Calibration-free Research Articles

LIBS depth profiling of Be-containing samples with different gaseous impurity concentrations

Understanding the interaction between the fusion plasma and the plasma-facing materials (PFMs) is crucial for achieving the optimal performance, safety, and lifetime of the fusion devices. Relevant materials have been intensely studied to determine fuel retention and the composition of the co-deposited layers on the PFMs by depth profile analysis using Laser-Induced Breakdown Spectroscopy (LIBS) and Calibration-Free (CF)-LIBS. However, the comparison between the layers containing a mixture of different (seeding) gases using LIBS, has not been studied systematically. Consequently, the aim of this work is the LIBS depth profile analysis of Be-based samples containing the fuel (D) and one of the seeding gases (N, Ne, He) with variable concentrations to study the potential impact on fuel retention in the PFMs. The LIBS measurements were performed using Nd:YAG laser (1064 nm) under Ar atmosphere (at 2 and 100 mbar). In LIBS the ablation rate was evaluated, spectral lines of all relevant elements except N and Ne were detected and compared with the SIMS depth profiles. The reasons for the non-detectability of Ne are discussed in detail.

Quantitative analysis of elemental concentrations of aluminum alloys using calibration-free femtosecond laser-ablation spark-induced breakdown spectroscopy

In this work, the calibration-free (CF) methodology combined with femtosecond laser-ablation spark-induced breakdown spectroscopy (fs LA-SIBS) was applied for the quantitative analysis of elements in aluminum alloy. A femtosecond laser (800 nm) operated at a repetition rate of 1 kHz with a pulse width of 35 fs was used as the laser-ablation source, and the plasma emission was enhanced by the spark discharge. Spectra were acquired using a compact fiber spectrometer coupled to a charge-coupled device and recorded at 200–500 nm. The aluminum alloy sample was mounted on a two-dimensional motion platform, and the effect of the sample moving speed on the spectral intensity was investigated. To evaluate the analysis performance of this technique, five standard aluminum alloy samples with certified elemental concentrations were tested. The average estimated electron density from these five transitions was (1.5 ± 0.3) × 1017 cm−3, which was determined by fitting the ion spectrum of Al II (281.62 nm) with Lorentz fitting. The plasma temperature was calculated to be 6300 ± 300 K using Saha–Boltzmann plots under the local thermodynamic equilibrium state. Trace elements with the content of <0.1% were detected by the proposed technique, and the analysis error of Al was <0.3%. This study shows that the CF fs LA-SIBS technique can be employed for quantitative analysis of major, minor, and trace elements in multi-composition alloys.

Real-time analysis of the fine particles in volcanic plumes: A pilot study of Laser Induced Breakdown Spectroscopy with Calibration-Free approach (CF-LIBS)

Volcanic plumes are rich in fine juvenile ash, representing magma fragments expelled from the crater during explosive eruptions. The composition of fine ash is of primary importance for volcano monitoring and hazard assessment, but not much effort has been put until now to build portable instrumentation allowing real-time measurements. In this paper, a laboratory experiment is carried out to build and test an apparatus based on Calibration-Free Laser Induced Breakdown Spectroscopy (CF-LIBS). This methodology is extremely promising because it does not require any standard calibration strategies and the elemental composition is directly obtained by the laser-induced breakdown optical emission. In the experiment, volcanic ash samples are suspended in the air by a laser-induced shockwave in a dedicated chamber, as to mimic the conditions of a volcanic plume, and contemporaneously the laser-induced plasma (LIP) spectrum is analyzed. After spectrum acquisition, the quantitative analysis is performed using the so-called Calibration-Free (CF) analytical method, which is based on the assumption of plasma local thermodynamic equilibrium (LTE). Results show that by such methodology it is possible to measure ash composition in real-time, during its dispersion, with good precision. Based on the result of this experiment, the construction of a portable instrument to be used in the field for the monitoring of active volcanoes could be possible in the future.

LIBS Protocol for the Assessment of Depth Profile, Homogeneity, and Quantification of Fe/Co - based Bilayer Ribbon

The present work explores the applicability of a single spectroscopic technique, Laser-induced breakdown spectroscopy (LIBS), for the rapid quality assessment and quantification of individual layers of an amorphous bilayer ribbon (thickness ~ 35 μm). This kind of materials (ribbon) offer a convolution of the two sets of unique properties of individual layer, in a single ribbon, in contrast to the layered systems prepared by thin film technologies, and are useful and applicable for sensing and actuating in different experimental conditions. The sample was prepared by rapid quenching using the modified double-nozzle technique. One side of the ribbon is a layer of iron (Fe) - silicon (Si) - boron (B) and other side of the ribbon consists of cobalt (Co) - silicon (Si) - boron (B). Owing to its versatility and advantages, LIBS has been used for assessing the elemental distribution on the surface of the investigated matrices and across the layer interface. After optimizing the experimental parameters, the LIBS measurements have been performed using a Q-switched Nd:YAG laser working at its second harmonic wavelength (532 nm) with the 30 mJ/pulse energy under ambient air and atmospheric pressure conditions. Following the LIBS spectral analysis, a chemometric approach, principal component analysis (PCA), has been used for the visualization of the spectra from the two layers and to observe dominant spectral lines responsible for the discrimination of both layers. The depth profile analysis of the layers has been carried out using LIBS and the number of pulses corresponding to the individual layers have been correlated with the depth of the ablation craters obtained using the 3D-optical profilometry in order to estimate the thickness of the individual layers and the ablation rates. Furthermore, the homogeneity of the sample has been examined by measuring the intensity of selected spectral lines corresponding to the composition of the sample. Calibration-free (CF) - LIBS analysis has been performed for the compositional quantification of both layers of the sample and found in a good agreement with the production ratio. This work paves the way towards the investigation and control of the properties of such intelligent materials.

Accessory laboratory measurements to support quantification of hydrogen isotopes by in-situ LIBS from a robotic arm inside a fusion vessel

In order to try to improve spectral separation for hydrogen isotope detection in plasma facing components, a flow of noble gas at reduced pressure is proposed as alternative to atmospheric pressure experiments in air during maintenance of fusion vessels. To this aim the already realized compact LIBS probe has been equipped with a sealable tip where a noble gas could flow. The tip was in contact with the selected point of the target and its proper positioning was guaranteed by an adjustable metallic cone. Laboratory measurements were carried out by flowing either He or Ar on ITER-like tiles. A positive effect of Ar flow on Hα signal intensity was observed, while a significant narrowing of the Hα band was obtained upon He addition.Additional measurements on deuterium doped samples simulating the tile's composition in ITER divertor region were performed by applying a local vacuum in the point of analysis or utilizing the set-up in double pulse (DP) mode. These experiments were aimed at optimizing the acquisition parameters of the LIBS setup (e.g, single or double pulse excitation, gate delay, gate width, interpulse delay) when operated in different conditions (vacuum, atmospheric pressure, under gas flow) in order to resolve the two nearby emission bands Hα and Dα, still preserving a satisfactory Signal-to-Noise-Ratio (SNR). Finally, considerations on applicability of Calibration Free (CF) method for the quantification of hydrogen isotopes are presented.

Direct determination of Al and Pb in waste printed circuit boards (PCB) by laser-induced breakdown spectroscopy (LIBS): Evaluation of calibration strategies and economic - environmental questions

Matrix-matching calibration (MMC), two-point calibration transfer (TP CT), one-point and multi-line calibration (OP MLC), single-sample calibration (SSC) and calibration free (CF) were evaluated in order to overcome matrix effects in laser-induced breakdown spectroscopy (LIBS). These calibration strategies were evaluated for direct determination of Al and Pb in waste printed circuit boards (PCB) using direct solids analysis by LIBS. Each strategy has limitations and advantages of its implementation, for the correction of matrix effects, so that it allows elementary determination with adequate accuracy. The MMC and CF proved to be excellent calibration strategies for the determination of strategic (Al) and toxic (Pb) elements by LIBS, with good recoveries (ranging from 80–120%) and low relative standard deviation (RSD%) values. A detailed discussion of the advantages and limitations of each of these five calibration strategies evaluated for LIBS is presented in this study. Lead concentrations in waste PCB samples are 5–12 times higher than established by Directive 2011/65/EU, and the samples analyzed contain between 3 and 55 g kg−1 Al, being an interesting economic and recycling source for this metal.

Application of calibration-free high repetition rate laser-ablation spark-induced breakdown spectroscopy for the quantitative elemental analysis of a silver alloy.

In this work, we report the application of a calibration-free (CF) method combined with high repetition rate laser-ablation spark-induced breakdown spectroscopy (HRR LA-SIBS) to the analysis of a silver alloy. The sample was ablated by a fiber laser operated at a 30 kHz pulse repetition rate, and a spark discharge was applied to enhance plasma emission. Electron number density and plasma temperature were estimated using Stark broadening of spectral lines and the Saha-Boltzmann plot method, respectively. The fulfillment of the local thermodynamic equilibrium (LTE) approximation of the measurement was verified. Averaged electron density and plasma temperature were calculated as 1.11×1017cm-3 and 7355 K, respectively. The elemental composition of a silver alloy sample was determined, and the result was compared with that analyzed with inductively coupled plasma optical emission spectrometry (ICP-OES). The analytical error was within a 15% range. It was demonstrated that the CF HRR LA-SIBS technique could potentially provide elemental analysis for silver alloys without requiring a standard sample.

Calibration-free elemental analysis combined with high repetition rate laser-ablation spark-induced breakdown spectroscopy

Calibration-free (CF) method combined with high repetition rate laser-ablation spark-induced breakdown spectroscopy (HRR LA-SIBS) was first utilized to realize elemental analysis of alloy samples. A compact fiber laser operated at 30 kHz pulse repetition rate was used to ablate the sample and the spectra were recorded with a compact fiber spectrometer in non-gated signal recording mode. Three standard aluminum alloy samples were analyzed to evaluate the performance of this technique. Median filtering method was applied to reduce the contribution of the continuum background to the intensity of the atomic lines. The averaged electron density was determined to be (2.36–2.49) × 1017 cm−3 according to the Stark broadening of four ionic lines. 11,800 K averaged plasma temperature was estimated from the Saha-Boltzmann plots. The plasma could be verified to be in a state close to local thermodynamic equilibrium. The analytical error was <0.5% for the major element and <35% for minor elements with >0.1% concentrations. It was demonstrated that CF method combined with HRR LA-SIBS was possible to realize reliable quantitative elemental analysis for aluminum alloy samples.

Quantitative analysis of Fuller's earth using laser-induced breakdown spectroscopy and inductively coupled plasma/optical emission spectroscopy.

Fuller's earth, most commonly known as Multani Matti (clay) in Urdu, among its various utilizations is traditionally used in skin care cosmetics, particularly for removing blackheads and to treat oily skin. It is also used for improving skin complexion. In this paper, laser-induced breakdown spectroscopy (LIBS) was effectively employed for the quantitative investigation of various clay samples for their special uses. To get the LIBS spectra with an optimal signal-to-noise as well as for a more robust and accurate analytical investigation, different experimental parameters (laser energy, gate delay time, and the distance between target and focusing lens) were optimized before the experiments on actual samples. The analysis of emission spectra revealed the presence of many different elements, including Al, Ca, Fe, Mg, Mn, Na, K, Li, S, Si, and Zn. The electron number density and plasma temperatures were determined using the Stark broadened line profile and Boltzmann plot method, respectively. To determine the relative concentration of observed elements, we used an integrated intensity ratio method, integrated intensity of every line from all elements, and calibration free (CF)-LIBS. The prevailing condition of local thermodynamic equilibrium during the experimental executions was verified with multiple criteria. The spectral lines used in CF-LIBS were characterized for the influence from the self-absorption phenomenon, but the same was found insignificant. The findings of our LIBS system were found to agree excellently with the outcomes of the inductively coupled plasma/optical emission spectroscopy, thereby yielding a high statistical correlation factor and hence enlighten the significance of LIBS as a safe and reliable tool for elemental analysis of clay samples.

Deuterium detection and quantification by laser-induced breakdown spectroscopy and calibration-free analysis in ITER relevant samples

Tritium (T) inventory in Plasma Facing Components (PFCs) will be one of the critical issues for ITER because of the impact tritium can have on the machine operation and safety. Laser Induced Breakdown Spectroscopy (LIBS) is a promising technique to accomplish this task, providing both qualitative and quantitative composition of the chemical elements retained in PFCs. LIBS does not require sample pretreatment or manipulation, it can work in-situ between fusion discharges or during maintenance periods, it is suitable for measurements at different residual pressures, with different background gases. It can detect all the chemical elements through their spectral emission. This paper presents the results of LIBS measurements at 100 mbar nitrogen pressure on metallic coating (W-Al-D) simulating the superficial composition of ITER divertor PFCs contaminated with nuclear fuel and material eroded from the first wall.LIBS spectra showed clear W, Al, D emission lines. A quantitative estimation of their relative concentration was performed by applying the Calibration Free (CF) analysis. CF does not require reference samples, so it's particularly suitable for this purpose. CF results were compared with the nominal concentrations and were found in good agreement with the latter.

Application of Laser Induced Breakdown in Air in Conjunction with Atomic Absorption Spectroscopy for Detection of Trace Elements in Fennel Seeds

A robust approach of laser-induced breakdown spectroscopy (LIBS) in ambient air has been employed to investigate concentration of the trace elements in fennel seeds (saunf) via generation of plasma through the second harmonic of solid state Nd: YAG pulsed laser 532 nm. Spectral emissions of saunf plasma were acquired with resolution of 0.06 nm in spectral range of 200–720 nm. The experimental determination showed the existence of elements namely, Ca, Al, K, Fe, S, P, Mg, Mn, Sr, Na, and Zn in the sample. However, no toxic elements such as Pb, Cr etc. were perceived. The relative concentrations of detected elements were measured through the intensity of the strongest peak, intensities of every emission from every specie, and calibration free (CF)-LIBS. To indorse the experimental determinations of LIBS, a comparative study was carried out with the outcomes of atomic absorption spectroscopy (AAS). The results of LIBS and AAS were compared by the statistical treatment.

Application of a laser-induced breakdown spectroscopy handheld instrument to the diagnostic analysis of stone monuments

Laser-induced breakdown spectroscopy (LIBS) has been in use for decades, but only recently the technique has progressed so to allow the construction of efficient handheld, self-contained commercial instruments featuring a large range of capabilities. In particular, the development of portable handheld instruments able to perform non-invasive, spatially resolved, multielement, in-situ analysis has provided an impressive impulse to the scientific investigation of cultural heritage materials. In this work, the design of a handheld LIBS instrument and the first test measurements performed on a fragment of a sedimentary rock monument are presented. A full broadband LIBS emission spectrum with a point and shoot operation was recorded directly within few seconds, so providing information on the elements present in the weathered layer in comparison to the stone surface. Further, the Calibration Free (CF)-LIBS approach was used to test the possibility to obtain a suitable quantitative composition of the main elements present in the sample.

Extension and investigation by numerical simulations of algorithm for calibration-free laser induced breakdown spectroscopy

Accuracy of calibration-free (CF) methods in laser-induced breakdown spectroscopy (LIBS) depends on experimental conditions and instrumental parameters that must match a CF LIBS model. Here, the numerical study is performed to investigate effects of various factors, such as the optical density, plasma uniformity, line overlap, noise, spectral resolution, electron density and path length on the results of CF-LIBS analyses. The effects are examined one-by-one using synthetic spectra of steel slag samples that fully comply with the mathematical model of the method. Also, the algorithm includes several new features in comparison with previously proposed CF algorithms. In particular, it removes limits on the optical thickness of spectral lines that are used for the construction of the Saha-Boltzmann plot; it retrieves the absorption path length (plasma diameter) directly from spectral lines; it uses the more realistic Voigt line profile function instead of the Lorentzian function; and it employs the pre-calculated and tabulated thin-to-thick line ratios instead of approximating functions for self-absorption correction.

Stand-off laser induced breakdown spectroscopy on meteorites: calibration-free approach

In this work, LIBS (Laser Induced Breakdown Spectroscopy) capability to operate in stand-off configuration, without the need of a direct contact with the sample, has been coupled with the calibration-free (CF) approach to LIBS data analysis. The latter does not require the use of standard calibration. The feasibility of the calibration free method on stand-off LIBS spectra has been thereby tested. The quantitative analysis was performed on samples of two well-known meteorites, Toluca (iron meteorite) and Sahara 98222 (L6 chondrite) by using a stand-off configuration at a distance of 5 m. The plasma temperature and the electron number densities were determined for each sample and for each laser shot in order to apply the CF method. For the Toluca meteorite sample Fe, Ni and Co content was quantified during the depth profile. For the Sahara 98222 major and minor elements (Fe, Mg, Si, Na, Ti, Al, Cr, Mn, Ca, Ni, Co) were analysed by averaging different meteorite zones because of its strong inhomogeneity. Results demonstrate the possibility of remote analysis of minor bodies and space debris.

New insights on the Dronino iron meteorite by double-pulse micro-Laser-Induced Breakdown Spectroscopy

Two fragments of an iron meteorite shower named Dronino were characterized by a novel technique, i.e. Double-Pulse micro-Laser Induced Breakdown Spectroscopy (DP-μLIBS) combined with optical microscope. This technique allowed to perform a fast and detailed analysis of the chemical composition of the fragments and permitted to determine their composition, the alteration state differences and the cooling rate of the meteorite. Qualitative analysis indicated the presence of Fe, Ni and Co in both fragments, whereas the elements Al, Ca, Mg, Si and, for the first time Li, were detected only in one fragment and were related to its post-falling alteration and contamination by weathering processes. Quantitative analysis data obtained using the calibration-free (CF) - LIBS method showed a good agreement with those obtained by traditional methods generally applied to meteorite analysis, i.e. Electron Dispersion Spectroscopy - Scanning Electron Microscopy (EDS-SEM), also performed in this study, and Electron Probe Microanalysis (EMPA) (literature data). The local and coupled variability of Ni and Co (increase of Ni and decrease of Co) determined for the unaltered portions exhibiting plessite texture, suggested the occurrence of solid state diffusion processes under a slow cooling rate for the Dronino meteorite.

Calibration-free quantitative elemental analysis of meteor plasma using reference laser-induced breakdown spectroscopy of meteorite samples

Aims. We aim to analyse real-time Perseid and Leonid meteor spectra using a novel calibration-free (CF) method, which is usually applied in the laboratory for laser-induced breakdown spectroscopic (LIBS) chemical analysis. Methods. Reference laser ablation spectra of specimens of chondritic meteorites were measured in situ simultaneously with a high-resolution laboratory echelle spectrograph and a spectral camera for meteor observation. Laboratory data were subsequently evaluated via the CF method and compared with real meteor emission spectra. Additionally, spectral features related to airglow plasma were compared with the spectra of laser-induced breakdown and electric discharge in the air. Results. We show that this method can be applied in the evaluation of meteor spectral data observed in real time. Specifically, CF analysis can be used to determine the chemical composition of meteor plasma, which, in the case of the Perseid and Leonid meteors analysed in this study, corresponds to that of the C-group of chondrites.

Determination of Metals Present in Textile Dyes Using Laser-Induced Breakdown Spectroscopy and Cross-Validation Using Inductively Coupled Plasma/Atomic Emission Spectroscopy

Laser-induced breakdown spectroscopy (LIBS) was used for the quantitative analysis of elements present in textile dyes at ambient pressure via the fundamental mode (1064 nm) of a Nd:YAG pulsed laser. Three samples were collected for this purpose. Spectra of textile dyes were acquired using an HR spectrometer (LIBS2000+, Ocean Optics, Inc.) having an optical resolution of 0.06 nm in the spectral range of 200 to 720 nm. Toxic metals like Cr, Cu, Fe, Ni, and Zn along with other elements like Al, Mg, Ca, and Na were revealed to exist in the samples. The %-age concentrations of the detected elements were measured by means of standard calibration curve method, intensities of every emission from every species, and calibration-free (CF) LIBS approach. Only Sample 3 was found to contain heavy metals like Cr, Cu, and Ni above the prescribed limit. The results using LIBS were found to be in good agreement when compared to outcomes of inductively coupled plasma/atomic emission spectroscopy (ICP/AES).

LIBS experiments for quantitative detection of retained fuel

Laser Induced Breakdown Spectroscopy (LIBS) provides chemical information from atomic and ionic plasma emissions generated by laser vaporization of a sample. At the ENEA research center, in collaboration with IPPLM, an equipment has been set up to qualitatively and quantitatively determine the chemical composition of impurities deposited on Plasma Facing Components (PFC). The strength of the LIBS, for its capability of light elements detection, is fully exploited to determine the deuterium content since this element can be considered as the best choice proxy for tritium; the latter being is of great importance in assessing safe conditions to assure the continuous operation in nuclear fusion tokamak.Here we present the results of the Double Pulse LIBS (DP-LIBS) probing of deuterated samples with the simultaneous optical detection by medium-resolution and high-resolution spectrometer. Deuterium emission at 656.1nm has been detected then the elemental composition has been quantified by applying the Calibration Free (CF) approach. The obtained results demonstrate that the DP-LIBS technique combined with CF analysis is suitable for the quantitative determination of tritium content inside the PFCs of next fusion devices like ITER.

Monte Carlo standardless approach for laser induced breakdown spectroscopy based on massive parallel graphic processing unit computing

The improved Monte-Carlo (MC) method for standard-less analysis in laser induced breakdown spectroscopy (LIBS) is presented. Concentrations in MC LIBS are found by fitting model-generated synthetic spectra to experimental spectra. The current version of MC LIBS is based on the graphic processing unit (GPU) computation and reduces the analysis time down to several seconds per spectrum/sample. The previous version of MC LIBS which was based on the central processing unit (CPU) computation requested unacceptably long analysis times of 10's minutes per spectrum/sample. The reduction of the computational time is achieved through the massively parallel computing on the GPU which embeds thousands of co-processors. It is shown that the number of iterations on the GPU exceeds that on the CPU by a factor >1000 for the 5-dimentional parameter space and yet requires >10-fold shorter computational time. The improved GPU-MC LIBS outperforms the CPU-MS LIBS in terms of accuracy, precision, and analysis time. The performance is tested on LIBS-spectra obtained from pelletized powders of metal oxides consisting of CaO, Fe2O3, MgO, and TiO2 that simulated by-products of steel industry, steel slags. It is demonstrated that GPU-based MC LIBS is capable of rapid multi-element analysis with relative error between 1 and 10's percent that is sufficient for industrial applications (e.g. steel slag analysis). The results of the improved GPU-based MC LIBS are positively compared to that of the CPU-based MC LIBS as well as to the results of the standard calibration-free (CF) LIBS based on the Boltzmann plot method.

Laser Induced Breakdown Spectroscopy of meteorites as a probe of the early solar system

This paper presents an evaluation of Laser Induced Breakdown Spectroscopy (LIBS) as a technique for gathering data relevant to Solar System geophysics. Two test cases were demonstrated: elemental analysis of chondrules in a chondrite meteorite, and space- resolved analysis of the interface between kamacite and taenite crystals in an octahedrite iron meteorite. In particular most major and minor elements (Fe, Mg, Si, Ti, Al, Cr, Mn, Ca, Fe, Ni, Co) in Sahara 98222 (chondrite) and its chondrules, as well as the profile of Ni content in Toluca (iron meteorite), were determined with the Calibration Free (CF) method. A special attention was devoted to exploring the possibilities offered by variants of the basic technique, such as the use of Fe I Boltzmann distribution as an intensity calibration method of the spectroscopic system, and the use of spatially resolved analysis.