Laser-induced breakdown spectroscopy of archaeological findings with calibration-free inverse method: comparison with classical laser-induced breakdown spectroscopy and conventional techniques.

A modified version of the calibration-free (CF) method was applied to the analysis of a set of archaeological brooches made of various copper-based alloys and coming from the archaeological site of Egnatia (Apulia, Southern Italy). The developed methodology consists in determining the plasma temperature by reversing the set of equations employed in the usual CF algorithm, and it is thus referred to as "inverse method". The plasma temperature is determined for one certified standard, by using its known elemental composition as an input data, and then applied to the set of unknown samples to evaluate their composition in a CF mode. The feasibility of such an approach is demonstrated by comparing the results obtained with classical LIBS (drawing calibration lines with a series of matrix-matched certified standards) and with independent measurements performed with a conventional technique (LA-ICP-MS).

Nanoparticle-enhanced laser-induced breakdown spectroscopy of metallic samples.

In this article, an increase of 1-2 orders of magnitude in laser-induced breakdown spectroscopy (LIBS) signals was obtained by depositing silver nanoparticles on metal samples. Nanoparticle-enhanced LIBS (NELIBS) was found to be a robust and flexible tool for the chemical analysis of metals because the sample emission signal did not appear to be affected much by the size and concentration of deposited nanoparticles (NPs) within the ranges of 10 nm for diameter and 1 order of magnitude for concentration. On the other hand, preliminary NELIBS tests on insulators and semiconductors did not show any significant enhancement with respect to conventional LIBS. In this article, we present a detailed investigation of the fundamental features of NELIBS spectra, in addition to some examples of analytical applications to the quantitative analysis of metal alloys.

Cavitation dynamics of laser ablation of bulk and wire-shaped metals in water during nanoparticles production.

Although the first nanoseconds to microseconds rule the resulting process yield of laser ablation in liquid, a comprehensive view involving combination of time-resolved measurement techniques is still lacking. In this paper, fundamental aspects of laser ablation of metals in water during the production of nanoparticles are discussed. Three fast diagnostic methods have been applied simultaneously. These are Optical Emission Spectroscopy for the plasma characterization, fast shadowgraph for plasma and cavitation bubble dynamics and laser scattering for the mechanisms of delivery of the produced materials in the liquid. Moreover, in order to validate the discussion, the effect on cavitation dynamics of the ablation of bulk and wire-shaped targets has been investigated together with the relative nanoparticles production yield. Unusual arrow-bow ejection phenomena between the cavitation bubble and the wire result in suppressed material back-deposition, causing efficient ejection of ablated matter into the liquid. The presented nanosecond and microsecond-resolved analysis allows estimating the timescale and role of the basic mechanisms involved in laser ablation in liquids as well as the thermodynamic characteristics of the processes.

Heavy metal concentrations in soils as determined by laser-induced breakdown spectroscopy (LIBS), with special emphasis on chromium.

Soil is unanimously considered as one of the most important sink of heavy metals released by human activities. Heavy metal analysis of natural and polluted soils is generally conducted by the use of atomic absorption spectroscopy (AAS) or inductively coupled plasma optical emission spectroscopy (ICP-OES) on adequately obtained soil extracts. Although in recent years the emergent technique of laser-induced breakdown spectroscopy (LIBS) has been applied widely and with increasing success for the qualitative and quantitative analyses of a number of heavy metals in soil matrices with relevant simplification of the conventional methodologies, the technique still requires further confirmation before it can be applied fully successfully in soil analyses. The main objective of this work was to demonstrate that new developments in LIBS technique are able to provide reliable qualitative and quantitative analytical evaluation of several heavy metals in soils, with special focus on the element chromium (Cr), and with reference to the concentrations measured by conventional ICP spectroscopy. The preliminary qualitative LIBS analysis of five soil samples and one sewage sludge sample has allowed the detection of a number of elements including Al, Ca, Cr, Cu, Fe, Mg, Mn, Pb, Si, Ti, V and Zn. Of these, a quantitative analysis was also possible for the elements Cr, Cu, Pb, V and Zn based on the obtained linearity of the calibration curves constructed for each heavy metal, i.e., the proportionality between the intensity of the LIBS emission peaks and the concentration of each heavy metal in the sample measured by ICP. In particular, a triplet of emission lines for Cr could be used for its quantitative measurement. The consistency of experiments made on various samples was supported by the same characteristics of the laser-induced plasma (LIP), i.e., the typical linear distribution confirming the existence of local thermodynamic equilibrium (LTE) condition, and similar excitation temperatures and comparable electron number density measured for all samples. An index of the anthropogenic contribution of Cr in polluted soils was calculated in comparison to a non-polluted reference soil. Thus, the intensity ratios of the emission lines of heavy metal can be used to detect in few minutes the polluted areas for which a more detailed sampling and analysis can be useful.

Elemental chemical analysis of submerged targets by double-pulse laser-induced breakdown spectroscopy.

Double-pulse laser-induced plasma spectroscopy (DP-LIPS) is applied to submerged targets to investigate its feasibility for elemental analysis. The role of experimental parameters, such as inter-pulse delay and detection time, has been discussed in terms of the dynamics of the laser-induced bubble produced by the first pulse and its confinement effect on the plasma produced by the second laser pulse. The analytical performance of this technique applied to targets in a water environment are discussed. The elemental analysis of submerged copper alloys by DP-LIPS has been compared with conventional (single-pulse) LIBS in air. Theoretical investigation of the plasma dynamics in water bubbles and open air has been performed.