In general, the detection of F and other halogens is challenging through conventional techniques. In this paper, various approaches for the qualitative and quantitative analysis of F using the laser-induced breakdown spectroscopy (LIBS) technique were demonstrated. In LIBS, fluorine detection can be realized by means of atomic lines and molecular bands. For the purposes of our experiment, two sets of pellets with various contents of CaF2, CaCO3 and cellulose were analyzed using a lab-based LIBS system under a He atmosphere. The fluorine atomic line at 685.60 nm was correlated with CaF signals proving their close relationship. Consequently, the limits of detection were determined for both analytical signals. Moreover, conditions necessary for the quantification of F via CaF band signals were estimated. The dependence of the CaF signal on the varying ratio of Ca and F contents was investigated. Finally, a chip of a real CaF2 crystal was prepared and its surface was mapped with Raman and LIBS systems. The obtained elemental and molecular maps showed good numerical correlations. Thus, the yielded results validated the possibility to substitute the fluorine atomic line by non-conventional CaF molecular bands in the qualitative and quantitative LIBS analysis of fluorine.

Laser-induced breakdown spectroscopy; Raman spectroscopy; Chemometrics; Bacteria;

In this work, we investigate the impact of data provided by complementary laser-based spectroscopic methods on multivariate classification accuracy. Discrimination and classification of five Staphylococcus bacterial strains and one strain of Escherichia coli is presented. The technique that we used for measurements is a combination of Raman spectroscopy and Laser-Induced Breakdown Spectroscopy (LIBS). Obtained spectroscopic data were then processed using Multivariate Data Analysis algorithms. Principal Components Analysis (PCA) was selected as the most suitable technique for visualization of bacterial strains data. To classify the bacterial strains, we used Neural Networks, namely a supervised version of Kohonen's self-organizing maps (SOM). We were processing results in three different ways - separately from LIBS measurements, from Raman measurements, and we also merged data from both mentioned methods. The three types of results were then compared. By applying the PCA to Raman spectroscopy data, we observed that two bacterial strains were fully distinguished from the rest of the data set. In the case of LIBS data, three bacterial strains were fully discriminated. Using a combination of data from both methods, we achieved the complete discrimination of all bacterial strains. All the data were classified with a high success rate using SOM algorithm. The most accurate classification was obtained using a combination of data from both techniques. The classification accuracy varied, depending on specific samples and techniques. As for LIBS, the classification accuracy ranged from 45% to 100%, as for Raman Spectroscopy from 50% to 100% and in case of merged data, all samples were classified correctly. Based on the results of the experiments presented in this work, we can assume that the combination of Raman spectroscopy and LIBS significantly enhances discrimination and classification accuracy of bacterial species and strains. The reason is the complementarity in obtained chemical information while using these two methods.

Laser-Induced Breakdown Spectroscopy; ;

In this work, we proposed a new data acquisition approach that significantly improves the repetition rates of Laser-Induced Breakdown Spectroscopy (LIBS) experiments, where high-end echelle spectrometers and intensified detectors are commonly used. The moderate repetition rates of recent LIBS systems are caused by the utilization of intensified detectors and their slow full frame (i.e. echellogram) readout speeds with consequent necessity for echellogram-to-1D spectrum conversion (intensity vs. wavelength). Therefore, we investigated a new methodology where only the most effective pixels of the echellogram were selected and directly used in the LIBS experiments. Such data processing resulted in significant variable down-selection (more than four orders of magnitude). Samples of 50 sedimentary ores samples (distributed in 13 ore types) were analyzed by LIBS system and then classified by linear and non-linear Multivariate Data Analysis algorithms. The utilization of selected pixels from an echellogram yielded increased classification accuracy compared to the utilization of common 1D spectra.

Laser-induced breakdown spectroscopy LIBS; Spatial confinement; Spectral emissions; Electron temperature;

Spatial confinement effects on plasma parameters and surface morphology of laser ablated Zr are studied by introducing a metallic blocker. Nd:YAG laser at various fluencies ranging from 8 J cm to 32 J cm was employed as an irradiation source. All measurements were performed in the presence of Ar under different pressures. Confinement effects offered by metallic blocker are investigated by placing the blacker at different distances of 6 mm, 8 mm and 10 mm from the target surface. It is revealed from LIBS analysis that both plasma parameters i.e. excitation temperature and electron number density increase with increasing laser fluence due to enhancement in energy deposition. It is also observed that spatial confinement offered by metallic blocker is responsible for the enhancement of both electron temperature and electron number density of Zr plasma. This is true for all laser fluences and pressures of Ar. Maximum values of electron temperature and electron number density without blocker are 12,600 K and 14 x 10 cm respectively whereas, these values are enhanced to 15,000 K and 21 x 10 cm in the presence of blocker. The physical mechanisms responsible for the enhancement of Zr plasma parameters are plasma compression, confinement and pronounced collisional excitations due to reflection of shock waves. Scanning Electron Microscope analysis was performed to explore the surface morphology of laser ablated Zr. It reveals the formation of cones, cavities and ripples. These features become more distinct and well defined in the presence of blocker due to plasma confinement. The optimum combination of blocker distance, fluence and Ar pressure can identify the suitable conditions for defining the role of plasma parameters for surface structuring.

ENERGY DEPOSITION; IGNITION ENERGY; DRAG REDUCTION; FLOW-CONTROL; SPARK-IGNITION; INDUCED PLASMA; HIGH-SPEED; COMBUSTION; MIXTURES; WAVE

To optimize a laser ignition scheme, absorption rate measurements and Schlieren visualizations are performed on dual-pulse laser-induced breakdowns at incident energies from 50 mJ to 200 mJ and pulse intervals that range from 20 ns to 250 mu s in quiescent air at atmospheric pressure. For comparison, experiments on single-pulse LIBs are also conducted. The shock loss is determined using a semi-empirical model , and quantitative information on the spatial distribution of the hot plume is extracted from Schlieren images using in-house code. The results reveal that multi-location laser ignition can be achieved without reducing the energy absorption or strengthening the shock loss only when the energy of each laser pulse exceeds 200 mJ. This requirement is because the absorption rate of single-pulse LIB decreases significantly when the laser energy is lower than 200 mJ, and the shock loss of single-pulse LIB invariably accounts for approximately 80% of the absorbed laser energy at various incident energies. Compared with single-pulse LIB, dual-pulse LIB with a pulse interval of less than 200 ns is slightly inferior in terms of energy absorption and shock loss; however, the advantages of a larger initial plasma volume and lower energy dissipation can compensate for this deficiency. Therefore, dual-pulse laser ignition is a promising alternative to single-pulse laser ignition. Moreover, ignition reliability can be enhanced by initially releasing the laser pulse with higher energy when the energies of the successive pulses are not the same because of higher energy absorption and lower shock loss. In addition, the spatial distribution of the resulting hot plume is relatively centralized, which helps to reduce energy and radical dissipation. However, a pulse interval longer than 200 ns should be avoided for dual-pulse LIB because the laser energy cannot be utilized efficiently.

SPECTRAL-LINE; EMISSION-LINES; INDUCED FLUORESCENCE; RESONANCE LINES; INDUCED PLASMAS; COEFFICIENTS; PRESSURE; ALUMINUM; CALIBRATION; LIBS

Reducing self-absorption is one of the most important steps in achieving accurate analyses in laser-induced breakdown spectroscopy . In this work, LIBSassisted with laser-stimulated absorption was used to reduce self-absorption effects in LIBS. A wavelength-tunable laser was used to resonantly excite cold atoms and reduce their amount in laser-induced plasmas, and thus fewer cold atoms at the plasma periphery re-absorb light from the plasma center. Accordingly, the self-absorption effect was reduced. Copper and chromium elements in steels were taken as examples to evaluate and compare the self-absorption effects in LIBS and LSA-LIBS. The results of calculated self-absorption coefficients supported the effectiveness in reducing self-absorption and improving analytical linearity using LSA-LIBS.

INDUCED BREAKDOWN SPECTROMETRY; INDUCED PLASMA SPECTROMETRY; JEWELRY INDUSTRY; SPECTROSCOPY; METALS; STEEL

In this study, galvanic coatings of Cu and Ni, typically applied in industrial standard routines, were investigated. Ablation experiments were carried out using the first two harmonic wavelengths of a pulsed Nd: YAG laser and the resulting plasma spectra were analysed using a linear Pearson correlation method. For both wavelengths the absorption/ablation behaviour as well as laser-induced breakdown spectroscopy (LIBS) depth profiles were studied varying laserfluences between 4.3-17.2 J/cm(2) at 532 nm and 2.9-11.7 J/cm(2) at 1064 nm. The LIBS-stratigrams were compared with energy-dispersive X-ray spectroscopy of cross-sections. The ablation rates were calculated and compared to theoretical values originating from a thermal ablation model. Generally, higher ablation rates were obtained with 532 nm light for both materials. The light-plasma interaction is suggested as possible cause of the lower ablation rates in the infrared regime. Neither clear evidence of the pure thermal ablation, nor correlation with optical properties of investigated materials was obtained.

SPECTRUM STANDARDIZATION; QUANTITATIVE-ANALYSIS; LIBS; NORMALIZATION; SIGNAL; MODEL

The uncertainty of collected spectral data is one of the most important issues for the application of laser-induced breakdown spectroscopy (LIBS) quantitative analysis. The fluctuation of the target surface simultaneously affects both the focus depth of the laser beam and the relative collection position, either of which may lead to severe fluctuation of the spectral signal. Thus, in this study, for detecting and reducing the fluctuation, an imaging system was deployed to monitor the plasma, and a mathematical model was also built based on both spectral signal and positional information. An ICCD camera was used to record the image of the plasma so as to detect the plasma and acquire positional information. Furthermore, the relationship between plasma position and specific spectral line intensity was obtained by the fitting function. Five aluminium alloy samples were employed to validate the reliability of the proposed method. As a result, the average RSDs of the samples (with a position fluctuation range of about 2 mm) in different spectral lines (Si 288.15 nm, Fe 273.95 nm, Cu 324.75 nm, Mn 259.37 nm and Mg 280.27 nm) were reduced from 34.57%, 38.86%, 31.05%, 39.74%, and 36.91% (without normalization) to 4.63%, 6.84%, 5.64%, 7.64%, and 4.83% (with the combination method presented in this paper), respectively; the determination coefficients (R-2) reached 0.996, 0.999, 0.989, 0.999, and 0.9999, respectively. These results prove that the proposed method can both improve measurement reliability and guarantee measurement accuracy.

INDUCED BREAKDOWN SPECTROSCOPY; DENSITY; GAS; TEMPERATURE; HYDROGEN; SPECTRA; LIBS

Laboratory plasmas inherently exhibit temperature and density gradients leading to complex investigations. We show that plasmas generated by laser ablation can constitute a robust exception to this. Supported by emission features not observed with other sources, we achieve plasmas of various compositions which are both uniform and in local thermodynamic equilibrium. These properties characterize an ideal radiation source opening multiple perspectives in plasma spectroscopy. The finding also constitutes a breakthrough in the analytical field as fast analyses of complex materials become possible.

ELECTRON NUMBER DENSITY; TEMPORAL EVOLUTION; ABEL-INVERSION; AIR; BREAKDOWN

Microplasma is generated in an ultra-high-pure H-2 and N-2 gas mixture with a Nd:YAG laser device that is operated at the fundamental wavelength of 1064 nm. The gas mixture ratio of H-2 and N-2 is 9 to 1 at a pressure of 1.21 +/- 0.03 10(5) Pa inside a chamber. A Czerny-Turner-type spectrometer and an intensified charge-coupled device are utilized for the recording of plasma emission spectra. The line-of-sight measurements are Abel inverted to determine the radial distributions of electron number density and temperature. Recently derived empirical formulas are utilized for the extraction of values for electron density. The Boltzmann plot and line-to-continuum methods are implemented for the diagnostic of electron excitation temperature. The expansion speed of the plasma kernel maximum electron temperature amounts to 1 km/s at a time delay of 300 ns. The microplasma, initiated by focusing 14 ns, 140 mJ pulses, can be described by an isentropic expansion model. (C) 2017 Optical Society of America

Laser induced breakdown spectroscopy LIBS; Plasma; Calibration; Matrix effect; Particles;INDUCED BREAKDOWN SPECTROSCOPY; ELEMENTAL ANALYSIS; QUANTITATIVE-ANALYSIS; SAMPLES; NORMALIZATION; PARAMETERS; AEROSOLS; LIBS

The laser induced plasma spectroscopy was applied on particles attached on substrate represented by a silica wafer covered with a thin oil film. The substrate itself weakly interacts with a ns Nd:YAG laser (1064 nm) while presence of particles strongly enhances the plasma emission, here detected by a compact spectrometer array. Variations of the sample mass from one laser spot to another exceed one order of magnitude, as estimated by on-line photography and the initial image calibration for different sample loadings. Consequently, the spectral lines from particles show extreme intensity fluctuations from one sampling point to another, between the detection threshold and the detector's saturation in some cases. In such conditions the common calibration approach based on the averaged spectra, also when considering ratios of the element lines i.e. concentrations, produces errors too large for measuring the sample compositions. On the other hand, intensities of an analytical and the reference line from single shot spectra are linearly correlated. The corresponding slope depends on the concentration ratio and it is weakly sensitive to fluctuations of the plasma temperature inside the data set. A use of the slopes for constructing the calibration graphs significantly reduces the error bars but it does not eliminate the point scattering caused by the matrix effect, which is also responsible for large differences in the average plasma temperatures among the samples. Well aligned calibration points were obtained after identifying the couples of transitions less sensitive to variations of the plasma temperature, and this was achieved by simple theoretical simulations. Such selection of the analytical lines minimizes the matrix effect, and together with the chosen calibration approach, allows to measure the relative element concentrations even in highly unstable laserinduced plasmas. (C) 2017 Elsevier B.V. All rights reserved.

Time-of-flight mass spectroscopy; Laser induced breakdown spectroscopy; Tungsten plasma; Multi-charged ions; Dynamic plasma sheath;INDUCED-BREAKDOWN-SPECTROSCOPY; ABLATION; SPECTROMETRY; LIBS

In this work, the plasma was produced by irradiating a tungsten target with an 8 ns pulsed Nd:YAG (lambda = 1064 nm) laser in a vacuum chamber under the pressure of 4 x 10(-4) Pa. The optical and particle emissions were systematically investigated using laser induced breakdown spectroscopy and time-of-flight mass spectroscopy respectively. The results showed that not only there were neutral and single ionized atoms in the laser induced plasma, but also quite a number of multi-charged ions were observed. The ion charge state was even up to 6 at the laser power density of similar to 11 GW/cm(2). Time and space resolved optical spectroscopy was investigated by using a bundle of lined fibers. Meanwhile, the time-resolved mass spectrometric study of laser produced tungsten plasma was carried out. The variation in intensities of the different species with time showed that higher charged ions reached their peak intensities earlier. This demonstrated that the higher charged ions had higher velocities and the different charged ions were separated during the expansion process. The kinetic energy corresponding to the velocity of the ions was found to increase exponentially with ionic charge state which was related to the acceleration of the dynamic plasma sheath. (C) 2017 Elsevier B.V. All rights reserved.

Magnetic field; Lithium plasma; Excited state; Recombination cross-section; Libs;INDUCED BREAKDOWN SPECTROSCOPY; OPTICAL-EMISSION SPECTROSCOPY

In this paper, the effect of magnetic field (1.1 T) on the atomic and ionic spectral emission of a laser produced lithium plasma at low pressure has been investigated. The experimental results indicate that magnetic field enhances the intensities of Li I spectral lines but reduces the Li II spectral lines intensities. In this study, two narrowband filters were placed before the ICCD camera to observe the evolution feature of Li II spectral line (548.39 nm, 2p(3)P(2,1,0)-> 2s(3)S(1)) and Li I spectral line (610.30 nm, 3d(2)P(3/2,5/2) -> 2p(2)P(1/2,3/2)), respectively. The plasma dynamic images show that with the magnetic field, the number density of luminous Li atoms is higher, while the number density of luminous Li ions is lower in comparison to the field-free case. The reduced Li II spectral intensities indicate that the quenching rate of Li ions in the excited state is greater than that without the magnetic field. The enhanced impact frequency of recombination indicates that magnetic field increases the recombination process of electron and Li ions. All of these observations strongly suggest that magnetic confinement increases the recombination process of the electrons with Li ions in the plasma, which results in the decrease in the intensity of Li II line. The results are useful for applying laser-induced breakdown spectroscopy (LIBS) to in-situ diagnose the processes of lithium wall conditioning in EAST tokamak. (C) 2017 Elsevier B.V. All rights reserved.

INDUCED BREAKDOWN SPECTROSCOPY; INDUCED ALUMINUM PLASMA; FEMTOSECOND LASER; ISOTOPIC SPECTROMETRY; TEMPORAL EVOLUTION; EMISSION-SPECTRA; ABLATION; ALO; DYNAMICS; CARBON

Measurements with Laser Ablation Molecular Isotopic Spectrometry (LAMIS) are usually performed in atmosphere for rapid isotope analysis, and an understanding of molecule formation via plasma-air chemical reactions is important for quantitative analysis by LAMIS. In this work, the expansion of a plasma plume from ablation of pure aluminum in air is studied with time-and space-resolved monochromatic imaging and emission spectroscopy. The distributions of neutral Al and O atoms and AlO radicals formed through plasma chemical reactions are characterized. The emission spectra of the AlO bands of a B-2 Sigma(+)-X-2 Sigma(+) system are recorded and the rotational-vibrational temperature was obtained through fitting experimental spectra. Inter-molecular vibrational band interference is well reconstructed, and self-absorption of bandheads, especially for the (0-0) band, is corrected. Interpretation of the spatial-temporal evolutions of plasma species and plasma temperature provides insights into the formation mechanism of AlO radicals in laser-induced plasma.

Laser-induced breakdown spectroscopy; Femtosecond laser; Double-pulse; Enhancement mechanism;INDUCED BREAKDOWN SPECTROSCOPY; SIGNAL ENHANCEMENT; METALLIC SAMPLES; OPTICAL-EMISSION; ABLATION; NANOSECOND; SILICON; ALUMINUM; SINGLE; COPPER

A dual-wavelength femtosecond double-pulse laser is used to induce the Cu plasma spectroscopy in air. The laser wavelengths are a fundamental wavelength (800 nm) and a second harmonic wavelength (400 nm) from Ti:sapphire laser. The inter-pulse delay of double-pulse is from 300 ps to 160 ps. The observed spectral intensity is dependent on the inter-pulse delay of the dual-wavelength femtosecond double-pulse. We analyze the characteristics of the plasma temperature and the electron number density on the inter-pulse delay of double-pulse with two different wavelengths. For 800 nm + 400 nm, the spectral emission enhancement is based on more material ablation. For 400 nm + 800 nm, the enhanced mechanism is plasma reheating effect. This study will provide a better way to understand the mechanism of femtosecond double-pulse LIBS. (C) 2017 Elsevier Ltd. All rights reserved.

Plasma; Laser; EPR; DP-LIBS; Mn-analysis; PVA polymer;INDUCED PLASMA SPECTROSCOPY; INDUCED BREAKDOWN SPECTROSCOPY; SINGLE; EPR; IDENTIFICATION; ULTRAVIOLET; CRYSTALS; LIBS

Series of manganese-co-precipitated poly (vinyl alcohol) (PVA) polymer were quantitatively and qualitatively analyzed using laser ablation system (LAS) based on double-pulse laser induced breakdown spectroscopy (DP-LIBS) and electron paramagnetic resonance (EPR) spectroscopy. The collinear nanosecond laser beams of 266 and 1064 nm were optimized to focus on the surface of the PVA polymer target. Both laser beams were employed to estimate the natural properties of the excited Mn-PVA plasma, such as electron number density (Ne), electron temperature (T-e), and Mn concentration. Individual transition lines of manganese (Mn), carbon (C), lithium (Li), hydrogen (H) and oxygen (0) atoms are identified based on the NIST spectral database. The results show better responses with DP-LIBS than the single-pulse laser induced breakdown spectroscopy (SP-LIBS). On the other hand, the EPR investigation shows characteristic broad peak of Mn-nano-particles (Mn-NPs) in the range of quantum dots of superparamagnetic materials. The line width (peak-to-peak, triangle H-pp) and g-value of the observed Mn-EPR peak are similar to 20 mT and 2.0046, respectively. The intensities of Mn-emission line at a wavelength 403.07 nm and the Mn-EPR absorption peak were used to accurate quantify the Mn-content in the polymer matrix. The results produce linear trends within the studied concentration range with regression coefficient (R-2) value of similar to 0.99, and limit of detection (LOD) of 0.026 mol.% and 0.016 mol.%, respectively. The LOD values are at a fold change of about -0.2 of the studied lowest mol.%. The proposed protocols of trace element detection are of significant advantage and can be applied to the other metal analysis. (C) 2017 Elsevier Ltd. All rights reserved.

MOLECULAR ISOTOPIC SPECTROMETRY; MASS-SPECTROMETRY; AB-INITIO; EMISSION-SPECTRA; ALO; AL2O; ABSORPTION; CHEMISTRY; SURFACE; SYSTEM

Identification of chemical intermediates and study of chemical reaction pathways and mechanisms in laser-induced plasmas are important for laser-ablated applications. Laser-induced breakdown spectroscopy (LIBS), as a promising spectroscopic technique, is efficient for elemental analyses but can only provide limited information about chemical products in laser-induced plasmas. In this work, time-resolved resonance fluorescence spectroscopy was studied as a promising tool for the study of chemical reactions in laser-induced plasmas. Resonance fluorescence excitation of diatomic aluminum monoxide (AlO) and triatomic dialuminum monoxide (Al2O) was used to identify these chemical intermediates. Time-resolved fluorescence spectra of AlO and Al2O were used to observe the temporal evolution in laser-induced Al plasmas and to study their formation in the Al-O-2 chemistry in air. (C) 2017 Optical Society of America

SPATIAL CONFINEMENT; BEAM GEOMETRY; SPECTROSCOPY; IMPROVEMENT; EXPOSURE

The inevitable problems in laser induced breakdown spectroscopy are matrix effect and statistical fluctuation of the spectral signal, which can be partly avoided by utilizing a proper confined unit. The dependences of spectral signal enhancement on relative permittivity were studied by varying materials to confine the plasma, which include polytetrafluoroethylene( PTFE), nylon/dacron, silicagel, and nitrile-butadiene rubber (NBR) with the relative permittivity 2.2, similar to 3.3, 3.6, 8 similar to 13, 15 similar to 22. We found that higher relative permittivity rings induce stronger enhancement ability, which restricts the energy dissipation of plasma better and due to the reflected electromagnetic wave from the wall of different materials, the electromagnetic field of plasma can be well confined and makes the distribution of plasma more orderly. The spectral intensities of the characteristic lines Si I 243.5 nm and Si I 263.1 nm increased approximately 2 times with relative permittivity values from 2.2 to similar to 20. The size dependent enhancement of PTFE was further checked and the maximum gain was realized by using a confinement ring with a diameter size of 5 mm and a height of 3 mm (D5mmH3mm), and the rings with D2mmH1mm and D3mmH2mm also show higher enhancement factor. In view of peak shift, peak lost and accidental peaks in the obtained spectra were properly treated in data progressing; the spectral fluctuation decreased drastically for various materials with different relative permittivities as confined units, which means the core of plasma is stabilized, attributing to the confinement effect. Furthermore, the quantitative analysis in coal shows wonderful results-the prediction fitting coefficient R-2 reaches 0.98 for ash and 0.99 for both volatile and carbon. (C) 2017 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

INDUCED BREAKDOWN SPECTROSCOPY; LASER-ABLATION; LIGHT FILAMENTS; PULSED-LASER; VAPOR PLUME; AIR; PROPAGATION; PLASMA; COPPER; EXPLOSION

High-peak-power fs-laser filaments offer unique characteristics attractive to remote sensing via techniques such as remote laser-induced breakdownspectroscopy (R-LIBS). The dynamics of several ablation mechanisms following the interaction between a filament and a solid determines the emission strength and reproducibility of target plasma, which is of relevance for R-LIBS applications. We investigate the space-and time-resolved dynamics of ionic and atomic emission from copper as well as the surrounding atmosphere in order to understand limitations of fs-filament-ablation for standoff energy delivery. Furthermore, we probe the shock front produced from filament-target interaction using time-resolved shadowgraphy and infer laser-material coupling efficiencies for both single and multiple filament regimes through analysis of shock expansion with the Sedov model for point detonation. The results provide insight into plasma structure for the range of peak powers up to 30 times the critical power for filamentation Pcr. Despite the stochastic nucleation of multiple filaments at peak-powers greater than 16 Pcr, emission of ionic and neutral species increases with pump beam intensity, and short-lived nitrogen emission originating from the ambient is consistently observed. Ultimately, results suggest favorable scaling of emission intensity from target species on the laser pump energy, furthering the prospects for use of filament-solid interactions for remote sensing.

INDUCED BREAKDOWN SPECTROSCOPY; DOUBLE-PULSE; OPTICAL-EMISSION; CAVITY CONFINEMENT; TEMPERATURE; IMPROVEMENT; SILICON

The effect of spatial confinement on femtosecond laser-induced Cu plasmas was investigated by time-resolved spectroscopy. The cylindrical cavities with various diameters (2 and 3 mm) and various heights (2, 3, and 4 mm) were placed on the sample surface. An obvious enhancement in the emission intensity of Cu atomic lines was observed when a cylindrical cavity was used to confine the femtosecond laser-induced Cu plasmas. The results showed that enhancement ratios in femtosecond laser-induced breakdown spectroscopy with spatial confinement varied with cavity diameters and atomic emission lines selected. The spatial confinement effect was not significantly influenced by the cavity height because the height of plasma plume is lower than the cavity height. The maximum enhancement ratio for the emission intensities of the Cu atomic lines was measured to be around 3 at a time delay of 3.5 mu s when the cavity diameter is 2 mm. The spectral enhancement is attributed to the compression of the plasma by the reflected shock wave. Published by AIP Publishing.

Laminar premixed methane-air flame; Laser-induced breakdown spectroscopy; Flames structure; Radial distribution;BURNING COAL PARTICLE; POLARIZATION SPECTROSCOPY; ANALYTICAL TOOL; ATOMIC SODIUM; JET FLAME; SPECTROMETRY; OH; TEMPERATURE; SPARK; RATIO

Laser-induced breakdown spectroscopy was evaluated for the analysis of the structure of laminar premixed methane-air flames. Firstly, breakdown threshold pulse energy and plasma energy in different areas of the flame were measured simultaneously, and an approximate linear relation between them was detected. Secondly, a new approach was proposed to qualitatively characterize the flame temperature distributions based on the plasma energy distributions. Finally, combination of the spatial analysis of the spectrum intensity, plasma energy and equivalence ratio, the laminar premixed flames structure was investigated deeply, including the distribution of the flame temperature, the width and distribution of different flame region (e.g. premixed combustion regions, high temperature regions.),as well as the location of the flame front. (C) 2017 Elsevier B.V. All rights reserved.

Laser induced plasma; Laser-ablation; Laser induced breakdown spectroscopy;INDUCED BREAKDOWN SPECTROSCOPY; ABLATION; DIAGNOSTICS; PICOSECOND; DEPOSITION; EMISSION; DYNAMICS; SURFACE; PULSES; SINGLE

A detailed theoretical and experimental analysis is performed for a wide range of laser operating conditions, typical for laser induced breakdown spectroscopy(LIBS) and laser ablation (LA) experiments on copper metallic target. The plasma parameters were experimentally estimated from the line intensities ratio which reflects the relative population of neutral excited species in the plasma. In the case of LA experiments the highest temperature observed was 8210 +/- 370 K. In case of LIBS measurements, a maximum temperature of 8123 K has been determined. The experimental results are in good agreement with a stationary, hydrodynamic model. We have theoretically investigated the plasma emission based on the generalized collisional-radiative model as implemented in the ADAS interconnected set of computer codes and data collections. The ionic population density distribution over the ground and excited states into the cooper plasma is graphically displayed as output from the code. The theoretical line intensity ratios are in good agreement with experimental values for the electron density and temperature range measured in our experiments. (C) 2017 Elsevier B.V. All rights reserved.

EMISSION-LINES; ALUMINUM; PLASMAS; COAL

A novel self-absorption-free laser-induced breakdown spectroscopy (SAF-LIBS) technique is proposed to directly capture the optically thin spectral line by matching the measured doublet atomic lines intensity ratios with the theoretical one. To realize the experimental SAF-LIBS, the integration time, the fiber collection angle, and the delay time are optimized. The optically thin conditions are validated by comparing the linearity of Boltzmann plots with the traditional self-absorption (SA) correction method and evaluating the SA coefficients. The applicability and limitation of SAF-LIBS on element concentration and laserenergy are also discussed. Univariate quantitative analysis results show that, compared with ordinary LIBS, the average absolute error of aluminum concentration has been reduced by an order of magnitude, which proves that this SAF-LIBS technique is qualified to realize accurate chemical composition measurements. (C) 2017 Optical Society of America

INDUCED BREAKDOWN SPECTROSCOPY; ABLATION; EMISSION; SPARK

The influence of distance between sample surface and focal point on optical emission spectroscopy of laser-induced silicon plasma by a nanosecond Nd:YAG laser operating at the wavelength of 1064 nm was investigated in air. Our results show that the emission intensity of Si (I) 390.6 nm line and N (II) 399.5 nm line depends strongly on the distance between sample surface and focal point. When the surface of ablated sample is away from the focal point of focusing lens, the neutral atomic line (Si(I) signal to be measured) is much higher than the ionic line (interference signal N (II)). Therefore, we can improve the intensity of Si (I) signal to be measured, and reduce the intensity of interference signal N (II). The presented result is mainly based on the reduction of interaction between the plasma plume and the ambient air, leading to much weaker collisions. (C) 2017 Author(s).

SPECTROSCOPY; INTENSITY; LINES; WATER

Temporal behavior of the intensity of Ba I emission lines (413.24 and 553.55 nm) in plasma of optical breakdown induced by femtosecond laser pulses (800 nm, 45 fs, 0.82 mJ) on the surface of BaCl2 aqueous solution was experimentally studied as dependent on delay time t (d) relative to the breakdown onset. The maximum intensity of the Ba I (413.24 nm) line was observed at t (d) = 20 ns, while the intensity of the Ba I (553.55 nm) line reached a maximum at t (d) = 40 ns. At t (d) = 10 ns, the intensity of the Ba I (413.24 nm) line was almost three times as large as that of Ba I (553.55 nm) line (despite the about two orders of magnitude lower probability of spontaneous transition for the former line), which is explained by the recombination cascade. It is established that, in the subsystem of 5d6p (3) D (0) and 6s6p (1) P (0) levels, the Boltzmann distribution is not valid and the local thermodynamic equilibrium is absent.

tungsten ion beam; double-pulse lasers ablation system; laser ablation system; optical Instrumentation;INDUCED BREAKDOWN SPECTROSCOPY; APPLIED ELECTRIC-FIELD; INDUCED PLASMA; SURFACE; SPECTROMETRY; DYNAMICS; WAVELENGTHS; NANOSECOND; PARAMETERS; RADIATION

New tungsten ion source is produced by using single and double-pulse laser ablation system. Combined collinear Nd:YAG laser beams (266+1064 nm) are optimized to focus on the sample in air. Optimization of the experimental parameters is achieved to enhance the signal-to-noise ratio of the emission spectra. The velocity distribution of the emitted plasma cloud is carefully measured. The influences of the potential difference between the bias electrodes, laserwavelength and intensity on the current signal are also studied. The results show that the increase in the tungsten ion velocity under the double-pulse lasers causes the output current signal to increase by about three folds. The electron density and temperature are calculated by using the Stark-broadened line profile of tungsten line and Boltzmann plot method of the upper energy levels, respectively. The signal intensity dependence of the tungsten ion angular distribution is also analyzed. The results indicate that the double-pulse laser ablation configuration is more potent technique for producing more metal ion source deposition, thin film formation, and activated plasma-facing component material.

Laser ablation (LA); Laser induced fluorescence (LIF); Laser-induced breakdown spectroscopy (UBS); Plasma chemistry; Combustion;INDUCED BREAKDOWN SPECTROSCOPY; EXCITED ATOMIC FLUORESCENCE; INDUCED ALUMINUM PLASMA; SELECTIVE EXCITATION; URANIUM; ALO; SOLIDS; SPECTROMETRY; EVOLUTION; DYNAMICS

Oxygen present in the ambient gas medium may affect both laser-induced breakdown spectroscopy (LIBS) and laser-induced fluorescence (LIF) emission through a reduction of emission intensity and persistence. In this study, an evaluation is made on the role of oxygen in the ambient environment under atmospheric pressure conditions in LIBS and laser ablation (LA)-LIF emission. To generate plasmas, 1064 nm, 10 ns pulses were focused on an aluminum alloy sample. LIF was performed by frequency scanning a CW laser over the 396.15 nm (3s(2)4s S-2(1/2) -> 3s(2)3p P-2 degrees(3/2)) Al I transition. Time-resolved emission and fluorescence signals were recorded to evaluate the variation in emission intensity caused by the presence of oxygen. The oxygen partial pressure (p(o)) in the atmospheric pressure environment using N-2 as the makeup gas was varied from 0 to 400 Torr O-2. 2D-fluorescence spectroscopy images were obtained for various oxygen concentrations for simultaneous evaluation of the emission and excitation spectral features. Results showed that the presence of oxygen in the ambient environment reduces the persistence of the LIBS and LIF emission through an oxidation process that depletes the density of atomic species within the resulting laser-produced plasma (LPP) plume. (C) 2017 Elsevier B.V. All rights reserved.

INDUCED BREAKDOWN SPECTROSCOPY; MULTIELEMENT; SAMPLES; CARBON; LINES

The laser induced breakdown spectroscopy (LIBS) technique is an effective method to detect material composition by obtaining the plasma emission spectrum. The overlapping peaks in the spectrum are a fundamental problem in the qualitative and quantitative analysis of LIBS. Based on a curve fitting method, this paper studies an error compensation method to achieve the decomposition and correction of overlapping peaks. The vital step is that the fitting residual is fed back to the overlapping peaks and performs multiple curve fitting processes to obtain a lower residual result. For the quantitative experiments of Cu, the Cu-Fe overlapping peaks in the range of 321-327 nm obtained from the LIBS spectrum of five different concentrations of CuSO4 . 5H(2)O solution were decomposed and corrected using curve fitting and error compensation methods. Compared with the curve fitting method, the error compensation reduced the fitting residual about 18.12-32.64% and improved the correlation about 0.86-1.82%. Then, the calibration curve between the intensity and concentration of the Cu was established. It can be seen that the error compensation method exhibits a higher linear correlation between the intensity and concentration of Cu, which can be applied to the decomposition and correction of overlapping peaks in the LIBS spectrum. (c) 2017 Optical Society of America

INDUCED BREAKDOWN SPECTROSCOPY; LASER-INDUCED FLUORESCENCE; EXCITED ATOMIC FLUORESCENCE; ELEMENTAL ANALYSIS; ABLATION; LIBS; SPECTROMETRY; MECHANISM; METALS; WASTE

Coupling laser-induced fluorescence to laser ablation can reduce detection limits relative to LIBS. The wing of the broadband similar to 193.3 nm emission from unmodified argon fluoride lasers can excite arsenic fluorescence via its 193.76 nm ground state transition for a simple fluorescence scheme. We present argon fluoride-excited laser-ablation laser-excited atomic fluorescence (LA-LEAF) measurements in steel and copper under argon and helium atmospheres. Because the ArF laser saturates the absorption transition and the steel samples show substantial nonspecific iron fluorescence, it is necessary to optimize the laser energy in addition to interpulse delay. LODs are slightly lower under helium (1.0 ppm in steel, 0.15 ppm in copper). These detection limits represent a modest improvement over previous LODs with LIBS, but suggest potential for improvement with line narrowing of the ArF laser.

Silicon; Laser-induced breakdown spectroscopy; Emission spectroscopy; Surface morphology; Periodic surface structures;PLASMA PARAMETERS; SURFACE-MORPHOLOGY; SILICON; ZINC; ALLOY; TEMPERATURE; DIAGNOSTICS; SPECTRA; DENSITY; GAS

The effect of nature and pressure of ambient environment on laser-induced breakdown spectroscopy (LIBS) and ablation mechanisms of silicon (Si) have been investigated. A Q-switched Nd-YAG laser with the wavelength of 1064 nm, pulse duration of 10 ns, and pulsed energy of 50 mJ was employed. Si targets were exposed under ambient environments of inert gases of argon, neon, and helium for different pressures ranging from 5 to 760 torr. The influence of nature and pressure of ambient gases on the emission intensity of Si plasma have been explored by using the LIBS spectrometer system. The plasma parameters such as electron temperature and number density were determined by applying Boltzmann plot and Stark broadening method, respectively. Our experimental results suggest that the nature and pressure of ambient environment play a significant role for generation, recombination, and expansion of plasma and consequently affect the excitation temperature as well as electron density of plasma. The surface morphological analysis of laser-irradiated Si was performed by using scanning electron microscope (SEM). Various kinds of structures, for example laser-induced periodic surface structures or ripples, cones, droplets, and craters have been generated and their density and size are found to be strongly dependent upon the ambient environment. A quantitative analysis of particulate size and crater depth measured from SEM images showed a strong correlation between plasma parameters and the growth of micro/nanostructures on the modified Si surface.

IWDTF; LIBS; Animal manure composts; Cu; Zn;HEAVY-METAL CONTENTS; MULTIELEMENT ANALYSIS; ACCURACY IMPROVEMENT; MINERAL FERTILIZERS; LIVESTOCK FEEDS; TRACE-ELEMENTS; SPECTROMETRY; LIBS; CONTAMINANTS; TRANSFORM

Spectral denoising offers a basis for effective and accurate quantitative modeling of laser-induced breakdown spectroscopy (LIBS). To provide a solution for the defects of the traditional hard threshold function (HTF) and the soft threshold function (STF) for wavelet denoising methods, an improved wavelet dual threshold function (IWDTF) has been developed. Simulation analyses proved that the IWDTF could provide abetter denoising performance than the traditional functions. The IWDTF was applied to LIBS denoising and quantitative modeling of the Cu and Zn contents in representative Chinese aerobic composting samples. The results showed that the best spectral denoising effects for the Cu and Zn models were achieved when the adjustment parameters k(0), a, and theta were 0.9, 0.7 x lambda(1), and 0.1 x pi, and 0.2, 0.2 x lambda(1), and 0.1 x pi, respectively, and corresponding models' performances for Cu and Zn were both greatly improved, yielding R-p(2) of 0.9807 and 0.9177, RMSEP of 67.49 mg/kg and 84.92 mg/kg, and RPD of 3.12 and 3.07, respectively. (C) 2017 Published by Elsevier B.V.

DUAL-PULSE LIBS; INDUCED PLASMA; ABLATION EFFICIENCY; SENSITIVE ANALYSIS; HELIUM PLASMA; FEMTOSECOND; ENHANCEMENT; NANOSECOND; MICROANALYSIS; DEUTERIUM

A time-resolved spectroscopic study is performed by using 125-500 micro-Joule (mu J) ps laser focused directly without the aid of microscope on a Cu plate sample in a variety of low-pressure ambient gases including air, helium and argon. It is shown that the ultrashort mu J laser-induced low-pressure plasma in Ar ambient gas exhibits the typical characteristics of shock wave plasma responsible for the thermal excitation and sharp emission of the analyte atoms. It is found that the highest signal to background (S/B) ratio of about 100 is achieved in 1.3 kPa argon ambient gas and detected with optical multichannel analyzer (OMA) gate delay of 1 ns and gate width of 50 mu s. The emission spectra obtained from pure Zn sample show the effective suppression of the ionic emission with ablation energy around and below 500 mu J. The experimental setup is successfully applied to Cr analysis with low detection limit in steel. In particular, its application to C analysis in steel is demonstrated to resolve the long standing problem of overlapping contributions from the neutral and ionic Fe emission. It is further found that an element of high excitation energy such as fluorine (F) can be clearly detected from a non metal teflon sample. Further, its application to alluminum sample containing various concentrations of Mg, Ca, Fe, and Si impurity elements clearly displays the existence of linear calibration lines promising for quantitative analyses in certain dynamical ranges. Finally, in view of the tiny crater sizes of less than 10 mu m diameter created by the very low ps laserenergy, this technique is promising for micrometer resolution mapping of elemental distribution on the sample surface and its depth profiling. (C) 2017 The Japan Society of Applied Physics

INDUCED BREAKDOWN SPECTROSCOPY; YAG LASER; EMISSION SPECTROSCOPY; PLANT MATERIALS; HYDROGEN; DEUTERIUM; RESIDUES; ABLATION; NITROGEN

We report the experimental evidence of shock wave plasma generation by direct observation of the plasma propagation using 68 mJ 1064 nm Nd-doped yttrium aluminum garnet laser irradiation on a relatively soft organic sample in He ambient gas at 2 kPa. The density jump associated with the arrival of the plasma front at a certain position is detected by means of the highly sensitive interferometric technique, in conjunction with the observation of the first appearance of the plasma emission at the same position and time of the plasma front arrival. The result shows that the plasma front moves at the Sedov speed, which is typical of shock wave propagation, yielding an excellent emission spectrum for the harder sample. The shock front speed is further found to decrease in the case of a softer sample, resulting in lesser spectroscopic performance, as demonstrated by the emission spectra measured from mochi samples of different hardnesses. The result of this study is promising for paving the way to extending the laser-induced breakdown spectroscopy application to the much needed spectrochemical analysis of agricultural and food products. (c) 2017 Optical Society of America

INDUCED BREAKDOWN SPECTROSCOPY; DUAL PULSE EXCITATION; BEAM-DEFLECTION; SINGLE-PULSE; WATER; UNDERWATER; SPECTRA; NANOMATERIALS; SCATTERING; INTERFACE

In this work, the impact of the cavitation bubble on a plasma emission produced after the interaction of the strong focused laser radiation with the target in the liquid was studied. Several experimental techniques were applied to assess different aspects of the complex phenomena of the laser induced breakdown in the liquid media. The results of the fast photography, Schlieren and shadowgraphy techniques were compared with the results of simpler probe beam techniques, transmission and scattering. In addition, emission from the plasma was analysed using optical emission spectroscopy, with aim to relate the quality of the recorded spectral lines to the bubble properties. Bubble had proved to be more convenient surrounding than the liquid for the long lasting plasma emission, due to the high temperature and pressure state inside of it and significantly lower density, which causes less confined plasma. Changes in refractive index of the bubble were also monitored, although in the limited time interval, when the bubble was sufficiently expanded and the refractive index difference between the bubble and the water was large enough to produce glory rings and the bright spot in the bubble's centre. Reshaping of the plasma emission due to the optical properties of the bubble was detected and the need for careful optimization of the optical system was stressed.

Laser induced breakdown spectroscopy (LIBS); Quantitative analysis; Matrix effect; Self-absorption;INDUCED PLASMA SPECTROSCOPY; ARTIFICIAL NEURAL-NETWORK; LEAST-SQUARES REGRESSION; ELEMENTAL ANALYSIS; MULTIVARIATE-ANALYSIS; EMISSION-SPECTROSCOPY; SPECTRAL-LINE; SOIL SAMPLES; IRON-ORE; CHEMCAM INSTRUMENT

This paper reviews methods to compensate for matrix effects and self-absorption during quantitative analysis of compositions of solids measured using LaserInduced Breakdown Spectroscopy (LIBS) and their applications to in-situ analysis. Methods to reduce matrix and self-absorption effects on calibration curves are first introduced. The conditions where calibration curves are applicable to quantification of compositions of solid samples and their limitations are discussed. While calibration-free LIBS (CF-LIBS), which corrects matrix effects theoretically based on the Boltzmann distribution law and Saha equation, has been applied in a number of studies, requirements need to be satisfied for the calculation of chemical compositions to be valid. Also, peaks of all elements contained in the target need to be detected, which is a bottleneck for in-situ analysis of unknown materials. Multivariate analysis techniques are gaining momentum in LIBS analysis. Among the available techniques, principal component regression (PCR) analysis and partial least squares (PLS) regression analysis, which can extract related information to compositions from all spectral data, are widely established methods and have been applied to various fields including in-situ applications in air and for planetary explorations. Artificial neural networks (ANNs), where non-linear effects can be modelled, have also been investigated as a quantitative method and their applications are introduced. The ability to make quantitative estimates based on LIBS signals is seen as a key element for the technique to gain wider acceptance as an analytical method, especially in in-situ applications. In order to accelerate this process, it is recommended that the accuracy should be described using common figures of merit which express the overall normalised accuracy, such as the normalised root mean square errors (NRMSEs), when comparing the accuracy obtained from different setups and analytical methods. (C) 2017 The Authors. Published by Elsevier B.V.

LIBS; Continuous background; Interpolation method; Quantitative;MODEL-FREE ALGORITHM; QUANTITATIVE-ANALYSIS; TRACE-ELEMENTS; CU; REGRESSION; SAMPLES; METALS; LIBS

Laser-induced breakdown spectroscopy (LIBS) is an analytical technique that has gained increasing attention because of many applications. The production of continuous background in LIES is inevitable because of factors associated with laser energy, gate width, time delay, and experimental environment. The continuous background significantly influences the analysis of the spectrum. Researchers have proposed several background correction methods, such as polynomial fitting, Lorenz fitting and model-free methods. However, less of them apply these methods in the field of LIBS Technology, particularly in qualitative and quantitative analyses. This study proposes a method based on spline interpolation for detecting and estimating the continuous background spectrum according to its smooth property characteristic. Experiment on the background correction simulation indicated that, the spline interpolation method acquired the largest signal-to-background ratio (SBR) over polynomial fitting, Lorenz fitting and model-free method after background correction. These background correction methods all acquire larger SBR values than that acquired before background correction (The SBR value before background correction is 10.0992, whereas the SBR values after background correction by spline interpolation, polynomial fitting, Lorentz fitting, and model-free methods are 26.9576, 24.6828,18.9770, and 25.6273 respectively). After adding random noise with different kinds of signal-to-noise ratio to the spectrum, spline interpolation method acquires large SBR value, whereas polynomial fitting and model-free method obtain low SBR values. All of the background correction methods exhibit improved quantitative results of Cu than those acquired before background correction (The linear correlation coefficient value before background correction is 0.9776. Moreover, the linear correlation coefficient values after background correction using spline interpolation, polynomial fitting, Lorentz fitting, and model-free methods are 0.9998, 0.9915, 0.9895, and 0.9940 respectively). The proposed spline interpolation method exhibits better linear correlation and smaller error in the results of the quantitative analysis of Cu compared with polynomial fitting, Lorentz fitting and model-free methods, The simulation and quantitative experimental results show that the spline interpolation method can effectively detect and correct the continuous background. (C) 2017 Elsevier B.V. All rights reserved.

Laser-induced breakdown spectroscopy; Baseline correction; Asymmetric penalty; Convex optimization;PARTIAL LEAST-SQUARES; WAVELET-TRANSFORM; MODEL; LIBS; COAL

For laser-induced breakdown spectroscopy (LIBS) quantitative analysis technique, baseline correction is an essential part for the LIBS data preprocessing. As the widely existing cases, the phenomenon of baseline drift is generated by the fluctuation of laser energy, inhomogeneity of sample surfaces and the background noise, which has aroused the interest of many researchers. Most of the prevalent algorithms usually need to preset some key parameters, such as the suitable spline function and the fitting order, thus do not have adaptability. Based on the characteristics of LIBS, such as the sparsity of spectral peaks and the low-pass filtered feature of baseline, a novel baseline correction and spectral data denoising method is studied in this paper. The improved technology utilizes convex optimization scheme to form a non-parametric baseline correction model. Meanwhile, asymmetric punish function is conducted to enhance signal-noise ratio (SNR) of the LIBS signal and improve reconstruction precision. Furthermore, an efficient iterative algorithm is applied to the optimization process, so as to ensure the convergence of this algorithm. To validate the proposed method, the concentration analysis of Chromium (Cr),Manganese (Mn) and Nickel (Ni) contained in 23 certified high alloy steel samples is assessed by using quantitative models with Partial Least Squares (PLS) and Support Vector Machine (SVM). Because there is no prior knowledge of sample composition and mathematical hypothesis, compared with other methods, the method proposed in this paper has better accuracy in quantitative analysis, and fully reflects its adaptive ability. (C) 2017 Elsevier B.V. All rights reserved.

Filament; AC Stark effect; Rabi sideband; Line broadening; Amplified spontaneous emission;INDUCED BREAKDOWN SPECTROSCOPY; SPECTRAL-LINES; RADIATION; SYSTEM

he temporal evolution of the width and shift of NI746.8 and OI777.4 nm lines is investigated in a filament plasma produced by a tightly focused femtosecond laser pulse (0.9 mJ, 48 fs). The nitrogen line shift and width are determined by the joint action of electron impact shift and the far-off resonance AC Stark effect. The intensive (I = 1.2.10(10) W/cm(2)) electric field of ASE (amplified spontaneous emission) and post-pulses result in a possible LS coupling break for the OI3p P-5 level and the generation of Rabi sidebands. The blueshifted main femtosecond pulse and Rabi sideband cause the stimulated emission of the N-2 1(+) system. The maximal widths of emission lines are approximately 6.7 times larger than the calculated Stark widths. (C) 2017 Elsevier B.V. All rights reserved.

Laser-induced breakdown spectroscopy; SF6 oxygen concentration; Wavelet transform; Partial least square; Quantitative analysis;DISCHARGE

Sulfur hexafluoride (SF6) is widely used in gas-insulated high-voltage equipments due to its excellent insulation and arc extinguishing performance. However, when impurities such as trace water and oxygen are present in SF6, the by-products, which are formed due to equipment faults and partial discharge, can react with these impuriti to form stable sulfur oxyfluorides. The equipment insulation performance can be degraded significantly by those stable sulfur oxyfluorides, causing threat to the safety of the power system. The detection and analysis of the impurities such as water, oxygen and decompositions in SF6 are therefore of great importance. In this paper, laser-induced breakdown spectroscopy is employed to measure trace O in SF6. CaF2 is used as window material to solve the degradation of the excitation energy caused by the corrosion of the window material by SF6 decompositions, to eliminate the pollution problem caused by the reaction between the window material and the breakdown products of SF6 gas, and to reduce the change of plasma state caused by the change of excitation condition. By correcting the spectral baseline with an iterative wavelet transform and suppressing the noise with a wavelet transform with soft thresholding, a limit of detection of 38ppm is achieved from the experimental calibration curve. Furthermore, a quantitative model based on partial least squares (PLS) is developed to achieve better stability and precision.

LIBS; plasma plume; sample temperature; expansion dynamics;INDUCED BREAKDOWN SPECTROSCOPY; DOUBLE-PULSE CONFIGURATION; OPTICAL-EMISSION; MAGNETIC-FIELD; QUANTITATIVE-ANALYSIS; LIBS ANALYSIS; SPECTROMETRY; SINGLE; STEEL; ABLATION

In this paper, we investigated the influence of sample temperature on the expansion dynamics and the optical emission spectroscopy of laser-induced plasma, and Ge was selected as the test sample. The target was heated from room temperature (22 degrees C) to 300 degrees C, and excited in atmospheric environment by using a Q-Switched Nd:YAG pulse laser with the wavelength of 1064 nm. To study the plasma expansion dynamics, we observed the plasma plume at different laser energies (5.0, 7.4 and 9.4 mJ) and different sample temperatures by using time-resolved image. We found that the heated target temperature could accelerate the expansion of plasma plume. Moreover, we also measured the effect of target temperature on the optical emission spectroscopy and signal-to-noise ratio.

Laser ablation; Dust deposition; COMSOL Multiphysics 4.4; Thermal conduction; Urban-industrial aerosols; Limestone;ROMANIA; MODEL; LIDAR; IASI

This paper reports preliminary results concerning thermal effects induced by urban/industrial air pollutants deposited on a limestone rock when heated by pulsed laser in the cleaning process. The process of laser cleaning treatment of the crust is simulated using COMSOL Multiphysics 4.4, finite element analysis software. Scanning Electron Microscopy coupled with Energy Dispersive X-ray Spectroscopy and Laser Induced Breakdown Spectroscopy techniques have been used to analyze the chemical composition of the samples. Two elements found as being present into the dust and in the crust, such as iron and magnesium particles are used for simulation in COMSOL. Therefore, the profiles heat evolutions on the crust surface and inside limestone are obtained as thermal interactions between the three components (iron, magnesium and limestone), simulating the non-homogeneous materials. It has been observed that iron impurities caused by the dust deposition may damage the limestone through a process of overheating, as a consequence of a high thermal conduction phenomenon, recorded for the region with iron impurities and sizes of micrometric order are localized. The thermal contact between the three components results in plots that reflect their thermal interactions. (c) 2017 Elsevier B.V. All rights reserved.

INDUCED BREAKDOWN SPECTROSCOPY; SELF-ABSORPTION; EMISSION-LINES

The temporal evolution of doublet lines intensity ratio, plasma temperature (T) and electron density (N-e) of different radial parts of aluminum plasma as well as the relationship between optically thin condition and plasma characteristics are investigated. With respect to doublet lines intensity ratio, the optimal delay time (t(ot)) when the plasma is optically thin is determined by comparing the experimental intensity ratio of doublet Al(I) lines with the theoretical value. The optimal integration time, fiber collection angle, and delay time corresponding to the optically thin condition are 400 ns, 45 degrees, and 500 ns, respectively, in which case the linearity of the calibration curve reaches 0.98, enabling more accurate composition measurements. The maximum temperature values are reached within 300 ns at 10 degrees, 30 degrees, 45 degrees, and 80 degrees, but after 900 ns at 55 degrees, 60 degrees, and 70 degrees. Combined with the morphologic image of the plasma, we infer that the time at which a radial part of plasma reaches the highest temperature is related to the extent of its expansion. It is generally understood that the faster the radial part of plasma expands, the sooner the temperature reaches its maximum. The radial part of plasma may not be optically thin when the corresponding temperature reaches its maximum. If the highest temperature is obtained earlier, the optically thin condition is likely to appear in the descending stage of the temporal evolution curve of temperature. Otherwise, it may appear in the ascending stage. There seems to be no simple positive correlation between electron density and optically thin condition.

INDUCED BREAKDOWN SPECTROSCOPY; LASER-INDUCED PLASMA; HIGH-PRESSURE BANDS; EXPLOSIVE RESIDUES; CULTURAL-HERITAGE; OPTICAL-EMISSION; ABLATION PLASMAS; SOLID-SURFACES; DYNAMICS; CARBON

In the present work, six novel high energy materials (HEMs) were investigated by femtosecond and nanosecond LIBS techniques with an intention to comprehend the influence of different functional groups as well as their positions on the LIBS emission. The examined HEMS are functional and structural isomers of triazole-substituted nitroarene derivatives and have methyl (CH3), methoxy (OCH3), and amino (NH2) groups in ortho and para positions. CN and C-2 molecular bands along with atomic lines of C, H, N and O were identified in the ns and fs LIBS spectra. As expected, the molecular signatures in the earlier times of plasma expansion were observed to be prominent in femtosecond LIBS spectra. The various formation pathways for CN and C-2 as well as the correlation of emission intensities with C-C, C=C, C-N, and C=N bonds and % O are investigated using the fs and ns LIBS data recorded in air and argon atmospheres. The influence of functional groups and their position on CN and C-2 emissions is elucidated through the CN/C-2 ratio. Furthermore, the detonation parameters of these materials namely oxygen balance, velocity of detonation, detonation pressure and chemical energy of detonation were found to correlate well with the (CN + C-2)/(C + H + N + O) ratio. Such correlation studies are expected to support the understanding and improve the discrimination procedures for such hazardous materials.

Calibration-free laser-induced breakdown spectroscopy; CF-LIBS; self-absorption; Saha-Boltzmann; Stark broadening; standard reference line;QUANTITATIVE ELEMENTAL ANALYSIS; INDUCED PLASMA SPECTROSCOPY; SELF-ABSORPTION; SPECTRAL-LINES; TEMPERATURE; ACCURACY; ALUMINUM

In this work, calibration-free laser-induced breakdown spectroscopy (CF-LIBS) is used to analyze a certified stainless steel sample. Due to self-absorption of the spectral lines from the major element Fe and the sparse lines of trace elements, it is usually not easy to construct the Boltzmann plots of all species. A standard reference line method is proposed here to solve this difficulty under the assumption of local thermodynamic equilibrium so that the same temperature value for all elements present into the plasma can be considered. Based on the concentration and rich spectral lines of Fe, the Stark broadening of Fe(I) 381.584nm and Saha-Boltzmann plots of this element are used to calculate the electron density and the plasma temperature, respectively. In order to determine the plasma temperature accurately, which is seriously affected by self-absorption, a pre-selection procedure for eliminating those spectral lines with strong self-absorption is employed. Then, one spectral line of each element is selected to calculate its corresponding concentration. The results from the standard reference lines with and without self-absorption of Fe are compared. This method allows us to measure trace element content and effectively avoid the adverse effects due to self-absorption.

INDUCED BREAKDOWN SPECTROSCOPY; EMISSION-SPECTROSCOPY; ABLATION; ENHANCEMENT; TITANIUM; ALUMINUM; METALS

The role of spatial confinement for improvement of laser-induced Mg plasma parameters and growth of surface features is investigated by introducing a metallic blocker. Nd: YAG laser at various fluences ranging from 7 to 28 J cm(-2) was employed as an irradiation source. All measurements were performed in the presence of Ar under different pressures. Confinement effects offered by metallic blocker are investigated by placing the blocker at different distances of 6, 8 and 10 mm from the target surface. It is revealed from laser-induced breakdown spectroscopy analysis that both plasma parameters, i.e., excitation temperature and electron number density initially increase with increasing laser fluence due to enhancement in energy deposition. With further increase in laser fluence, a decreasing trend followed by saturation is observed which is attributable to shielding effect and self-regulating regime. It is also observed that spatial confinement offered by metallic blocker is responsible for the significant enhancement of both electron temperature and electron number density of Mg plasma. This is true for all laser fluences and pressures of Ar. Maximum values of electron temperature and electron number density without blocker are 8335 K and 2.4 x 10(16) cm(-3), respectively, whereas these values are enhanced to 12,200 K and 4 x 10(16) cm(-3) in the presence of the blocker. The physical mechanisms responsible for the enhancement of Mg plasma parameters are plasma compression, confinement and pronounced collisional excitations due to reflection of shock waves. Scanning electron microscope analysis was performed to explore the surface morphology of laser-ablated Mg. It reveals the formation of cones, cavities and ripples. These features become more distinct and well defined in the presence of the blocker due to plasma confinement. The optimum combination of blocker distance, fluence and Ar pressure can identify the suitable conditions for defining the role of plasma parameters for surface structuring.

Magnetically confined LIBS; Diatomic transition lines; TiO gamma;INDUCED BREAKDOWN SPECTROSCOPY; OPTICAL-EMISSION; LASER; ALLOYS; FIELD; ENHANCEMENT; NDYAG

This paper is focused on the clarification of the behaviour of various atomic, ionic, and TiO gamma (A(3)Phi-X-3 Delta, Delta v =0) diatomic transition lines as well as the continuum radiations in laser-induced titanium plasma plume by a pair of NdFeB. Depending on their different amount of impressionability from applied fields and electron-impact excitation rate, the responses of each component in optical emission spectrum and background continuum radiation to different applied magnetic field strengths (similar to 0.42-1.12 T) are significantly different. At magnetic fields of 0.98 and 1.12 T, the amount of impressionability for Ti i: 388.2 nm is higher than others, while for TiO gamma molecular transitions, the amount of impressionability factor in a 0.98 T field strength is considerable, because in the first moments after the laser pulse the continuum radiation is dominant, by applying an external magnetic field, this amount of radiation be reduced. The temporal evolution of the optical emission lines shows that choosing a suitable time delay and gate width has a considerable role in further impressionability of externally applied field in case of different elements. The electron density Ne varied from 0.99x10(17) to 11.53x10(17) cm(-3), and the plasma temperature T-e, was obtained in a range of 4835-16818 K by employing maximum applied field of 1.12 T. The supplementary investigations will be conducted towards further improvements of the purposeful analysis of each component in confined plasma by magneto-LIBS technique in order to find new approaches in the field of magnetic confinement.

Femtosecond laser; Laser-induced breakdown spectroscopy; Nanoparticle; Double pulse;FIELD ENHANCEMENT; METALLIC SAMPLES; PLASMA; LIBS; CONFINEMENT; IMPROVEMENT; DISCHARGE; ABLATION; SURFACE; ARRAYS

Metal nanoparticle deposition on sample surface is a promising approach to enhance the emission signal during laser-induced breakdown spectroscopy(LIBS). In this article, strong optical emission enhancement was achieved by combining nanoparticle enhanced LIBS (NELIBS) and double pulse LIBS (DP-LIBS) on a crystal SiO2 sample by using femtosecond laser. Thermal dewetting was used to deposit gold (Au) nanoparticles (NPs) on sample surface and NPs with different size were obtained by altering the thickness of the Au film. It was found that both the size and distribution of Au NPs significantly affected the enhancement effect of NELIBS and the Au NPs made from 7.5 nm gold film had the best enhancement effect. The fundamental features of NELIBS enhancement for dielectric target were investigated by studying the photon absorption process. At a low laser fluence of 4.4 J/cm(2), an enhancement factor of about 13 for spectrum intensity was obtained in NELIBS and reached to 30 after being combined with DP-LIBS. (C) 2017 Elsevier Ltd. All rights reserved.

INDUCED BREAKDOWN SPECTROSCOPY; MOLECULAR ISOTOPIC SPECTROMETRY; URANIUM MONOXIDE; INDUCED PLASMAS; SPECTRA; UO; COMPUTATION; STATES; ORE

We have measured vibronic emission spectra of an oxide of uranium formed after laser ablation of the metal in gaseous oxygen. Specifically, we have measured the time-dependent relative intensity of a band located at approximately 593.6 nm in O-16(2). This band grew in intensity relative to neighboring atomic features as a function time in an oxygen environment but was relatively invariant with time in argon. In addition, we have measured the spectral shift of this band in an O-18(2) atmosphere. Based on this shift, and by comparison with earlier results obtained from free-jet expansion and laser excitation, we can confirm that the oxide in question is UO, consistent with recent reports based on laser ablation in O-16(2) only. Published by AIP Publishing.

Laser induced plasma; Spectral line profile; Continuum intensity; Full width at half maximum (FWHM); Spectral line shift;INDUCED BREAKDOWN SPECTROSCOPY; INDUCED PLASMA DYNAMICS; ABLATION

There are many methods to characterize plasma parameters for laser-induced plasma, optical emission spectra method is a very important one to diagnose laser-induced plasma parameters. In this paper, Nd:YAG solid state laser which output 1064 nm wavelength interact with aluminum alloy sample, the temporal evolution of spectral line profile, spectral line intensity, continuum intensity, line to background intensity ratio, spectral line broadening and spectral line shift were investigated in detail for laser induced aluminum alloy plasma. The results show that the interaction of electrons between atoms and ions are very intense, which leads to electrons production of laser induced plasma at the early stage. Stark broadening effect of spectra lines are distinct and multiple spectral lines are overlapped. With temporal evolution, the electron density and electron temperature decreased quickly, the multiple spectral lines are separated slowly, and the spectral line profile is becoming thinner and symmetric. For Mg I 285.2126 nm characteristic spectral line, the intensity increased with temporal evolution at first, the intensity reached maximum value about 100 ns, and then the intensity decreased with temporal evolution, which is due to the fact that electron and ion are dominated at early stage of laser-induced plasma, atomic spectral line is very weak, with temporal evolution, the process of recombination between electrons dominated and the atomic number density increased, when the atomic number density reached maximum value, the spectral line intensity decreased with temporal evolution because excitation temperature decreased quickly. Taking wavelength in NIST database as reference wavelength, the spectral line shift for Mg I 285.212 7 nm and Zn II 206.200 4 nm take place red shift at early stage of laser induced plasma, the continuum intensity decreased dramatically by power law with temporal evolution, on the contrary, comparing with continuum intensity and spectral line intensity, continuum intensity attenuate sharply, the line to background intensity ratio increase with temporal evolution. This early phenomenon of laser inducedaluminum alloy plasma were discussed in detail from theoretical perspective.

SILICON-WAFERS; CRYSTAL-GROWTH; SOLAR-CELL; AEROSOLS; ABLATION; CU(IN,GA)SE-2; TRANSISTORS; CAPACITANCE; THICKNESS; RESIDUES

The current Largest market share and continually growing industry of the semiconductor manufacturing sector in the US demands rapid and cost-effective quality control and characterization of thin film semiconducting materials. To this end, we demonstrate Laser Induced Breakdown Spectroscopy (LIBS) as a facile and effective analytical tool for rapid process-Line characterization of metal-oxide semiconductor (MOS) transistors and capacitors. Specifically, we carry out quantitative LIBS analysis on siLicon oxide (Si02) thin-films of various thicknesses grown by high-temperature moisture-free oxidation on industrial-grade Si wafers. The stoichiometric ratios of oxygen to siLicon ([O]/[Si]) in various SiO2 films are measured by LIBS anaLyses using an internal calibration technique. The results are verified against benchmark anaLyses based on oxide Layer thicknesses and Laser-induced crater profile topographies from eLLipsometry, scanning electron microscopy (SEM), atomic force microscopy (AFM), and profflometry measurements. The stoichiometric ratios of [O]/[Si] calculated from thickness and profflometry measurements are used to compare with our direct LIBS measurements. Our results indicate good agreement between the LIBS and profibmetry calculation results, demonstrating the future capability of LIBS for thin film characterization during their industrial processing.

Baseline removal; Raman spectroscopy; laser-induced breakdown spectroscopy; LIBS; very near; infrared spectroscopy; VNIR;X-RAY-SPECTRA; LEAST-SQUARES; RAMAN-SPECTRA; NMR-SPECTRA; RECOGNITION; SUBTRACTION; REGRESSION; ALGORITHM

The task of proper baseline or continuum removal is common to nearly all types of spectroscopy. Its goal is to remove any portion of a signal that is irrelevant to features of interest while preserving any predictive information. Despite the importance of baseline removal, median or guessed default parameters are commonly employed, often using commercially available software supplied with instruments. Several published baseline removal algorithms have been shown to be useful for particular spectroscopic applications but their generalizability is ambiguous. The new Custom Baseline Removal (Custom BLR) method presented here generalizes the problem of baseline removal by combining operations from previously proposed methods to synthesize new correction algorithms. It creates novel methods for each technique, application, and training set, discovering new algorithms that maximize the predictive accuracy of the resulting spectroscopic models. In most cases, these learned methods either match or improve on the performance of the best alternative. Examples of these advantages are shown for three different scenarios: quantification of components in near-infrared spectra of corn and laser-induced breakdown spectroscopydata of rocks, and classification/matching of minerals using Raman spectroscopy. Software to implement this optimization is available from the authors. By removing subjectivity from this commonly encountered task, Custom BLR is a significant step toward completely automatic and general baseline removal in spectroscopic and other applications.

CHEMICAL-ANALYSIS; SINGLE-PULSE; AQUEOUS-SOLUTIONS; INDUCED PLASMA; LIQUIDS; PRESSURES; ABLATION; EMISSION; SEA

The influence of laser wavelength on the characteristics of laser-induced breakdown spectroscopy (LIBS) in bulk water was investigated by using 532-and 1064-nm lasers. We demonstrated that higher laser energy does not lead to higher LIBS signals because of the strong plasma shielding occurring at high laser energies, as shown by the spectroscopic and fast imaging results in this work. At threshold energies of 100% breakdown probability, the 1064nm beam could induce a plasma with higher electron density and temperature than the 532nm beam, which leads to higher signal-to-noise ratios and longer lifetimes of the emission lines. (C) 2017 The Japan Society of Applied Physics

Laser-induced breakdown spectroscopy (LIBS); Magnetic properties; Uniaxial anisotropy;INDUCED BREAKDOWN SPECTROSCOPY; LASER-PRODUCED PLASMA; OPTICAL-EMISSION; SAMPLE TEMPERATURE; ALLOYS

Laser-induced breakdown spectroscopy (LIBS) has been investigated as a potential analytical tool for better understanding the role of sample temperature and magnetization on the optical emission of laser-induced plasma for NdFeB sample. The mechanism of optical emission by increasing of sample temperature (T (s) ) and plasma confinement including shock wave in the presence of magnetic field is discussed. The heated samples show a significant decrease in magnetic properties, especially the coercivity and saturation of magnetization. The coercivity and saturation of magnetization of NdFeB were 15000 Oe and 95 emu/g, respectively. The intensity of emission lines decreased with an increase in T (s) for NdFeB sample. The coercivity and saturation of magnetization of samples was monotonically decreased and caused to decrease in LIBS signal intensities.

Laser-induced breakdown spectroscopy; Deep Sea; Double pulse; Cavitation bubble; High pressure;BULK AQUEOUS-SOLUTIONS; ELEMENTAL ANALYSIS; SINGLE-PULSE; SHOCK-WAVES; LIQUIDS; LIBS; EXCITATION; INTENSITY; ABLATION; INSIGHTS

There is a growing interest in the development of sensors use in exploration of the deep ocean. Techniques for the chemical analysis of submerged solids are of special interest, as they show promise for subsea mining applications where a rapid sorting of materials found in the sea bottom would improve efficiency. Laser-Induced Breakdown Spectroscopy (LIBS) has demonstrated potential for this application thanks to its unique capability of providing the atomic composition of submerged solids. Here we present a study on the parameters that affect the spectral response of metallic targets in an oceanic pressure environment. Following laser excitation of the solid, the plasma persistence and the cavitation bubble size are considerably reduced as the hydrostatic pressure increases. These effects are of particular concern in dual pulse excitation as reported here, where a careful choice of the interpulse timing is required. Shadowgraphic images of the plasma demonstrate that cavitation bubbles are formed early after the plasma onset and that the effect of hydrostatic pressure is negligible during the early stage of plasma expansion. Contrarily to what is observed at atmospheric pressure, emission spectra observed at high pressures are characterized by self-absorbed atomic lines on continuum radiation resulting from strong radiative recombination in the electron-rich confined environment. This effect is much less evident with ionic lines due to the much higher energy of the levels involved and ionization energy of ions, as well as to the lower extent of absorption effects occurring in the inner part of the plasma, where ionized species are more abundant. As a result of the smaller shorter-lived cavitation bubble, the LIBS intensity enhancement resulting from dual pulse excitation is reduced when the applied pressure increases. (C) 2017 Elsevier B.V. All rights reserved.

INDUCED BREAKDOWN SPECTROSCOPY; OPTICAL 2ND-HARMONIC GENERATION; PULSES; NANOSECOND; IONIZATION; PLASMA; MEDIA

We observe the third-harmonic generation and second-harmonic generation together with element fluorescence from the interaction of a femtosecond laserfilament with a rough surface sample (sandy soil) in non-phase-matched directions. The harmonics prove to originate from the phase-matched surface harmonics and air filament, then scatter in non-phase-matched directions due to the rough surface. These harmonics occurr when the sample is in the region before and after the laser filament, where the laser intensity is not high enough to excite the element fluorescence. The observed harmonics are related to the element spectroscopy, which will benefit the understanding of the interaction of the laser filament with a solid and be helpful for the application on filament induced breakdown spectroscopy.

laser-induced breakdown spectroscopy; femtosecond laser filament; plasma temperature; electron density;INDUCED BREAKDOWN SPECTROSCOPY

Laser-induced breakdown spectroscopy (LIBS), which is also known as laser-induced plasma spectroscopy (LIPS), is a very promising spectral analysis technique for detecting elemental composition. The possibility of remote operation of LIBS is one of the properties, which expands the application scope of this technique. The remote LIBS technique is based on a long-range lens. With the increase of focusing distance, it is difficult to tightly focus laser pulse due to the diffraction limits. The size of focusing spot increases with focusing distance increasing. This will require extremely high laser energy. Femtosecond laserfilamentation due to optical Kerr effect can be applied to the remote LIBS. During the filament propagation, the waist of laser beam is close to a constant value. The laser intensity inside the filament is about 10(13) W/cm(2) (intensity clamping). The intensity is sufficient to ablate sample and produce the plasma. It can overcome the influence of the diffraction limit in nanosecond LIBS. Although many researchers have studied the femtosecond geometrical focusing and femtosecond filamentation LIBSs, the spectral characteristics have not been completely understood. In this paper, we study the femtosecond laser filament-induced Cu plasma spectroscopy. Femtosecond laser system is an ultrafast Ti:sapphire amplifier (Coherent Libra). The full-width at the half maximum is 50 fs at a wavelength of 800 nm with a repetition rate of 1 kHz and its output energy is 3.5 mJ. A quartz lens with a focal length of 1 m is used to focus the laser to generate a filament channel. The spectral intensity of produced Cu plasma along the filament channel is measured by using the optical emission spectroscopy, and the distribution of Cu(I) intensity versus the distance between sample and focused lens is obtained. The results indicate that in a longer distance range along the filament, plasma spectroscopy has stronger emission due to the intensity clamping effect in femtosecond laser filamentation. In addition, we also calculate the plasma temperature and electron density by using the Boltzmann plot and the Stark broadening. The plasma temperature and electron density along the filament channel can be divided into three main regions:region 1) from 950 mm to 970 mm, in which the plasma temperature and electron density increase with the increase of distance; region 2) from 970 mm to 1030 mm, in which the change of plasma excitation temperature is opposite to the change of electron density; region 3) from 1030 mm to 1050 mm, in which the plasma temperature and electron density decrease with the increase of distance.

PRECURSOR IONIZATION; TEMPORAL EVOLUTION; AMBIENT CONDITIONS; ENERGY-ABSORPTION; SHOCK-WAVE; AIR; SPECTROSCOPY; SPARK; ARGON; ABLATION

Laser-heated gas breakdown plasmas or sparks emit profoundly in the ultraviolet and visible region of the electromagnetic spectrum with contributions from ionic, atomic, and molecular species. Laser created kernels expand into a cold ambient with high velocities during their early lifetime followed by confinement of the plasma kernel and eventually collapse. However, the plasma kernels produced during laser breakdown of gases are also capable of exciting and ionizing the surrounding ambient medium. Two mechanisms can be responsible for excitation and ionization of the surrounding ambient: photoexcitation and ionization by intense ultraviolet emission from the sparks produced during the early times of their creation and/or heating by strong shocks generated by the kernel during its expansion into the ambient. In this study, an investigation is made on the spectral features of on-and off-axis emission of laser-inducedplasma breakdown kernels generated in atmospheric pressure conditions with an aim to elucidate the mechanisms leading to ambient excitation and emission. Pulses from an Nd:YAG laser emitting at 1064 nm with a pulse duration of 6 ns are used to generate plasma kernels. Laser sparks were generated in air, argon, and helium gases to provide different physical properties of expansion dynamics and plasma chemistry considering the differences in laserabsorption properties, mass density, and speciation. Point shadowgraphy and time-resolved imaging were used to evaluate the shock wave and spark self-emission morphology at early and late times, while space and time resolved spectroscopy is used for evaluating the emission features and for inferring plasma physical conditions at on- and off-axis positions. The structure and dynamics of the plasma kernel obtained using imaging techniques are also compared to numerical simulations using the computational fluid dynamics code. The emission from the kernel showed that spectral features from ions, atoms, and molecules are separated in time with early time temperatures and densities in excess of 35 000 K and 4 x 10(18)/cm(3) with an existence of thermal equilibrium. However, the emission from the off-kernel positions from the breakdown plasmas showed enhanced ultraviolet radiation with the presence of N-2 bands and is represented by non-local thermodynamic equilibrium (non-LTE) conditions. Our results also highlight that the ultraviolet radiation emitted during the early time of spark evolution is the predominant source of the photo-excitation of the surrounding medium. Published by AIP Publishing.

Electron number density; Electron temperature; Laser-induced breakdown spectroscopy; Spatial confinement; Spectral emissions;PLASMA; TEMPERATURE; ABLATION; DENSITY

Spatial confinement effects on plasma parameters and surface morphology of laser-ablated Mg are studied by introducing a metallic blocker as well as argon (Ar) gas at different pressures. Nd: YAG laser at various fluences ranging from 7 to 28 J/cm(2) was employed to generate Mg plasma. Confinement effects offered by metallic blocker are investigated by placing the blocker at different distances of 6, 8, and 10 mm from the target surface; whereas spatial confinement offered by environmental gas is explored under four different pressures of 5, 10, 20, and 50 Torr. Laser-induced breakdown spectroscopy analysis revealed that both plasma parameters, that is, excitation temperature and electron number density initially are strongly dependent upon both pressures of environmental gases and distances of blockers. The maximum electron temperature of Mg plasma is achieved at Ar gas pressure of 20 Torr, whereas maximum electron number density is achieved at 50 Torr. It is also observed that spatial confinement offered by metallic blocker is responsible for the significant enhancement of both electron temperature and electron number density of Mg plasma. Maximum values of electron temperature and electron number density without blocker are 8335 K and 2.4 x 10(16) cm(-3), respectively, whereas these values are enhanced to 12,200 K and 4 x 10(16) cm(-3) in the presence of blocker. Physical mechanisms responsible for the enhancement of Mg plasma parameters are plasma compression, confinement and pronounced collisional excitations due to reflection of shock waves. Scanning electron microscope analysis was performed to explore the surface morphology of laser-ablated Mg. It reveals the formation of ripples and channels that become more distinct in the presence of blocker due to plasma confinement. The optimum combination of blocker distance, fluence and Ar pressure can identify the suitable conditions for defining the role of plasma parameters for surface structuring.

NONLINEAR OPTICS; FILAMENTATION; AIR; OPERATION; PULSES; WATER; GAS

We extend the detection range of laser-induced breakdown spectroscopy by combining high-intensity femtosecond laser pulses with high-energy nanosecond - CO2 laser pulses. The femtosecond laser pulses ionize the molecules and generate filament in air. The free electrons generated in the self-confined plasma channel by the femtosecond laser serve as the seed electrons which cause efficient avalanche ionization in the nanosecond - CO2 laser field. We show that the detection distance has been extended by three times with the assistance of femtosecond laser filamentation.

INDUCED BREAKDOWN SPECTROSCOPY; SINGLY IONIZED ALUMINUM; DUAL PULSE EXCITATION; EXPANSION DYNAMICS; ELEMENTAL ANALYSIS; ABLATION PLUME; GENERATION; EMISSION; UNDERWATER; LIQUID

We report on the findings of double-pulse studies performed on an aluminium target submerged in water using Nd: YAG laser pulses. Shadowgraphy measurements were performed to examine the dynamic behaviour of the cavitation bubble that eventually forms some considerable time post-plasma ignition. These measurements were used to inform subsequent investigations designed to probe the bubble environment. The results of time-resolved imaging from within the cavitation bubble following irradiation by a second laser pulse reveal the full dynamic evolution of a plasma formed in such an environment. Rapid displacement of the plasma plume in a direction normal to the target surface followed by a diffusive outwards expansion is observed and a qualitative model is proposed to explain the observed behaviour. Line profiles of several ionic and atomic species were observed within the irradiated cavitation bubble. Electron densities were determined using the Stark broadening of the Al II line at 466.3 nm and electron temperatures inferred using the ratio of the Al II (466.3 nm) and Al I (396.15 nm) lines. Evidence of self-reversal of neutral emission lines was observed at times corresponding to growth and collapse phases of the cavitation bubble suggesting high population density for ground state atoms during these times.

Laser Induced Plasma; LIBS; Radially resolved spectroscopy; Doppler broadening; Shock waves;EXPANSION DYNAMICS; ABLATION; PLASMA

We present a classical spectroscopic approach for investigation of the fast plasma expansion present in Laser Induced Plasma. We show that characteristic form of the spectral lines, caused by significant Doppler effect, contains valuable information regarding the expansion velocity, plasma deceleration, emitters temperature, electron density and so on. The proposed numerical procedure is simple since the inverse Abel transform is not a necessary step. We illustrate this technique analyzing expansion of laser induced copper plasma in ambient gas at low (20Pa) pressure. (C) 2017 Elsevier B.V. All rights reserved.

INDUCED BREAKDOWN SPECTROSCOPY; QUANTITATIVE-ANALYSIS; PULSE; HELIUM; LIBS; CONFIGURATION; MICROANALYSIS; ENHANCEMENT; DEUTERIUM; NM

An experimental study is performed on the time-dependent intensity variations of Zn emission focusing on the triplet (Zn I 481.0 nm) and singlet (Zn I 636.2 nm) emission lines induced under three experimental conditions. A single nanosecond (ns) Nd:YAG laser in standard laser-induced breakdown spectroscopy(LIBS) setup is employed for the investigation of direct shock wave-induced emission characteristics with N-2 ambient gas at 0.4 kPa and the different effects of He ambient gas at 2 kPa. An additional two-laser system consisting of ns and picosecond (ps) lasers in an orthogonal setup is used to study the exclusive role of a He-assisted excitation (HAE) process for the generation of those two Zn emission lines. The results of this study consistently exhibit the dominant triplet emission over the singlet emission marked by initial maximum intensity ratios of 8 and 12 obtained from the experiments using a single-laser setup in N-2 and He ambient gases, respectively, indicating the significant contribution of the HAE mechanism to the enhanced and longer lasting Zn emission in He gas. The experiment using the special two-laser setup further demonstrates the exclusive role of the HAE process in the Zn emission featuring an even markedly higher triplet/singlet intensity ratio of 22. Thus, the results of this study suggest the possibly more general nature of dominant triplet emission phenomena previously found in laser-induced He and Ca emission spectra. (C) 2017 The Japan Society of Applied Physics

laser-induced; plasma emission; molecular spectra;INDUCED-BREAKDOWN-SPECTROSCOPY; LOCAL THERMAL-EQUILIBRIUM; GAS-PHASE REACTIONS; ELEMENTAL ANALYSIS; ISOTOPIC SPECTROMETRY; SELF-ABSORPTION; INDUCED FLUORESCENCE; TITANIUM MONOXIDE; ABLATION PLUMES; FEMTOSECOND

The aim of this paper is the description of the optical emission spectral features of the plasma produced by laser-matter interaction, from a fundamental point of view. The laser induced plasma emission spectra are discussed in connection with the basic mechanisms that take place in the plasma phase at different time delays from the laser pulse. The laser induced plasma being a dynamic system, the hierarchy of the elementary mechanisms changes continuously because the electron number density and the electron temperature decrease during the expansion. As a consequence of this, over the duration of the plasma's persistence the prevailing emitting species changes from ions to atoms and from atoms to molecules. Both atomic and molecular emission spectroscopy are discussed, to convey a complete description of the temporal evolution of laser induced plasma. Current literature, as well as the traditional plasma theories, are presented and discussed in order to give to the reader a general idea of the potentialities and drawbacks of emission spectroscopy in the study of laser induced plasma and its various applications.

laser-induced breakdown spectroscopy; time-resolved; plasma temperature; electron density;INDUCED BREAKDOWN SPECTROSCOPY; AIR PLASMAS; GAS; DISCHARGES; MIXTURES

As an important analytical tool, laser-induced breakdown spectroscopy (LIBS) has been widely used in material analysis, environmental monitoring, and other fields. In recent years, due to increasingly serious air pollution, various LIBS-based on-line air pollution detection techniques are being developed. The temporal evolution of nitrogen plasma characteristics is of great importance for investigating the atmospheric plasma dynamics and developing the LIBSbased air pollution monitoring techniques. Temperature and electron density, which are the most important parameters of a plasma state, directly influence the kinetic behaviors of plasma formation, expansion and degradation processes, as well as the energy transfer efficiency in plasma. In this paper, the temporal evolutions of continuous background radiation, molecular spectral strength, and signal-to-background ratio (SBR) are studied based on time-resolved spectra. The results show that the lifetime of the continuous background radiation is about 700 ns, the N-2(+) (B-2 Sigma(+)(u) -X-2 Sigma(+)(g), v: 0-0) transition line strength reaches a maximum value within 12-15 mu s, the SBR first increases and then stabilizes. Accordingly, the optimal observation period for N-2(+) (B-2 Sigma(+)(u) -X-2 Sigma(+)(g)) band system based plasma temperature investigation should be selected to be between 10 and 25 mu s. The temporal evolution of plasma temperature is determined by fitting experimental spectra to theoretical ones simulated by LIFBASE (a spectral simulation program). As the radiation loss is less than the loss due to the collision cooling, the plasma temperature decays exponentially from similar to 10000 K to similar to 6000 K within 10 28 mu s. By taking into account the instrumental broadening lineshape (Voigt lineshape), the temporal evolutions of Stark broadening and Stark shift of N 746.831 nm atomic line are obtained via Nelder-Mead simplex algorithm, and then the electron density is calculated accordingly. The results show that the electron density decays between 10(17) and 10(16) cm(-3) in magnitude. By comparing the experimental electron decay rate with theoretical values calculated from different mechanisms, it is concluded that a three-body collision recombination is the main mechanism of electron decay.

Laser induced plasma spectroscopy; Spectroscopic plasma diagnostics; Stark broadening; Electron number density; Spectral line shapes and intensities;SINGLY IONIZED SILICON; VISIBLE SIII LINES; II SPECTRAL-LINES; EMISSION-SPECTROSCOPY; OPTICAL-EMISSION; THERMODYNAMIC-EQUILIBRIUM; BROADENING PARAMETERS; SELF-ABSORPTION; HYDROGEN-ATOMS; NEUTRAL ATOM

In this work we summarize, analyze and critically evaluate experimental procedures and results of LIBS electron number density plasma characterization using as examples Stark broadened Si I and Si II line profiles. Selected publications are covering the time period from very beginning of silicon LIBS studies until the end of the year 2015. To perform the analysis of experimental LIBS data, the testing of available semiclassical theoretical Stark broadening parameters for Si I and Si II lines was accomplished first. This is followed by the description of experimental setups, results and details of experimental procedure relevant for the line shape analysis of spectral lines used for plasma characterization. Although most of results and conclusions of this analysis are related to the application of silicon lines for LIBS characterization they are of general importance and may be applied to other elements and different low-temperature plasma sources. The analysis of experimental procedures used for LIBS diagnostics from emission profiles of non-hydrogenic spectral lines is carried out in the following order: the influence of laser ablation and crater formation, spatial and temporal plasma observation, line self-absorption and experimental profile deconvolution, the contribution of ion broadening in comparison with electron impacts contributions to the line width in case of neutral atom line and some other aspects of line shape analysis are considered. The application of Stark shift for LIBS diagnostics is demonstrated and discussed. Finally, the recommendations for an improvement of experimental procedures for LIBS electron number density plasma characterization are offered. (C) 2017 Elsevier B.V. All rights reserved.

Laser-induced breakdown spectroscopy; LIBS; Calibration-free LIBS; Limit of detection; Analytical sensitivity; Calibration; Spatial heterodyne spectroscopy;QUANTITATIVE-ANALYSIS; ELEMENTAL ANALYSIS; PLANT MATERIALS; MOISTURE-CONTENT; CARBON CONTENT; LIBS; COAL; IDENTIFICATION; SOIL; METHODOLOGY

The goal of this review article is to provide a description of recent and novel laser-induced breakdown spectroscopy (LIBS) applications and developments, especially those discussed during the NASLIBS Conference, held during SciX in Providence, RI, in September 2015. This topic was selected in view of the numerous recent overall review papers that have successfully given a broad view of the current understanding of laser-material interactions and plasma development and have also discussed the wide landscape of analytical applications of LIBS. This paper is divided into sections that focus on a few of the many applications under development in the LIBS community. We provide a summary of updates to calibration-free LIBS (CF-LIBS) and associated developments using plasma characteristics to improve quantification in LIBS output, both in a dedicated section and as applications are discussed. We have also described the most recent publications studying the sources, generation, and use of molecular features in LIBS, including those naturally present in the spectra of organic materials, and those induced with the addition of salts to enable the measurement of halogens, not typically present in LIBS signals. In terms of development of applications of LIBS, we focused on the use of LIBS for indirect measurements such as pH and degree of humification in soil and heating value in coal. We also reviewed the extant literature on LIBS analysis of agricultural materials, coal, minerals, and metals. Finally, we discuss the nascent developments of spatially heterodyne spectroscopy, a method that seeks to circumnavigate a serious drawback of most spectrometers - very small optical throughput - through the use of interferometers.

Laser-induced breakdown spectroscopy; remote LIBS; standoff LIBS; spatial heterodyne spectrometer; remote spectroscopy;IN-SITU ANALYSIS; RAMAN-SPECTROSCOPY; QUANTITATIVE-ANALYSIS; SOLID-SURFACES; SAMPLES; PLATFORM; PLASMA; SENSOR; PROBE

A spatial heterodyne spectrometer (SHS) is described for standoff laser-induced breakdown spectroscopy (LIBS) measurements. The spatial heterodyne LIBS spectrometer (SHLS) is a diffraction grating based interferometer with no moving parts that offers a very large field of view, high light throughput, and high spectral resolution in a small package. The field of view of the SHLS spectrometer is shown to be similar to 1 degrees in standoff LIBS measurements. In the SHLS system described here, the collection aperture was defined by the 10mm diffraction gratings in the SHS and standoff LIBS measurements were made up to 20m with no additional collection optics, corresponding to a collection solid angle of 0.2 mu sr, or f/2000, and also using a small telescope to increase the collection efficiency. The use of a microphone was demonstrated to rapidly optimize laser focus for 20m standoff LIBS measurements.

Laser-induced breakdown spectroscopy; LIBS; elemental identification; wavelength similarity coefficient;SEARCH ALGORITHMS; SPECTROSCOPY; PLASMA; LIBRARY

This work proposes a method to perform elemental identification on plasmas produced using the laser-induced breakdown spectroscopy (LIBS) technique. The method is based on the preservation of the relative relevance of the spectral line emission intensities, which is lost during the parametric correlation procedure, by the introduction of a similitude coefficient called wavelength similarity coefficient. Furthermore, it was shown that for identification purposes, a simplified plasma model is sufficient to predict adequately the relative emission intensities in LIBS plasmas. As a result, it is possible to automatically identify the species with high emission signals, while trace detection is also possible by relaxing search conditions, although manual refinement is still required.

Laser-induced breakdown spectroscopy; LIBS; lens-to-sample distance; sample positioning; repeatability;

A simple device based on two commercial laser pointers is described to assist in the analysis of samples that present uneven surfaces and/or irregular shapes using laser-induced breakdown spectroscopy (LIBS). The device allows for easy positioning of the sample surface at a reproducible distance from the focusing lens that conveys the laser pulse to generate the micro-plasma in a LIBS system, with reproducibility better than +/- 0.2 mm. In this way, fluctuations in the fluence (J cm(-2)) are minimized and the LIBS analytical signals can be obtained with a better precision even when samples with irregular surfaces are probed.

Laser-induced breakdown spectroscopy; LIBS; self-absorption; curve-of-growth; COG;INDUCED PLASMA; GROWTH; CURVES

Laser-induced breakdown spectroscopy (LIBS) is a widely used laser spectroscopic technique in various fields, such as material science, forensic science, biological science, and the chemical and pharmaceutical industries. In most LIBS work, the analysis is performed using radiative transitions from atomic emissions. In this study, the plasma temperature and the product Nl (the number density N and the absorption path length l) were determined to evaluate the optical depths and the self-absorption of Sr and Al lines. A binary mixture of strontium nitrate and aluminum oxide was used as a sample, consisting of variety of different concentrations in powder form. Laser-induced breakdown spectroscopy spectra were collected by varying various parameters, such as laserenergy, gate delay time, and gate width time to optimize the LIBS signals. Atomic emission from Sr and Al lines, as observed in the LIBS spectra of different sample compositions, was used to characterize the laser induced plasma and evaluate the optical depths and self-absorption of LIBS.

LiSn alloy; CF LIBS; Surface analysis; Fusion; Liquid metal;LASER-INDUCED-BREAKDOWN; LIQUID LITHIUM; SPECTROSCOPY; DIAGNOSTICS; PLASMAS; LEAD

The difference between the composition of the surface and the inner part of the LiSn sample was studied using Calibration Free Laser Induced BreakdownSpectroscopy (CF-LIBS) method. The sample was analysed under the low pressure (1330 Pa) in Ar atmosphere. The spectra were record using Echelle spectrometer (Mechelle ME5000). Gate delay and gate width was optimised and set to 300 ns. In order to analyse depth profile the LIBS spectra was recorded after each laser shot. The electron density analysed by laser induced plasma was determined separately for each laser shot, which means for each ablated layer of investigated sample. The difference between the individual shots taken at distinct sites of the sample are shown. The CF-LIBS method was used to determine the elemental composition near the surface and in the central part of the LiSn sample. (C) 2016 Published by Elsevier B.V.

laser-induced breakdown spectroscopy; plasma temperature; electron density; limit of detection;ND-YAG LASER; EMISSION

The plasma is generated by focusing a long-pulse (80 mu s) Nd:YAG laser on chromium-doped soil samples. The calibration curves are drawn using the intensity ratio of the chromium spectral line at 425.435 nm with the iron spectral line (425.079 nm) as reference. The regression coefficient of the calibration curve is 0.993, and the limit of detection is 16 mg/kg, which is 19% less than that for the case of a Q-switched laser In the method of long-pulse laser-inducedbreakdown spectroscopy, the laser-induced plasma had a temperature of 15795.907 K and an electron density of 2.988 x 10(17) cm(-3), which exceeded the corresponding plasma parameters of the Q-switched laser-induced breakdown spectroscopy by 75% and 24% respectively.

Laser-induced breakdown spectroscopy; Electron temperature; Number density; Magnetic confinement; Surface structuring;X-RAY-EMISSION; OPTICAL-EMISSION; ELECTRON-DENSITY; CARBON PLASMA; AMBIENT GAS; ABLATION; PLUME; TEMPERATURE; CONFINEMENT; PARAMETERS

The effect of the transverse magnetic field on laser-induced breakdown spectroscopy and surface modifications of germanium (Ge) has been investigated at various fluences. Ge targets were exposed to Nd: YAG laser pulses (1064 nm, 10 ns, 1 Hz) at different fluences ranging from 3 to 25.6 J/cm(2) to generate Ge plasma under argon environment at a pressure of 50 Torr. The magnetic field of strength 0.45 Tesla perpendicular to the direction of plasma expansion was employed by using two permanent magnets. The emission spectra of laser-induced Ge plasma was detected by the laser-induced breakdown spectroscopysystem. The electron temperature and number density of Ge plasma are evaluated by using the Boltzmann plot and stark broadening methods, respectively. The variations in emission intensity, electron temperature (T-e), and number density (n(e)) of Germanium plasma are explored at various fluences, with and without employment of the magnetic field. It is observed that the magnetic field is responsible for significant enhancement of both excitation temperature and number density at all fluences. It is revealed that an excitation temperature increases from T-e,T-max,T-without B = 16,190 to T-e,T-max,T-with B = 20,123 K. Similarly, the two times enhancement in the electron density is observed from n(e,max,without B) = 2 x 10(18) to n(e,max,with B) = 4 x 10(18) cm(-3). The overall enhancement in Ge plasma parameters in the presence of the magnetic field is attributed to the Joule heating effect and adiabatic compression. With increasing fluence both plasma parameters increase and achieve their maxima at a fluence of 12.8 J/cm(2) and then decrease. In order to correlate the plasma parameters with surface modification, scanning electron microscope analysis of irradiated Ge was performed. Droplets and cones are formed for both cases. However, the growth of ridges and distinctness of features is more pronounced in case of the absence of the magnetic field; whereas surface structures become more diffusive in the presence of the magnetic field.

Laser-induced breakdown plasma spectrometry; laser ablation; surface oxide layer; Fe-Ni alloy; Fe-Cr alloy;INDUCED PLASMA SPECTROMETRY; SELF-ABSORPTION; SPECTROSCOPY; CALIBRATION; COPPER

This paper describes the fundamental process of laser ablation occurring in a laser-induced plasma. The sampling process in laser-induced breakdownplasma spectrometry is very complicated and thus has not been fully understood. Our study focused on a relationship between the composition of ablation amounts and the bulk composition, when Fe-based binary alloys were employed as test samples. For this purpose, the ablation amounts of constituent elements in the alloys were determined by ICP-OES, through a method in which ablated deposits by laser irradiation were collected on a glass plate and then dissolved in an acid solution. In Fe-Ni binary alloys, the Ni content in the ablated deposits was almost the same as the bulk composition, which implied that Ni and Fe atoms evaporated along with the chemical composition of the samples; however, in Fe-Cr binary alloys, the Cr content in the ablated deposits was half of the bulk composition, probably because Cr atoms were difficult to be released from the sample surface. X-ray photoelectron spectra of ablated Fe-Cr alloy samples indicated that the resultant surface layer after laser irradiation comprised a thin oxide layer, consisting of Cr2O3 and FeO, and a relatively thick oxide layer beneath the outermost surface oxide, of which the composition was a complex of Cr2O3, Fe and FeO. The reason for this is that the dissociation energy of Cr2O3 is obviously higher than that of FeO, and thus Cr2O3 decomposed with more difficulty and thus left preferentially in a surface oxide layer of the Fe-Cr alloys. As a result, the Cr2O3 layer could suppress the ablation of Cr.

DP-LIBS; Double-ionized Al spectral lines; Electron impact excitation coefficient; De-excitation rate coefficients for Al ions;ABLATION; SINGLE; ATOMS; FIELD

We built a collinear dual-pulse laser-induced breakdown spectroscopy (DP-LIBS) system to study the aluminum (Al) plasma emission by installing a pair of Nd: YAG lasers operating at 266 and 1064 nm. The spectral intensities of selected aluminum doubly-ionized lines were employed to evaluate the optical emission spectra. The influences of the energy ratio of two pulsed lasers on the LIBS intensity for different Al doubly-ionized spectral lines were investigated. The de-excitation rate parameters of the excited ion and the electron impact excitation were computed using the analytical formulas proposed by Smeets and Vriens. The transition probabilities and energy states were computed using Hibbert's configuration interaction, computer package (CIV3). By solving the coupled rate equations including 1s(2)2s(2)2p(6)ns (S-2), 1s(2)2s(2)2p(6)np (P-2), 1s(2)2s(2)2p(6)nd (D-2) (n = 3-5) and 1s(2)2s(2)2p(6)nf (F-2) (n = 4, 5) states, the level population densities were computed. We also proposed a theoretical population model in order to investigate the effectiveness of the various processes that might affect the population of the upper levels in Al plasma by using the rate coefficients. In addition, the population densities for the 19 upper levels were also computed. Good compatibility between the experimental and the theoretical model data had been observed. Our results might be significant as reference data for the optimization of the DP-LIBS spectrometry and diagnostics of laser produced plasmas.

INDUCED BREAKDOWN SPECTROSCOPY; TRANSFORM; IDENTIFICATION; CALIBRATION; SIGNALS; ALLOYS

Laser-induced breakdown spectroscopy (LIBS) is becoming a rapid and easy technique for quantitative elemental analysis. However, the implementation of accurate quantitative LIBS analysis is always subject to noise interference. In this work, in order to improve LIBS analysis performance for trace elements in aluminium alloys, a modified trade-off soft and hard threshold method is proposed based on the wavelet theory, where optimal parameters are deduced to eliminate noise interference. By using the modified algorithm combined with an Al I line at 308.215 nm as an internal standard, the statistical parameters including the determination coefficient (R-2), the root mean square error (RMSE) and the relative standard deviation (RSD) of magnesium (Mg), manganese (Mn) and cuprum (Cu) in aluminium alloys are all significantly improved. The most significant improvement of R-2 is 0.066 for Cu. The maximum RMSE reduction value is 0.583 for Mg, and the mean value of RMSE reduction is 0.261 for all three trace elements. And after de-noising, the value of RSD gets smaller for each trace element. Such results indicate that the optimized algorithm is valid for the effective improvement of the accuracy of quantitative LIBS analysis in the trace element determination of aluminium alloys.

INDUCED BREAKDOWN SPECTROSCOPY; MOLECULAR ISOTOPIC SPECTROMETRY; LASER-INDUCED PLASMA; SECONDARY EXCITATION SOURCE; PRESSURE GLOW-DISCHARGE; OPTICAL-EMISSION; STEEL ANALYSIS; LINE LISTS; BANDS; QUANTIFICATION

Enhancement of the emission intensity by a secondary electric pulse following a laser ablation pulse was investigated in application to the chemical analysis by Laser-Induced Breakdown Spectroscopy (LIBS) and Laser Ablation Molecular Isotopic Spectrometry (LAMIS). A stable reheating pulsed discharge presumably sustained in a diffuse glow regime at atmospheric pressure was demonstrated as a rational approach to increase the sensitivity of the optical emission analysis over the conventional single-pulse laser ablation techniques. The enhancement in the emission intensity was illustrated by several examples of both atomic (Ca, Na) and molecular (OH, AlO, CaF) emission in LIBS and LAMIS, respectively. Especially large emission enhancement was realized for isotopologues (OH)-O-16, (OH)-O-18 and (OD)-O-16 at the transition A(2)Sigma(+)/X-2 Pi(i) (1-0) with clearly resolved lines of their rotational branches. An increase in rotational temperature from 3370 to 4560 K was measured subsequently to the reheating of plasma by a pulsed electric discharge. Such reheating can be especially useful for the minimally destructive analysis, chemical mapping and depth profiling by LIBS. Enhancement in the emission intensity of CaF can be used for further reduction of the detection limits in fluorine determination. A brief review of the earlier publications on the cross-excitation by an electric pulse after laser ablation is provided and a comparison is made to the similar reheating of the ablation plasma in double-pulse LIBS.

Nanoparticle; Counterflow flame; Laser diagnostics; Transport;INDUCED BREAKDOWN SPECTROSCOPY; LIGHT-SCATTERING MEASUREMENTS; SOOT-VOLUME FRACTION; INDUCEDINCANDESCENCE; TITANIA NANOPARTICLES; PARTICLES; SIZE; DEPOSITION

The transport of nanoparticles in the boundary layer is closely related to particle mixing or deposition. We present an in situ imaging of TiO2 particle volume fraction near gas stagnation plane in a counterflow flame by recently developed phase-selective laser-induced breakdown spectroscopy technique. The concentration boundary layer is well resolved with a spatial resolution of 10 pm. Together with a numerical analysis of particle transport equation, the roles of convection, diffusion and thermophoresis are discussed. The calculated profile of particle volume fraction agrees well with experimental measurements, which indicates that current model of nanoparticle transport is capable to quantitatively predict the concentration profile in boundary layers. Further study shows that altering thermophoretic velocity shifts the concentration boundary layer but does not change the shape of concentration profile. The decaying slope is mainly controlled by diffusion process that is dependent on particle size.

Double-pulse laser ablation; Molecular dynamics; Hydrodynamics; Crater depth; Plume reheating;INDUCED BREAKDOWN SPECTROSCOPY; SIGNAL ENHANCEMENT; MOLECULAR-DYNAMICS; METAL TARGETS; SPALLATION; SINGLE

We elaborated two numerical methods, two-temperature hydrodynamics and hybrid two-temperature molecular dynamics, which take into account basic mechanisms of a metal target response to ultra short laser irradiation. The model used for the description of the electronic subsystem is identical for both approaches, while the ionic part is defined by an equation of state in hydrodynamics and by an interatomic potential in molecular dynamics. Since the phase diagram of the equation of state and corresponding potential match reasonably well, the dynamics of laser ablation obtained by both methods is quite similar. This correspondence can be considered as a first step towards the development of a self consistent combined model. Two important processes are highlighted in simulations of double-pulse ablation: (1) the crater depth decrease as a result of recoil flux formation in the nascent plume when the delay between the pulses increases; (2) the plume reheating by the second pulse that gives rise to two three-fold growth of the electron temperature with the delay varying from 0 to 200 ps. (C) 2016 Published by Elsevier B.V.

plasma parameter; laser induced plasma; plasma electron density; Saha-Boltzmann method; Stark broadening method;INDUCED BREAKDOWN SPECTROSCOPY; SPECTROCHEMICAL ANALYSIS; ALUMINUM-ALLOYS; SOLID SAMPLES; ABLATION; LINES; EMISSION; PARAMETERS; TEMPERATURE; LIBS

We report spectroscopic studies on plasma electron number density of laser-induced plasma produced by ns-Nd: YAG laser light pulses on an aluminum sample in air at atmospheric pressure. The effect of different laser energy and the effect of different laser wavelengths were compared. The experimentally observed line profiles of neutral aluminum have been used to extract the excitation temperature using the Boltzmann plot method, whereas the electron number density has been determined from the Stark broadened as well as using the Saha-Boltzmann equation (SBE). Each approach was also carried out by using the Al emission line and Mg emission lines. It was observed that the SBE method generated a little higher electron number density value than the Stark broadening method, but within the experimental uncertainty range. Comparisons of N-e determined by the two methods show the presence of a linear relation which is independent of laser energy or laser wavelength. These results show the applicability of the SBE method for N-e determination, especially when the system does not have any pure emission lines whose electron impact factor is known. Also use of M-g lines gives superior results than Al lines.

LIBS; spatial confinement; cavity height; signal enhancement;INDUCED ALUMINUM PLASMA; TIME-RESOLVED EMISSION; OPTICAL-EMISSION; MAGNETIC-FIELD; PULSE; ENHANCEMENT; ABLATION; SILICON; LIBS; OPTIMIZATION

In this paper, we present a study on the spatial confinement effect of laser-induced plasma with a cylindrical cavity in laser-induced breakdown spectroscopy(LIBS). The emission intensity with the spatial confinement is dependent on the height of the confinement cavity. It is found that, by selecting the appropriate height of cylindrical cavity, the signal enhancement can be significantly increased. At the cylindrical cavity (diameter = 2mm) with a height of 6 mm, the enhancement ratio has the maximum value (approximately 8.3), and the value of the relative standard deviation (RSD) (7.6%) is at a minimum, the repeatability of LIBS signal is best. The results indicate that the height of confinement cavity is very important for LIBS technique to reduce the limit of detection and improve the precision.

SINGLE-PULSE; CAVITATION BUBBLE; ABLATION; CERAMICS; WATER; NANOPARTICLES; LIQUID; DYNAMICS; SPECTRA; METALS

The goal of this study was to investigate whether a secondary plasma can be formed on a non-metallic target under water and to give insight into the related processes. The material of choice here was alumina, since its physical, thermal and mechanical properties are substantially different from those of pure Al, only for which secondary plasma formation was recently demonstrated. To achieve this, plasma and bubble formation on alumina under water after single pulse laser excitation were studied using fast photography, shadowgraphy, Schlieren and LIBS techniques. The results show that the secondary plasma caused by backward heating of the target and successive slow target evaporation into the growing vapour bubble also occurs for alumina. The secondary plasma formed on alumina involves only a narrow interaction region on the target resulting in an almost spherical plume shape. In contrast, on thermally conductive and easily melting/evaporating aluminium, the secondary plasma is intense, with a large volume which is flattened on the target surface. Inside the expanded bubble above the alumina target, glowing particles were not observed. Due to less efficient secondary plasma formation on alumina compared to aluminium, its optical emission only slightly increases at a delay of 400 ns from the laser pulse but emission persists during three bubble cycles with a total duration of about 650 ms. The LIBS spectra related to the secondary plasma are almost free from any continuum component and show narrow emission lines from low excited states. Here we discuss the observed differences in the plasma's spatial, temporal and spectral evolution on the two considered target materials. The obtained results indicate that under water a secondary plasma might be formed on very different materials and that its detection produces a good quality LIBS signal from single pulse excitation using a commercial nanosecond laser source.

FEMTOSECOND DOUBLE-PULSE; OPTICAL-EMISSION; PLASMA; ENHANCEMENT; SILICON

The spatial confinement effect in laser-induced plasma with different distances between the target surface and focal point is investigated by optical emission spectroscopy. A Nd: YAG laser is used to produce plasma from a silicon sample in air atmosphere. When the appropriate distance is selected, the duration of spectral emission enhancement is much longer, and the enhancement effect is much stronger. The phenomenon is attributed to the aspect ratio of the lateral to axial direction of the plasma plume. The plasma plume of a large aspect ratio will interact with the reflected shockwave in a long range of delay time, leading to high particle density. This provided a better understanding about the effect of the distance between the target surface and focal point, leading to better conditions for spatially confined laser-induced breakdown spectroscopy.

chemometrics; ion recombination; laser-induced breakdown spectroscopy; LIBS; MCR-ALS; mean field-independent components analysis; MFICA; molecular formation; multivariate curve resolution-alternating least squares; temporal evolution;ARTIFICIAL NEURAL-NETWORKS; QUANTITATIVE-ANALYSIS; TEMPORAL EVOLUTION; WAVELET-TRANSFORM; ABSORPTION-SPECTROSCOPY; ANALYTICAL-CHEMISTRY; CHEMOMETRIC METHODS; LIBS; IDENTIFICATION; OPTIMIZATION

Laser-induced breakdown spectroscopy (LIBS) is an analytical technique allowing the determination of elemental concentrations in a variety of matrices in the solid, liquid, and gaseous phases. Because of the inherent complexity of the signal and to the high dimensionality of experimental data, chemometrics has been more and more applied in LIBS to perform samples identification or quantitative measurements. But multivariate methods can also be used for the description and physical interpretation of the plasma, particularly to exploit the temporal dimension of the LIBS signal, which is usually neglected in spectrochemical measurements. In this work, time-resolved spectra of a pure aluminum sample were treated with 2 methods, mean field-independent components analysis and multivariate curve resolution-alternating least squares, applying non-negativity constraints for scores and components in both cases. Results obtained were compared with reference univariate measurements of the emission of the species of interest (ions, neutral atoms, and molecules). The interpretation of scores and components provided a physical description of phenomena that take place between species in the plasma, like ionic recombination and molecules formation. Overall, mean field-independent components analysis and multivariate curve resolution-alternating least squares yield equivalent solutions with our dataset. This new approach is very promising for the treatment of time-resolved data obtained by LIBS.

laser ablation; laser induced breakdown spectroscopy; picosecond pulse train ablation;ND-YAG LASER; QUANTITATIVE-ANALYSIS; Q-SWITCH; ABLATION; PLASMA; SAMPLES; STEEL; GENERATION

Picosecond pulse train and nanosecond pulse were compared for laser ablation and laser induced breakdown spectroscopy (LIBS) measurements. A detailed study revealed that the picosecond pulse train ablation improved the quality of laser craters (symmetric crater walls and the absence of large redeposited droplets), which was explained by a smaller heat affected zone and suppression of melt splash. Greater plasma dimensions and brighter plasma emission were observed by gated imaging for picosecond pulse train compared to nanosecond pulse ablation. Increased intensity of atomic and ionic lines in gated and time integrated spectra provided better signal-to-noise ratio for picosecond pulse train sampling. Higher temperature and electron density were detected during first microsecond for the plasma induced by the picosecond pulse train. Improved shot-to-shot reproducibility for atomic/ionic line intensity in the case of picosecond pulse train LIBS was explained by more effective atomization of target material in plasma and better quality of laser craters. Improved precision and limits of detections were determined for picosecond pulse train LIBS due to better reproducibility of laser sampling and increased signal-to-noise ratio.

INDUCED BREAKDOWN SPECTROSCOPY; CAVITATION BUBBLE; NANOPARTICLES; SIMULATION; UNDERWATER; COLLAPSE; LIQUID; VALIDATION; TRACKING; GROWTH

Laser ablation of a solid target immersed in liquid (such as water) has many important applications such as laser synthesis of nanoparticles, lasermicromachining in water, and laser shock peening. Laser ablation of a solid target in water involves complicated physical processes. One important process often involved is the generation and evolution of a bubble in water and attached to the target surface, which may have significant effects on the target and the ambient water, and hence may greatly affect the relevant practical applications. Some experimental studies were reported in the literature on bubble evolutions induced by laser ablation of a solid target in water. However, the reported previous relevant physics-based modeling work is not sufficient. A physics-based model may help improve the process fundamental understanding and generate valuable information to related applications. In this paper, physics-based modeling work has been performed on the shrinking process of a bubble induced by laser metal ablation in water, together with time-resolved shadowgraph imaging experiments to verify the model. The model-predicted bubble evolution agrees reasonably well with the experimental measurement shown in the paper. Under the studied conditions, it has been found that near the bubble collapse moment (i.e., the moment when the bubble shrinks to a minimum size): (1) the bubble shrinks very fast, and the peak fluid velocity magnitude occurs inside the bubble and can exceed similar to 550 m/s; (2) the temperature inside the bubble increases very quickly and approaches similar to 2000 K; and (3) the pressure inside the bubble becomes very high, and can reach a peak magnitude of similar to 380 MPa at the collapse moment at the bubble center. During the shrinking process, a high-pressure region outside and near the bubble wall is generated near the collapse moment, but the temperature of the region outside the bubble mostly remains low. Published by AIP Publishing.

laser produced plasma; spatial confinement; laser induced breakdown spectroscopy;PLASMA FORMATION; CENTRAL SCHEMES; ABLATION; PARTICLES; PULSES; LIBS

The spatial confinement of plasma produced by a nanosecond laser is investigated using time resolved spectroscopy, fast imaging, interferometry, and numerical computation. The dynamics of the plasma, depending on shock waves, laser power, and wall distances, are studied. Experimental results confirm that the plasma is constricted by the reflected shock associated with a temperature and density gradient. The peak laser power determines the initial plasma parameters which affect the spectral intensities and the velocity of the reflective shock waves. The wall distance determines the reflection time of the shocks, which in turn influences the time delay of the collision between the two reflective shocks. The numerical results reveal a fast propagation process surrounding the reflective shocks, which indicates that the velocity of the reflective shock wave is influenced by the density of the plasma. The maximum enhancement factor similar to 5.2 is realized at a delay time of 11.7 mu s under a pulse laser energy of 180 mJ and a wall distance of 9 mm.

LIBS; Plasma; Carbon; Cluster; Infrared; Emission;INDUCED BREAKDOWN SPECTROSCOPY; LONG-WAVE; C-60; BUCKMINSTERFULLERENE; SPECTRA; C-70; LIBS

Mid infrared time-resolved emission spectra were recorded from laser-induced carbon plasma. These spectra constitute the first study of carbon materials LIB spectroscopy in the mid infrared range. The carbon plasma was induced using a Q-switched Nd: YAG laser. The laser beam was focused to high purity graphite pellets mounted on a translation stage. Mid infrared emission from the plasma in an atmospheric pressure background gas was detected by a cooled HgCdTe detector in the range 4A-11.6 mu m, using long-pass filters. LIB spectra were taken in argon, helium and also in air. Despite a gate delay of 10 its was used there were strong backgrounds in the spectra. Superimposed on this background broad and noisy emission bands were observed, the form and position of which depended somewhat on the ambient gas. The spectra were digitally smoothed and background corrected. In argon, for instance, strong bands were observed around 4.8, 6.0 and 7.5 mu m. Using atomic spectral data by NISI it could be concluded that carbon, argon, helium and nitrogen lines from neutral and ionized atoms are very weak in this spectral region. The width of the infrared bands supports molecular origin. The infrared emission bands were thus compared to vibrational features of carbon molecules (excluding C-2) of various sizes on the basis of previous carbon cluster infrared absorption and emission spectroscopic analyses in the literature and quantum chemical calculations. Some general considerations are given about the present results. (C) 2016 Elsevier B.V. All rights reserved.

Laser-induced breakdown spectroscopy; femtosecond laser; double-pulse; signal enhancement;INDUCED BREAKDOWN SPECTROSCOPY; AIR; IRRADIATION; ABLATION; DAMAGE; FILMS

In this paper, we present a study on the influence of interpulse delay in laser-induced silicon plasma with femtosecond double-pulse, and two subpulses have different laser energies. The optical emission line collected by a lens is the Si (I) at 390.55 nm. The range of double-pulse interpulse delay is from -150 ps to 150 ps. Unlike the femtosecond double pulses with two same energies, the combination of low + high energies can enhance the spectral emission intensity, while the combination of high + low energies probably reduces the spectral line intensity compared with single-pulse femtosecond laser. The results indicate that the interpulse delay is very important for laser-induced breakdown spectroscopy with femtosecond double-pulse to improve the optical emission intensity.

Laser-induced breakdown spectroscopy; spatial confinement; signal enhancement;INDUCED BREAKDOWN SPECTROSCOPY; PULSE

In laser-induced breakdown spectroscopy (LIBS), a serious of cylindrical cavities are used to spatially confine the plasmas produced from silicon (Si) target by using a Nd: YAG laser in air. Time-resolved spectrum of Si plasma with different diameters of cylindrical spatial cavities is measured. Compared with the plasmas generated without the confined cavity, the spectral emission intensity of plasma generated with cylindrical cavity is enhanced at a certain delay time. As the diameter of cylindrical cavity increases, the spectral emission is enhanced later in time and the enhancement becomes weaker. The result shows that the presence of the confined cavity leads to an increase in the spectral emission of plasma which is attributed to compressed plasma by the reflected shockwave.

Stimulated Raman; Laser-induced breakdown; Pulses laser; The fluorescence lifetime;STIMULATED RAMAN-SCATTERING; MATERIAL REMOVAL; ENHANCEMENT; EMISSION; SINGLE

To study the time evolution characteristics of plasma fluorescence, aluminum feature spectrum was measured and analyzed through dual-pulse laser-inducedbreakdown spectroscopy in the standard ambient temperature and pressure experimental conditions. Two Nd:YAG lasers were used to perform the experiment; one laser ablated the target, and the other reheated the plasma in air. The plasma emission intensity was enhanced at an optimal inter-pulse delay time of 200 ns. The plasma fluorescence lifetime was measured in a dual-pulse laser excitation mode at different inter-pulse delays. The plasma fluorescence lifetime changed with the changing of inter-pulse delay under double pulse excitation. The results can further understand of the time evolution of the plasma under double-pulse laser excitation. (C) 2017 Elsevier GmbH. All rights reserved.

CROSS-SECTIONS; IONIZATION; EXCITATION; COLLISIONS; ELECTRONS

The most relevant approach leading to a thorough understanding of the behavior of non equilibrium atomic plasmas is to elaborate state-to-state models in which the mass conservation equation is applied directly to atoms or ions on their excited states. The present communication reports the elaboration of such models and the results obtained. Two situations close to each other are considered. First, the plasmas produced behind shock fronts obtained in ground test facilities (shock tubes) or during planetary atmospheric entries of spacecrafts are discussed. We focused our attention on the nitrogen case for which a complete implementation of the CoRaM-N2 collisional-radiative model has been performed in a steady one-dimensional computation code based on the Rankinc-Hugoniot assumptions. Second, the plasmas produced by the interaction between an ultra short laser pulse and a tungsten sample are discussed in the framework of the elaboration of the Laser-Induced Breakdown Spectroscopy (LIBS) technique. In the present case, tungsten has been chosen in the purpose of validating an in situ experimental method able to provide the elemental composition of the divertor wall of a tokamak like WEST or ITER undergoing high energetic deuterium and tritium nuclei fluxes.

Laser-induced Breakdown Spectroscopy; Atomic Spectroscopy; Molecular Spectroscopy; Laser Ablation; 'lime-resolved Spectroscopy; Spectroscopy in Chemical Analysis;INDUCED BREAKDOWN SPECTROSCOPY; LINES; DENSITY; SPECTRA

This article gives a brief review of experimental studies of hydrogen Balmer series emission spectra. Ongoing research aims to evaluate early plasma evolution following optical breakdown in laboratory air. Of interest is as well laser ablation of metallic titanium and characterization of plasma evolution, Emission of titanium monoxide is discussed together with modeling of diatomic spectra to infer temperature. The behavior of titanium particles in plasma draws research interests ranging from the modeling of stellar atmospheres to the enhancement of thin film production via pulsed laser deposition,

Laser-plasma interaction; Emission of electromagnetic radiation; Thermodynamics of plasma;INDUCED BREAKDOWN SPECTROSCOPY; CARBON; ARGON; LIBS; AIR

In this study, graphite laser induced plasma dynamics are investigated by optical emission spectroscopy. Graphite plasma is generated using a 1064 nm Nd: YAG laser in helium environment under different ambient pressures. Characteristics of graphite spectra as lines intensity variations and signal to noise ratio are presented with main focus on the influence of the helium environment and pressure on plasma dynamics. Carbon atomic emission lines are used to study the dynamical behavior of plasma such as the excitation temperature and electron density to describe emission differences in different ambient conditions. The excitation temperature and plasma electron density are the primary factor contribute to the differences among the atomic carbon emission in different ambient pressures.

INDUCED BREAKDOWN SPECTROSCOPY; LIBS; SAMPLES

In this study, Nd: YAG laser pulse is used to ablate the Magnesium sample for laser induced breakdown spectroscopy analysis. The emission lines are plotted for ionic and atomic element of Mg I and Mg II respectively. The emission lines of Mg I and Mg II were recorded at wavelength of 279.55 nm, 280.27 nm and 285.21 nm. The analysis including the different of gate delay, determination of signal to background ratio and calibration curve of different concentration of magnesium is discussed in details.

Recent developments in Laser Induced Breakdown Spectroscopy (LIBS) instrumentation allow the acquisition of several spectra in a second. The dataset from a typical LIBS experiment can consist of a few thousands of spectra. To extract the useful information from that dataset is painstaking effort and time consuming process. Most of the currently available softwares for spectral data analysis are expensive and used for offline data analysis. LabVIEW software compatible with spectrometer (in this case Ocean Optics Maya pro spectrometer), can be used to for data acquisition and real time analysis. In the present work, a LabVIEW based automated system for real-time LIBS analysis integrated with spectrometer device is developed. This system is capable of performing real time analysis based on as-acquired LIBS spectra. Here, we have demonstrated the LIBS data acquisition and real time calculations of plasma temperature and electron density. Data plots and variations in spectral intensity in response to laser energy were observed on LabVIEW monitor interface. Routine laboratory samples of brass and calcine bone were utilized in this experiment. Developed program has shown impressive performance in real time data acquisition and analysis.

LIBS; high pressure; fuel-air ratio; ultrafast LIBS;

Application of time-resolved ultrashort-pulse-laser-based laser-induced breakdown spectroscopy (LIBS) is proposed for diagnostics in hydrocarbon flames at elevated pressures. Earlier study in nanosecond-laser-based LIBS for measuring fuel-to-air (F/A) ratios in stable hydrocarbon flame at high pressures is reported to have high measurement instabilities. A correlated measurement of time-resolved LIBS and electron number density measurement is carried out to develop an understanding of the source of the aforesaid measurement instability. The planned correlated measurements of LIBS and electron number density with short picosecond to femtosecond excitations have potentials to significantly reduce the instability in F/A ratio measurements at high pressure.

Laser induced breakdown spectroscopy; Magnetic field confinement; Emission intensity; Electron temperature; Electron density; ZrO2 plume;X-RAY-EMISSION; OPTICAL-EMISSION; ALUMINUM PLASMA; MASS REMOVAL; ENHANCEMENT; PLUME; DIAGNOSTICS; SATURATION; DEPOSITION; ABLATION

Laser induced breakdown spectroscopy of ZrO2 plasma in the presence and absence of magnetic field has been investigated. The plasma was generated by employing Nd:YAG laser (1064 nm, 10 ns) at various fluences ranging from 6.4J cm(-2) to 25.6J cm(-2) under argon environment of pressure of 100 Torr. Both emission intensity and electron temperature show increasing trend with increasing the fluence, whereas, electron number density of ZrO2 plasma decreases with increasing the laser fluence. It is revealed that values of emission intensity, electron temperature and electron number density of ZrO2 plasma are slightly higher in the presence of magnetic field as compared to field free case at all fluences. This increase in plasma parameters is attributed to magnetic confinement and Joule heating effect. With the variation of fluence the electron temperature of ZrO2 plasma varies slightly from 5345 K to 5475 K in the absence of magnetic field, whereas in case of magnetic field this value enhances from 5435 K to 5600 K. Similarly the electron number density of ZrO2 plasma varies from 1.80 x 10(18) cm(-3) to 3.50 x 10(18) cm(-3) in the absence of magnetic field, whereas in case of magnetic field, the variation in electron number density varies from 1.75 x 10(18) cm(-3) to 4.25 x 10(18) cm(-3). The existence of magnetic confinement effects is confirmed by the analytical evaluation of plasma parameter beta, which is smaller than 1 under all experimental conditions. It is also revealed that both the laser fluence as well as magnetic field significantly influence the ZrO2 plasma parameters. (C) 2017 Elsevier GmbH. All rights reserved.

LIBS; plasma; temperature; crops; weeds;INDUCED BREAKDOWN SPECTROSCOPY; TRITICUM-AESTIVUM L.; WINTER-WHEAT; SAMPLES; LIBS

The ability to distinguish between crops and weeds using sensors from a distance will greatly benefit the farming community through improved and efficient scouting for weeds, reduced herbicide input costs and improved profitability. In the present study, we examined the utility of femtosecond laser- inducedbreakdown spectroscopy (LIBS) for plant species differentiation. Greenhouse-grown plants of dallisgrass, wheat, soybean and bell pepper were evaluated using LIBS under an ambient environment. LIBS experiments were performed on the leaf samples of different plant species using a femtosecond laser system with an inexpensive lightweight detector. Temperatures of laser-induced plasma in plants depend on many parameters and were determined for each of the study species by the constituent elements interacting with femtosecond laser pulses. Using elemental calcium transitions in plant tissue samples to measure plasma temperatures, we report consistent differences among the four study species, with average values ranging from 5090 +/- 168 K (soybean) to 5647 +/- 223 K (dallisgrass).

laser; analysis; substances; materials; environmental objects; chirp; filamentation; generation; pulse; radiation; sensitivity;SPECTROSCOPY

The main achievements in the analytical application of lasers, their potential applications, and prospects for further development of this field were described. The role of laser generation conditions and modes, especially of pulse duration, on laser applicability in analysis was discussed. The propagation of powerful ultrashort laser pulses (USPs) in transparent samples and the positive role of chirping and filamentation were considered. New methods of laser-inducedbreakdown spectroscopy based on ultrashort pulses, chirping, and filamentation were discussed.

INDUCED BREAKDOWN SPECTROSCOPY; TIME; EQUILIBRIUM; PARAMETERS; DEPOSITION; DENSITY; SPACE; NDYAG; GAS; CO2

The magnesium plasma induced by a 1064-nm Q-switched Nd: YAG laser in atmospheric air was investigated. The evolution of the plasma was studied by acquiring spectral images at different laser energies and delay times. We observed that the intensities of the spectral lines decrease with larger delay times. The electron temperature was determined using the Boltzmann plot method. At a delay time of 100 ns and laser energy of 350 mJ, the electron temperature attained their highest value at 10164 K and then decreases slowly up to 8833.6 K at 500 ns. We found that the electron temperature of the magnesium plasma increases rapidly with increasing laser energy.

INDUCED BREAKDOWN SPECTROSCOPY; POLARIZATION SPECTROSCOPY

The polarisation anisotropy of the emission from a laser produced aluminium plasma has been studied using time and polarisation resolved spectroscopy at various background pressures of air. A Wollaston prism was used to resolve the emission from the plasma into polarisation components that are parallel and orthogonal to the plasma expansion axis. Spectroscopy reveals that as the background pressure is increased, strongly polarised continuum emission dominates at early stages of the plasma formation. The results are compared and contrasted to similar experiments and discussed in the framework of a recombining plasma. Published by AIP Publishing.

Laser ablation; Micro structuring; Crater depth; Molybdenum; LIBS; Electron temperature and number density;ABLATED PLASMA EMISSION; NDYAG LASER; THIN-FILMS; METALS; ATMOSPHERE; BEAM; VAPORIZATION; PARAMETERS; FLUENCES; VACUUM

Surface modifications of laser irradiated molybdenum have been correlated with plasma parameters. Nd:YAG laser (1064 nm, 10 ns) was employed at various laser irradiances ranging from 6 to 50 GW/cm(2) under argon environment. The ablation efficiency has been investigated by measuring the crater depth using surface profilometry analysis. Scanning electron microscope (SEM) analysis reveals the formation of coarse grains along with cracked boundaries, cavities and cones at the central ablated areas. Whereas, uplifted re-solidified material, cavities, ridges, droplets and cones were observed at boundary regions. LaserInduced Breakdown Spectroscopy (LIBS) analysis has been performed to evaluate electron temperature and number density of molybdenum plasma. Electron temperature and electron density varies from 6670 to 9305 K and 0.62 x 10(18) to 0.72 x 10(18) cm(-3) respectively. Both the parameters showed similar trend in variation with laser irradiance i.e. an initial increase from 13 to 19 GW/cm(2) followed by a decrease from 19 to 25 GW/cm(2) and then a saturation from 25 to 50 GW/cm(2). The initial increasing trend is attributed to the enhanced excited vapor content of the ablated material, confinement effects of the surrounding argon and absorption of laser energy into the molybdenum vapor plasma during the trailing part of laser pulse leading to ignition of laser supported combustion (LSW) waves. The decreasing trend is attributed to the shielding effect and saturation is explainable on the basis of the formation of a self-regulating regime. Surface modifications of laser irradiated molybdenum were correlated with the plasma parameters.

Aluminum; Tungsten; Collisional-radiative model; Laser-induced plasma; Non-equilibrium plasma; Ultrashort pulse;INDUCED BREAKDOWN SPECTROSCOPY; THERMODYNAMIC-EQUILIBRIUM; FACING COMPONENTS; FEMTOSECOND; ARGON; NANOSECOND; PICOSECOND; NITROGEN; LIBS; EXPANSION

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 (10(5) Pa), 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 10,000 IC from 200 ns. Conversely, at low pressure (10 Pa), the extinction of the plasma is observed at similar to 500 ns, 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. (C) 2016 Elsevier B.V. All rights reserved.

Laser-induced breakdown spectroscopy; LIBS; Plasma confinement; signal-to-noise ratio; signal precision;INDUCED BREAKDOWN SPECTROSCOPY; OPTICAL-EMISSION; GALVANIZED STEEL; ENHANCEMENT; IMPROVEMENT; EXCITATION; LIBS; SENSITIVITY; ABLATION; PULSES

The present work focuses on the influence of the angle of observation on the emission signal from copper plasmas. Plasma plumes have been generated inside a home-made chamber consisting of two parallel glass windows spaced by 2.5mm. This chamber allows observing plasma plumes from different collection angles throughout their perimeter, spanning from 20 degrees to 80 degrees with respect to the surface of the Cu target. In order to minimize the observed volume of the plasma, measurements were made from the closest distance possible through a metallic hollow tube. Single-pulse and collinear double-pulse excitation schemes with a Nd:YAG laser (1064nm, 5ns) have been investigated. The results have shown that the selection of the best angle to collect light from the plasma is related to the excitation mode. On the other hand, the shot-to-shot signal variability has been found to depend on the shape of plasma plumes. In single-pulse excitation, a good correlation between the observed laser-induced breakdown spectroscopy (LIBS) emission (from spatially confined plumes) and their integrated signal of plasma image has been ascertained. However, this fact was less evident in double-pulse LIBS, which could be due to a different mechanism involved in the ablation process.

Laser-Induced Breakdown Spectroscopy; Multivariate classification; Echelle spectrometer; Czerny-Turner spectrometer;

The objective of this work was to assess a part of echelle Laser-Induced Plasma spectra (ranging from 200 to 1000 nm) that could be most effectively employed for rocks classification. Therefore, a 60 nm wide spectral window mask was iteratively moved over the broadband echelle spectra. Each created narrow artificial spectral windows (60 nm) was used for the classification of rock samples using various Multivariate Data Analysis (MVDA) algorithms, reaching more than 99% of the overall accuracy in certain cases. Afterwards, the Czerny-Turner spectrometer (having higher sensitivity compared to the echelle spectrometer) was aligned to the a priori selected and the most effective spectral regions and rocks samples were re-measured. Consequently the MVDA analyses were utilized again, providing also satisfying classification results yielding more than 99% of the overall accuracy. Measurements of 28 sedimentary ores (certified reference materials) were done utilizing commercially available X-Trace device (AtomTrace), where spectrometers in both configurations (echelle and Czerny-Turner) were exploited.

Laser-induced breakdown spectroscopy; Generalized extreme value distribution; shot-to-shot statistics ;

The purpose of this work is to provide detailed study of statistical behavior of different types of analytical signals in typical of Laser-Induced Breakdown Spectroscopy (LIBS) measurements. The main goal of this work is to justify usage of arithmetic mean and standard deviation as statistical estimates of expected value of selected analytical signal. In contrary to the general assumption that LIBS data show Gaussian distribution, this paper deals with the hypothesis that the data rather demonstrate Generalized Extreme Value Distribution. The study is realized on 10 selected lines measured on NIST glass standard. In order to cover wide range of possible applications three different spectra internal standardization techniques and their influence on distribution were studied. Finally, assuming that the data comes from a single distribution and the central limit theorem is valid, the influence of accumulations on the line distribution is examined and discussed. Statistical tools used and described in this paper can be utilized by other researchers to confirm their hypotheses and verify utilization of Gaussian distribution or even novel data processing methods.

Laser-Induced Breakdown Spectroscopy, LIBS; Outlier filtering; Principal Component Analysis, PCA; Linear correlation; Total spectral intensity; Soft Independent Modelling of Class Analogies, SIMCA;

In this manuscript we highlight the necessity of outlier filtering prior the multivariate classification in Laser-Induced Breakdown Spectroscopy (LIBS) analyses. For the purpose of classification we chose to analyse BAM steel standards that possess similar composition of major and trace elements. To assess the improvement in figures of merit we compared the performance of three outlier filtering approaches (based on Principal Component Analysis, linear correlation and total spectral intensity) already separately discussed in the LIBS literature. The truncated data set was classified using Soft Independent Modelling of Class Analogies (SIMCA). Yielded results showed significant improvement in the performance of multivariate classification coupled to filtered data. The best performance was observed for the total spectral intensity filtering approach gaining the analytical figures of merit (overall accuracy, sensitivity, and specificity) over 98%. It is noteworthy that the results showed relatively low sensitivity and high specificity of the SIMCA algorithm regardless of the presence of outliers in the data sets. Moreover, it was shown that the variance in the data topology of training and testing data sets has a great impact on the consequent data classification.

Single pulse (SP) LIBS setup was modified to DP setup to achieve more accurate analytical sensitivity and spatial resolution. All parameters, like interpulse delay, acquisition delay or energy of ablation and excitation laser pulses were optimized.

Laser-ablation based spectrochemical Analytical Methods could be used in applications in which the capability for spatially resolved analysis is required. Such analysis gives a 2-D or 3-D map of the monitored chemical elements. Here we introduce automation of a 2-D surface analysis in the laser-induced breakdown spectroscopy setup by implementation of an autofocus algorithm based on the evaluation of the image sharpness. The most suitable algorithm with respect to its speed, accuracy, and durability against digital noise is chosen by testing different gradient-based methods and methods working in the frequency domain.

laser induced breakdown spectroscopy; LIBS; Acoustic signal; Normalization; Internal standard; Ceramic tile; Depth profiling;

An acoustic signal was used for the internal standardization of laser-induced breakdown spectroscopy (LIBS) of a glazed wall tile. For the LIBS analyses, 1064 nm and 532 nm wavelengths of the Nd:YAG laser were utilized. The tile was depth profiled by a single-spot ablation from the glaze into the substrate. Some lines of major elements Si(I) 252.418, Si(I) 252.851, Al(I) 257.509, Cr(I) 295.368, Al(I) 309.271 nm and Ti(II) 334.904 nm were monitored. The decrease in the optical emissions during the ablation was successfully compensated for by normalization to the square power of the acoustic signal in the interval of 290–340 nm. This approach failed for the lines between 250–270 nm. The results were the same for both lasing wavelengths despite different irradiances. The acquired profiles are in good agreement with the reference X-ray fluorescence measurement.

laser induced breakdown spectroscopy; LIBS; double pulse LIBS; plasma characterization; time resolved measurement; ICCD; photomultiplier;

In this study, we present orthogonal re-heating double pulse experimental system equipped with both ICCD and PMT detection and preliminary measurements of temperatures of plasmas generated on an iron sample.