Typical Laser-induced Breakdown Spectroscopy Research Articles

Laser‐Induced Breakdown Spectroscopy Online Quantitative Analysis for Laser Processing

Plasma fluctuations, the uncertainty of laser ablation, and bremsstrahlung limit the identification of online element analysis during laser processing and cause difficulty in achieving concentration results with sufficient accuracy and repeatability. A laser‐induced breakdown spectroscopy (LIBS) online monitoring system with plasma spatial filtering and spectral screening is proposed to solve this problem. In this system, the high‐frequency ablation noise component of the plasma is eliminated using a specially designed optical Fourier filtering structure, and a spectral screening system based on plasma time waveform monitoring is used to suppress the influence of plasma fluctuations. Without noise filters or algorithm optimizations and based only on the basic internal standard method, the calibration curves of all nine elements in the alloy sample exhibits a Pearson's R2 value ranged from 0.91 to 0.99, with a mean of 0.94. The relative standard deviations are all in the range of 3.5%–8.4% with a mean of 5.4%. The accuracy and repeatability are comparable to those of typical LIBS systems.

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.

Spectral enhancement mechanism and analysis of defocused collinear DP-LIBS technology

Laser-induced breakdown spectroscopy (LIBS) is a modern analytical technique emerging in recent years, which widely used in qualitative and quantitative determination of various samples. However, because the plasma spectral enhancement mechanism of the two typical LIBS technologies(pre-ablation and reheating LIBS) varies greatly, how to choose the spectral enhancement solution and rationally configure the LIBS system in different applications still needs further research and discussion. In this paper, we constructed a defocusing collinear dual-pulse LIBS(DP-LIBS) experimental system, and carried out relevant experiments for pre-ablation and reheating plasma spectral enhancement, and studied separately the effects of ablation sampling, reheating and re-excitation of plasma in collinear DP-LIBS. The experimental results show that the pre-ablation defocus collinear DP-LIBS is an indirect spectral enhancement technology, which uses the pre-ablation laser to change the surface environment of the sample, so that the sample is more conducive to the excitation of plasma, thus achieving spectral enhancement. The spectral and ablative crater analysis of the reheating defocus collinear DP-LIBS show that it enhances the spectral signal by reheating and re-exciting the plasma by the second laser beam, which is a direct spectral enhancement technology and has better enhancement effect than indirect enhancement technologies such as pre-ablation DP-LIBS. In addition, the laser inter-pulse delay time is an important factor in maintaining the temperature of the plasma to sustain the atomic radiation. Under different spectral enhancement solution, proper configuration of laser inter-pulse delay time is the key factor to obtain high spectral intensity and good signal-to-noise ratio.

Assessment of laser induced breakdown spectroscopy accuracy for determination of hydrogen accumulation in tungsten

• The influence of various factors on a relative error of determination of H content in a sample by LIBS using the Saha-Boltzmann (SB) plot is investigated. • It is shown that for typical LIBS pulse parameters (10 9 W/cm 2 , 12 ns duration) the error can be quite large, about 70%. • Even in the case of largest error SB plot remains a straight line making it difficult to anticipate the error from the experimental results. • The pulse power increase tends to reduce the relative error. Laser-induced breakdown spectroscopy (LIBS) is an in situ method of determining hydrogen (H) content in plasma-facing materials in tokamak fusion reactors. Observing radiation from the plasma plume produced by a powerful laser pulse during the target exposition characterizes the sample composition. This is typically accomplished using the Saha-Boltzmann (SB) plot technique under local thermodynamic equilibrium (LTE) conditions. Despite many experimental studies dedicated to applying LIBS to determine H isotope retention in fusion reactor materials, the current understanding of this method’s intrinsic accuracy remains inadequate. In this report, we use numerical calculations to estimate the relative error of determining H content in a sample using LIBS. As an example. we consider LIBS to study a W sample loaded with H in a vacuum. Under typical LIBS pulse parameters (10 9 W/cm 2 and 12 ns duration), the error can be quite large, approximately 70%. We demonstrate that the error tends to decrease as the laser pulse intensity increases. Various factors contributing to the relative error are examined and their dependence on the LIBS plasma parameters is discussed. The SB plot remains a straight line even when LTE conditions are violated, making it difficult to anticipate the experimental results’ error.

Methodology for the Implementation of Internal Standard to Laser-Induced Breakdown Spectroscopy Analysis of Soft Tissues.

The improving performance of the laser-induced breakdown spectroscopy (LIBS) triggered its utilization in the challenging topic of soft tissue analysis. Alterations of elemental content within soft tissues are commonly assessed and provide further insights in biological research. However, the laser ablation of soft tissues is a complex issue and demands a priori optimization, which is not straightforward in respect to a typical LIBS experiment. Here, we focus on implementing an internal standard into the LIBS elemental analysis of soft tissue samples. We achieve this by extending routine methodology for optimization of soft tissues analysis with a standard spiking method. This step enables a robust optimization procedure of LIBS experimental settings. Considering the implementation of LIBS analysis to the histological routine, we avoid further alterations of the tissue structure. Therefore, we propose a unique methodology of sample preparation, analysis, and subsequent data treatment, which enables the comparison of signal response from heterogenous matrix for different LIBS parameters. Additionally, a brief step-by-step process of optimization to achieve the highest signal-to-noise ratio (SNR) is described. The quality of laser–tissue interaction is investigated on the basis of the zinc signal response, while selected experimental parameters (e.g., defocus, gate delay, laser energy, and ambient atmosphere) are systematically modified.

Two-lines method for estimation of plasma temperature and characterization of plasma parameters in optically thick plasma conditions.

In this paper, the characteristics of laser-induced plasmas are studied by investigation of the spectral line features in laser-induced breakdown spectroscopy (LIBS) experiments. The plasma is produced by focusing of a Nd:YAG laser on standard Al-alloy samples at 30 mJ energy. Here, with the assumption of having a homogenous plasma and by using a semiemperical technical method, the plasma temperature is calculated by the proposal of a new two-lines method. Moreover, by utilizing some theoretical equations, the plasma parameters and the self-absorption magnitude are evaluated according to the radiative transfer equations in local thermodynamic equilibrium (LTE) conditions. The main advantages of this method are that without discrimination between thin plasmas and thick ones, and as well as without straight quantification of the degree of self-absorption, the plasma temperature can be calculated. The results showed that determination of the intensities of the spectral lines, transition parameters, and Stark broadening parameter is adequate for plasma characterization in a typical LIBS experiment.

Applications of laser‐induced breakdown spectroscopy for soil characterization, part II: Review of elemental analysis and soil classification

AbstractIn‐field soil health assessments, including plant nutrients and toxic elements, are needed and could improve the sustainability of agriculture production. Among the available analytical techniques for these analyses, laser‐induced breakdown spectroscopy (LIBS) has become one of the most promising techniques for real‐time soil analysis at low cost and without the need for reagents. The first part of this two‐part review (Part I, Villas‐Boas, P.R., de Franco, M.A., Gollany, H.T., Martin‐Neto, L. & Milori, D.M.B.P. 2019. Applications of laser‐induced breakdown spectroscopy for soil characterization, Part I: Review of Fundamentals and Chemical and Physical Properties.) in this issue focused on the fundamentals of LIBS for soil analysis and its use for soil chemical and physical characterization. Our objectives in this review article (Part II) are to review (a) the main applications of LIBS in the determination of soil carbon (C), nutrients and toxic elements, spatial elemental mapping, and (b) its use in soil classification. Traditional and more recent techniques will be compared to LIBS, considering their advantages and disadvantages. Laser‐induced breakdown spectroscopy is a promising, versatile technique for detecting many elements in soil samples, requires little or no sample preparation, takes only a few seconds per sample, and has a low cost per sample compared to other techniques. However, overcoming matrix effects is a challenge for LIBS applications in soil analysis, because most studies are conducted with limited changes in the matrix. In spite of the limitation of matrix effects, a typical LIBS system has a limit of detection of 0.3, 0.6, 4, 7, 10, 18, 46 and 89 mg kg−1for Mo, Cu, Mg, Mn, Fe, Zn, K and Ca, respectively. Laser‐induced breakdown spectroscopy holds potential for real‐time in‐field spatial elemental analysis of soils and practical applications in precision farming with proper calibration. This could lead to immediate diagnoses of contaminated soil and inefficient nutrient supplies and facilitate well‐informed soil management, increasing agricultural production while minimizing environmental impacts.HighlightsLaser‐induced breakdown spectroscopy (LIBS) is a fast analytical technique with great potential for elemental mapping of soils.Elemental analyses of soil and plants and soil classification by LIBS are reviewed.Soil and rhizosphere spatial elemental analyses by LIBS are presented.LIBS advantages, limitations and challenges are discussed for soil elemental analysis.

Observation of dual-peak signal-to-noise ratios from plasmas produced in typical laser-induced breakdown spectroscopy (LIBS) experiments

In this work, emission properties of representative trace and major species in steel plasma plumes produced in typical laser-induced breakdown spectroscopy (LIBS) experiments under standard atmospheric conditions are investigated. The correlation between laser fluence and spatially integrated measurements of emission characteristics of the plasma at a typical delay time of 2 µs from the laser pulse onset is thoroughly explored. Q-switched neodymium-doped yttrium aluminum garnet (Nd: YAG) laser emitting at its fundamental wavelength of 1064 nm was employed to generate the plasmas under investigation. The results showed that the signal-to-noise ratio of all lines investigated exhibit irregular behaviour in which two maxima can be identified at specific laser fluence values. This behaviour is attributed to lower standard deviation of the background intensity indicating stable plasma conditions relevant for spectrochemical analysis. Plasma shielding of the incident laser energy, due to electron-atom inverse bremsstrahlung (IB), becomes more critical beyond laser fluencies larger than about 45 J cm-2.

State-to-state modeling of ultrashort laser-induced plasmas

The question of the Local Thermodynamic Equilibrium (LTE) of laser-induced plasmas is crucial regarding the Laser-Induced Breakdown Spectroscopy (LIBS) technique. The most relevant way to assess theoretically the possible departure from LTE is to develop state-to-state models of the chemical species involved. The present paper illustrates such an elaboration in the case of aluminum and tungsten. Based on this state-to-state approach, the two collisional-radiative models CoRaM-Al and CoRaM-W are elaborated. They include elementary processes under electron and heavy particle impact in thermal non-equilibrium, spontaneous emission, radiative recombination and thermal Bremsstrahlung. These models are applied to the case of ultrashort laser-induced plasmas expanding in an argon gas at different pressure, for which a relevant collisional-radiative model is also elaborated to predict the propagation of the shock wave. The laser conditions are close to those used for a typical LIBS analysis under ultrashort regime.At high argon pressure (105Pa), the relaxation of the plasma takes place according to a rather low departure from LTE, as revealed by the thorough examination of the Boltzmann plots derived from the state-to-state models. This relaxation occurs at temperature higher for aluminum than for tungsten, but close to 10,000K from 200ns. Conversely, at low pressure (10Pa), the extinction of the plasma is observed at ∼ 500ns, just after a phase corresponding to significant departure from equilibrium. These results support the idea of the choice of short gate delays close to the laser pulse for the LIBS characterization of tungsten matrices in tokamak-like conditions.

Laser-Induced Plasma Spectroscopy of Hydrogen Balmer Series in Laboratory Air

Stark-broadened emission profiles for the hydrogen alpha and beta Balmer series lines in plasma are measured to characterize electron density and temperature. Plasma is generated using a typical laser-induced breakdown spectroscopy (LIBS) arrangement that employs a focused Q-switched neodymium-doped yttrium aluminum garnet (Nd : YAG) laser, operating at the fundamental wavelength of 1064 nm. The temporal evolution of the hydrogen Balmer series lines is explored using LIBS. Spectra from the plasma are measured following laser-induced optical breakdown in laboratory air. The electron density is primarily inferred from the Stark-broadened experimental data collected at various time delays. Due to the presence of nitrogen and oxygen in air, the hydrogen alpha and beta lines become clearly discernible from background radiation for time delays of 0.4 and 1.4 μs, respectively.

Time-resolved characterization of laser-induced plasma from fresh potatoes

Optical emission of laser-induced plasma on the surface of fresh vegetables provides sensitive analysis of trace elements for in situ or online detection of these materials. This emergent technique promises applications with expected outcomes in food security or nutrition quality, as well as environment pollution detection. Characterization of the plasma induced on such soft and humid materials represents the first step towards quantitative measurement using this technique. In this paper, we present the experimental setup and protocol that optimize the plasma generation on fresh vegetables, potatoes for instance. The temporal evolution of the plasma properties are investigated using time-resolved laser-induced breakdown spectroscopy (LIBS). In particular, the electron density and the temperatures of the plasma are reported as functions of its decay time. The temperatures are evaluated from the well known Boltzmann and Saha-Boltzmann plot methods. These temperatures are further compared to that of the typical molecular species, CN, for laser-induced plasma from plant materials. This comparison validates the local thermodynamic equilibrium (LTE) in the specific case of fresh vegetables ablated in the typical LIBS conditions. A study of the temporal evolution of the signal to noise ratio also provides practical indications for an optimized detection of trace elements. We demonstrate finally that, under certain conditions, the calibration-free LIBS procedure can be applied to determine the concentrations of trace elements in fresh vegetables.

Evaluation of a compact spectrograph for in-situ and stand-off Laser-Induced Breakdown Spectroscopy analyses of geological samples on Mars missions

Laser-induced Breakdown Spectroscopy (LIBS) is actively under development for future use on surface probes to Mars. The analytical method can be deployed for in-situ and/or stand-off analysis with the latter embodiment providing the greatest advantages compared to previous and current elemental analysis methods used for planetary surface analysis. For this application, LIBS must be thoroughly investigated in terms of analytical capabilities and flight-rated instruments must be developed. Because of the low pressure of the predominantly CO 2 atmosphere on Mars, studies are needed to understand analytical requirements and to determine performance under these conditions. Stand-off analysis demands the most stringent requirements on instrumentation. Therefore, it must be determined if the high performance components that are normally used in a typical LIBS laboratory setup, which are generally not optimized for small size and weight, are essential to obtain the maximum scientific return from a mission. A key component of a LIBS apparatus is the detection system consisting of a spectrograph and a detector. Here we present an evaluation of one design of a compact spectrograph (Ocean Optics HR2000) for in-situ and stand-off LIBS analyses of geological samples under Mars atmospheric conditions.