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A new portable miniaturized atmospheric microplasma discharge (μAPD) system coupled with the optical emission spectrometry (OES) detection for the determination of Hg in water samples was developed. The device was built from cheap, easily replaceable, and commercially available parts and was able to work with the photo-induced chemical vapor generation (PCVG). To optimize the photochemical volatile Hg generation process, a wide range of low molecular weight organic compounds (LMWOCs), namely formic, oxalic, acetic, propionic, and malonic acids, in addition to methanol, ethanol, glycerin, ethylene glycol, formaldehyde, and acetaldehyde, were tested to establish their influence on the signal of Hg. To assess the excitation and atomization potential of the newly developed μAPD system and its impact on the analytical performance of this microplasma excitation source, the plasma temperatures and the electron number density were evaluated. The analytical figures of merit were determined for the coupled PCVG-μAPD system. Additionally, the usability of the method was tested in reference to the analysis of selected environmental samples, i.e., tap, well, and river water spiked with Hg. A recovery test was also performed to evaluate the accuracy of the method. The examined analytical system allowed to detect Hg in water at a level lower than 0.33 μg L−1 when operating it at relatively low sample flow rates (2 mL min−1) and Ar supporting and plasma forming gas rates (20 mL min−1). The precision of measurements was better than 5% for formic acid. We believe that the presented system might be an attractive, cheaper alternative to commercial, highly expensive systems, e.g. based on inductively coupled plasma optical emission spectrometry (ICP OES). [ABSTRACT FROM AUTHOR]

The mechanism of double-pulse laser irradiation under spatial confinement remains unclear due to complex plasma plume dynamics and multiple shock wave interactions. In this study, coupling of spatial confinement and double-pulse irradiation was investigated using fast photography, laser shadowgraphy, and spectroscopy. The experimental results demonstrated unique dynamic processes of plasma plume and shock waves, confirming that the plasma plume was eventually reshaped into a jet-like structure, and the combined enhancement effect can be regulated through different parameters, including inter-pulse delay and plate spacing. The inter-pulse delay dictates the primary mechanism of the secondary pulse's interaction with the initial plasma and the target surface; as it increases, plasma front absorption decreases while target surface ablation intensifies. Plate spacing determines the delay from laser incidence to plasma plume compression; along with the inter-pulse delay, it influences whether the secondary pulse generates a second-generation shock wave that merges with the initial shock wave for compression or performs a secondary compression after the first. Compared to double-pulse irradiation alone, combined enhancement increased emission intensity of Fe, Ni, and C spectra by up to 4.1 times accompanied by the increase in plasma temperature. The R2 of calibration curves was increased, and the sensitivity for trace components Cr and C was improved with limits of detection reaching 255 and 659 ppm. [ABSTRACT FROM AUTHOR]

The poor spectral stability of laser-induced breakdown spectroscopy (LIBS) seriously affects its analytical performance, which is a key obstacle to its further development. To overcome this challenge, an improved spectral standardization method based on plasma image-spectrum fusion (ISS-PISF) was proposed in this study. This method, for the first time, considers and quantifies the influence of plasma morphology on spectral intensity based on the line-integrated intensity formula of LIBS spectra. It recognizes that the spectral fluctuations mainly stem from variations in total number density, plasma temperature, electron number density, and plasma morphology. Therefore, ISS-PISF innovatively utilizes easily accessible features from plasma images and spectra to eliminate the influence of these four plasma parameters, thereby improving the spectral stability and analytical performance of LIBS. To validate the effectiveness of this method, the spectra of aluminum alloy samples obtained under complex detection conditions simulated by varying laser energy and defocusing amount were analyzed. After correction by ISS-PISF, the R2 for Mg I 516.73 nm, Mn II 294.92 nm, and Si I 288.16 nm improved to 0.990, 0.976, and 0.961, and the average RMSE of the validation set decreased by 46.154%, while the average STD of the validation set decreased by 37.405%. These experimental results indicate that this study provides a simple, effective, and physically supported spectral standardization method, which contributes to the further promotion and application of LIBS. [ABSTRACT FROM AUTHOR]

We explore the application of artificial neural networks (ANNs) for predicting plasma temperatures in Laser-Induced Breakdown Spectroscopy (LIBS) analysis. Estimating plasma temperature from emission spectra is often challenging due to spectral interference and matrix effects. Traditional methods like the Boltzmann plot technique have limitations, both in applicability due to various matrix effects and in accuracy owing to the uncertainty of the underlying spectroscopic constants. Consequently, ANNs have already been successfully demonstrated as a viable alternative for plasma temperature prediction. We leverage synthetic data to isolate temperature effects from other factors and study the relationship between the LIBS spectra and temperature learnt by the ANN. We employ various post-hoc model interpretation techniques, including gradient-based methods, to verify that ANNs learn meaningful spectroscopic features for temperature prediction. Our findings demonstrate the potential of ANNs to learn complex relationships in LIBS spectra, offering a promising avenue for improved plasma temperature estimation and enhancing the overall accuracy of LIBS analysis. [ABSTRACT FROM AUTHOR]

Laser-induced breakdown spectroscopy (LIBS) faces a notable obstacle in the presence of substantial spectral fluctuations, hindering its progress and prompting researchers to prioritize resolving this complex problem. Considering the circumstances above, a novel methodology referred to as spectral standardization based on plasma image-spectrum fusion (SS-PISF) was introduced. The approach utilizes the valuable information in plasma images and spectra to correct variations in total number density, plasma temperature, and electron number density, resulting in improved spectral stability. To ascertain the efficacy of the SS-PISF method, comprehensive experimental validation is conducted, comparing its performance against the full spectrum normalization method and the simplified spectral standardization method. Experimental tests on aluminum alloy samples demonstrate a remarkable improvement, with the determination coefficient (R2) value of calibration curves increasing by 25.307% after SS-PISF correction. Additionally, the root mean square error of validation (RMSEV) and standard deviation (STDV) experience a notable reduction by 28.374% and 2.323%, respectively. For alloy steel samples, the SS-PISF corrected calibration curves exhibit a 14.630% increase in R2 and a 17.303% decrease in STDV. Similarly, for ore pressed samples, the SS-PISF corrected calibration curves witness a 7.031% enhancement in R2, alongside a decrease in RMSEV and STDV by 21.939% and 4.726%, respectively. These empirical results substantiate the efficacy of the SS-PISF method in significantly improving the spectral stability of LIBS. As a result, SS-PISF holds substantial promise for widespread application in laser-induced breakdown spectroscopy. [ABSTRACT FROM AUTHOR]

Collinear double-pulse laser-induced breakdown spectroscopy has been developed to enhance the emission signal of coal plasma. The influence of the energy ratio and the inter-pulse delay time on the intensity enhancement factors of the emission lines of representative elements in coal (i.e. carbon, hydrogen, oxygen, together with some metal elements such as iron, calcium, sodium and potassium) was investigated. The results showed that the collinear double-pulse configuration could sufficiently enhance the emission signals with an optimized inter-pulse delay time and energy ratio, and significant intensity enhancement factors were achieved for most of the selected lines with an energy ratio of 20 : 100. Meanwhile, the correlation between the signal enhancement and the upper energy level was investigated using neutral and ionic calcium lines. Finally, the plasma temperature, lifetime and morphology were calculated and observed to better explain the enhancement mechanism with different energy ratios and inter-pulse delay times. [ABSTRACT FROM AUTHOR]

Laser-induced breakdown spectroscopy (LIBS) has the disadvantages of weak signal, unreliability, and low sensitivity. Spatial confinement can enhance the spectra to overcome these shortcomings. The current related research is based on the observation that shock wave confines the plasma. Considering that the plasma is a light source and most of its emitted light is hindered by a cavity, in this work we designed an open smooth triangular cavity to enhance the LIBS spectra via plasma confinement and light collection. The spatial and temporal evolution of the plasma and optical traces in the cavity were simulated respectively. We researched the optimal parameters of the designed cavity and its influence on LIBS detection and then compared its enhancement effects with that of an open rough triangular cavity and a smooth parallel plate. The results indicate that the optimal angle of the cavity is 40° and the optimal diffusion distance of the shock wave is 2 mm. The plasma is confined at about 2.2 μs. The spectra confined by the designed cavity have the best enhancement factor, spectral stability, and sensitivity compared with the other two cavities. The enhancement factors of Fe I 500.5703 nm and Cr I 513.8852 nm with the designed cavity are 2.35 and 2.08, respectively. The contributions of improving light collection efficiency and plasma confinement effect to the enhancement factors are 31.2% and 68.8%, respectively. The plasma temperature shows that the plasma confinement effects of the three cavities are close. The designed cavity can improve the quantitative detection accuracy of Fe and Cr in stainless steel and reduce the limit of detection. This study provides theoretical and data support for the development of spatial confinement technology. [ABSTRACT FROM AUTHOR]

Accurate temperature measurement of the gas flow field is of great significance in theoretical research and engineering applications. Here, we found that when the laser-induced breakdown spectroscopy (LIBS) technique is performed in gas, there is a monotonic correlation between the line broadening of the atomic spectrum in the plasma and the initial gas temperature. Based on this monotonic correlation, we propose a method for gas temperature measurements under constant pressure. First, a series of experimental parameters that can sharply capture the linewidth variation were found through preliminary experiments, including the appropriate gate width, ICCD camera delay, and laser pulse energy. We found that the full width at half maximum (FWHM) of the H Balmer α line varies significantly with the increase of the flow field temperature, and the two show a power function dependence. The effect of the initial gas temperature on the plasma parameters and how this effect is passed on to the FWHM of the spectral lines were discussed from the perspective of electron density, which well explains the calibration curve obtained experimentally. The FWHM of the H Balmer α line at 656.3 nm, serving as an indicator, exhibits a decrease of about 30% in the temperature range of 300–1100 K, while the FWHM change tends to flatten out in the combustion field with higher temperatures. In exploring the effect of matrix effects (gas component changes) on this thermometry technique, we did not observe this nuisance, which is usually prevalent in solid LIBS, demonstrating the potential of this technique for wide applications. For flow fields without hydrogen atoms, we propose to deal by injecting the inert gas Kr. We found that the FWHM of the Kr I 810 nm spectral line follows the same trend with temperature as that of the H Balmer α line and also shows good applicability independent of the components. The results provide an experimental basis for developing LIBS-based gas temperature measurement techniques. They may provide support in potential application situations such as flow field organization and thermal system design. [ABSTRACT FROM AUTHOR]

The electron density and temperature of a laser-induced plasma can be determined from the width and intensity of the spectral lines, provided that the corresponding optical transitions are optically thin. However, the lines in laser induced plasma are often self-absorbed. One of the methods of correction of this effect is based on the use of the Planck function and an iterative numerical calculation of the plasma temperature. In this study, the method is further explored and its inherent errors and limitations are evaluated. For this, synthetic spectra are used that fully correspond to the assumed conditions of a homogeneous isothermal plasma at local thermodynamic equilibrium. Based on the error analysis, the advantages and disadvantages of the method are discussed in comparison with other methods of self-absorption correction. [ABSTRACT FROM AUTHOR]

Laser-induced Breakdown Spectroscopy (LIBS) is widely applied to the quantitative measurement of gas composition concentrations. However, studies on the effect of gas temperature on LIBS are still lacking. Here, we investigated the effect of gas temperature on LIBS in terms of composition measurements in an air flow field. The air flow field was heated using a resistance wire to different gas temperatures ranging from 300–930 K in a heating tube. We evaluated the effect of gas temperature on the ratio of spectral line pairs, which is typically used for the calibrations of LIBS measurements. The variations in gas temperature change the ratio of spectral line pairs, which ultimately affects the accuracy of LIBS measurements. Further, the effect of gas temperature on the accuracy of LIBS measurements with different acquisition strategies was compared. The effects of gate width and delay time were investigated. An optimized acquisition strategy was proposed to reduce the effect of gas temperature on LIBS measurements. For LIBS measurements in gas flow fields, the effect of gas temperature on LIBS measurements can be reduced by using a large gate width and a suitable long delay time. The optimized acquisition strategy uses long-time averaging after an appropriate delay time to reduce the effect of gas temperature on plasma parameters. Finally, higher laser energy also helps to reduce the effect of gas temperature on LIBS measurements. In this paper, the LIBS measurement error caused by increasing the gas temperature from 300 K to 930 K is about 5%, roughly 0.8% per 100 K, with the optimized acquisition strategy. This paper can provide some help for LIBS measurements in gas samples with temperature variations. [ABSTRACT FROM AUTHOR]

Chlorinated volatile organic compounds (Cl-VOCs) have severe toxicity and low biodegradability, and are listed as priority pollutants in most countries. However, air pollution occurs intermittently, which is difficult to monitor by traditional methods with low temporal resolutions (1–24 h). With the specific advantages of fast and in situ detection, laser-induced breakdown spectroscopy (LIBS) has been regarded as a viable technology for Cl-VOCs analysis. However, strong atomic lines of Cl are easily absorbed by oxygen in air. To solve this problem, some researchers set the whole or part LIBS instrument in a vacuum or inert environment, and other researchers focus on increasing plasma temperature and electron number density. These methods can achieve satisfactory results for Cl detection, but they present the problems of the complex device, harsh detection conditions, and high cost, which weaken the simplicity and fast detection ability of LIBS technology. Fortunately, the molecular spectra can be detected in air, but the intrinsic molecules in Cl-VOCs are weak. In this regard, a novel approach is proposed for realizing the controllable formation of high-intensity CaCl molecules, in which calcite is selected as the substrate to supply sufficient Ca. The results show that Cl can be sensitively detected using LIBS assisted with molecular spectra, and the limit of detection was 12.74 ppm, which meets the occupational exposure limits recommended by the American Conference of Governmental Industrial Hygienists (ACGIH). What's more, the prediction performance, generalization ability, and analytical efficiency (below 5 s) of the established calibration model were evaluated. It can be confirmed that the precise formation of LIBS molecular spectra shows great potential for the real-time and in situ analysis of Cl-VOCs. [ABSTRACT FROM AUTHOR]

The double pulse technology increases the energy transmission between the plasma plume and the target by coupling the laser beam, which greatly enhances the signal, reduces the detection limit of laser-induced breakdown spectroscopy (LIBS) and improves the ability of trace elemental analysis. In this paper, the emission characteristics of plasma in orthogonal double-pulse LIBS (DP-LIBS) are studied theoretically by using the hydrodynamics model, including the effects of pulse interval and spot position of the second laser pulse on the emission intensity of various species in the reheating mode. The results show that in the reheating mode, the pulse interval corresponding to the maximum intensity ratio of double pulse to single pulse occurs at 0.2–0.5 μs, while in the pre-ablation mode, it increases with the increase of pulse interval. According to the decrease of the number density of the background gas above the sample before the ablation pulse in the pre-ablation mode, the enhancement mechanism of spectral line intensity is explained from two aspects: plasma–plasma coupling effect and pressure effect. In addition, the spatial distribution and raising mechanism of plasma temperature in these modes are also explored. It shows that in the reheating mode, the plasma temperature is increased by directly absorbing laser energy, while in the pre-ablation mode, it is increased by reducing the energy loss between vapor plasma and gas plasma and weakening the shielding effect. The theoretical analysis of double pulse plasma provides a theoretical basis for the experimental research and application of DP-LIBS. [ABSTRACT FROM AUTHOR]

We studied the effect of O2 content in the range of 0.1–1.2% in plasma gas on the plasma characteristics, the analytical signal and the intensity of the molecular species in nitrogen MIP. The plasma temperature decreases from 4.50 × 103 to 4.39 × 103 K with increasing O2 content. The Mg(II)/Mg(I) intensity ratio decreases from 1.14 to 0.90, and the electron density decreases from 1.16 × 1014 to 0.85 × 1014. The intensities of N2, N2+ and NH decrease, and the NO and OH intensities increase when O2 is added. The influence of O2 content on the intensity of several atomic and ionic emission lines (covering Esum values from 2.1 to 15.4 eV) of 12 elements has been studied. The intensity of atomic lines with Esum values lower than 6 eV was enhanced in the presence of O2 but it was suppressed for the ionic lines tested. It was shown that the O2 addition leads to a decrease in the LOD calculated from atomic lines and to an increase in the LOD calculated from ionic lines. [ABSTRACT FROM AUTHOR]

The analytical accuracy is often seriously affected by the self-absorption effect in laser-induced breakdown spectroscopy (LIBS). To investigate the self-absorption temporal evolution, time-resolved LIBS was adopted to analyze K, Ca, Na, and Mg element lines from the soil. The self-absorption coefficients of analyzed element lines in LIBS were calculated and investigated. To physically understand the mechanism of self-absorption, the evolution of the plasma image after Abel inversion, plasma temperature, and electron number density in time-resolved plasma were studied. The results show that the self-absorption effect was weaker at the early stage of the plasma because the emission intensity of plasma from the inner layer to the outer layer is high, and the plasma temperature is high with fewer low-energy particles. And less energy loss is caused by inelastic collision with air particles. The consequences of this work provide a convenient approach for reducing the self-absorption effect in LIBS and a deeper understanding of the mechanism of self-absorption evolution. [ABSTRACT FROM AUTHOR]

Heat-resistant steel is widely used in various types of industrial pressure-bearing equipment, and the changes in the metallographic structure and properties of the steel are of great importance for the function and safety of this equipment. In this work, laser-induced breakdown spectroscopy (LIBS) was applied to estimate the aging grade of industrial heat-resistant steel. First, representative spectra of the metal matrix of an industrial pipe were obtained via depth profile analysis, and the effects of surface oxides on the matrix plasma parameters were evaluated and compared. The results indicated that correlation analysis of the emission intensities along the radial direction can accurately identify the boundary between the surface oxide and the matrix. The presence of surface oxides would decrease the plasma temperature and increase the electron density. Secondly, multiplicative scattering correction (MSC) was applied to correct for the interference of surface oxides, and K-fold-support vector machine-recursive feature elimination (K-SVM-RFE) was exploited to select the optimal spectral feature subset. Finally, estimation of the aging grade model was established based on the support vector machine (SVM) and the optimal feature subsets. The estimation accuracy of the validation set after spectral correction was improved from 80.56% to 84.72%, and the model exhibited similar capability for the industrial pipe and the corresponding samples with mechanical polishing to eliminate surface oxides. The work demonstrates that LIBS is suitable for the in situ estimation of steel aging grade for industrial pipe. [ABSTRACT FROM AUTHOR]

The traditional large-dosage and dangerous methods for the determination of the sensitivities of energetic materials (EMs) have always led to low-accuracy diagnoses with poor repeatability, since they are affected by crystalline quality, experimental conditions, etc. Herein, a simple method is developed to determine various sensitivities, such as impact sensitivity, friction sensitivity, electrostatic sensitivity, and laser sensitivity, via laser spark spectrometry (LSS), with the consumption of only several milligrams of EM, rather than macro-detonation testing. Based on suitable correlated prediction models using the entire LSS spectrum and physical-parameter-corrected statistical regression, the friction sensitivity, electrostatic sensitivity, and laser sensitivity can be well predicted, evaluating the impact of various factors on sensitivity. The correlations between plasma temperature and impact sensitivity, electron density and friction sensitivity, and oxygen balance and electrostatic sensitivity are also clarified. This can facilitate sensitivity predictions with high precision. This method provides a safe, low-dosage, high-precision, and low-cost approach for sensitivity estimations of EMs. [ABSTRACT FROM AUTHOR]

An analytical method to validate local thermodynamic equilibrium (LTE) in laser-induced plasmas is reported in this article. A more universal and general than Maxwellian electron energy distribution function (EEDF) is used to describe the emission intensity as a function of plasma temperature and transition levels. Spatially and temporally resolved spectra recorded in laser ablation experiments at a pressure of 10−5 mbar provide access to the insight into the actual EEDF of electrons at individual positions in the local plasma plume, and the evolution of the thermodynamic state in plasma is therefore estimated by using the EEDF departure from the Maxwellian distribution. The consistency of similar EEDFs derived from emission lines associated with differently charged ions at the same position and time delay justifies the method as a reasonable LTE criterion. [ABSTRACT FROM AUTHOR]

Laser-induced breakdown spectroscopy (LIBS) has been successfully applied for in situ detection in the sea, and the water pressure is found to be the main influence on the LIBS signal compared to temperature or salinity. In this study, we explored self-absorption to evaluate the pressure effects on LIBS detection. By using fast imaging and spectroscopic technique, it is proved that self-absorption (SA) was significantly enhanced with increased pressure, and the severe inhomogeneity of plasma distribution might be the reason. With this SA model, the LIBS intensity could be well-estimated according to the simulation results. Moreover, the self-absorption of LIBS underwater was more likely determined by the plasma temperature when the detection was carried out in a low-pressure regime. The obtained results would be helpful for the signal correction of LIBS in the deep sea. [ABSTRACT FROM AUTHOR]

We report results and analysis from a series of laser ablation experiments conducted to study high-temperature plutonium (Pu) spectroscopy and gas-phase oxidation. Time-resolved emission spectra were compared to a Pu I spectral model to infer plasma temperature. At later times in the laser-produced plasma evolution, temperatures are lower, and resonant emission bands indicative of molecular species are observed. We tentatively assign these bands to plutonium oxides (PuxOy). [ABSTRACT FROM AUTHOR]

The effect of the shape of the nanoparticles on the nanoparticle-enhanced LIBS (NELIBS) signal should be clarified. The present study reports on the effect of the silver (silver chloride) nanoparticle shape (nanospheres, nanocubes, and nanowires) on the LIBS signal for different target materials; two metals (aluminum and zinc) and one semiconductor (silicon). The shape enhancement factor and the plasma parameters, namely plasma temperature and electron density, have also been evaluated. Silver nanoparticles have been characterized using different techniques, including SEM, UV-vis, and XRD. The results showed that the clusters formed in the silver nanowires and nanocubes play an essential role in the laser pulse's absorption mechanism and, consequently, enhance the LIBS signal. Nanowires followed by nanocubes showed better enhancement than nanospheres, confirmed by the shape-dependent enhancement factor. However, the laser-induced plasma parameters (plasma temperature and electron density) have not been affected much by the nano-shape change. [ABSTRACT FROM AUTHOR]

The fluorine and bromine limits of detection (LoDs), based on emission from CaF and CaBr, using Microwave-assisted Laser Induced Breakdown Spectroscopy (MW-LIBS) have been determined. The molecular emission bands of CaF and CaBr in the spectral range of 605 nm and 627.1 nm are utilised for quantitative fluorine and bromine detection. The optimum gating has been established for CaF, at 603.3 nm and 605 nm, following 1.5 ms long microwave pulses. The MW-LIBS plasma temperature and electron density against laser energy have been demonstrated at constant microwave power coupling to optimise laser energy using Ca I lines. A linear relationship between the CaF signal strength and fluorine concentration, and CaBr signal strength and bromine in cement has been validated. The recorded limits of fluorine and bromine detection were 106 ± 6 μg g−1 and 0.2 ± 0.04%, respectively. The results represent an improved detection limit at low laser energy and 4-fold improved detection limit for bromine. [ABSTRACT FROM AUTHOR]

The goal of this work is to examine the effect of a third additional laser pulse on orthogonal double-pulse laser-induced breakdown spectroscopy (DP LIBS). Namely, a pre-ablation laser pulse and re-heating laser pulse were combined into triple-pulse LIBS (3P LIBS) to achieve plasma emission enhancement. The experiment was designed with emphasis on causing minimal sample damage by utilizing nanosecond laser pulses. It means that the energy of ablation laser pulses was set to the minimal value for which the intensities of selected spectral lines were above the limits of detection. This energy as well as the energies of the pre-ablation and the re-heating laser pulses were kept constant for all experimental arrangements. The interpulse delays for both DP LIBS and for 3P LIBS configurations were optimized for signal enhancements. The 3P LIBS results showed up to 5-fold improvement of the signal to background ratio compared with both DP LIBS arrangements and up to 228-fold improvement in comparison to conventional SP LIBS. In addition, it has been shown that the spectral lines with a higher value of excitation energy prove higher enhancement in both DP LIBS and 3P LIBS configurations. To explain this effect, the dimensions of ablation craters were measured for each configuration using a 3D optical microscope and the temperature was determined from the slope of the Boltzmann plot. It was shown that the pre-ablation causes an increase of ablation crater dimensions and the re-heating increases the plasma temperature. [ABSTRACT FROM AUTHOR]

The analytical capabilities of laser-induced breakdown spectroscopy (LIBS) for in situ elemental analysis of nuclear materials at elevated temperatures were estimated. A certified molybdenum–tungsten alloy (Mo 70 wt% and W 30 wt%) was chosen as a replacement for the high Z impurities deposited on plasma facing components (PFCs) in tokamak. The influence of sample temperature (Ts) on the optical emission of the laser-induced molybdenum–tungsten plasma was investigated with a nanosecond infrared (1064 nm) laser pulse. LIBS experiments were carried out in a wide temperature range from 20 to 410 °C. Surface morphology and depth profiling measurements of the ablated crater for the different temperature conditions were performed. A noticeable dependence of signal emission intensity on Ts has been found. An increase in Ts leads to an increase in the spectral line emissions. In the laser ablation process, the ablation rate, plasma temperature and electron density increase significantly with Ts. In addition, the reflectivity of the alloy surface drops dramatically once oxidation occurs. The decrease of surface reflectivity leads to a greater laser energy coupled to the target and a higher LIBS signal. These results will help improve the LIBS quantitative analysis of high Z impurities in the tokamak device. [ABSTRACT FROM AUTHOR]

The Microwave Plasma Torch (MPT) is an excellent excitation source for on-line monitoring of environmental samples. However, the feasibility of particle detection and plasma diagnosis through particle introduction has not been reported yet. In this paper, Eu2O3/Ag and SiO2 suspensions were prepared, characterized and then introduced sequentially into the laboratory-made oxygen shielding argon flow MPT (OS-Ar-MPT) plasma for OES measurements with a time resolution of 6 ms. Signal spikes of Eu, Ag and Si lines from individual particles were observed, respectively, which demonstrates the feasibility of MPT-OES for particle detection. By using the line intensities from signal spikes and the measured sizes, the detection limits of the current instrument for Si, Ag and Eu in individual particles are estimated to be 1.8, 0.15 and 0.19 pg, respectively. The Eu(i) and Eu(ii) line intensities extracted from the signal spikes were used to calculate the excitation temperature (Texc) of the OS-Ar-MPT plasma through the Boltzmann slope method. As a comparison study, the Texc was also calculated by using the traditional Fe(i) line Boltzmann slope method through solution introduction. The results show that Texc,Eu-I = 3293 K, Texc,Eu-II = 3414 K, and Texc,Fe-I = 4883 K. Meanwhile, the OH (0,0) band spectrum was simulated by varying the rotational temperature (Trot) by LIFBASE, and then compared with the measured spectrum when the Fe solution was nebulized. The best value of Trot lies between 3100 and 3400 K. Through this work, the capability of Ar-MPT-OES for particle detection is confirmed. Besides, the range of elements suitable for plasma diagnosis is widened and more diagnostic data of MPT plasma temperature are obtained. [ABSTRACT FROM AUTHOR]

The temporal evolution of doublet lines intensity ratio, plasma temperature (T) and electron density (Ne) of different radial parts of aluminum plasma as well as the relationship between optically thin condition and plasma characteristics are investigated. With respect to doublet lines intensity ratio, the optimal delay time (tot) when the plasma is optically thin is determined by comparing the experimental intensity ratio of doublet Al(i) lines with the theoretical value. The optimal integration time, fiber collection angle, and delay time corresponding to the optically thin condition are 400 ns, 45°, and 500 ns, respectively, in which case the linearity of the calibration curve reaches 0.98, enabling more accurate composition measurements. The maximum temperature values are reached within 300 ns at 10°, 30°, 45°, and 80°, but after 900 ns at 55°, 60°, and 70°. Combined with the morphologic image of the plasma, we infer that the time at which a radial part of plasma reaches the highest temperature is related to the extent of its expansion. It is generally understood that the faster the radial part of plasma expands, the sooner the temperature reaches its maximum. The radial part of plasma may not be optically thin when the corresponding temperature reaches its maximum. If the highest temperature is obtained earlier, the optically thin condition is likely to appear in the descending stage of the temporal evolution curve of temperature. Otherwise, it may appear in the ascending stage. There seems to be no simple positive correlation between electron density and optically thin condition. [ABSTRACT FROM AUTHOR]

In this work, we use the Boltzmann plot, Saha's equation and the Mg II/Mg I signal ratio to determine temperature (T), electron number density (ne) and robustness of different regions of a microwave-induced nitrogen plasma. A 2-D profile based on plasma observation position and nebulization flow rate is generated for each of these properties and their effects on sensitivity, accuracy and matrix-related interferences in microwave-induced plasma optical emission spectrometry (MIP OES) are evaluated. Plasma temperatures vary between 4220 and 5360 K by changing nebulization flow rate and plasma observation position. These same instrumental parameters are varied to produce ne values in the 0.47–3.72 × 1013 cm−3 range, and Mg II/Mg I ratios between 0.26 and 2.01. Limits of detection (LODs) were calculated for different T and ne conditions, and for analytes with a wide range of Esum values (Esum = ionization energy + excitation energy). The best LODs were calculated for determinations at high ne plasma regions. More robust plasma conditions allowed for more accurate results when determining analytes with Esum ＞ 9 eV or ＜ 3 eV. For intermediate Esum elements, the best recoveries in complex sample analyses were obtained at high ne conditions. Although the microwave applied power is fixed at 1000 W for the commercial MIP OES evaluated, one can still control plasma conditions by varying other operating parameters, which may contribute to fewer matrix effects, better accuracies and lower LODs. [ABSTRACT FROM AUTHOR]

Accuracy is still a challenge for classical calibration-free laser-induced breakdown spectroscopic (CF-LIBS) quantitative analysis since absolute theoretical calculation and mathematical models cannot compensate for the self-absorption effect and plasma temperature variability. The aim of this research is to obtain a more accurate plasma temperature which contributes to the precise determination of the elemental composition of unknown samples for CF-LIBS. Herein, an internal reference-external standard with iteration correction (IRESIC) method is proposed to correct for the self-absorption effect and plasma temperature in CF-LIBS based on an internal reference line and one standard sample. The spectral intensities of each species are corrected by an internal reference line via the iteration procedure, and the internal reference line suffers from a negligible self-absorption effect for self-absorption correction. Furthermore, one standard sample matrix-matched with the unknown samples along with the genetic algorithm (GA) is utilized to simulate the accurate plasma temperature of the unknown samples. It is worth mentioning that the GA is used for plasma temperature correction through iteration correction for the first time in CF-LIBS. The proposed method demonstrates a significant improvement in accuracy compared with the classical CF-LIBS in the quantitative analysis of aluminum-bronze alloy samples due to the integrated merits of internal reference line usage and accurate plasma temperature evaluation. [ABSTRACT FROM AUTHOR]

The selection of analytical lines to determine Pb, Cr, Cd, Hg, and Ni in gallstones in the recently published paper with the above title is criticized. Also, the unreliable calibration of their spectrometer is demonstrated as a reason for incorrect assignment of spectral lines. [ABSTRACT FROM AUTHOR]

Collinear dual pulse laser-induced breakdown spectroscopy with and without cavity confinement were carried out on a Si crystal sample by using two Nd : YAG laser sources emitting at 1064 nm and a 1 mm-height and 3 mm diameter aluminum cylindrical cavity. Nearly 2-3 times enhanced optical emission intensity with a higher signal-to-noise ratio was observed when an additional cylindrical cavity was used to confine the laser plasma. The inter-pulse delay time to achieve the maximum atomic and ionic line intensity was optimized for both confined and unconfined collinear dual pulse laser plasma, and a modest difference of the optimized inter-pulse delay time was found. Based on the relative standard deviation of several selected Si line intensities, it was ascertained that the signal intensity from confined collinear dual laser plasma emission showed a better stability. Plasma temperature and electron number density of confined collinear dual pulse laser plasma was measured and compared with that of unconfined laser plasma as well. [ABSTRACT FROM AUTHOR]

In this paper, a new method is introduced for studying optically thick plasma in local thermodynamic equilibrium condition by laser induced breakdown spectroscopy (LIBS) technique. The method presented here is very simple, exact, and appropriate for simultaneously quantifying the plasma parameters and instrumental function of the experimental system from self-absorbed spectral lines. A LIBS experiment is performed on an aluminum target in air atmosphere by combination of two techniques of shadowgraphy and spectroscopy, and by utilizing a theoretical approach. In this work, plasma parameters can be accurately calculated when the electron density, plasma length and intensities of three spectral lines are experimentally known. This model suggests that instead of using two spectral lines in thin plasmas, three lines are required in thick plasmas for exactly estimating the plasma temperature. In this paper, the temporal evolution of plasma dynamics, such as the number densities of the emitting species, plasma length, velocity of plasma expansion and its temperature variation is obtained by the presented procedure. [ABSTRACT FROM AUTHOR]

The present study investigates the collinear double-pulse LIBS (DP-LIBS) configuration using microjoule nanosecond pulses. It is shown that this approach can achieve typical double pulse improvement in the analytical performances for elemental analysis of aluminium alloys. In addition, the effect of the chronological sequence of the short and long nanosecond pulses in the collinear DP-LIBS experiment was also studied. The results show a significant increase of the intensity and repeatability of the emission signals in the double pulse configuration. Standard DP-LIBS signal improvement over the signal-to-noise ratio and the signal-to-background ratio for the analytical lines of different elements has been observed in comparison to single pulse LIBS of equal energy. Limits of detection in the low µg-1 range have been obtained for the different elements studied. The improvement resulting from the use of DP-LIBS was about 2-4 fold when compared to SP-LIBS in all cases. These results are useful in the context of studies investigating how the µUBS will assist in the development of portable LIBS systems and improve the utility of this spectroscopy technique for field applications. Finally, the plasma temperature is found to be approximately less than 15% higher with the double-pulse. [ABSTRACT FROM AUTHOR]

In this study, the element dependence of spatial confinement effects in LIBS has been studied. Hemispheric cavities were used to confine laser-induced plasmas from aluminum samples with other trace elements. The enhancement factors were found to be dependent on the elements. Equations describing the element-dependent enhancement factors were successfully deduced from the local thermodynamic equilibrium conditions, which have also been verified by the experimental results. Research results show that enhancement factors in LIBS with spatial confinement depend on the temperature, electron density, and compression ratio of plasmas, and vary with elements and atomic/ionic emission lines selected. Generally, emission lines with higher upper level energies have higher enhancement factors. Furthermore, with enhancement factor of a spectral line, temperatures and electron densities of plasmas known, enhancement factors of all the other elements in the plasmas could be estimated by the equations developed in this study. [ABSTRACT FROM AUTHOR]

An inductively coupled plasma, connected to a sampling cone of a mass spectrometer, is computationally investigated. The effects of the sampler orifice diameter (ranging from 1 to 2 mm) and distance of the sampler cone from the load coil (ranging from 7 to 17 mm) are studied. An increase in sampler orifice diameter leads to a higher central plasma temperature at the place of the sampler, as well as more efficient gas transfer through the sampler, by reducing the interaction of the plasma gas with the sampling cone. However, the flow velocity at the sampler position is found to be independent of the sampler orifice diameter. Moreover, by changing the sampler orifice diameter, we can control whether only the central gas or also the auxiliary gas can exit through the sampler. Finally, with the increasing distance of the sampler from the load coil, the plasma temperature at the place of the sampler decreases slightly, which might also have consequences for the ion generation and transport through the sampling cone. [ABSTRACT FROM AUTHOR]

Titanium (Ti) in Al2O3 was accurately and quantitatively analyzed by laser-induced breakdown spectroscopy (LIBS) with a fixed plasma temperature calibration method. Two calibration methods with fixed energy of laser pulses and fixed plasma temperature were employed to establish the calibration curves of Ti in the measured samples. Experimental results showed that the calibration method with fixed energy of laser pulses traditionally used in LIBS is not suitable for the analysis of Ti in Al2O3 due to the difference of the plasma temperature of samples with different Ti content caused by strong matrix effects. Instead, the calibration method with fixed plasma temperature can minimize the matrix effects and provide a more accurate calibration curve. The correlation coefficients R2 of the calibration curve with fixed plasma temperature reaches 0.9938 with a relative standard deviation of 4.3%, which is significantly improved compared with values of 0.9457 and 12.5% for the calibration curve with fixed energy of laser pulses. The results illustrate that the LIBS technique with the fixed plasma temperature calibration method presents great potential for the analysis of metal in metal oxides. [ABSTRACT FROM AUTHOR]