Laser-induced Breakdown Spectroscopy Setup Research Articles

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.

Quantitative analysis of metal scraps using laser-induced breakdown spectroscopy measurements via unsupervised adversarial domain adaptation

In this study, we propose a domain adaptation-based scheme for the compositional analysis of metal scraps using laser-induced breakdown spectroscopy (LIBS) measurements. LIBS analysis along with machine learning models has demonstrated feasibility for estimating elemental compositions of various materials such as metal scraps. However, LIBS-captured spectra can significantly vary depending on the physical and chemical properties of samples, configuration of the experimental setup, and prevailing environmental conditions such as temperature or humidity levels. Consequently, schemes based on calibration methods and the formulation of experimental parameters have been previously proposed by assuming that the training set is acquired under the same setup and conditions as the test set. Furthermore, current transfer learning solutions simply limit the pretrained model on the new test set, thus requiring a labeled test set in advance for finetuning. To address these limitations, this study proposes a novel transfer learning-based approach that depends on the domain adaptation of a source domain to transfer knowledge and reduce the difference between domains, and thus improving the performance of the target learner. We used LIBS measurements from certified reference materials (CRMs) to pretrain a source model to estimate the elemental concentration with known compositions of CRM metal samples. Then, the pretrained model is adapted in an unsupervised manner for the test/target dataset, and the adapted target model is used to quantify the elemental concentration of metal scraps. For evaluation, the CRMs of five representative metal types, including aluminum, copper, iron, stainless steel, and brass of known compositions, are measured under a typical LIBS setup to develop the pretrained model. For unsupervised domain adaptation and testing, metal scraps from actual industrial fields are tested using LIBS under different conditions such as lasers of different wavelengths and moving stages. The experimental results demonstrate that the proposed scheme achieves a root mean square error of 1.47 wt% or less for all test datasets, which is significantly better than the results of conventional regression schemes. The proposed quantitative analysis approach can be generalized to the regression of metal scraps and other industrial applications using LIBS.

Inline process analysis of copper-bearing aerosols using laser-induced breakdown spectroscopy, laser-induced incandescence and optical imaging

The quantification and identification of aerosols in industry plays a key role in process monitoring and control and lays the foundation for process automation aspired by the industry 4.0 initiative. However, measuring particulate matter's mass and number concentrations in harsh environments poses great analytical constraints. The presented approach comprises a comprehensive set of light- and imaging-based techniques, all contactless, in-line, and real-time. It includes, but is not limited to, stroboscopic imaging, laser-induced breakdown spectroscopy (LIBS) and laser-induced incandescence (LII). Stroboscopic imaging confirmed the particles sphericity and was used to measure the particle number density. A phase-selective LIBS setup with low fluence and 500 Hz repetition rate was used to classify each particle with a single-pulse and in real time. Simultaneously, the created plasma was captured by CCD imaging to determine the detection volume and hit rate of the LIBS setup. Both data sets combined were converted to a particle number density, which was consistent with the particle number density of the stroboscopic measurements. Furthermore, using a photodiode and microphone in parallel to the LIBS setup allowed for the photoacoustic normalization of the spectral line intensity at the laser repetition rate of 500 Hz. This was done as a partial photoacoustic normalization method with the cut-off based on the coefficient of variation (CV), reducing it by 25%. Aside from that photodiode and microphone were proven to be valuable event counting with the advantage of the less spatially constricted. A second laser setup was used for laser-induced incandescence (LII) making it possible to classify the particles based on their incandescence tendency. Given its larger probing volume, LII could be employed at very low particle number densities. With respect to the current literature, this is the first approach of using LII as an in-line, real-time analytical technique for the compositional classification of metal-bearing aerosols.

Detection of hypokalemia disorder and its relation with hypercalcemia in blood serum using LIBS technique for patients of colorectal cancer grade I and grade II.

Cancer continues to be the most dangerous disease around the world; it causes electrolyte imbalance as well as metabolic changes. There is a complicated relationship between electrolyte disorder and cancer. Cancer patients commonly pass with abnormalities in serum electrolyte levels such as hypokalemia, hyperkalemia, hyponatremia, and hypercalcemia. So, these electrolyte imbalances indicate the existence of paraneoplastic processes and help come to a more informed prognosis. Hypokalemia is defined as a serum potassium concentration below 3.5mmol/L and it is the second common electrolyte imbalance seen in patients with malignant diseases. In this paper, the contribution of serum potassium concentration to tumor progression was studied by applying a promising and non-invasive technique called laser-induced breakdown spectroscopy (LIBS). It was found that there is a correlation between hypokalemia and the colorectal cancer problem. Also, significant serum potassium concentration differences were detected among two different stages of the same cancer and also between two groups of the same stage of a cancer held in common but one of them suffers from hypercalcemia. In addition, the optimum conditions of LIBS setup were arranged such that it will be suitable to work with serum samples on glass substrate.

LIBS technique combined with blow gas and vacuum suction to remove particle cloud and enhance emission intensity during characterization of powder samples

The present study reports developing a bench-top Laser-Induced Breakdown Spectroscopy (LIBS) set up for the online analysis of powder samples without sample preparation. The powder particle blow-off during pulsed laser ablation was mitigated by adding a blow gas (an inert gas blown across the ablation surface) and a suction unit (for extraction of the blow gas and blown-off particle cloud) to the existing LIBS setup. The influence of a blow-gas combined with a suction unit on LIBS emission intensity from coal powder and flyash particles is studied in the present work. The effect of the blow gas flow rate and the suction pressure was studied on the LI-BS emission intensity and removal of the laser blown-off particle cloud. The combination gas flow at 2 lpm (liter per minute) flow rate and suction at 925 mbar (absolute) show an increase in the LIBS emission intensity and effective particle removal. The ratio of LIBS emission intensity of the powder sample and solid-target (pellet) sample improved from 0.25 without the Ar gas flow and the suction unit to 0.85, which is by a factor of 3.4 times with the proposed approach.

Optimization of laser-induced breakdown spectroscopy parameters from the design of experiments for multi-element qualitative analysis in river sediment

Laser-induced breakdown spectroscopy (LIBS) is a fast, low analytical cost, environmentally clean technique that does not require the use of reagents for sample preparation. However, regardless of the LIBS setup, it has limitations in terms of sensitivity and precision, especially when applied to complex samples, such as river sediment. To overcome these limitations, in this work, different experimental parameters were optimized for multi-element analysis of a river sediment sample using design of experiments (DOE) approaches, i.e., fractional factorial and central composite designs (CCD). The findings demonstrated that DOE applied to the LIBS technique can be used as an efficient tool for optimizing the key parameters affecting sediment analysis by LIBS.

Forensic Analysis of Commercial Inks by Laser-Induced Breakdown Spectroscopy (LIBS).

Laser-induced breakdown spectroscopy (LIBS) was tested for all of the relevant issues in forensic examinations of commercial inks, including classification of pen inks on one paper type and on different paper types, determination of the deposition order of layered inks, and analysis of signatures and toners on one questioned document. The scope of this work was to determine the potential of a single LIBS setup that is compatible with portable instruments for different types of ink analysis, rather than building a very large database for inks and papers. We identified up to seven metals characteristic for the examined inks, which allowed to fully discriminate all eight black inks on one type of printing paper. When the inks were tested on ten different papers, the correct classification rates for some of them were reduced for reasons thoroughly studied and explained. The replicated tests on three crossing points, each one involving a pair of blue or black inks, were successful in five cases out of six. In the test simulating documents of forensic interest (questioned documents), LIBS was able to correctly identify the differences in three inks used for signatures on one of the three pages and the use of different printing inks on each page of the document.

Double pulse laser induced breakdown spectroscopy at 600 bar water pressure

The demand for raw materials is growing and deep-sea mining is becoming increasingly important. It is of great interest to be able to analyze materials directly in the deep sea for mining or research applications. Laser induced breakdown spectroscopy (LIBS) is a laser-based, non-contact method for analyzing material in terms of its elemental composition. This paper presents the design of a LIBS system to be operated in a water depth of up to 6000 meters. A compact double pulse laser with adaptable pulse interval was developed to address different water depths. The complete LIBS setup was tested in a pressure chamber and shows emission lines from zinc up to a water pressure of 600 bar. To the best of our knowledge, this was the first LIBS measurement at 600 bar water pressure.

Accuracies of lithium, boron, carbon, and sulfur quantification in geological samples with laser-induced breakdown spectroscopy in Mars, Earth, and vacuum conditions

Laser-induced breakdown spectroscopy (LIBS) is valued for its ability to remotely detect a wide range of elements, including light elements, under a variety of atmospheric conditions. This study uses LIBS spectra of 402 rock standards to quantify lithium (Li), boron (B), carbon/carbon dioxide (C/CO2), and sulfur (S) in Mars and Earth atmospheres and under vacuum. Two regression methods were tested: univariate analysis (UVA), here using peak areas to predict concentrations, and multivariate analysis (MVA). Partial least squares (PLS) and the least absolute shrinkage and selection operator (lasso) use information from larger regions of LIBS spectra. Rock powders were doped with up to 10 wt% of each light element to help identify strongly correlated peaks for UVA. UVA and MVA models were assessed using root mean square errors (RMSEs) of cross-validation (CV), calibration RMSEs, and R2 correlation between predicted and true concentrations. Li had the most strongly correlated peaks, similar UVA and MVA model performance, and the lowest relative prediction errors. B and C had few weakly-correlated peaks, leading to extremely poor UVA R2 correlations despite having similar RMSEs to MVA models with mediocre performance. S had no visible peaks in our LIBS setup and as a result, MVA models had extremely high prediction errors. Model performance was not significantly affected by atmospheric differences despite visible changes in peak appearance, as long as model and test data were acquired under identical conditions. PLS regression on the entire LIBS spectrum consistently created models with the lowest quantification errors and highest R2 correlations. Light element predictions may be improved using higher resolution, gated spectrometers that cover a wider wavelength range than those used in our setup, which matches ChemCam.

Echelle LIBS-Raman system: A versatile tool for mineralogical and archaeological applications

There are a number of analytical techniques used to study material related problems. Most of them imply experimental determination of parameters and functions by means of which elemental, optical and other properties of materials can be described. Laser Induced Breakdown Spectroscopy (LIBS) and Raman spectroscopy are highly complementary spectroscopic techniques used for lab, in-situ, and remote analyses of materials. The LIBS-Raman system provides further information compared to other conventional techniques since it can detect the presence of low atomic number-elements, isotopic composition, hydration and structure of trace materials which may be present as surface layers etc., which are very difficult, if not impossible, by portable X-ray based systems. A setup for LIBS and Raman spectroscopy measurements in a single unit has been developed and reported recently by us using an echelle spectrograph system. The system utilizes a single nanosecond pulsed Nd:YAG laser (532 nm) and an ICCD coupled echelle spectrograph for both measurements. The unit has been successfully used for multipurpose applications such as identification of minerals, pigments etc and also for checking quality assurance. The combined atomic and molecular information from the same location on a sample, at several locations, can provide more comprehensive information regarding its properties than using either of these quantities taken singly. In many cases, it has been observed that the high resolution of the echelle spectrograph provides better quality Raman signals by virtue of the small degeneracy/crystal field splitting of many fundamental Raman bands. This can provide valuable information on inclusions in bulk samples, changes due to symmetry alteration or complex formation with surroundings, hydrogen bonding etc. The advantage of echelle system to identify natural and artificial pigments by identifying the minor and trace components by the spectra of the elements therein, is also helpful in many situations. In the present paper, the orthogonal use of LIBS and Raman spectroscopy is assessed and highlighted. The results clearly demonstrate the potential of echelle-based LIBS-Raman system in applications where more detailed information on complex samples like minerals, archaeological artifacts etc, is required with minimum sample damage or consumption.

Influence of laser wavelength and laser energy on depth profiling of easel painting samples

The depth-resolved analysis by means of the laser-induced breakdown spectroscopy (LIBS) is a useful tool in the investigation of multi-layered structures of paintings. The LIBS technique is considered micro-destructive, as it is associated with the formation of the ablation crater. It is important to optimize the laser pulse parameters to minimize the crater size and also to avoid some possible side effects of the laser radiation, such as the material redeposition and the light- or heat-induced pigment discoloration. In the present work, mock-up painting samples were used to investigate the influence of laser radiation characteristics on the ablation process. The first LIBS set-up contains a Nd:YAG laser at the second harmonic frequency (laser wavelength 532 nm, pulse duration ~ 10 ns) and the second set-up is comprised of a modified laser-ablation system equipped with a Nd:YAG laser at the fourth harmonic frequency (laser wavelength 266 nm, pulse duration ~ 5 ns). The influence of different laser wavelengths and different laser energies on the properties of the craters was examined. The effects caused by the laser-ablation process were described.

Pre-bond surface inspection using laser-induced breakdown spectroscopy for the adhesive bonding of multiple materials

To inspect surface contamination of the surfaces for adhesive bonding, laser-induced breakdown spectroscopy (LIBS) was examined. A LIBS setup which gave an improved limit of detection (LOD) of 5.29 mg mm−2 was used for evaluation of Si contamination on steel and CFRP substrates. The LOD values obtained were 1.35 and 11.4 mg mm−2 for steel and CFRP, respectively. These LOD values were affected by several factors such as efficiency of energy transfer to Si and interference with trace substances included in the surface layer of substrates. Silicone included in the resin layers of CFRP was investigated by multiple pulse LIBS measurements.

Listening to laser sparks: a link between Laser-Induced Breakdown Spectroscopy, acoustic measurements and crater morphology

In preparation for the SuperCam/Mars Microphone scientific investigation, the acoustic signal associated with the plasma formation during Laser-Induced Breakdown Spectroscopy (LIBS) experiment is studied with regard to the shot-to-shot evolution of the laser induced crater morphology and plasma emission lines. A set of geological targets are depth profiled using a specifically designed LIBS setup coupled with acoustic test bench under ambient terrestrial atmosphere. Experiments confirm that the decrease of the acoustic energy as a function of the number of shots is well correlated with the target hardness/density and also demonstrate that the acoustic energy can be used as a remote tracer of the ablated volume of the target. Listening to LIBS sparks provides a new information relative to the ablation process that is independent from the LIBS spectrum.

Laser-based Diagnostics for Use in Ex-situ Lithium Co-deposit Analysis

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Optimized laser-induced breakdown spectroscopy for the determination of high toxic lead in edible colors.

An optimized laser-induced breakdown spectroscopy (LIBS) system was utilized as a robust tool for the detection of high toxic lead (Pb) in often used edible colors available in local markets. Edible colors are extensively used in different food stuffs and sweet dish items. To attain a highly sensitive LIBS system for the determination of trace amounts of toxic Pb in edible colors and to achieve the best detection limit, various parametric dependence studies were performed. The quantitative determinations were accomplished under the condition of local thermodynamic equilibrium in terms of optically thin plasma. Besides toxic Pb, other elements like Ca, Mg, Fe, and Na were also detected in edible colors. To estimate the concentration of toxic lead in edible colors, calibration curves were plotted by preparing standard samples of different lead concentrations in an edible colors matrix. Results of the LIBS technique were compared with the outcomes of the same samples studied using a standard analytical technique of inductively coupled plasma-optical emission spectroscopy to confirm the contemporary LIBS setup. The color samples were found above the safe permissible level due to the mass of toxic lead. Limit of detection of the LIBS setup was found at 0.86+/-0.03 ppm for toxic lead present in edible color samples.

Optimized laser-induced breakdown spectroscopy for determination of xenobiotic silver in monosodium glutamate and its verification using ICP-AES

Laser-induced breakdown spectroscopy (LIBS) was applied as a potential tool for the determination of xenobiotic metal in monosodium glutamate (MSG). In order to achieve a high-sensitivity LIBS system required to determine trace amounts of metallic silver in MSG and to attain the best detection limit, the parameters used in our experiment (impact of focusing laser energy on the intensity of LIBS emission signals, the influence of focusing lens distance on the intensity of LIBS signals, and time responses of the plasma emissions) were optimized. The spectra of MSG were obtained in air using a suitable detector with an optical resolution of 0.06nm, covering a spectral region from 220 to 720nm. Along with the detection of xenobiotic silver, other elements such as Ca, Mg, S, and Na were also detected in MSG. To determine the concentration of xenobiotic silver in MSG, the calibration curve was plotted by preparing standard samples having different silver abundances in an MSG matrix. The LIBS results of each sample were cross-verified by analyzing with a standard analytical technique such as inductively coupled plasma-atomic emission spectroscopy (ICP-AES). Both (LIBS and ICP-AES) results were in mutual agreement. The limit of detection of the LIBS setup was found to be 0.57ppm for silver present in MSG samples.

Alternative analytical method for direct determination of Mn and Ba in peppermint tea based on laser induced breakdown spectroscopy

In this study, analytical capability of Laser Induced Breakdown Spectroscopy (LIBS) system based on Transversely Excited Atmospheric pressure (TEA) CO2 laser for determination of elemental composition of tea samples was demonstrated. Analysis of LIBS spectra indicated emission lines attributed to the elements Fe, Mg, Cu, Ca, Al, Mn, Ba, P, K and Sr. For quantitative analysis of Mn and Ba, a standard addition method was employed. Linear calibration curves with regression coefficients exceeding 0.95 were obtained. The accuracy of LIBS results was confirmed by inductively coupled plasma optical emission spectroscopy (ICP-OES) analysis. Calculated recoveries for Ba and Mn were 99.7 and 102.3%, respectively. The results presented confirm the suitability of the proposed LIBS setup for rapid quantitative analysis of tea, while at the same time simplifying the overall analytical procedure. This approach can be easily used as a helpful analytical tool for food quality and safety control.

Three dimensional characterization of laser ablation craters using high resolution X-ray computed tomography

Laboratory X-ray computed tomography is an emerging technology for the 3D characterization and dimensional analysis of many types of materials. In this work we demonstrate the usefulness of this characterization method for the full three dimensional analysis of laser ablation craters, in the context of a laser induced breakdown spectroscopy setup. Laser induced breakdown spectroscopy relies on laser ablation for sampling the material of interest. We demonstrate here qualitatively (in images) and quantitatively (in terms of crater cone angles, depths, diameters and volume) laser ablation crater analysis in 3D for metal (aluminum) and rock (false gold ore). We show the effect of a Gaussian beam profile on the resulting crater geometry, as well as the first visual evidence of undercutting in the rock sample, most likely due to ejection of relatively large grains. The method holds promise for optimization of laser ablation setups especially for laser induced breakdown spectroscopy.

Long-Wave Infrared (LWIR) Molecular Laser-Induced Breakdown Spectroscopy (LIBS) Emissions of Thin Solid Explosive Powder Films Deposited on Aluminum Substrates.

Thin solid films made of high nitro (NO2)/nitrate (NO3) content explosives were deposited on sand-blasted aluminum substrates and then studied using a mercury-cadmium-telluride (MCT) linear array detection system that is capable of rapidly capturing a broad spectrum of atomic and molecular laser-induced breakdown spectroscopy (LIBS) emissions in the long-wave infrared region (LWIR; ∼5.6-10 µm). Despite the similarities of their chemical compositions and structures, thin films of three commonly used explosives (RDX, HMX, and PETN) studied in this work can be rapidly identified in the ambient air by their molecular LIBS emission signatures in the LWIR region. A preliminary assessment of the detection limit for a thin film of RDX on aluminum appears to be much lower than 60 µg/cm2. This LWIR LIBS setup is capable of rapidly probing and charactering samples without the need for elaborate sample preparation and also offers the possibility of a simultaneous ultraviolet visible and LWIR LIBS measurement.

An exploratory study of the potential of LIBS for visualizing gunshot residue patterns

The study of gunshot residue (GSR) patterns can assist in the reconstruction of shooting incidences. Currently, there is a real need of methods capable of furnishing simultaneous elemental analysis with higher specificity for the GSR pattern visualization. Laser-Induced Breakdown Spectroscopy (LIBS) provides a multi-elemental analysis of the sample, requiring very small amounts of material and no sample preparation. Due to these advantages, this study aims at exploring the potential of LIBS imaging for the visualization of GSR patterns. After the spectral characterization of individual GSR particles, the distribution of Pb, Sb and Ba over clothing targets, shot from different distances, were measured in laser raster mode. In particular, an array of spots evenly spaced at 800μm, using a stage displacement velocity of 4mm/s and a laser frequency of 5Hz was employed (e.g. an area of 130×165mm2 was measured in less than 3h). A LIBS set-up based on the simultaneous use of two spectrographs with iCCD cameras and a motorized stage was used. This set-up allows obtaining information from two different wavelength regions (258–289 and 446–463nm) from the same laser induced plasma, enabling the simultaneous detection of the three characteristic elements (Pb, Sb, and Ba) of GSR particles from conventional ammunitions. The ability to visualize the 2D distribution GSR pattern by LIBS may have an important application in the forensic field, especially for the ballistics area.