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 CO₂ 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.     

Assessment of statistical uncertainty in the quantitative analysis of solid samples in motion using laser-induced breakdown spectroscopy

Statistical uncertainty in the quantitative analysis of solid samples in motion by laser-induced breakdown spectroscopy (LIBS) has been assessed. For this purpose, a LIBS demonstrator was designed and constructed in our laboratory. The LIBS system consisted of a laboratory-scale conveyor belt, a compact optical module and a Nd:YAG laser operating at 532 nm. The speed of the conveyor belt was variable and could be adjusted up to a maximum speed of 2 m s^− 1. Statistical uncertainty in the analytical measurements was estimated in terms of precision (reproducibility and repeatability) and accuracy. The results obtained by LIBS on shredded scrap samples under real conditions have demonstrated that the analytical precision and accuracy of LIBS is dependent on the sample geometry, position on the conveyor belt and surface cleanliness. Flat, relatively clean scrap samples exhibited acceptable reproducibility and repeatability; by contrast, samples with an irregular shape or a dirty surface exhibited a poor relative standard deviation.     

Progress in Research and Application of Micro-Laser-Induced Breakdown Spectroscopy

The technique of micro-laser-induced breakdown spectroscopy (μLIBS) usually refers to analyzing the surface of the sample using a compact focused laser beam in the optical microscope range. Compared to conventional laser-induced breakdown spectroscopy (LIBS), it can provide more abundant form, structure, and content information on a smaller, less sample condition. Hence, the application field is very wide. In this paper, the basic status of μLIBS in the selection of laser source and the structure of optical path system is introduced, and its application in metal, semiconductor, animal and plant fields is reviewed. The existing problems and potential development direction is pointed out.     

A study of stalagmite samples from Baradla Cave (Hungary) by laser induced plasma spectrometry with automatic signal correction

In the present work, we studied the applicability of laser induced plasma/breakdown spectrometry (LIPS/LIBS) to speleothem analysis. Problems related to the use of time- and spatially integrating compact LIBS instrumentation, speleothem sample preparation, spectral line assignation and signal intensity correction have been addressed. A novel signal correction scheme, based on the total integrated spectral background, was developed and employed for the qualitative study of the lateral distribution profiles of major (Ca, Mg, C, O) and minor (Al, Si, Fe, Mn) elements detected in horizontally cut slices of stalagmite samples from Baradla Cave (Aggtelek, Hungary). Several new computer program modules were also developed to aid the spectral data evaluation. Correlations and trends found in the lateral distribution profiles were discussed, and based on their relations, tentative suggestions for the chemical compounds present in the samples were made.     

Combined Raman spectrometer/laser-induced breakdown spectrometer for the next ESA mission to Mars

Among the different instruments that have been pre-selected to be on-board the Pasteur payload on ExoMars is the Raman/laser induced breakdown spectroscopy (LIBS) instrument. Raman spectroscopy and LIBS will be integrated into a single instrument sharing many hardware commonalities. An international team under the lead of TNO has been gathered to produce a design concept for a combined Raman spectrometer/LIBS elegant bread-board (EBB). The instrument is based on a specially designed, extremely compact, spectrometer with high resolution over a large wavelength range, suitable for both Raman spectroscopy and LIBS measurements. Low mass, size and power consumption are the main drivers of the instrument's design concept. In this paper, science objectives for the combined instrument are detailed. Background information on Raman spectroscopy and LIBS are presented, focussing on the synergy of these two techniques. In the last section, the instrument concept resulting from the assessment of the feasibility of the combined Raman/LIBS EBB is presented.     

Double pulse laser induced breakdown spectroscopy applied to natural and artificial materials from cultural heritages: A comparison with micro-X-ray fluorescence analysis

The laser-induced breakdown spectroscopy (LIBS) is an applied physical technique that has shown in recent years its great potential for rapid qualitative analysis of materials. Thanks to the possibility to implement a portable instrument that perform LIBS analysis, this technique is revealed to be particularly useful for in situ analysis in the field of cultural heritages. The purpose of this work is to evaluate the potentiality of LIBS technique in the field of cultural heritages, with respect to the chemical characterization of complex matrix as calcareous and refractory materials for further quantitative analyses on cultural heritages. X-Ray Fluorescence (XRF) analyses were used as reference. Calibration curves of certified materials used as standards were obtained by XRF analyses. The LIBS measurements were performed with a new mobile instrument called Modì (Mobile Double pulse Instrument for LIBS Analysis). The XRF analyses were performed with a portable instrument ArtTAX. LIBS and XRF measurement were performed on both reference materials and samples (bricks and mortars) sampled in the ancient Greek–Roman Theatre of Taormina. Although LIBS measurements performed on reference materials have shown non linear response to concentrations, and so we were not able to obtain quantitative results, an integrated study of XRF and LIBS signals permitted us to distinguish among chemical features and degradation state of measured building materials.     

Analysis of environmental lead contamination: comparison of LIBS field and laboratory instruments

The Army Research Office of the Army Research Laboratory recently sponsored the development of a commercial laser-induced breakdown spectroscopy (LIBS) chemical sensor that is sufficiently compact and robust for use in the field. This portable unit was developed primarily for the rapid, non-destructive detection of lead (Pb) in soils and in paint. In order to better characterize the portable system, a comparative study was undertaken in which the performance of the portable system was compared with a laboratory LIBS system at the Army Research Laboratory that employs a much more sophisticated laser and detector. The particular focus of this study was to determine the effects on the performance of the field sensor's lower spectral resolution, lack of detector gating, and the multiple laser pulsing that occurs when using a passively Q-switched laser. Surprisingly, both the laboratory and portable LIBS systems exhibited similar performance with regards to detection of Pb in both soils and in paint over the 0.05–1% concentration levels. This implies that for samples similar to those studied here, high-temporal resolution time gating of the detector is not necessary for quantitative analysis by LIBS. It was also observed that the multiple pulsing of the laser did not have a significant positive or negative effect on the measurement of Pb concentrations. The alternative of using other Pb lines besides the strong 406-nm line was also investigated. No other Pb line was superior in strength to the 406-nm line for the latex paint and the type of soils used in the study, although the emission line at 220 nm in the UV portion of the spectrum holds potential for avoiding elemental interferences. These results are very encouraging for the development of lightweight, portable LIBS sensors that use less expensive and less sophisticated laser and detector components. The portable LIBS system was also field tested successfully at sites of documented Pb contamination on military installations in California and Colorado.     

Double pulse laser induced breakdown spectroscopy applied to natural and artificial materials from cultural heritages : A comparison with micro-X-ray fluorescence analysis

The laser-induced breakdown spectroscopy (LIBS) is an applied physical technique that has shown in recent years its great potential for rapid qualitative analysis of materials. Thanks to the possibility to implement a portable instrument that perform LIBS analysis, this technique is revealed to be particularly useful for in situ analysis in the field of cultural heritages. The purpose of this work is to evaluate the potentiality of LIBS technique in the field of cultural heritages, with respect to the chemical characterization of complex matrix as calcareous and refractory materials for further quantitative analyses on cultural heritages. X-Ray Fluorescence (XRF) analyses were used as reference. Calibration curves of certified materials used as standards were obtained by XRF analyses. The LIBS measurements were performed with a new mobile instrument called Modì (Mobile Double pulse Instrument for LIBS Analysis). The XRF analyses were performed with a portable instrument ArtTAX. LIBS and XRF measurement were performed on both reference materials and samples (bricks and mortars) sampled in the ancient Greek–Roman Theatre of Taormina. Although LIBS measurements performed on reference materials have shown non linear response to concentrations, and so we were not able to obtain quantitative results, an integrated study of XRF and LIBS signals permitted us to distinguish among chemical features and degradation state of measured building materials.     

Laser Induced Breakdown Spectroscopy machine for online ash analyses in coal

Presently, online coal ash content monitoring is performed by PGNAA (Prompt Gamma Neutron Activation Analyses) machines. Laser Detect Systems has developed an online mineral analysis system using Laser Induced Breakdown Spectroscopy (LIBS). The main advantages of the system are that it is without a radioactive source, compact (1.5 m × 0.8 m × 1.3 m), comparatively light (250 kg) and easy to install. The main disadvantage is that a LIBS system analyzes surface chemistry of the mineral exclusively and not the volume. To prove the LIBS machine analytical ability for coal ash content evaluation, a trial was arranged at Optimum Colliery (South Africa). The LIBS machine was installed in line with a PGNAA machine and laboratory data served as a referee in the final assessment for analytical accuracy. The trial was carried out over a four month period. This paper presents the successful trial results achieved for accurate (at least +/− 0.5% mean absolute error) online coal ash content monitoring.     

Laser-induced breakdown spectroscopy analysis of minerals: Carbonates and silicates

Laser-induced breakdown spectroscopy (LIBS) provides an alternative chemical analytical technique that obviates the issues of sample preparation and sample destruction common to most laboratory-based analytical methods. This contribution explores the capability of LIBS analysis to identify carbonate and silicate minerals rapidly and accurately. Fifty-two mineral samples (18 carbonates, 9 pyroxenes and pyroxenoids, 6 amphiboles, 8 phyllosilicates, and 11 feldspars) were analyzed by LIBS. Two composite broadband spectra (averages of 10 shots each) were calculated for each sample to produce two databases each containing the composite LIBS spectra for the same 52 mineral samples. By using correlation coefficients resulting from the regression of the intensities of pairs of LIBS spectra, all 52 minerals were correctly identified in the database. If the LIBS spectra of each sample were compared to a database containing the other 51 minerals, 65% were identified as a mineral of similar composition from the same mineral family. The remaining minerals were misidentified for two reasons: 1) the mineral had high concentrations of an element not present in the database; and 2) the mineral was identified as a mineral with similar elemental composition from a different family. For instance, the Ca–Mg carbonate dolomite was misidentified as the Ca–Mg silicate diopside. This pilot study suggests that LIBS has promise in mineral identification and in situ analysis of minerals that record geological processes.     

激光诱导击穿光谱(LIBS)技术在低碳钢铁冶金行业的应用

激光诱导击穿光谱技术(Laser induced breakdown spectroscopy,简称LIBS)是一种基于激光等离子体的发射光谱技术,具有样品制备简单,分析迅速,多元素同时分析,现场在线和远程分析等独特优势,已在钢铁冶金领域取得了越来越广泛的应用与发展。综述了近年来LIBS技术在钢铁冶金领域的应用研究进展,从冶金生产的全流程进行介绍,包括矿石、熔融钢水/铁水、钢铁产品及炉渣和废气分析。同时,还总结了LIBS技术在钢铁冶金领域应用的优点和缺点,并对该技术的应用前景及未来发展方向进行展望。     

Quantitative determination of wear metals in engine oils using LIBS: The use of paper substrates and a comparison between single- and double-pulse LIBS

A comparison between single- and double-pulse LIBS for the quantitative elemental analysis of used engine oils has been performed. Paper substrates have been utilised for the analysis and are shown to provide better limits of detection (LODs), no splashing and easier sample handling compared to the previously reported experiments using laminar liquid jets and static liquid surfaces. Single-pulse LIBS analysis of oil on paper substrates has had on average 2× better LODs than was obtained using flowing liquid jets, while double-pulse LIBS showed 4× improvement. Single-pulse LIBS has been found preferable for the analysis, as the use of an additional laser in double-pulse LIBS yielded only a minor improvement while adding substantially to the complexity and cost of the system.     

Multivariate classification of pigments and inks using combined Raman spectroscopy and LIBS

The authenticity of objects and artifacts is often the focus of forensic analytic chemistry. In document fraud cases, the most important objective is to determine the origin of a particular ink. Here, we introduce a new approach which utilizes the combination of two analytical methods, namely Raman spectroscopy and laser-induced breakdown spectroscopy (LIBS). The methods provide complementary information on both molecular and elemental composition of samples. The potential of this hyphenation of spectroscopic methods is demonstrated for ten blue and black ink samples on white paper. LIBS and Raman spectra from different inks were fused into a single data matrix, and the number of different groups of inks was determined through multivariate analysis, i.e., principal component analysis, soft independent modelling of class analogy, partial least-squares discriminant analysis, and support vector machine. In all cases, the results obtained with the combined LIBS and Raman spectra were found to be superior to those obtained with the individual Raman or LIBS data sets.     

Characterization and forensic analysis of soil samples using laser-induced breakdown spectroscopy (LIBS)

A method for the quantitative elemental analysis of surface soil samples using laser-induced breakdown spectroscopy (LIBS) was developed and applied to the analysis of bulk soil samples for discrimination between specimens. The use of a 266 nm laser for LIBS analysis is reported for the first time in forensic soil analysis. Optimization of the LIBS method is discussed, and the results compared favorably to a laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) method previously developed. Precision for both methods was <10% for most elements. LIBS limits of detection were <33 ppm and bias <40% for most elements. In a proof of principle study, the LIBS method successfully discriminated samples from two different sites in Dade County, FL. Analysis of variance, Tukey’s post hoc test and Student’s t test resulted in 100% discrimination with no type I or type II errors. Principal components analysis (PCA) resulted in clear groupings of the two sites. A correct classification rate of 99.4% was obtained with linear discriminant analysis using leave-one-out validation. Similar results were obtained when the same samples were analyzed by LA-ICP-MS, showing that LIBS can provide similar information to LA-ICP-MS. In a forensic sampling/spatial heterogeneity study, the variation between sites, between sub-plots, between samples and within samples was examined on three similar Dade sites. The closer the sampling locations, the closer the grouping on a PCA plot and the higher the misclassification rate. These results underscore the importance of careful sampling for geographic site characterization.     

Multivariate analysis of laser-induced breakdown spectroscopy chemical signatures for geomaterial classification

A large suite of natural carbonate, fluorite and silicate geological materials was studied using laser-induced breakdown spectroscopy (LIBS). Both single- and double-pulse LIBS spectra were acquired using close-contact benchtop and standoff (25 m) LIBS systems. Principal components analysis (PCA) and partial least squares discriminant analysis (PLS-DA) were used to identify the distinguishing characteristics of the geological samples and to classify the materials. Excellent discrimination was achieved with all sample types using PLS-DA and several techniques for improving sample classification were identified. The laboratory double-pulse LIBS system did not provide any advantage for sample classification over the single-pulse LIBS system, except in the case of the soil samples. The standoff LIBS system provided comparable results to the laboratory systems. This work also demonstrates how PCA can be used to identify spectral differences between similar sample types based on minor impurities.     

Applications of laser-induced breakdown spectroscopy for geochemical and environmental analysis: A comprehensive review

Applications of laser-induced breakdown spectroscopy (LIBS) have been growing rapidly and continue to be extended to a broad range of materials. This paper reviews recent application of LIBS for the analysis of geological and environmental materials, here termed "GEOLIBS" . Following a summary of fundamentals of the LIBS analytical technique and its potential for chemical analysis in real time, the history of the application of LIBS to the analysis of natural fluids, minerals, rocks, soils, sediments, and other natural materials is described.     

Review: Applications of single-shot laser-induced breakdown spectroscopy

As applications for laser-induced breakdown spectroscopy (LIBS) become more varied with a greater number of field and industrial LIBS systems developed and as the technique evolves to be more quantitative that qualitative, there is a more significant need for LIBS systems capable of analysis with the use of a single laser shot. In single-shot LIBS, a single laser pulse is used to form a single plasma for spectral analysis. In typical LIBS measurements, multiple laser pulses are formed and collected and an ensemble-averaged method is applied to the spectra. For some applications there is a need for rapid chemical analysis and/or non-destructive measurements; therefore, LIBS is performed using a single laser shot. This article reviews in brief several applications that demonstrate the applicability and need for single-shot LIBS.     

Sampling statistics and considerations for single-shot analysis using laser-induced breakdown spectroscopy

A statistical analysis of single-shot spectral data is reported for laser-induced breakdown spectroscopy (LIBS). Fluctuations in both atomic emission and plasma continuum emission are investigated in concert for a homogenous gaseous flow, and fluctuations in plasma temperature are reported based on iron atomic emission in an aerosol-seeded flow. Threshold irradiance for plasma initiation and plasma absorption were investigated for pure gaseous and aerosol streams, with detailed statistical measurements performed as a function of pulse energy in the breakdown regime. The ratio of the analyte atomic emission intensity to the continuum emission intensity (peak/base) provided a robust signal for single-shot LIBS analysis. Moreover, at optimal temporal delay, the precision of the LIBS signal was maximized for pulse energies within the saturation regime with respect to plasma absorption of incident energy. Finally, single-shot temperature measurements were analyzed, leading to the conclusion that spatial variations in the plasma volume formation and subsequent plasma emission collection, play important roles in the overall shot-to-shot precision of the LIBS technique for gaseous and aerosol analysis.     

Comparisons between LIBS and ICP/OES

In the framework of the development of new techniques, the ability of laser-induced breakdown spectroscopy (LIBS) to analyse remotely complex aqueous solutions was investigated. The jet configuration with a collimated gas stream was chosen because it appeared to be the most promising method for the LIBS probe, particularly in terms of sensitivity and repeatability. For emission collection, the echelle spectrometer offers a simultaneously recorded wavelength range from the UV to the near IR and is interesting for multielemental analysis for LIBS and also for inductively coupled plasma (ICP) optical emission spectroscopy (OES). The importance of parameters influencing the quantitative results of LIBS such as multispecies analysis, sheath gas, use of an internal standard and temporal parameters for analysis is described. LIBS quantitative data have been directly compared with results from the more standard ICP/OES technique.     

Dual-pulse laser induced breakdown spectroscopy: Time-resolved transmission and spectral measurements

Spectral analysis of laser-induced plasmas for surface ablation has demonstrated the possibility of analyte signal enhancement with dual-pulse configurations as compared with traditional single-pulse LIBS. Using an orthogonal dual-pulse arrangement, measurements were performed using glass microscope slides to allow both spectral analysis as well as optical transmission measurements. Order of magnitude enhancements in Mg and Si atomic emission signal peak intensities were recorded along with similar enhancements of the continuum emission for dual-pulse LIBS as compared to single-pulse. Peak-to-base measurements showed a roughly 50% increase, while signal-to-noise ratios were enhanced by a factor of 2–3. Temporal analysis of the measured transmitted laser pulse waveforms showed no significant differences between dual-pulse and single-pulse LIBS configurations, providing additional insight into the possible laser coupling processes for the dual-pulse configuration.