Double-pulse Laser-induced Breakdown Spectroscopy Research Articles

Quantitative analysis of chromium in vegetable oil by collinear double pulse laser-induced breakdown spectroscopy combined with dual-line internal standard method

The safety quality of vegetable oil is very important for human life. The objective of this research is to determine the content of heavy metal chromium (Cr) in each of three kinds of vegetable oils (soybean oil, peanut oil, and corn oil) quantitatively by collinear double pulse laser-induced breakdown spectroscopy (DP-LIBS). In this study, a total of 24 vegetable oil samples are prepared, and each kind of vegetable oil has 8 samples. Fortune paulownia wood chips with a diameter of 20 mm and thickness of 3 mm are placed into the vegetable oil samples to collect the Cr element. After that, the 24 samples (fortune paulownia wood chips that have enriched Cr element) are dried in the oven, and the LIBS spectra of samples are acquired in a wavelength range of 206.28-481.77 nm by a dual-channel high-precision spectrometer. The spectral line of Cr (Cr I 425.39 nm) is chosen as the quantitative analysis spectral line, while CN (CN 421.39 nm) molecular spectral line, Ca (Ca I 422.64 nm) atomic spectral line and the sum of their spectral line intensities are selected as the internal standard lines. Then the calibration curves of Cr are obtained by the basic calibration method, single-line internal standard method (CN 421.39 nm or Ca I 422.64 nm as the internal standard line) and dual-line internal standard method (CN 421.39 nm and Ca I 422.64 nm as the internal standard lines). Finally, the validation samples are used to verify the performances of the calibration curves of Cr element. The results show that the values of fitting degree (R2) of the basic calibration curves for three kinds of vegetable oils are all above 0.97, and the relative errors of validation samples with low concentration are bigger than those with high concentration. The values of (R2) of calibration curves obtained by single-line internal standard method are above 0.98, and the relative errors of validation samples are lower than those obtained using basic calibration method. And the values of (R2) of calibration curves for soybean oils, corn oils and peanut oils are 0.995, 0.992 and 0.996, respectively, with using dual-line internal standard method. The relative errors between the two validation samples are 12.8%, 1.73%, 9.19%, 6.05% and 6.23%, 6.69%, respectively. And the results obtained by the dual-line internal standard method are better than those obtained by the basic calibration method and single-line internal standard method. Thus it can be seen that the dual-line internal standard method can reduce the error of quantitative analysis effectively and improve the predicting ability of LIBS technique for Cr element detection in vegetable oil.

Hydrogen isotope detection in metal matrix using double-pulse laser-induced breakdown-spectroscopy

The amount of hydrogen isotopes retained in plasma facing components (PFCs) and the determination of their surface layer composition are among the most critical issues for the next generation fusion device, ITER, under construction in Cadarache (France). Laser Induced Breakdown Spectroscopy (LIBS) is currently under evaluation as a technique suitable for quantitative, in situ, non-invasive measurements of these quantities. In order to detect traces of contaminant in metallic samples and improve its limit of detection (LOD), the Double Pulse LIBS (DP-LIBS) variant can be used instead of the standard Single Pulse LIBS (SP-LIBS), as it has been proven by several authors that DP-LIBS can considerably raise the analytical performances of the technique.In this work Mo samples coated with a 1.5–1.8μm thick W-Al mixed layer, contaminated with co-deposited deuterium (D) were measured by SP- and DP-LIBS under vacuum (p~5×10−5mbar), with an experimental set-up simulating conditions that can be found in a real fusion device between plasma discharges. A partial Calibration Free procedure (pCF) was applied to the LIBS data in order to retrieve the relative concentration of W and Al in the mixed layer. The amount of deuterium was then inferred by using tungsten as internal standard, accounting for the intensity ratio between the Dα line and nearby W I lines. The results are in satisfactory agreement with those obtained from preliminary Ion Beam Analysis measurements performed immediately after the specimen's realization.

Re-Heating Effect on the Enhancement of Plasma Emission Generated from Fe Under Femtosecond Double-Pulse Laser Irradiation**supported by the National Basic Research Program of China (No. 2013CB922200), the China Postdoctoral Science Foundation (No. 2014M551169), National Natural Science Foundation of China (Nos. 11674128, 11474129 and 11504129)

In this paper, we present a study on the effect of inter-pulse delay using femtosecond double-pulse laser-induced breakdown spectroscopy in a collinear geometry. The temporal evolution of spectral intensity is performed for the lines of Fe I 423.60 nm, Fe I 425.08 nm and Fe I 427.18 nm. It is found that, by selecting appropriate inter-pulse delay, the signal enhancement can be significantly increased compared with the single-pulse case. A three-fold enhancement in the current experiment is obtained. The plasma temperature and electron density are also investigated based on the theory of Boltzmann plot and Stark broadening. We attribute the main mechanism for emission enhancement to the plasma re-heating effect.

Angle of Observation Influence on Emission Signal from Spatially Confined Laser-Induced Plasmas.

The present work focuses on the influence of the angle of observation on the emission signal from copper plasmas. Plasma plumes have been generated inside a home-made chamber consisting of two parallel glass windows spaced by 2.5 mm. This chamber allows observing plasma plumes from different collection angles throughout their perimeter, spanning from 20° to 80° with respect to the surface of the Cu target. In order to minimize the observed volume of the plasma, measurements were made from the closest distance possible through a metallic hollow tube. Single-pulse and collinear double-pulse excitation schemes with a Nd:YAG laser (1064 nm, 5 ns) have been investigated. The results have shown that the selection of the best angle to collect light from the plasma is related to the excitation mode. On the other hand, the shot-to-shot signal variability has been found to depend on the shape of plasma plumes. In single-pulse excitation, a good correlation between the observed laser-induced breakdown spectroscopy (LIBS) emission (from spatially confined plumes) and their integrated signal of plasma image has been ascertained. However, this fact was less evident in double-pulse LIBS, which could be due to a different mechanism involved in the ablation process.

In situ analysis of magnesium alloy using a standoff and double-pulse laser-induced breakdown spectroscopy system

To monitor the components of molten magnesium alloy during the smelting process in real time and online, we designed a standoff double-pulse laser-induced breakdown spectroscopy (LIBS) analysis system that can perform focusing, collecting and imaging of long-range samples. First, we tested the system on solid standard magnesium alloy samples in the laboratory to establish a basis for the online monitoring of the components of molten magnesium alloy in the future. The experimental results show that the diameters of the focus spots are approximately 1 mm at a range of 3 m, the ablation depth of the double-pulse mode is much deeper than that of the single-pulse mode, the optimum interpulse delay of the double pulse is inconsistent at different ranges, and the spectral intensity decays rapidly as the range increases. In addition, the enhancement effect of the double pulse at 1.89 m is greater than that at 2.97 m, the maximum enhancement is 7.1-fold for the Y(I)550.35-nm line at 1.89 m, and the calibration results at 1.89 m are better than those at 2.97 m. At 1.89 m, the determination coefficients (R2) of the calibration curves are approximately 99% for Y, Pr, and Zr; the relative standard deviations (RSDs) are less than 10% for Y, Pr, and Zr; the root mean square errors (RMSEs) are less than 0.037% for Pr and Zr; the limits of detection (LODs) are less than 1000 ppm for Y, Pr, and Zr; and the LODs of Y, Pr, and Zr at 2.97 m are higher than those at 1.89 m. Additionally, we tested the system on molten magnesium alloy in a magnesium alloy plant. The calibration results of the liquid magnesium alloy are not as favorable as those of the sampling solid magnesium alloys. In particular, the RSDs of the liquid magnesium alloy are approximately 20% for Pr and La. However, with future improvements in the experimental conditions, the developed system is promising for the in situ analysis of molten magnesium alloy.

Spatially-offset double-pulse laser-induced breakdown spectroscopy: A novel technique for analysis of thin deposited layers

A novel technique, spatially-offset double-pulse laser-induced breakdown spectroscopy (SODP-LIBS), is invented for analysis of thin layers. In this technique, two laser spots are spatially offset by a few mm, while there is no spatial gap for the standard collinear DP-LIBS. It is demonstrated from analysis of thin W layers (∼30–250nm thickness) deposited on Mo substrates at a reduced ambient pressure of ∼ 5×10−3 Torr that (1) the W I signal intensity is enhanced with SODP-LIBS and (2) a clearer transition between W and Mo is obtained with SODP-LIBS, compared to the standard DP-LIBS.

Enhanced laser-induced breakdown spectroscopy on Co sample with double femtosecond laser pulses

This paper presents the study on the enhancement mechanism of laser-induced breakdown spectroscopy on cobalt sample with double femtosecond pulse. The double-pulse experiments were carried out in the collinear beam geometry in air. The influence of the delay between the two collinear laser pulses was investigated by changing the pulses path length. In cases of no delay between the two pulses, the laser-induced breakdown spectroscopy is equivalent to that induced by a single pulse laser with energy equals to the sum of the double collinear pulse energy. The obtained results show that with an optimized delay, the double-pulse laser-induced breakdown spectroscopy has a very clear enhancement comparing with the single-pulse laser induced breakdown spectroscopy. In addition, the dependence of the electron temperature obtained by linear Boltzmann method on the pulse interval was investigated. The experiment shows that the dependence of spectral enhancement factor on the pulse interval is the same as that of the electron temperature, both of them go through two obvious changing processes. Analysing by the Boltzmann equation, we draw the conclusion that the spectral signal enhancement depends on the electron temperature.

Multivariate approach to the chemical mapping of uranium in sandstone-hosted uranium ores analyzed using double pulse Laser-Induced Breakdown Spectroscopy

The goal of this work is to provide high resolution mapping of uranium in sandstone-hosted uranium ores using Laser-Induced Breakdown Spectroscopy (LIBS) technique. In order to obtain chemical image with highest possible spatial resolution, LIBS system in orthogonal double pulse (DP LIBS) arrangement was employed. Owing to this experimental arrangement the spot size of 50μm in diameter resulting in lateral resolution of 100μm was reached. Despite the increase in signal intensity in DP LIBS modification, the detection of uranium is challenging. The main cause is the high density of uranium spectral lines, which together with broadening of LIBS spectral lines overreaches the resolution of commonly used spectrometers. It results in increased overall background radiation with only few distinguishable uranium lines. Three different approaches in the LIBS data treatment for the uranium detection were utilized: i) spectral line intensity, ii) region of apparent background and iii) multivariate data analysis. By utilizing multivariate statistical methods, a specific specimen features (in our case uranium content) were revealed by processing complete spectral information obtained from broadband echelle spectrograph. Our results are in a good agreement with conventional approaches such as line fitting and show new possibilities of processing spectral data in mapping. As a reference technique to LIBS was employed X-ray Fluorescence (XRF). The XRF chemical images used in this paper have lower resolution (approximately 1–2mm per image point), nevertheless the elemental distribution is apparent and corresponds to presented LIBS experiments.

An Innovative Approach to Meteorite Analysis by Laser‐Induced Breakdown Spectroscopy

An innovative approach of double pulse laser‐induced breakdown spectroscopy (DP‐LIBS) coupled with optical microscopy was applied to the characterisation and quantitative analysis of the Agoudal iron meteorite in bulk sample and in petrographic thin section. Qualitative analysis identified the elements Ca, Co, Fe, Ga, Li and Ni in the thin section and the whole meteorite. Two different methods, calibration‐free LIBS and one‐point calibration LIBS, were used as complementary methodologies for quantitative LIBS analysis. The elemental composition data obtained by LIBS were in good agreement with the compositional analyses obtained by traditional methods generally applied for the analysis of meteorites, such as ICP‐MS and EDS‐SEM. Besides the recognised advantages of LIBS over traditional techniques, including versatility, minimal destructivity, lack of waste production, low operating costs, rapidity of analysis, availability of transportable or portable systems, etc., additional advantages of this technique in the analysis of meteorites are precision and accuracy, sensitivity to low atomic number elements such as Li and the capacity to detect and quantify Co contents that cannot be obtained by EDS‐SEM.

High-resolution three-dimensional compositional imaging by double-pulse laser-induced breakdown spectroscopy

In this paper we present a new instrument specifically realized for high-resolution three-dimensional compositional analysis and mapping of materials. The instrument is based on the coupling of a Double-Pulse Laser-Induced Breakdown Spectroscopy (LIBS) instrument with an optical microscope. The compositional mapping of the samples is obtained by scanning the laser beam across the surface of the sample, while the in depth analysis is performed by sending multiple laser pulses on the same point. Depths of analysis of several tens of microns can be obtained. The instrument presented has definite advantages with respect to Laser Ablation-ICP Mass Spectrometry in many applications related to material analysis, biomedicine and environmental diagnostics. An application to the diagnostics of industrial ceramics is presented, demonstrating the feasibility of Double-Pulse LIBS Imaging and its advantages with respect to conventional single-pulse LIBS imaging.

Double pulse laser induced breakdown spectroscopy: A potential tool for the analysis of contaminants and macro/micronutrients in organic mineral fertilizers

Organic fertilizers are obtained from waste of plant or animal origin. One of the advantages of organic fertilizers is that, from the composting, it recycles waste-organic of urban and agriculture origin, whose disposal would cause environmental impacts. Fast and accurate analysis of both major and minor/trace elements contained in organic mineral and inorganic fertilizers of new generation have promoted the application of modern analytical techniques. In particular, laser induced breakdown spectroscopy (LIBS) is showing to be a very promising, quick and practical technique to detect and measure contaminants and nutrients in fertilizers. Although, this technique presents some limitations, such as a low sensitivity, if compared to other spectroscopic techniques, the use of double pulse (DP) LIBS is an alternative to the conventional LIBS in single pulse (SP). The macronutrients (Ca, Mg, K, P), micronutrients (Cu, Fe, Na, Mn, Zn) and contaminant (Cr) in fertilizer using LIBS in SP and DP configurations were evaluated. A comparative study for both configurations was performed using optimized key parameters for improving LIBS performance. The limit of detection (LOD) values obtained by DP LIBS increased up to seven times as compared to SP LIBS. In general, the marked improvement obtained when using DP system in the simultaneous LIBS quantitative determination for fertilizers analysis could be ascribed to the larger ablated mass of the sample. The results presented in this study show the promising potential of the DP LIBS technique for a qualitative analysis in fertilizers, without requiring sample preparation with chemical reagents.

Signal enhancement in femtosecond laser induced breakdown spectroscopy with a double-pulse configuration composed of two polarizers

Femtosecond double-pulse laser induced breakdown spectroscopy (LIBS) has been performed with a double-pulse configuration composed of two polarizers. The effect of interpulse separation on the Cu I line at 510.55, 515.32, and 521.82 nm showed an optimum enhancement at 50–150 ps delays, which is more than 3–5 times greater compared with the single-pulse excitation case. This enhanced emission may open new possibilities for remote LIBS detection.

Optimization of liquid jet system for laser-induced breakdown spectroscopy analysis

A complex optimization of geometrical and temporal parameters of a jet system (developed in Laser-induced breakdown spectroscopy (LIBS) laboratory of Brno University of Technology) for direct elemental analysis of samples in a liquid state of matter using LIBS was carried out. First, the peristaltic pump was synchronized with the flashlamp of the ablation laser, which reduced variation of the ablated sample amount. Also, the fluctuation of the laser ray angle incident on the jet surface was diminished. Such synchronization reduced signal standard deviations and thus increased repeatability of the measurements. Then, laser energy and distance of the focusing lens from the sample were optimized. The gate delay time and the gate width were optimized for single pulse (SP) experiments; the gate delay time and the inter-pulse delay were optimized for the use of double pulse (DP) variant. Results were assessed according to the highest signal to noise ratios and the lowest relative standard deviations of the signal. The sensitivity of the single pulse and the double pulse LIBS for the detection of heavy metals traces, copper (Cu i at 324.754 nm) and lead (Pb i at 405.781 nm), in aqueous solution of copper (ii) sulfate and lead (ii) acetate, was estimated in terms of limits of detection (LODs). As a result, sensitivity improvement of DP LIBS system was observed, the LOD of Cu obtained with DP was calculated 40% lower than LOD gained from SP technique.

Quantitative determination of copper in a glass matrix using double pulse laser induced breakdown and electron paramagnetic resonance spectroscopic techniques

A series of lithium–lead–borate glasses of a variable copper oxide loading were quantitatively analyzed in this work using two distinct spectroscopic techniques, namely double pulse laser induced breakdown spectroscopy (DP-LIBS) and electron paramagnetic resonance (EPR). DP-LIBS results measured upon a combined nanosecond lasers irradiation running at 266nm and 1064nm pulses of a collinear configuration directed to the surface of borate glass samples with a known composition. This arrangement was employed to predict the electron's temperature (Te) and density (Ne) of the excited plasma from the recorded spectra.The intensity of elements' responses using this scheme is higher than that of single-pulse laser induced breakdown spectroscopy (SP-LIBS) setup under the same experimental conditions. On the other hand, the EPR data shows typical Cu (II) EPR-signals in the borate glass system that is networked at a distorted tetragonal Borate-arrangement. The signal intensity of the Cu (II) peak at g⊥=2.0596 has been used to quantify the Cu-content accurately in the glass matrix. Both techniques produced linear calibration curves of Cu-metals in glasses with excellent linear regression coefficient (R2) values. This study establishes a good correlation between DP-LIBS analysis of glass and the results obtained using EPR spectroscopy. The proposed protocols prove the great advantage of DP-LIBS system for the detection of a trace copper on the surface of glasses.

Comparative Study of Two Methods of Orthogonal Double-Pulse Laser-Induced Breakdown Spectroscopy of Aluminum

Double-pulse laser induced breakdown spectroscopy (DP-LIBS) of aluminum sample is studied experimentally in orthogonal configuration in air. In this configuration, two schemes of reheating and pre-ablation are examined and the results are compared with single pulse one. The effect of delay time between two laser pulses on emission line intensities of plasma is investigated. Some of the parameters that have been involved in different mechanism of signal enhancement such as plasma temperature, sample heating effects, atmospheric effects, and modification of the ablation dynamics are more discussed. Investigation of the effect of laser pulse energy on emission line intensities in single pulse LIBS experiment demonstrate that because of saturation effects the intensities will not increase necessarily by increasing the laser pulse energy. Moreover, the results show that the electron temperature and rate of mass removal in orthogonal configuration of DP-LIBS is higher than that of single pulse with the same total energy. It is suggested that for correct comparison between single and double pulse results, the optimum pulse energy in single pulse should be considered. Overall, our results demonstrate that under optimized conditions the signal enhancement is much more in pre-ablation configuration than re-heating configuration.

A Comparative Study of Single-pulse and Double-pulse Laser-Induced Breakdown Spectroscopy with Uranium-containing Samples.

Laser-induced breakdown spectroscopy (LIBS) holds potential advantages in special nuclear material (SNM) sensing and nuclear forensics, which require rapid analysis, minimal sample preparation, and stand-off distance capability. SNM, such as U, however, result in crowded emission spectra with LIBS, and characteristic emission lines are challenging to discern. It is well-known that double-pulse LIBS (DPLIBS) improves the signal intensity for analytes over conventional single-pulse LIBS (SPLIBS). This study investigates the U signal in a glass matrix using DPLIBS and compares it to signal obtained using SPLIBS. Double-pulse LIBS involves sequential firing of a 1.06 µm Nd:YAG pre-pulse and 10.6 µm TEA CO2 heating pulse in a near collinear geometry. Optimization of experimental parameters including inter-pulse delay and energy follows identification of characteristic lines for the bulk analyte Ca and the minor constituent analyte U for both DPLIBS and SPLIBS. Spatial and temporal coupling of the two pulses in the proposed DPLIBS technique yields improvements in analytical merits with a negligible increase in damage to the sample compared to SPLIBS. Subsequently, the study discusses optimum plasma emission conditions of U lines and relative figures of merit in both SPLIBS and DPLIBS. Investigation into plasma characteristics also addresses plausible mechanisms related to the observed U analyte signal variation between SPLIBS and DPLIBS.

Double-pulse neodymium YAG/Carbon dioxide laser-induced breakdown spectroscopy for excitation of bulk and trace analytes

ABSTRACTThe mechanisms involved in signal enhancement and persistence of the plasma in double-pulse laser-induced breakdown spectroscopy are investigated, and their implications to improving figures of merit for bulk and trace analytes in sample are discussed. For double-pulse laser-induced breakdown spectroscopy, 1064 nm neodymium YAG laser is used for ablation and 10.6 µm transversely excited atmospheric carbon dioxide laser in near-collinear geometry is used for reheating. Significant improvement in signal detection and sensitivity of both bulk and trace analytes using double-pulse laser-induced breakdown spectroscopy as compared to conventional single-pulse laser-induced breakdown spectroscopy are observed. Using double-pulse laser-induced breakdown spectroscopy in near-collinear geometry, Cu and Fe as bulk and trace analytes, respectively, in brass sample, showed 5 and 6 times improvement in persistence of the spectral emission. Temporal and time-integrated studies show that ionic lines are significantly enhanced compared to neutral lines. Plasma characterization employing spectroscopic methods showed significant enhancement in plasma temperature resulting in higher signal as well as increased plasma persistence of the species studied.

Measurements of deuterium retention and surface elemental composition with double pulse laser induced breakdown spectroscopy

Estimating the tritium amount retained in the plasma facing components and their surface layer composition is of crucial importance for ITER. Laser-induced breakdown spectroscopy (LIBS) is an analytical technique suitable for in situ measurements of both these quantities. For improving its sensitivity, the double pulse (DP) variant can be used, instead of the standard single pulse (SP). In this work Mo samples coated with 1.5–1.8 μm thick W–Al (as a proxy for Be) mixed layer, with co-deposited deuterium were analyzed under vacuum (∼5 × 10−5 mbar) by SP and DP LIBS, showing enhancement of the spectral intensity for the latter. Calibration free method was applied to the LIBS data for getting the elemental concentration of W and Al. Results are in satisfactory agreement with those obtained from preliminary, ion beam analysis measurements. Deuterium concentration was tentatively estimated by accounting for the intensity ratio between Dα and nearby WI lines.

Laser-induced breakdown spectroscopy analyses of tungsten surfaces

Tungsten (W) surfaces are analyzed with laser-induced breakdown spectroscopy (LIBS). Interactions of W with nanosecond (ns) and femtosecond (fs) laser pulses are found to be quite different in terms of the ambient Ar gas pressure dependence of the average ablation rate and W I line intensity. Collinear double-pulse LIBS (115 + 115 mJ) using two ns lasers (with interpulse separation Δt12 = 5.32 μs) improves the signal-to-noise ratio over the whole Ar pressure range PAr = 6.7 × 10−1 − 6.7 × 104 Pa in contrast with single-pulse LIBS (SP-LIBS) with 230 mJ, where a signal enhancement by a factor of ∼2–3 is obtained only at PAr > 103 Pa. SP-LIBS with a ns laser has succeeded in obtaining a sharp transition between thin W layer with a thickness of ∼100 nm and the graphite substrate. A He I (587.5 nm) line has been successfully detected with SP-LIBS with a ns laser from W containing He bubbles (∼20–30 nm layers) in the near-surface region.

Signal Detection of Carbon in Iron-Based Alloy by Double-Pulse Laser-Induced Breakdown Spectroscopy**supported by National Natural Science Foundation of China (No. 51374040) and the National Key Scientific Instrument and Equipment Development Project of China (No. 2014YQ120351)

Although single-pulse lasers are often used in traditional laser-induced breakdown spectroscopy (LIBS) measurements, their measurement outcomes are generally undesirable because of the low sensitivity of carbon in iron-based alloys. In this article, a double-pulse laser was applied to improve the signal intensity of carbon. Both the inter-pulse delay and the combination of laser wavelengths in double-pulse laser-induced breakdown spectroscopy (DP-LIBS) were optimized in our experiment. At the optimized inter-pulse delay, the combination of a first laser of 532 nm and a second laser of 1,064 nm achieved the highest signal enhancement. The properties of the target also played a role in determining the mass ablation enhancement in DP-LIBS configuration.