Single-pulse Laser-induced Breakdown Spectroscopy Research Articles

Enhancing analytical merits of laser-induced breakdown spectroscopy of hydrogen isotopes using an orthogonal double-pulsing scheme

Accurate detection and quantification of hydrogen isotopes in solid materials are vital for diverse applications, including fusion energy, hydrogen storage, and tritium production. Laser-induced breakdown spectroscopy (LIBS) is a well-established, rapid, standoff method for this purpose, but it faces challenges related to the analytical merits required for isotopic analyses. In this study, we enhance the analytical and detection capabilities of traditional single-pulse LIBS by implementing an orthogonal double pulsing approach, focusing on the analysis of a range of 2H concentrations in Zircaloy-4 substrates (acting as a proxy for 3H). The double-pulse experiments employed an orthogonal re-heating configuration with two nanosecond Nd:YAG lasers. We systematically evaluated critical parameters affecting the signal intensity in double-pulse LIBS, including interpulse delay, ambient gas pressure, and heating laser energy. Our results demonstrate that employing an orthogonal double-pulse scheme significantly enhances 2Hα emission while minimizing line broadening and self-absorption, ultimately improving the technique's analytical capabilities.

Detection of gold alloy elements by target-enhanced orthogonal triple-pulse laser-induced breakdown spectroscopy with improved sensitivity and minimal sample ablation

In order to realize more sensitive elemental analysis of precious samples under minimal sample ablation, target-enhanced orthogonal triple-pulse laser-induced breakdown spectroscopy (TEOTP-LIBS) was first developed. In this technique, a pre-ablation laser with adequate interpulse delay was introduced in reheating target-enhanced orthogonal double-pulse laser-induced breakdown spectroscopy (TEODP-LIBS); the pre-ablation laser was collinearly propagated with the reheating laser and both interacted with a solid KHCO3 target. 5–7 folds signal enhancement caused by the pre-ablation laser could be observed. A maximum of 256 folds total signal enhancement has been achieved for Au I 267.595 nm transition line while analyzing an 18 K gold sample, if comparing TEOTP-LIBS with single-pulse LIBS using equal pulse energy for the ablation laser. 5.4–11.3 folds total improvement on the signal-to-noise ratio could be observed. The mechanism of the signal enhancement contributed by the pre-ablation laser was also discussed. It was demonstrated that TEOTP-LIBS was able to provide a better solution on the sensitive elemental analysis of precious samples under minimal sample ablation than TEODP-LIBS.

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

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

UV femtosecond single-pulse and collinear double-pulse laser-induced breakdown spectroscopy (LIBS) for depth-resolved characterization of nano-scaled films

In the current work, we demonstrate the UV femtosecond (248 nm, 450 fs) single-pulse and double-pulse laser-induced breakdown spectroscopy (LIBS) as an effective method for depth profiling of nanometer-thick multi-layered structures, including photovoltaic thin films. Femtosecond LIBS enabled selective detection of both organic and inorganic materials at different depths within nanometer-scale (10–250 nm) multi-layered samples having thicknesses comparable to the etching depth produced by a single laser shot ablation. To enhance the analytical capabilities of the method, we applied the collinear double-pulse LIBS technique, using a Michelson interferometer to split the laser pulse into two equal-energy pulses. Results obtained with Indium Tin Oxide (ITO) nanofilms (115 nm layer thickness) present a clear increase of the intensity emission by a factor of 3 to 10, depending on laser fluence, when the double-pulse approach is used. Single-pulse LIBS achieved an ablation rate of around 60 nm, while the double-pulse configuration achieved 40 nm/pulse, in a sequence of seven laser shots. Furthermore, via double-pulse LIBS spectra were recorded even at fluences as low as 150 mJ/cm2, compared to 250 mJ/cm2 required for capturing spectra, when the same total energy per pulse was maintained.

LIBS at high duty-cycles: effect of repetition rate and temporal width on the excitation laser pulses

Laser-induced breakdown spectroscopy (LIBS) is becoming a more mature technology every year with new variants such as laser ablation molecular isotopic spectrometry, reheating by various discharge techniques, and multiple pulse excitation schemes, in which sometimes lasers of different pulse lengths are used. However, lasers with inherent parameters like pulse length and repetition rate are still almost exclusively employed. Recent years have witnessed the advent of novel high-repetition-rate laser concepts for machining processes, like welding, milling, and engraving. Here, a comprehensive study of single-pulse LIBS spectra of a single aluminum target is presented to showcase the applicability of flexible high duty-cycle master oscillator power amplifier (MOPA) lasers. Although traditional flashlamp-pumped Fabry–Pérot lasers only permit a variation in the pulse energy and are operated at very low duty-cycles, MOPA lasers add repetition rate and pulse length as variable parameters. A thorough analysis of the temporal plasma behavior revealed the emission dynamic to closely match the excitation laser pulse pattern. An aluminum sample’s spectral response was shown to be significantly impacted by variations in both rate and length. Although the spectral emission strength of the elemental lines of Al, Sr, and Ca all peaked at slightly different parameter settings, the strongest impact was found on the relative abundance of molecular AlO bands. Unlike in previous laser ablation molecular isotopic spectrometry (LAMIS) publications, the latter could be readily detected with a good intensity and well-resolved spectral features without any temporal gating of the detector. This finding, together with the fact that MOPA lasers are both inexpensive and dependable, makes for a promising combination for future studies including the detection of diatomic band structures.

Detection of Y, La, Yb, and Dy elements in rare earth ores by double-pulse laser-induced breakdown spectroscopy

The sensitivity of double-pulse laser-induced breakdown spectroscopy (DP-LIBS) in the detection of trace elements in samples was confirmed to be superior to that of single-pulse laser-induced breakdown spectroscopy (SP-LIBS). However, DP-LIBS is not economical because it requires two lasers. A DP-LIBS system based on beam splitting was proposed in this work, and the experimental equipment was used to analyze Y, La, Yb, and Dy elements in rare earth ores. The comparison of spectral line intensities and sensitivities of rare earth elements in rare earth ore samples between DP-LIBS and SP-LIBS was studied. The results show that the enhancement of the spectral line signal intensity of DP-LIBS is more than two times compared with that of SP-LIBS. The time evolution of signal intensities of four rare earth element characteristic lines (Y II 437.49 nm, La II 433.37 nm, Yb II 328.94 nm, and Dy II 353.17 nm) was given. The enhancements of signal intensities were found to be due to that the plasma temperature of DP-LIBS is increased by more than 500 K. The limits of detection of Y, La, Yb, and Dy were 40.97, 104.09, 47.13, and 56.25 ppm for SP-LIBS and can be reduced to 21.19, 56.93, 28.69, and 36.41 ppm for DP-LIBS. It is showed that DP-LIBS based on a single Nd:YAG laser can better improve the signal intensity and sensitivity of Y, La, Yb, and Dy elements in rare earth ore samples.

Fraunhofer-type absorption lines from a submerged Cu target by long-pulse laser-induced breakdown spectroscopy: toward non-gated detection

Clear underwater Fraunhofer-type absorption lines can be well observed by long-pulse LIBS with non-gated detection, enabling it to show significant advantages in underwater on-site analysis.

Characterization of CdTe Thin Films Using Orthogonal Double-Pulse Laser-Induced Breakdown Spectroscopy

Orthogonal reheating double-pulse laser-induced breakdown spectroscopy (LIBS) was applied to the elemental analysis of CdTe thin film samples. Films were grown through nanosecond pulsed laser ablation over silicon and glass substrates. The analysis was performed by applying a 266 nm pulsed laser devised to minimize sample damage. Re-excitation was conducted using a nanosecond laser emitting at 1064 nm that induced air breakdown 1 mm above the target. Emission enhancement was investigated as a function of both time acquisition delay and inter-pulse delay. The plasma temperature and electron density calculations made showed that the double-pulse scheme produced higher temperature values and a longer plasma duration than single-pulse LIBS. The self-absorption coefficient of the lines was determined from the measured ablated matter, plasma volume and collected spectra. The results of the double-pulse LIBS configuration showed a significant increase in emission intensity, reducing the self-absorption effect. In addition, the relative concentration of the thin films was determined for both experimental schemes. The calculated elemental values for the double-pulse configuration coincide with those expected and are more accurate than those obtained using a single laser.

Studies on target-induced enhancement in pre-ablation orthogonal double-pulse laser-induced breakdown spectroscopy

To investigate the signal enhancement of pre-produced target plasma on the optical emissions of sample plasma in air under atmospheric pressure and its mechanisms, target-enhanced orthogonal double-pulse laser-induced breakdown spectroscopy (TEODP-LIBS) in pre-ablation scheme was studied. The signal enhancement factors with respect to single pulse LIBS were compared while using KHCO3 target and aluminum target in pre-ablation TEODP-LIBS. It was demonstrated that KHCO3 target could provide higher signal enhancement than aluminum target. Two orders signal enhancement could be observed at short inter-pulse delay from −0.4 to −0.6 μs when KHCO3 target was used. Both plasma temperature and electron density in pre-ablation TEODP-LIBS were increased if compared with those in pre-ablation orthogonal double-pulse laser-induced breakdown spectroscopy (ODP-LIBS) without solid target. Significant improvement on the detection limits of lead and iron in brass sample caused by the target-induced signal enhancement have also been experimentally demonstrated. This technique is especially useful for in-situ sensitive elemental analysis under minimal sample ablation or high spatial resolution.

Coal Analysis by Single-Beam-Splitting Laser-Induced Breakdown Spectroscopy (LIBS) with Support Vector Machine (SVM)

Laser-induced breakdown spectroscopy (LIBS) has been widely used in coal analysis. In this work, single-beam-splitting LIBS (SBS-LIBS) was used to quantitatively analyze coal. This technique was performed by adding a beam splitter to a conventional single-pulse LIBS (SP-LIBS) set-up. The laser light was split into two beams and focused upon the same point on the sample surface. Carbon, hydrogen, nitrogen, ash, and volatile components were determined in this work. A support vector machine (SVM) model was constructed for quantitative analysis. The root mean square error of prediction (RMSEP), average relation error of prediction (AREP), and average absolute error of prediction (AAEP) were employed to evaluate the accuracy of the SVM with SBS-LIBS and SP-LIBS. The results showed an overall improvement in SBS-LIBS for coal analysis, in which the AAEP of carbon, hydrogen, nitrogen, ash and volatile components were decreased to 1.04%, 0.18% 0.08%, 1.80%, and 4.30% from 3.70%, 0.27%, 0.09%, 3.06%, and 7.99%, respectively.

Collinear double-pulse laser-induced breakdown spectroscopy based Cd profiling in the soil.

Cadmium (Cd) can migrate in the soil and is readily absorbed by crops. High Cd accumulated in grains poses a huge threat to human health by inhibiting the function of the kidney system. Thus, it is crucial to reveal the content of soil Cd in vertical-depth series using a fast, real-time, and reliable method. For this purpose, laser-induced breakdown spectroscopy (LIBS) combined with multivariate chemometrics was developed to analyze Cd content in the soil with vertical-depth series. Soil samples spiked with different levels of Cd were prepared, and LIBS spectra were obtained by single-pulse LIBS (SP-LIBS) and collinear double-pulse LIBS (CDP-LIBS) with wavelengths of 532 nm and 1064 nm. With appropriate parameters, CDP-LIBS showed better performance in detecting Cd than SP-LIBS. Partial least squares regression (PLSR), genetic algorithm (GA)-optimized back propagation artificial neural network (BP-ANN), and particle swarm optimization (PSO)-optimized least squares-support vector machine (LS-SVM) were tested for quantitative analysis of the spectra after median absolute deviation (MAD), multiple scattering correction (MSC), wavelet transform (WT), spectral averaging, and normalization. PSO-optimized LS-SVM yielded an ideal result, with a coefficient of determination (R2, 0.999) and root mean square error (RMSE, 0.359 mg/Kg) in the prediction dataset. Finally, CDP-LIBS coupled with PSO-optimized LS-SVM was employed to analyze soil Cd content in vertical-depth series to reveal the migration pattern of Cd. Our results indicated that soil Cd had a significant positive relationship with the inverse of soil depth. However, Cd was mainly concentrated in 0-20 cm and rarely leached below 45 cm in the soil. This study suggests that LIBS and its enhancement techniques provide a reliable method for revealing the content of soil Cd in vertical-depth series.

Direct determination of Cu, Cr, and Ni in river sediments using double pulse laser-induced breakdown spectroscopy: Ecological risk and pollution level assessment.

Double pulse laser-induced breakdown spectroscopy (DP LIBS) has attracted much attention for analyzing trace elements due to its higher sensitivity when compared to single pulse laser-induced breakdown spectroscopy (SP LIBS). However, the development of quantitative methods in LIBS for the analysis of complex samples, such as sediments, is a great challenge due to the matrix effects that are very accentuated in this technique. In this study, different spectral treatments and calibration strategies were investigated to obtain calibration models that allow determinations with satisfactory accuracy and precision of Cr, Cu, and Ni in river sediments from different hydrographic basins. The best model developed for Cr was using MMC without spectral normalization and for Cu and Ni it was using MMC with spectral normalization, and using inverse regression, an increase in the accuracy of the determinations of all analytes was obtained. These models showed limit of quantification (LOQ) of 7.87 mg kg-1, 1.62 mg kg-1, and 2.21 mg kg-1 and root mean square error of prediction (RMSEP) of 7.54 mg kg-1, 14.53 mg kg-1, and 8.29 mg kg-1 for Cr, Cu, and Ni, respectively. Therefore, the models have adequate sensitivity and precision for the quantification of the potentially toxic elements (PTEs) evaluated, since, according to Brazilian legislation, the lower concentration of threshold effect level (TEL) for Cr, Cu, and Ni is <37.3 mg kg-1, <35.7 mg kg-1, and <18 mg kg-1, respectively. The concentrations of Cr, Cu, and Ni determined by DP LIBS allowed to obtain a partial ecological risk assessment of the studied sediments. Also, the chemometric tool Kohonen self-organizing map (KSOM) were used for data interpretation.

Quantitative analysis of trace carbon in steel samples using collinear long-short double-pulse laser-induced breakdown spectroscopy

The trace carbon (C) composition in ultra-low carbon steel is measured by Laser-Induced Breakdown Spectroscopy (LIBS). Five standard steel samples, with C content between 9 and 89 μg/g, are used to study the performance of LIBS quantitative analysis. Single-pulse LIBS (SP-LIBS) and long-short double-pulse LIBS (LS-DP-LIBS) have been used to measure these five samples. Due to the carbon contamination on sample surface, SP-LIBS cannot obtain an available analysis result. To reduce the influence of carbon contamination, the pretreatment pulse method is employed in this work. The experimental results of the continuous irradiation show that the long-short pretreatment pulses can effectively eliminate the influence of carbon contamination. Finally, the trace carbon in steel samples has been successfully measured by LS-DP-LIBS with pretreatment pulses. The LOD value of carbon is 22.6 μg/g. For the measured five samples, the relative error of prediction (REP%) is between 6.1% and 35.7% and the relative standard deviation (RSD%) is between 13.9% and 58.3%.

Double pulse laser-induced breakdown spectroscopy for the analysis of plasma-facing components

Laser-induced breakdown spectroscopy is applied successfully for plasma-wall interaction studies in several fusion devices and post-mortem analyses of plasma-facing materials. However, the quantitative as well as qualitative analysis of low hydrogen isotope contents in tungsten plasma-facing components is still challenging. A promising approach to increase the optical signal in laser-induced breakdown spectroscopy is to apply a second laser pulse to the laser-produced plasma. We present two setups for post mortem plasma-facing component analyses using different laser pulse properties and different excitation geometries. The enhancement factors and changes in spectral line shapes for double pulse compared to single pulse laser-induced breakdown spectroscopy are presented.

Quantitative Analysis of Manganese in Underwater Steel Samples Using Long-Short Double-Pulse Laser-Induced Breakdown Spectroscopy.

The long-short double-pulse laser-induced breakdown spectroscopy (LS-DP-LIBS) method was applied to qualitative and quantitative analyses of underwater steel samples to improve the detection ability of underwater measurement. The stable plasma intensity and discrete emission lines were detected using LS-DP-LIBS when comparing the measured results of single-pulse LIBS (SP-LIBS) and LS-DP-LIBS. The long pulse produces a cavitation bubble without plasma, and the short pulse induces the plasma of steel samples within the bubble. The detection features of LS-DP-LIBS for underwater steel samples were discussed in different intra-pulse delay time, long-pulse width, and delay time conditions when analyzing the measured spectra, the signal intensity of Fe(I) at 400.524 nm and 402.187 nm, Mn(I) at 404.136 nm, and intensity ratio of Mn(I) 404.136 nm/Fe(I) 402.187 nm. The results indicated that the plasma stability and spectral signal intensity were improved significantly with a long-pulse width of 80 µs in the intra-pulse delay time of 70 µs, which were appropriate for bubble formation and plasma generation. According to the discussion of the delay time effect, the state of generated plasma was almost stable from 650 ns to 850 ns. Manganese (Mn) contents in steel samples were analyzed quantitatively when measuring five steel samples with different Mn contents using LS-DP-LIBS in optimal experimental conditions. A strong linear dependence was observed with R2=0.9842, which demonstrated the feasibility and appropriateness of quantitative analysis for underwater measurement using LS-DP-LIBS.

Unusual parallel laser irradiation for suppressing self-absorption in single pulse laser-induced breakdown spectroscopy.

This study demonstrates a new approach for suppressing the self-absorption effect in single-pulse laser-induced breakdown spectroscopy (LIBS) using unusual parallel laser irradiation. A nanosecond Nd:YAG laser with a wavelength of 1064 nm was fired parallel to and focused at a very close distance of 1 mm to the sample surface. The experiment was carried out in air at atmospheric pressure. In this configuration, the sample was ablated by a shockwave generated from the air breakdown plasma formed near the sample surface. Under this condition, we successfully obtained spectra of the resonance emission line for high concentration K (K I 766.4 nm and K I 769.9 nm) that are free from self-reversal and weakly affected by the self-absorption. Furthermore, the quantitative analysis results for the element K showed that a linear calibration curve over a wide concentration range could be achieved, which indicates the effectiveness of this technique in reducing the self-absorption effect and improving the analytical performance of ordinary single-pulse LIBS.

Determination of As, Hg, S, and Se in liquid jets by laser-based optical diagnostic technique

Laser-induced breakdown spectroscopy (LIBS) has been evaluated for measurement of As, Hg, S, and Se in aqueous samples. Single pulse (SP) and double pulse (DP) LIBS, with a 1064 nm Nd: YAG laser source, were utilized to generate micro plasma from the surface of a liquid jet containing these elements. Plasma emission was collected at a 45° angle with the laser beam for As and Se detection in UV wavelength range. However, the confocal mode was used to collect the atomic emission for Hg and S detection in visible and near IR range, respectively. Atomic emission lines 228.81 nm for As, 546.07 nm for Hg, 921.2 nm for S, and 196.09, 203.98 and 206.32 nm for Se were detected in the LIBS spectra. Calibration curves were developed to estimate the limit of detection for each analyte and found to be 2, 16, 16, and 29 ppm for As, Hg, S, and Se, respectively, with SP LIBS and 0.4, 8, 8 and 11 ppm, respectively, with DP LIBS. The study has implications in monitoring of these pollutants in flue gas desulfurization (FGD) wastewater.

Suppression of self-absorption in laser-induced breakdown spectroscopy using a double pulse orthogonal configuration to create vacuum-like conditions in atmospheric air pressure

Self-absorption, which is known to severely disturb identification of the emission peak intensity in emission-based spectroscopy, was first studied using ordinary single pulse laser-induced breakdown spectroscopy (LIBS). It was found that severe self-absorption, with an evident self-reversal, occurs in the resonance emission lines of high concentration Na, K, and Al, and thus it is impossible to obtain the linear calibration curve required for quantitative analysis. To overcome this problem, we introduce a double pulse orthogonal technique in which the first laser is fired in a parallel orientation at a varied distance of 2–6 mm from the sample surface. It is well known that the strong shock wave generated by this laser irradiation temporarily creates a vacuum-like condition immediately in front of the sample surface. This action is followed by a second laser irradiation oriented perpendicular to the sample surface. The sample ablated by the second laser irradiation expands following the shockwave excitation process in the vacuum-like air atmosphere created by the first laser. The obtained spectra of the resonance emission lines of high concentration Na, K, and Al are free from the self-reversal and weakly affected by the self-absorption effect. A linear calibration curve that intercepts near zero point for K element over a wide concentration range is also demonstrated in this study. This simple modification is considered notably helpful in overcoming the self-absorption that occurs in ordinary single pulse atmospheric pressure LIBS.

Spectral Characterization of Collinear Double-Pulse Laser Induced Breakdown Spectroscopy (DP-LIBS) for the Analysis of the Chinese Traditional Medicine Artemisia annua

A collinear dual-pulse laser induced breakdown spectroscopy (DP-LIBS) method was employed to analyze Chinese traditional medicine Artemisia annua. The spectral intensities and signal-to-background ratios of magnesium (II) 279.54 nm, CN 388.29 nm, calcium (II) 393.37 nm, and iron (II) 404.27 nm were used to evaluate the optical emission characteristics of A. annua induced by DP-LIBS. The temporal evolution characteristics, inter-pulse time, and laser energy values were optimized. In particular, the electron density and the temperatures of the plasma were reported as functions of the delay time. The results showed that the DP-LIBS had stronger intensity and better accuracy compared to single-pulse (SP) LIBS. The enhancement factors obtained using DP-LIBS for Mg, CN, Ca, and Fe were 7.2, 8.9, 13.8, and 3.4, respectively. This study provides important information about A. annua.

Sample Temperature Effect on Steel Measurement Using SP-LIBS and Collinear Long-short DP-LIBS

Laser induced breakdown spectroscopy (LIBS) has been investigated as a potential multi-element quantitative analysis tool for the quality control of on-line steel production. This research investigated influence of sample temperature on steel sample measurement using collinear long-short dual-pulse LIBS (long-short DP-LIBS) and single-pulse LIBS (SP-LIBS). The standard steel sample has been uniformly heated in a muffle furnace from 20°C to 700°C. The experimental results show that sample temperature has significantly effect on measurement result using SP-LIBS. However, long-short DP-LIBS can effectively reduce the sample temperature effect on measurement result. The detection characteristics of long-short DP-LIBS and SP-LIBS were compared using the intensity ratio of I Mn 404.136 nm/I Fe 400.524 nm and I Fe 402.187 nm/I Fe 400.524 nm under different delay time and different sample temperature conditions. The signal intensity and plasma temperature can be maintained higher and more stable for a period of time and at different sample temperature by long-short DP-LIBS with smaller error bar compared with that of SP-LIBS, which indicated long-short DP-LIBS has better measurement repeatability than SP-LIBS. The plasma temperature correction method was applied to compare the detection features of long-short DP-LIBS and SP-LIBS. The signal stability of long-short DP-LIBS measurement was improved significantly at different sample temperature with plasma temperature correction. These results demonstrated that the effect of sample temperature can be reduced using long-short DP-LIBS method to improve the on-line detection capability for steel measurement in complex environment.