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 PLASMA SPECTROMETRY; IN-SITU ANALYSIS; HIGH-TEMPERATURE; ELEMENTAL ANALYSIS; GRADE TRANSITION; MOLECULAR BANDS; REAL-TIME; MOLD; LIBS; SAMPLES

Among the several controlling routines utilized in the steelmaking process, analytical operations during continuous casting are especially demanding due to the extreme environment of steel plants and the crude conditions of the steel surface at the exit of the casting system. This report presents how dual-pulse laser-induced breakdown spectroscopy (LIBS) can be used for the real-time monitoring of continuous casting sequences in a steel plant and the operations needed for detecting the separation between grades of close chemical compositions. Diverse dual-pulse laser conditions have been tested in order to improve the LIBS system performance. Apart from the scale layer formed by the oxidation of steel by the surrounding air, the presence of residues of mould powder on the steel surface tends to complicate the LIBS analysis as elements present in the powder such as manganese interfere with the steel components. LIBS data processing by discriminant function analysis has been demonstrated to be beneficial for the identification of steel transitions. Changes in steel composition as low as 0.20 percentage points Cr in a stainless steel sample containing above 17% of this element are detected by corresponding changes in Wilks' lambda values from 1.0 to 0.75 during the transition. Changes in the concentration of nickel are of minor relevance as its concentration on the steel surface at the time of continuous casting is depleted. For steel concentrations differing to a larger extent, differentiation of steel grades is straight, involving changes in Wilks' lambda values from 1 to below 0.1.

INDUCED PLASMA; LIGHT-BEAMS; AIR; WATER; PARTICLES; VAPORIZATION; CONSTITUENTS; SPECTROMETRY; CLOUDS

Nanosecond laser-induced breakdown spectroscopy has been examined for the analysis of suspended matter in a free stream of air. The real-time monitoring of this scenario poses major challenges for an accurate categorization due to its changing characteristics such as composition, size, and density of particles. The effects of particle size and matrix in the optical emission responses registered from such scenarios have been evaluated. Distant (10 m) plasmas of saline solutions, containing either NaCl or Na2SO4 at different concentrations, have been induced by nanosecond laser pulses at a wavelength of 1064 nm. The effects of the droplet size and its concentration on differences in the laser-induced breakdown probability, the intensity of the characteristic lines, and the plasma emission continuum have been discussed. The quantification of sodium in distant water droplets has been proved. However, an initial knowledge on the average droplet size is required. The average droplet size could be determined from the slope of H I and O I lines versus the continuum plasma emission, which is only weakly influenced by the salt content in the droplets. (C) 2017 Optical Society of America.

Laser-induced breakdown spectroscopy; LIBS; Solid aerosols; Single particle analysis; Optical catapulting; Optical trapping; Atomization efficiency; Photon yield;RADIATION PRESSURE; AEROSOL-PARTICLES; AIR-POLLUTION; BLACK CARBON; SIMULATION; LEVITATION; HEALTH; LIBS

Laser-induced breakdown spectroscopy (LIBS) was employed for investigating the influence of particle size on the dissociation efficiency and the absolute production of photons per mass unit of airborne solid graphite spheres under single-particle regime. Particles of average diameter of 400 nm were probed and compared with 2 pm particles. Samples were first catapulted into aerosol form and then secluded in an optical trap set by a 532 nm laser. Trap stability was quantified before subjecting particles to LIBS analysis. Fine alignment of the different lines comprising the optical catapulting-optical trapping-laser-inducedbreakdown spectroscopy instrument and tuning of excitation parameters conditioning the LIBS signal such as fluence and acquisition delay are described in detail with the ultimate goal of acquiring clear spectroscopic data on masses as low as 75 fg. The atomization efficiency and the photon yield increase as the particle size becomes smaller. Time-resolved plasma imaging studies were conducted to elucidate the mechanisms leading to particle disintegration and excitation. (C) 2017 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 (LIBS) and laser ablation (LA) inductively coupled plasma (ICP) mass spectrometry (MS) were utilized for microspatial analyses of a prehistoric bear (Ursus arctos) tooth dentine. The distribution of selected trace elements (Sr, Ba, Fe) was measured on a 26 mm×15 mm26 mm×15 mm large and 3 mm3 mm thick transverse cross section of a canine tooth. The Na and Mg content together with the distribution of matrix elements (Ca, P) was also monitored within this area. The depth of the LIBS craters was measured with an optical profilometer. As shown, both LIBS and LA-ICP-MS can be successfully used for the fast, spatially resolved analysis of prehistoric teeth samples. In addition to micro chemical analysis, the sample hardness was calculated using LIBS plasma ionic-to-atomic line intensity ratios of Mg (or Ca). To validate the sample hardness calculations, the hardness was also measured with a Vickers microhardness tester.