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.

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

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.

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.

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.

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.

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.

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.

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.

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.

Process monitoring; Plasma temperature; Blast-wave theory; Laser microdrilling; Ablation;SHOCK-WAVE; ABLATION; DEPTH

In this work, self-mixing interferometry (SMI) was used to monitor the optical path difference induced by the ablation plasma and plume. The paper develops the analytical relationships to explain the fringe appearance in the SMI during laser microdrilling. The monitoring principle was tested under a large experimental campaign of laser microdrilling on TiAlN ceramic coating with a low-ns green fibre laser. Key process parameters namely pulse energy, number and repetition rate were varied. The effect of side gas on the SMI signal characteristic was analysed. Laser induced breakdown spectroscopy (LIBS) was used to identify the plasma temperature and electron number density. The SMI signals were correlated to the plume size and its evolution as a function of process parameters, as well as electron number density estimated by spectroscopy. In addition to proving the validity of the proposed new method, the results show insights to the micromachining of the ceramic material with low ns pulses.

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; 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.

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.

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.

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.

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.

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.

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).

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.

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.