance as its concentration on the steel surface at the time of continuous casting is depleted. For steel concentrations differing to a larger extent, differentiation of steel grades is straight, involving changes in Wilks' lambda values from 1 to below 0.1.

PRE-ABLATION SPARK; ORTHOGONAL BEAM GEOMETRY; INDUCED PLASMAS; CONFIGURATION; SPECTROMETRY; EMISSION; MATRICES; SINGLE; LIBS

Two Q-switched Nd: YAG lasers at 1064-nm wavelength have been employed to detect the trace elements in microalloy steel samples by single-pulse and reheating double-pulse laser-induced breakdown spectroscopy. It is found that the emission lines intensities of the trace elements were significantly enhanced by reheating double-pulse scheme. Furthermore, the extent of the enhancement of the line intensity was related to the excitation energy level of the emission line. Then, the emission enhancement was explained by the investigation of the spatial resolution of the plasma temperatures. The results have shown that the enhancement mechanism can be attributed to the greater and hotter plasma generated by the re-excitation of the reheating laser pulse in double-pulse scheme. Finally, calibration plots were constructed for Mn, Cr, and Cu using a set of certified microalloy steel samples. The detection limits of the trace elements were calculated for the reheating double-pulse scheme and compared to those of single-pulse scheme. It has been shown that the detection limits of the trace elements were improved by a factor of 1.81-3.46 when the reheating double-pulse scheme was used.

Laser-induced breakdown spectroscopy; Stress corrosion cracking; Chlorine; Alkali elements;ATMOSPHERE

Chlorine can play an important role in the process of stress corrosion cracking of dry cask storage canisters for used nuclear fuel, which are frequently located in marine environments. It is of significant interest to determine the surface concentration of chlorine on the stainless steel canister surface, but measurements are often limited by difficult access and challenging conditions, such as high temperature and high radiation fields. Laser-induced breakdown spectroscopy(LIBS) could enable chlorine concentration measurements while meeting the other constraints of this application, but suffers from high excitation energy of chlorine and the interference of the atomic emission lines of iron, thus limiting the sensitivity of detection, especially when LIBS has to be delivered over an optical fiber. We demonstrate that chlorine surface concentrations in the range of 0.5-100 mg/m(2) can be inferred by the detection and quantification of sodium contained in chlorine salts if the speciation and neutralization of salts are not of major concern, whereas minor components of sea salt such as magnesium and potassium are less attractive as surrogates for chlorine due to the lower sensitivity of LIBS for their detection and quantification. The limit of detection, measurement accuracy, and other features and limitations of this surrogate measurement approach are discussed. (C) 2017 Elsevier B.V. All rights reserved.

QUANTITATIVE-ANALYSIS; INSTRUMENT; ABSORPTION; PLASMA; COBALT; LEAD; SOIL; AIR

Spatially selective excitation was proposed to improve excitation efficiency in laser-induced breakdown spectroscopy combined with laser-inducedfluorescence (LIBS-LIF). Taking chromium (Cr) and nickel (Ni) elements in steels as examples, it was discovered that the optimal excitation locations were the center of the plasmas for the matrix of the iron (Fe) element but the periphery for Cr and Ni elements. By focusing an excitation laser at the optimal locations, not only excitation efficiency but also the analytical accuracy and sensitivity of quantitative LIBS-LIF were better than those with excitation at the plasma center in conventional LIBS-LIF. This study provides an effective way to improve LIBS-LIF analytical performance. (C) 2017 Optical Society of America

IMPROVEMENT; CHEMOMETRICS; SPECTROMETRY; CONFINEMENT; CALIBRATION; SELECTION; PLASMA; LIBS; SOIL

In this work, a genetic algorithm (GA) was employed to select the intensity ratios of the spectral lines belonging to the target and domain matrix elements, then these selected line-intensity ratios were taken as inputs to construct an analysis model based on an artificial neural network (ANN) to analyze the elements copper (Cu) and vanadium (V) in steel samples. The results revealed that the root mean square errors of prediction (RMSEPs) for the elements Cu and V can reach 0.0040 wt. % and 0.0039 wt. %, respectively. Compared to 0.0190 wt. % and 0.0201 wt. % of the conventional internal calibration approach, the reduction rates of the RMSEP values reached 78.9% and 80.6%, respectively. These results indicate that the GA combining ANN can excellently execute the quantitative analysis in laser-induced breakdown spectroscopy for steel samples and further improve analytical accuracy. (C) 2017 Optical Society of America

Nd:YAG laser; DPSS laser; LIBS; steel analysis;INDUCED BREAKDOWN SPECTROMETRY; VACUUM-ULTRAVIOLET; CARBON DETECTION; IRON-ORE; SPECTROSCOPY; INDUSTRY

LIBS-technology holds the potential for on-site real-time measurements of steel products. However for a mobile and robust LIBS measurement system, an adequate small and ruggedized laser source is a key-requirement. In this contribution, we present tests with our novel compact high power laser source, which, initially, was developed for ignition applications. The CTR HiPoLas (R) laser is a robust diode pumped solid state laser with a passive Q-switch with dimensions of less than 10 cm(3). The laser generates 2.5 ns-pulses with 30 mJ at a maximum continuous repetition rate of about 30 Hz. Feasibility of LIBS experiments with the laser source was experimentally verified with steel samples. The results show that the laser with its current optical output parameters is very well suited for LIBS measurements. We believe that the miniaturized laser presented here will enable very compact and robust portable high-performance LIBS systems.

Laser-Induced Breakdown Spectroscopy, LIBS; Outlier filtering; Principal Component Analysis, PCA; Linear correlation; Total spectral intensity; Soft Independent Modelling of Class Analogies, SIMCA;

In this manuscript we highlight the necessity of outlier filtering prior the multivariate classification in Laser-Induced Breakdown Spectroscopy (LIBS) analyses. For the purpose of classification we chose to analyse BAM steel standards that possess similar composition of major and trace elements. To assess the improvement in figures of merit we compared the performance of three outlier filtering approaches (based on Principal Component Analysis, linear correlation and total spectral intensity) already separately discussed in the LIBS literature. The truncated data set was classified using Soft Independent Modelling of Class Analogies (SIMCA). Yielded results showed significant improvement in the performance of multivariate classification coupled to filtered data. The best performance was observed for the total spectral intensity filtering approach gaining the analytical figures of merit (overall accuracy, sensitivity, and specificity) over 98%. It is noteworthy that the results showed relatively low sensitivity and high specificity of the SIMCA algorithm regardless of the presence of outliers in the data sets. Moreover, it was shown that the variance in the data topology of training and testing data sets has a great impact on the consequent data classification.