Double-pulse Laser-induced Breakdown Spectroscopy Research Articles

Effect of single and double pulse laser-induced breakdown spectroscopy towards steel alloy in different gaseous media

In recent years, laser-induced breakdown spectroscopy (LIBS) technique showed its promising for material analysis, quality control, forensic science, and environmental safety monitoring. Besides, due to its rapid measurement capability and minimal sample-preparation requirements, it is a widely recognized elemental analysis approach used in a variety of study domains. The current work compares spatially resolved single (SP) and double pulse (DP), especially orthogonal DP, setups for LIBS to examine and enhance the limit of detection (LOD) in duplex stainless steels alloy. Using the Boltzmann plot method and the Stark broadening mechanism, the electron temperature and density of local arc plasma are highlighted due to single pulse and orthogonal pre-pulse double pulse configurations. With delay time, the circumstances of arc plasma's local thermodynamic equilibrium (LTE) of emission spectral lines are investigated. The experimental results show that there are significant increases in the spectral intensities of the Fe lines in double pulse LIBS under Ar-gas compared to those under He-gas. Internal standardization was used to create calibration curves for the spectral lines of Cr, Cu, and Mn in the alloy sample for the both studied media. It demonstrated that argon outperforms helium in determining the elemental composition of steel alloys. Furthermore, LOD for SP-LIBS and DP-LIBS in both media were calculated, which showed a higher detection LOD for DP-LIBS in the presence of Ar-gas compared to that in He-gas.

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.

Comparison of single and double pulse laser-induced breakdown spectroscopy for the detection of biomolecules tagged with photon-upconversion nanoparticles

BackgroundLaser-induced breakdown spectroscopy (LIBS) is a well-recognized analytical technique used for elemental analysis. This method is gaining considerable attention also in biological applications thanks to its ability for spatial mapping and elemental imaging. The implementation of LIBS in the biomedical field is based on the detection of metals or other elements that either naturally occur in the samples or are present artificially. The artificial implementation of nanoparticle labels (Tag-LIBS) enables the use of LIBS as a readout technique for immunochemical assays. However, one of the biggest challenges for LIBS to meet immunoassay readout standards is its sensitivity. ResultsThis paper focuses on the improvement of LIBS sensitivity for the readout of nanoparticle-based immunoassays. First, the LIBS setup was optimized on photon-upconversion nanoparticle (UCNP) droplets deposited on the microtiter plate wells. Two collection optics systems were compared, with single pulse (SP) and collinear double pulse (DP) LIBS arrangements. By deploying the second laser pulse, the sensitivity was improved up to 30 times. The optimized SP and DP setups were then employed for the indirect detection of human serum albumin based on immunoassay with UCNP-based labels. Compared to our previous LIBS study, the detection limit was enhanced by two orders of magnitude, from 10 ng mL−1 to 0.29 ng mL−1. In addition, two other immunochemical methods were used for reference, based on the readout of upconversion luminescence of UCNPs and absorbance measurement with enzyme labels. Finally, the selectivity of the assay was tested and the practical potential of Tag-LIBS was demonstrated by the successful analysis of urine samples. Significance and noveltyIn this work, we improved the sensitivity of the Tag-LIBS method by combining new labels based on UCNPs with the improved collection optics and collinear DP configuration. In the instrumental setup optimization, the DP LIBS showed better sensitivity and signal-to-noise ratio than SP. The optimizations allowed the LIBS readout to surpass the sensitivity of enzyme immunoassay, approaching the qualities of upconversion luminescence readout, which is nowadays a state-of-the-art readout technique.

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.

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

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

Accurate determination of plasma temperature and electron density using a reference target: one-point calibration LIBS elemental analysis ofalloy samples.

Elemental analysis of aluminum alloy samples with calibration-free laser-induced breakdown spectroscopy (CF-LIBS) encounters two difficulties: the inconvenience of determining accurate temperature and electron density of the plasma and the influence of self-absorption of the observed aluminum lines. To solve this problem, target-enhanced orthogonal double-pulse laser-induced breakdown spectroscopy in the reheating regime combined with the one-point calibration method was proposed in this work. A mixture of copper powders and K H C O 3 grains was pressed to a pellet and used as the target. Accurate determination of plasma temperature and electron density can be obtained using a reference target. The plasma temperature could be determined with Saha-Boltzmann plot of copper, and the electron density of the plasma could be determined according to the Stark broadening of the H α line of hydrogen. Aluminum alloy samples were analyzed with a relative error of better than 0.02% for a major element. This approach provides a convenient way to determine the temperature and electron density of the plasma more accurately and is able to reduce the influence of self-absorption, which is helpful for realizing quantitative elemental analysis of different samples while using a calibration-free algorithm.

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.

Quantitative elemental analysis of bismuth brass with target-enhanced orthogonal double-pulse LIBS combined with variant one-point calibration.

Self-absorption and unknown transition probabilities of the analytical lines hinder the accurate quantitative elemental analysis of bismuth brass with conventional calibration-free laser-induced breakdown spectroscopy (LIBS). In this work, target-enhanced orthogonal double-pulse LIBS combined with a variant one-point calibration method was used to solve this problem and realize quantitative elemental analysis of bismuth brass with a relative error of less than 4%. This approach is able to reduce the influence of self-absorption and capable of using analytical lines with unknown transition probabilities while using a calibration-free algorithm, which is helpful for accurate quantitative elemental analysis of bismuth brass and other samples.

Copper signal characteristics using collinear LS-DP-LIBS for underwater measurement

The collinear long-short double-pulse laser-induced breakdown spectroscopy (LS-DP-LIBS) was employed in the detection of underwater copper samples. Discrete emission lines were obtained using LS-DP-LIBS with an appropriate delay between two pulses, while characteristic emission lines were covered by continuous background and noise using LIBS with a single pulse. In the condition of LS-DP-LIBS, signal characteristics of the measured spectra at different experimental parameters including long-pulse width, lens-to-sample distance (LTSD), and long-pulse energy have been investigated to determine the optimal condition. The results indicated that the long-pulse width and the long-pulse energy were closely related to the formation of a cavitation bubble, thus affecting the plasma state and signal characteristics for underwater measurement. The parameter of the LTSD imposed an effect on the spectral signal through changing the ablation mass of the sample and the plasma temperature. The experimental results demonstrated the feasibility of the underwater measurement of metal samples using the collinear LS-DP-LIBS and showed a significant signal improvement through this method. With further development, it is of great potential to apply this new method based on LIBS to ocean exploration.

Discrimination of tooth composition through temporally shaped femtosecond laser-induced breakdown spectroscopy

Dental caries has attracted widespread concern because of its universality. However, the current diagnosis of dental caries depends largely on naked eyes and dentists' experience, which causes considerable randomness and inaccuracy in the diagnosis. In this study, temporally shaped double pulse (DP) femtosecond laser-induced breakdown spectroscopy (LIBS) has been used for tooth composition detection for the first time. Under the laser fluence of 20 J/cm2, the spectra intensity for DP LIBS with a pulse delay of 200 ps was 13 times higher than that of single pulse. For further prediction, the detection model based on DP LIBS and partial least squares discrimination analysis could discriminate dentin, enamel, and caries with a prediction accuracy of above 90%. This method may provide rapid and accurate feedback to dentists for real-time diagnosis in the future.

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.

Collinear double-pulse laser-induced breakdown spectroscopy using Nd:YAG laser generating two nanosecond pulses of regulated energy ratios

Collinear double-pulse laser-induced breakdown spectroscopy using Nd:YAG laser generating two nanosecond pulses of regulated energy ratios

Multiple-element analysis of coal using collinear double-pulse laser-induced breakdown spectroscopy

Collinear double-pulse laser-induced breakdown spectroscopy has been developed to enhance the emission signal of coal plasma.

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.

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.

Influence of inter-pulse delay on CN molecular emission from femtosecond-nanosecond double-pulse laser-induced breakdown spectroscopy of PMMA

An experimental study on molecular emission in laser-induced breakdown spectroscopy (LIBS) was performed using an integrated femtosecond (fs) and nanosecond (ns) double-pulse (DP) laser scheme at the different inter-pulse delay between the fs and ns pulses. This work mainly included the influence of the DP inter-pulse delay on the spectral emission intensity and signal-to-background ratio (SBR). The ablated sample was polymethyl methacrylate (PMMA), and the measured molecular band was CN (Δv = 0) in the B2Σ+ − X2Σ+ transition. The results showed that the negative (ns + fs scheme) and positive (fs + ns scheme) inter-pulse delays were not much different in terms of spectral emission. The SBR excited by the fs + ns DP was higher than that excited by the ns + fs DP, and the maximum value of the SBR in the fs + ns DP-LIBS scheme was about two times that in the ns + fs DP-LIBS scheme. The higher SBR was suitable for spectral analysis, and was easy to reduce the influence of continuous emission on spectral analysis. Also, the vibration temperature of the CN molecule as a function of the inter-pulse delay between the two laser pulses was discussed. This discovery fully demonstrates that the fs + ns DP-LIBS is of great significance for detecting molecular emissions in LIBS.

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.

Graphene thin film microextraction and nanoparticle enhancement for fast LIBS metal trace analysis in liquids

Several strategies have been effectively tested in the past to improve the Laser Induced Breakdown Spectroscopy (LIBS) signal for the analysis of liquid samples, involving peculiar experimental configurations, such as Double Pulse LIBS (DP-LIBS). Recently, sample treatment has proven to be a viable and simple way to enhance the performances of LIBS towards the analysis of solutions. Among the various strategies, the most promising and versatile appears to be Thin Film Microextraction (TFME) using carbon-based adsorbents.Another sample pre-treatment procedure, Nanoparticle-Enhanced LIBS (NELIBS), has gained significant interest due to its relative simplicity and effectiveness. This methodology uses a deposition of silver nanoparticles (AgNPs) on the sample to greatly increase the emission of the LIBS plasma.In this work, we investigate for the first time the possibility of combining TFME and NELIBS. We developed TFME supports by depositing an aqueous graphene nano-sheets (aq-GRA) prepared by Pulsed Laser Ablation in Liquid (PLAL) on a glass substrate. The preparation of the supports was optimized with regards to the substrate nature, deposition method, sorbent volume and drying method. Then, the TFME supports were tested for the extraction of Chromium from aqueous solution at different extraction times and analyte concentration. Subsequently, the TFME supports were treated with a deposition of silver nanoparticles (AgNP) to test the feasibility of the NELIBS approach.We observed an enhancement in the emission lines of Cr when the AgNPs were applied, as well as a lower estimated LOD value when compared to plain graphene TFME supports.

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%.