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.

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.

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.

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.

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

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; 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.

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; MOLECULAR-EMISSION; LASER; AIR; SPECTROMETRY; CHLORINE

The determination of fluorine in solid samples using Laser Induced Breakdown Spectroscopy (LIBS) is a challenging task due to the low excitation efficiency of this element. Recently, the use of molecular CaF bands was demonstrated to improve the analytical capabilities of LIBS fluorine detection in Ca-containing samples. In this work, a novel approach has been developed to extend this methodology for fluorine quantification in calcium-free samples. In particular, the on-line nebulization of a Ca-containing solution on the surface of a fluorine containing sample has been successfully evaluated to obtain the desired CaF molecular emission. Nebulization parameters have been optimized in order to maximize the molecular emission. A linear relationship between the CaF molecular emission signal and the amount of F in the solid samples has been obtained. The calculated limit of detection for fluorine (about 50 mu g g(-1)) is in the same order of magnitude as that obtained for Ca-containing samples. This novel approach for fluorine quantification opens new ways for the analysis of halogens in solid samples.

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.