1,721,054 research outputs found
Laser induced breakdown spectroscopy inside liquids: Processes and analytical aspects
No full textThis paper provides an overview of the laser induced breakdown spectroscopy (LIBS) inside liquids, applied for detection of the elements present in the media itself or in the submerged samples. The processes inherent to the laser induced plasma formation and evolution inside liquids are discussed, including shockwave generation, vapor cavitation, and ablation of solids. Types of the laser excitation considered here are single pulse, dual pulse and multi-pulse. The literature relative to the LIBS measurements and applications inside liquids is reviewed and the most relevant results are summarized. Finally, we discuss the analytical aspects and release some suggestions for improving the LIBS sensitivity and accuracy in liquid environment
Insights in the laser induced breakdown spectroscopy signal generation underwater using dual pulse excitation - Part II: Plasma emission intensity as a function of interpulse delay
No full textInfluence of time delay between two laser pulses on the LIBS (laser induced breakdown spectroscopy) signal inside liquids was investigated and the results are compared with data from literature. Plasma was produced by laser ablation (LA) of aluminum inside water and its emission after the second laser pulse was characterized by spectrally and time resolved detection. Light propagation through the vapor bubble formed by the first laser pulse was studied by measurements of beam scattering and transmission. Optical absorption by the evolving bubble is not significant, but its growth is accompanied by lowering of its refraction index nb with respect to surrounding liquid; this effect increases defocusing both of the incident beam and of the out-coming plasma radiation. Collection efficiency of the secondary plasma emission rapidly degrades with the cavity growth, but close to its full expansion the LIBS signal partially recovers through Snell's reflections at the liquid-vapor interface, which produce a bright spot close to the bubble center. Such a light redistribution allows detecting of the emission from external plasma volume, otherwise deflected out of the collection system. Except for strong line transitions from the main sample constituents, self-absorbed inside the high-pressure cavity, we observed the highest LIBS signal when sending the second pulse well before the bubble is fully expanded. Transitions of the pressure wave through the focal volume, formed by the first laser pulse and reflected from the cell's walls and sample back-plane, enhances the LIBS signal importantly. The measured lifetime of the secondary plasma rapidly decreases with the bubble expansion. Here, we also discuss the optimization of the optical collection system and some analytical aspects of double-pulse (DP) LIBS inside liquids. © 2013 Elsevier B.V
Influence of the target material on secondary plasma formation underwater and its laser induced breakdown spectroscopy (LIBS) signal
No full textThe 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 μs. 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. © 2017 The Royal Society of Chemistry
LIBS analysis of liquids and of materials inside liquids
No full textLaser induced plasma formation on or inside liquids is characterized by large energy losses due to liquid evaporation. Ablation of a liquid surface is followed by hydro-dynamical instabilities and splashing. Plasma generation inside bulk liquids is affected by the light absorption and scattering, and it is accompanied by intense pressure waves and successive vapor cavitation. Efficient LIBS analyses in presence of liquids require different considerations; the examples are reported and discussed in following. © 2014 Springer-Verlag Berlin Heidelberg
Secondary plasma formation after single pulse laser ablation underwater and its advantages for laser induced breakdown spectroscopy (LIBS)
No full textIn this work we present studies of spatial and temporal plasma evolution after single pulse ablation of an aluminium target in water. The laser ablation was performed using 20 ns long pulses emitted at 1064 nm. The plasma characterization was performed by fast photography, the Schlieren technique, shadowgraphy and optical emission spectroscopy. The experimental results indicate the existence of two distinct plasma stages: the first stage has a duration of approximately 500 ns from the laser pulse, and is followed by a new plasma growth starting from the crater center. The secondary plasma slowly evolves inside the growing vapor bubble, and its optical emission lasts over several tens of microseconds. Later, the hot glowing particles, trapped inside the vapor cavity, were detected during the whole cycle of the bubble, where the first collapse occurs after 475 μs from the laser pulse. Differences in the plasma properties during the two evolution phases are discussed, with an accent on the optical emission since its detection is of primary importance for LIBS. Here we demonstrate that the LIBS signal quality in single pulse excitation underwater can be greatly enhanced by detecting only the secondary plasma emission, and also by applying long acquisition gates (in the order of 10-100 μs). The presented results are of great importance for LIBS measurements inside a liquid environment, since they prove that a good analytical signal can be obtained by using nanosecond pulses from a single commercial laser source and by employing cost effective, not gated detectors. © the Owner Societies 2016
Insights in the laser-induced breakdown spectroscopy signal generation underwater using dual pulse excitation - Part I: Vapor bubble, shockwaves and plasma
No full textPlasma and vapor bubble formation and evolution after a nanosecond laser pulse delivered to aluminum targets inside water were studied by fast photography. This technique was also applied to monitor the plasma produced by a second laser pulse and for different interpulse delays. The bubble growth was evident only after 3 μs from the first laser pulse and the bubble shape changed during expansion and collapse cycles. The evolution and propagation of the initial shockwave and its reflections both from the back sample surface and cell walls were detected by Schlieren photography. The primary plasma develops in two phases: violent particle expulsion and ionization during the first μs, followed by slow plasma growth from the ablation crater into the evolving vapor bubble. The shape of the secondary plasma strongly depends on the inner bubble pressure whereas the particle expulsion into the expanded bubble is much less evident. Both the primary and secondary plasma have similar duration of about 30 μs. Detection efficiency of the secondary plasma is much reduced by light refraction at the curved bubble-water interface, which behaves as a negative lens; this leads to an apparent reduction of the plasma dimensions. Defocusing power of the bubble lens increases with its expansion due to the lowering of the vapor's refraction index with respect to that of the surrounding liquid (Lazic et al., 2012 [1]). Smell's reflections of secondary plasma radiation at the expanded bubble wall redistribute the detected intensity on a wavelength-dependent way and allow gathering of the emission also from the external plasma layer that otherwise, would not enter into the optical system. © 2013 Elsevier B.V
Standoff monitoring of aqueous aerosols using nanosecond laser-induced breakdown spectroscopy: Droplet size and matrix effects
No full textNanosecond 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. © 2017 Optical Society of America
Determination of antimony concentrations in widely used plastic objects by laser induced breakdown spectroscopy (LIBS)
No full textIn this study, the feasibility of measuring the Sb content in different plastic materials by laser induced plasma spectroscopy (LIBS) is explored. Measurements were performed initially on a sample of pure Sb in order to identify the most prominent element transitions before different consumer plastics of varying matrix, composition and color were examined. The experimental set-up was based on a single pulse laser excitation at 1064 nm and a detection system consisting of an array of three compact spectrometers covering the range 236-796 nm. On pure Sb material, many atomic lines, particularly intense in the UV region, were observed, together with much weaker ionic transitions mainly in the visible spectral region. Unfortunately, all of the strong Sb transitions partially overlapped with those from Si, Fe and Ti, elements common in many plastic materials. For constructing the calibration curve for Sb content we exploited the Sb concentration values obtained by X-ray fluorescence (XRF) spectrometry, which varied from the detection limit (∼200 ppm) up to 65000 ppm. The analytical Sb I line at 276.99 nm was selected because, even if it has a weak contribution from one Fe I transition, its empirical subtraction leads to a well-correlated linear calibration graph. The corresponding detection limit was around 1400 ppm while in the absence of Fe, having an intense ionic transition at 259.93 nm, it is possible to use a more intense Sb I transition at 259.81 nm, achieving sensitivity on the order of 100 ppm. © 2018 The Royal Society of Chemistry
Analysis of rock samples collected from rock hewn churches of Lalibela, Ethiopia using laser-induced breakdown spectroscopy
No full textWith the aim to study alteration processes of the rock hewn churches from Lalibela (Ethiopia), we applied Laser Induced Breakdown Spectroscopy (LIBS) technique to measure the elemental composition both of the bulk rock materials and their external layers, exposed to the environmental factors. The analytical plasma was generated by nanosecond pulses of an Nd: YAG laser emitting at 1064 nm. Different major and minor sample constituents were detected, including Ca, Mg, Na, Fe, Ti, Al and K. The detected O emission originates both from air surrounding and the sample, while the intensity of N lines, coming exclusively from air, was used for the LIBS signal normalization. By depth profiling of the weathered basalt rock, we observed a lower presence of K in the external layers, corresponding to the first 5 laser shots. The emission from this element is anti-correlated with the line intensities from O, and this was attributed to the variations in relative abundances of clay minerals and K-feldspar. The analogue measurements were performed on the tuff rock, and compared to the spectra from powder samples containing only the external soft material, scratched from the rocks. These analyses show an abundance of H in the weathered, wetted layers and suggest that cations are lost from the constituent primary minerals and replaced by H+; this process disrupts the lattice structure and causes a marked loss of strength. The studies presented here demonstrate that LIBS is a useful technique for studying the alteration processes in the rocks, caused by environmental factors. © 2013 Elsevier Ltd
Enforcement of the Decisions on the Rights of Access and Return Orders issued by the Courts of Child’s Habitual Residence Immediately before a Wrongful Removal or Retention – Articles 40-45 and 47 and Other Provisions Applicable to the Enforcement – Articles 48-52 : Brussels IIbis
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