Laser Ablation Molecular Isotopic Spectrometry Research Articles

LIBS at high duty-cycles: effect of repetition rate and temporal width on the excitation laser pulses

Laser-induced breakdown spectroscopy (LIBS) is becoming a more mature technology every year with new variants such as laser ablation molecular isotopic spectrometry, reheating by various discharge techniques, and multiple pulse excitation schemes, in which sometimes lasers of different pulse lengths are used. However, lasers with inherent parameters like pulse length and repetition rate are still almost exclusively employed. Recent years have witnessed the advent of novel high-repetition-rate laser concepts for machining processes, like welding, milling, and engraving. Here, a comprehensive study of single-pulse LIBS spectra of a single aluminum target is presented to showcase the applicability of flexible high duty-cycle master oscillator power amplifier (MOPA) lasers. Although traditional flashlamp-pumped Fabry–Pérot lasers only permit a variation in the pulse energy and are operated at very low duty-cycles, MOPA lasers add repetition rate and pulse length as variable parameters. A thorough analysis of the temporal plasma behavior revealed the emission dynamic to closely match the excitation laser pulse pattern. An aluminum sample’s spectral response was shown to be significantly impacted by variations in both rate and length. Although the spectral emission strength of the elemental lines of Al, Sr, and Ca all peaked at slightly different parameter settings, the strongest impact was found on the relative abundance of molecular AlO bands. Unlike in previous laser ablation molecular isotopic spectrometry (LAMIS) publications, the latter could be readily detected with a good intensity and well-resolved spectral features without any temporal gating of the detector. This finding, together with the fact that MOPA lasers are both inexpensive and dependable, makes for a promising combination for future studies including the detection of diatomic band structures.

Rare-earth elements detection using diatomic molecular laser-induced plasma spectroscopy

The detection of Rare-Earth-Elements by LIBS by their atomic and ionic emission in many cases is difficult due to significant spectral interferences from other members of this group and accompanying elements. Another potential detection mode is to use molecular emission. It was previously considered that only La, Y, and Sc form analytically useful molecules in Laser-Induced Plasma. We proved that the molecules of other rare-earth elements (Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Y, and Lu) with oxygen appear effective for analytical purposes. The type of the emission spectrum depends on specific element molecular weight and differs for Light and Heavy REE sub-groups. This approach is demonstrated for Gd analysis in ceria (CeO2) and in permanent B-Fe-Nd and Sm-Co-Ni magnets. The presence of molecular emission of Rare-Earth-Elements opens an opportunity to apply Laser Ablation Molecular Isotopic Spectrometry and Molecular Laser-Induced Fluorescence - LIBS combination for their isotopes analysis.

Laser ablation molecular isotopic spectrometry for analysis of OD/OH isotopologues in plasma

Laser ablation molecular isotopic spectrometry (LAMIS) was recently reported for isotope analysis of samples and for molecules formation mechanism investigation by analyzing the isotopologues in laser induced plasma. LAMIS was utilized to quantify the OD and OH molecules in fs-laser ablated plasma from moist water samples carried by pure Ar gas at ambient environment. A theoretical spectral fitting model for OD and OH molecules was developed and was used to extract the isotopic ratio OD/OH by fitting of experimental spectra. Time-resolved spectra were measured and the influences of spectrum intensity and signal to noise ratio (SNR) on isotopic quantitative analysis performance were evaluated. The relative concentration of OD and OH molecules in laser induced plasma from a set of water samples with D2O concentrations in the range of 0% to 99.8% are quantified, and a very good linear relationship between D concentration and D2O concentration was obtained. The linear curve exhibited R2 exceeding 0.9997 and a slope of 1.006. In addition, no standard sample is necessary for quantitative analysis, demonstrating the advantages of spectral fitting LAMIS.

Remote isotope detection and quantification using femtosecond filament-laser ablation molecular isotopic spectrometry

We demonstrate the detection and quantification of isotopes from solid samples remotely at a distance of 36 m. This was accomplished through the combination of femtosecond filaments and laser ablation molecular isotopic spectrometry (F2-LAMIS). Isotopically enriched graphite samples with varying 13C concentration were used and the F2-LAMIS emission was measured remotely using a fieldable spectrometer system. A standardless quantification approach was used to determine the corresponding isotopic ratios. The use of F2-LAMIS for the detection and quantification of isotopes at atmospheric pressure without the use of calibration standards opens the possibility to implement this technology for remote sensing of isotopes in field applications.

The use of a digital micromirror array as a temporal gate and spatial-filtering device for laser-induced breakdown spectroscopy and laser ablation molecular isotopic spectrometry

A digital micromirror array (DMMA) is used in a simple and inexpensive approach for spatially resolved temporal gating of atomic emission detection in laser-induced breakdown spectroscopy (LIBS). Selected mirrors in the array are actuated at a time delayed from the primary laser pulse, permitting optical gating with a response time of 160 ns while using a conventional CCD detector. Detector gating is shown to decrease noise from short-lived spectroscopic background (both continuum and N II from air), improving signal-to-background ratios by 22-times for selected samples and emission lines. The utility of rapid temporal gating is also demonstrated for the optical detection of isotopes using the laser-ablation molecular isotope spectrometry (LAMIS) experiment. Optical temporal gating and spatial filtering are used to isolate regions of the laser-induced plasma, enhancing signal from molecular emission. The potential of the simple technique for use in field-portable LIBS and LAMIS experiments is explored.

Isotope analysis of iron on structural materials of nuclear power plants using double-pulse laser ablation molecular isotopic spectrometry

The isotope analysis of iron was performed using laser ablation molecular isotopic spectrometry (LAMIS) for the detection of radioactive hotspots in nuclear power plant (NPPs).

Determination of boron in aqueous solution using a method combining laser ablation molecular isotopic spectrometry with molecular laser-induced fluorescence and isotopic dilution

Laser-induced breakdown spectroscopy (LIBS) has been applied in quantitative and isotopic detection of boron.

Determination of the isotopic composition of enriched materials using laser ablation molecular isotopic spectrometry: partial least squares and multivariate curve resolution for the determination of 15N content in enriched urea.

A quantitative analytical method based on laser ablation molecular isotopic spectrometry (LAMIS) and multivariate analysis was developed and evaluated for the determination of the isotopic composition of enriched materials. The method consists preparing a concentrated solution of the enriched material, using small quantities of a sample (125mg), and ensuring the economic efficiency of the analysis. Standard solutions of known isotopic contents are prepared by employing mixtures of urea highly enriched in 15N and urea of natural isotopic ratio and analyzed by mass spectrometry. A small volume (30μL) of these solutions is delivered to a filter paper disc (3cm diameter). After drying, the disc, offering a homogeneously distributed analyte, is presented to a LAMIS equipment to acquire the vibronic emission spectra containing information about the isotopologues of interest. To illustrate the proposed method, the content of 15N is determined in enriched samples of urea. In this case, each spectrum is normalized by the intensity of emission of the CN isotopologues for the electronic (Δν = 0) emission band at 387.1nm, ensuring better accuracy. Selected regions and single wavelengths of the vibronic emission spectrum (Δν = + 1 or - 1) related to CN species were employed to construct multivariate partial least squares (PLS) and univariate regression models to predict the isotopic content of new samples. Besides, the LAMIS data set was evaluated by multivariate curve resolution (MCR) algorithm. The best MCR and PLS models presented similar results regarding the accuracy to determine 15N content in enriched urea. MCR is capable of identifying spectral interferences and minimizing its effect. The results show that the proposed method based on LAMIS and PLS or MCR multivariate analysis can determine the 15N content in the range 5-50% with a root mean square error of prediction (RMSEP) respectively equal to 0.5 or 0.7% (m/m) in comparison with reference results obtained by mass spectrometry. Graphical abstract.

Hydrogen isotopic analysis using molecular emission from laser-induced plasma on liquid and frozen water

The hydrogen isotopes in liquid and frozen water samples were analyzed by laser ablation molecular isotopic spectrometry (LAMIS), which employs the molecular emission from laser-induced plasma for isotope analysis. Molecular emission bands of OH and NH radicals were observed, and their spectral features were characterized in accordance with sample matrix and measurement conditions. The OH and NH bands exhibit different emission behavior, which was attributed to formation kinetics and thermodynamic factors. Under optimized condition, isotopic shift between hydrogenated (OH and NH) and deuterated (OD and ND) species was measured at individual rotational branches. By using these molecular bands, the partial least squares regression (PLSR) structure was established for quantitative analysis of hydrogen isotope and evaluated by cross-validation in terms of accuracy and precision. The PLSR result was good with root mean square error of prediction (RMSEP) of 0.3–0.7% for all species. Particularly, the case using OH/OD emission from liquid water revealed the most accurate result with RMSEP of 0.33%. It was affected by the quality and reproducibility of spectral data determined by utilized species. This study not only supports the behavioral understanding of molecular radicals in laser-induced plasma, but also identifies the feasibility of LAMIS for real-time application to quantitative analysis in various sample matrices.

Standoff Detection of Uranium and its Isotopes by Femtosecond Filament Laser Ablation Molecular Isotopic Spectrometry

The ability to perform not only elementally but also isotopically sensitive detection and analysis at standoff distances is impor-tant for remote sensing applications in diverse ares, such as nuclear nonproliferation, environmental monitoring, geophysics, and planetary science. We demonstrate isotopically sensitive real-time standoff detection of uranium by the use of femtosecond filament-induced laser ablation molecular isotopic spectrometry. A uranium oxide molecular emission isotope shift of 0.05 ± 0.007 nm is reported at 593.6 nm. We implement both spectroscopic and acoustic diagnostics to characterize the properties of uranium plasma generated at different filament-uranium interaction points. The resulting uranium oxide emis-sion exhibits a nearly constant signal-to-background ratio over the length of the filament, unlike the uranium atomic and ionic emission, for which the signal-to-background ratio varies significantly along the filament propagation. This is explained by the different rates of increase of plasma density and uranium oxide density along the filament length resulting from spectral and temporal evolution of the filament along its propagation. The results provide a basis for the optimal use of filaments for standoff detection and analysis of uranium isotopes and indicate the potential of the technique for a wider range of remote sensing applications that require isotopic sensitivity.

Combination of atomic lines and molecular bands for uranium optical isotopic analysis in laser induced plasma spectrometry

Through computer simulation on experimentally acquired optical spectra, uranium isotopic analysis by laser ablation molecular isotopic spectrometry and laser induced breakdown spectroscopy were studied. The use of only one spectral feature, either the strong UO band at 593.55 nm or the nearby U I 593.382 nm line, are similar in precisions (~ 1.5% in absolute 235U abundances). Precision improves to 0.72% with the use of a group of U atomic lines from 591.6 to 596.5 nm. The use of both molecular bands and atomic lines further advances the precision to 0.42% and compares well with the U II 424.437 nm single-line benchmark (0.48% precision).

Mid-IR enhanced laser ablation molecular isotopic spectrometry

A double-pulsed laser-induced breakdown spectroscopy (DP-LIBS) technique utilizing wavelengths in the mid-infrared (MIR) for the second pulse, referred to as double-pulse LAMIS (DP-LAMIS), was examined for its effect on detection limits compared to single-pulse laser ablation molecular isotopic spectrometry (LAMIS). A MIR carbon dioxide (CO2) laser pulse at 10.6μm was employed to enhance spectral emissions from nanosecond-laser-induced plasma via mid-IR reheating and in turn, improve the determination of the relative abundance of isotopes in a sample. This technique was demonstrated on a collection of 10BO and 11BO molecular spectra created from enriched boric acid (H3BO3) isotopologues in varying concentrations. Effects on the overall ability of both LAMIS and DP-LAMIS to detect the relative abundance of boron isotopes in a starting sample were considered. Least-squares fitting to theoretical models was used to deduce plasma parameters and understand reproducibility of results. Furthermore, some optimization for conditions of the enhanced emission was achieved, along with a comparison of the overall emission intensity, plasma density, and plasma temperature generated by the two techniques.

Reduction of spectral interferences and noise effects in laser ablation molecular isotopic spectrometry with partial least square regression – a computer simulation study

The fundamental analytical accuracies and precisions attainable by laser ablation molecular isotopic spectrometry (LAMIS), with emphasis on the impacts from spectral interferences and measurement noise, were investigated by means of computer simulation. The study focused on the analysis of a minor isotope at sub- to single-percentage abundance level. With a natural abundance about 1.1% for 13C, the C2 Swan band (d3Πg–a3Πu) with Δν=+1 was selected as a representative system. The characteristics (e.g., noise amplitude and distribution, signal strength, and signal-to-background ratio) of the simulated spectra were experimentally characterized. Partial least square (PLS) regression was used to extract isotopic information from the simulated molecular spectra. In the absence of any spectral interference and with the use of a calibration set consisting of eleven isotopic standards, the theoretical accuracies and precisions with signal accumulation from 100 laser shots are about 0.002% and 0.001%, respectively, in absolute percentage abundance of 13C. The theoretical analytical accuracies slightly degrade, but are adequate for many applications, to 0.004% and 0.008% respectively, for calibrations involving only three and two isotopic standards. It was found that PLS regression is not only immune to both source-flicker and photon-shot noise, but is also effective in differentiating the spectral patterns from the analyte against those from spectral interferences. The influences of spectral interference from single or multiple atomic emission lines were simulated, and new ways to minimize their impacts were formulated and demonstrated. It was found that the wavelength range selected for the computation of the normalization factor should not contain any spectral-interfering peak, and a properly chosen wavelength range increases the tolerance of spectral interference by at least one order of magnitude. With matrix-matched calibration standards, the precisions (expressed as RSDs of the determined 13C isotopic abundances) degrade from ~1‰ in the absence of spectral interference, to ~3‰, 10‰ and 20‰ with multiple spectral-interfering peaks that are 10×, 100× and 1000×, respectively, stronger than the molecular bandhead of the analyte. The study concluded that PLS regression is a powerful and indispensable tool for extraction of isotopic information from LAMIS spectra.

Laser ablation molecular isotopic spectrometry (LAMIS): current state of the art

Laser Ablation Molecular Isotopic Spectrometry (LAMIS) is a direct and rapid technique that measures optical emission in laser-induced plasmas for isotopic analysis.

Femtosecond filament-laser ablation molecular isotopic spectrometry

A new remote sensing technology for real-time isotopic analysis is introduced: Femtosecond Filament-Induced Laser Ablation Molecular Isotopic Spectrometry (F2-LAMIS). The technique combines femtosecond (fs) laser filamentation and ablation-based molecular isotopic spectroscopy, thereby enabling isotopic analysis of samples at a distance, in ambient air and at ambient pressure conditions. Isotopic analysis of zirconium (Zr) samples by F2-LAMIS is demonstrated, and the molecular and atomic emission intensity, and properties of the filament-induced plasma generated at different filament propagation distances were investigated. Spectral fitting of F2-LAMIS spectra enabled semi-quantitative isotopic analysis without the use of calibration standards, which was independent of the filament propagation distance for the studied range. This technology provides new capabilities for direct isotopic ratio measurements at remote distances.

Laser ablation molecular isotopic spectrometry of carbon isotopes

Quantitative determination of carbon isotopes using Laser Ablation Molecular Isotopic Spectrometry (LAMIS) is described. Optical emission of diatomic molecules CN and C2 is used in these measurements. Two quantification approaches are presented: empirical calibration of spectra using a set of reference standards and numerical fitting of a simulated spectrum to the experimental one. Formation mechanisms of C2 and CN in laser ablation plasma are briefly reviewed to provide insights for implementation of LAMIS measurements. A simulated spectrum of the 12C2 Swan system was synthesized using four constituents within 473.5–476.5nm. Simulation included three branches of 12C2 (1-0), branches R(0-0) and R(1-1), and branch P(9-8) of 12C2. Spectral positions of the tail lines in R(0-0) and R(1-1) were experimentally measured, since they were not accurately known before. The Swan band (1-0) of the isotopologue 13C12C was also simulated. Fitting to the experimental spectrum yielded the ratio 13C/12C=1.08% in a good agreement with measurements by isotope ratio mass spectrometry. LAMIS promises to be useful in coal, oil and shale exploration, carbon sequestration monitoring, and agronomy studies.

Femtosecond laser ablation molecular isotopic spectrometry for zirconium isotope analysis.

Laser ablation molecular isotopic spectrometry (LAMIS) for rapid isotopic analysis of zirconium at atmospheric pressure was studied with a femtosecond-laser system operated under high repetition rate (1 kHz) and low pulse energy (160μJ). The temporal evolution of zirconium neutral-atomic and ionic lines, as well as zirconium oxide molecular bands, were studied. Six molecular bands, belonging to the d(3)Δ-a(3)Δ (i.e., the α system) and E(1)Σ(+)-X(1)Σ(+) transitions, were observed with appreciable isotopic shifts. The assignments of the isotopic bandheads were first based on theoretical predictions of the band origins and the associated isotopic shifts of various dipole-allowed ZrO electronic transitions, followed by an experimental confirmation with a (94)Zr-enriched ZrO2 sample. In this work, the α(0,1) band from the d(3)Δ3-a(3)Δ3 subsystem was utilized for Zr isotope analysis based on a compromise between the magnitude of isotopic shifts in emission wavelengths, emission strengths, signal-to-background ratios, and spectral interferences. The analysis was performed in a standardless calibration approach; the isotopic information was extracted from the experimentally measured molecular spectra through theoretical spectral fitting. The results demonstrate the feasibility to obtain isotopic information for a spectrally complicated element like zirconium, without the need to use isotopically labeled calibration standards. The availability of comprehensive molecular constants will further improve the analytical accuracy of this standardless calibration approach.

Elucidation of C2 and CN formation mechanisms in laser-induced plasmas through correlation analysis of carbon isotopic ratio

Laser ablation molecular isotopic spectrometry (LAMIS) was recently reported for rapid isotopic analysis by measuring molecular emission from laser-induced plasmas at atmospheric pressure. With 13C-labeled benzoic acid as a model sample, this research utilized the LAMIS approach to clarify the formation mechanisms of C2 and CN molecules during laser ablation of organic materials. Because the isotopic ratios in the molecular bands could deviate from statistical distribution depending on their formation pathways, the dominant mechanism can be identified through a comparison of the experimental observed isotopic patterns in the molecular emission with the theoretical statistical pattern. For C2 formation, the experimental 12C12C/13C12C ratios not only support a recombination mechanism through atomic carbon at early delay time but also indicate the presence of other operating mechanisms as the plasma evolves; it is proposed that some of the C2 molecules are released directly from the aromatic ring of the sample as molecular fragments. In contrast, the temporal profiles in the 12C/13C ratios derived from CN emission exhibited opposite behavior with those derived from C2 emission, which unambiguously refutes mechanisms that require C2 as a precursor for CN formation; CN formation likely involves atomic carbon or species with a single carbon atom.

Matrix effects in laser ablation molecular isotopic spectrometry

Recently, it has been shown that laser-induced breakdown spectroscopy (LIBS) can be used for the detection of isotopes of elements via isotopic shifts in diatomic species in a technique known as laser ablation molecular isotopic spectrometry (LAMIS). While LAMIS works quite well for isotopic analysis of pure compounds under optimal conditions, it is desirable for it to be applicable for a variety of compounds and matrices. However, the LIBS plasma emission associated with LAMIS depends on several parameters, including the applied electric field of the laser pulse, the physical properties of the material being investigated, and the presence of additional elements other than the element of interest. In this paper, we address some of the pitfalls arising from these dependencies when using LAMIS for the determination of the relative isotopic abundance of boron-containing materials with varying chemical matrices.

Atomic spectrometry updates: Review of advances in atomic spectrometry and related techniques

This review covers developments in ‘Atomic Spectrometry’. It covers atomic emission, absorption, fluorescence and mass spectrometry, but excludes material on speciation and coupled techniques which is included in a separate review. It should be read in conjunction with the other related reviews in the series.1–6 A critical approach to the selection of material has been adopted, with only novel developments in instrumentation, techniques and methodology being included. A number of themes have emerged from this year's review. Novel developments in sample preparation include the use of magnetic nanoparticles for solid phase extraction and an increase in the number of viable methods for use in quantitation of peptides, proteins and DNA by elemental tagging, particularly the development of multiplexed techniques. There were also some advances in electrochemical vapour generation, such as the use of reducing reagents immobilized on electrodes and development of electrolytic membrane diffusion cells. New instrumentation has been to the fore, with research into some novel and interesting miniaturized plasma sources being of particular interest, plus the development of a new distance of flight (DOF) mass spectrometer. There have been some insightful fundamental studies of particle atomization and ionization in ICP-MS, and subsequent space-charge effects after ion sampling, which should enable practical steps to solving some of these problems. One of the main drivers of research in isotope ratio analysis has been to increase detection power to enable smaller and smaller quantities of analyte to be measured, which yields advantages in geochronology and nuclear forensics. Laser ablation has played a large part in many types of analysis where high resolution is required, including analysis of single particles, small inclusions or elemental mapping of tissues, so the development of LA methods with extremely small spot sizes and efficient sample transport to the source has been key. In addition, several novel methods have been developed, such as laser ablation molecular isotopic spectrometry (LAMIS) for isotope ratio analysis, and stand-off LIBS techniques such as ‘underwater LIBS’. In contrast, very little research into the use of chemometrics has been reported, and fundamental studies are generally confined to characterization of new plasma sources.