V. Palleschi

Quantitative micro-analysis by laser-induced breakdown spectroscopy: a review of the experimental approaches☆

Abstract The laser-induced breakdown spectroscopy (LIBS) technique has shown in recent years its great potential for rapid qualitative analysis of materials. Because of the lack of pre-treatment of the material, as well as the speed of analysis, not mentioning the possibility of in situ analysis, this technique offers an attractive solution for a wide range of industrial applications. As a consequence, a lot of work has been devoted towards the application of LIBS technique for quantitative micro-analysis. The purpose of this paper is to give a review of the current experimental approaches used for obtaining quantitative micro-analysis using the LIBS technique. The influence on LIBS analytical performances of laser power, wavelength and pulse length, the proper choice of experimental geometry, the importance of ambient gas choice and the role of detectors for improving the precision of LIBS analysis are among the topics discussed in this paper.

A procedure for correcting self-absorption in calibration free-laser induced breakdown spectroscopy

Abstract A model of the self-absorption effect in laser-induced plasma has been developed, with the aim of providing a tool for its automatic correction in the Calibration-Free algorithm recently developed for standardless analysis of materials by LIBS (Laser Induced Breakdown Spectroscopy). As a test of the model, the algorithm for self-absorption correction is applied to three different certified steel NIST samples and to three ternary alloys (Au, Ag, Cu) of known composition. The experimental results show that the self-absorption corrected Calibration-Free method gives reliable results, improving the precision and the accuracy of the CF-LIBS procedure by approximately one order of magnitude.

Trace Element Analysis in Water by the Laser-Induced Breakdown Spectroscopy Technique

In this paper, results are presented showing the feasibility of the laser-induced breakdown spectroscopy (LIBS) technique as a fast and sensitive analytic tool for quantitative measurement of trace elements in water. Many ionic elements were detected; the system linearity was tested by analyzing water samples containing known concentration of Mg and Ca, whereas Cr-polluted samples were exploited to test the system sensitivity limit to impurities.

Application of laser-induced breakdown spectroscopy technique to hair tissue mineral analysis

The concentration of the main minerals present in human hair is measured on several subjects by Calibration-Free Laser-Induced Breakdown Spectroscopy (CF-LIBS) and compared with the results obtained through a commercial analytical laboratory. The possibility of using CF-LIBS for mineral analysis in hair is discussed, as well as its feasibility for the fast and inexpensive determination of the occurrence of heavy-metal poisoning in hair.

Characterization of azurite and lazurite based pigments by laser induced breakdown spectroscopy and micro-Raman spectroscopy ☆

The most commonly used blue pigments in medieval manuscripts are azurite and lapis-lazuli. The first one is a copper-based pigment; the coloring compound of the latter is lazurite, a sodium silicoaluminate in a sulfur matrix. Knowledge of the chemical composition of the materials is essential for the study of illuminated manuscripts. In this paper, micro-Raman and LIBS have been used for the study of azurite and lapis-lazuli, as well as different mixtures of these pigments applied to parchment to simulate an illuminated manuscript. The results of our work show the importance of using more than one technique for a good comprehension of a manuscript. In particular, the Ž. opportunity of combining elemental information obtained from laser induced breakdown spectroscopy and Ž. vibrational spectroscopy information obtained from Raman will be fully exploited. 2001 Elsevier Science B.V. All rights reserved.

Effect of Laser-Induced Crater Depth in Laser-Induced Breakdown Spectroscopy Emission Features:

The influence of crater depth on plasma properties and laser-induced breakdown spectroscopy (LIBS) emission has been evaluated. Laser-induced plasmas were generated at the surface and at the bottom of different craters in a copper sample. Plasmas produced at the sample surface and at the bottom of the craters were spatially and temporally resolved. LIBS emission, temperature, and electronic number density of the plasmas were evaluated. It is shown that the confinement effect produced by the craters enhances the LIBS signal from the laser-induced plasmas.

Self-calibrated quantitative elemental analysis by laser-induced plasma spectroscopy: application to pigment analysis

Abstract A new laser-based spectroscopic technique, called calibration-free LIPS (laser-induced plasma spectroscopy), is proposed for fast and precise elemental analysis in the field of cultural heritage conservation and study. Quantitative stratigraphic results, obtained by CF-LIPS on ancient Roman frescoe samples, are shown. The application of this calibration-free procedure frees the LIPS technique from the need of reference samples or an internal standard. This characteristic, along with the intrinsic speed (the whole process of data collection and analysis takes a few minutes) and precision (of the order of a few parts percent) make the CF-LIPS a viable technique for in situ quantitative analysis of artworks.

Quantitative analysis of aluminium alloys by low-energy, high-repetition rate laser-induced breakdown spectroscopy

With the aim of reducing the dimensions of a laser-induced breakdown spectroscopy (LIBS) apparatus for building a portable instrument, a diode-pumped Nd:YAG mini-laser at high repetition rate was tested as an excitation source for the quantitative analysis of aluminium alloy samples. Moreover, LIBS spectra acquired by using an ICCD-echelle spectrometer detection system were compared with those obtained by a traditional spectrometer coupled to a non-intensified linear array detector. Calibration curves were built and limits of detections were calculated using both detection systems for magnesium, silicon, copper, titanium, manganese, nickel and iron. The results were compared with those obtained by recently proposed LIBS systems based on the use of microchip lasers.

Study of foxing stains on paper by chemical methods, infrared spectroscopy, micro-X-ray fluorescence spectrometry and laser induced breakdown spectroscopy

Abstract Foxing spots appear on the paper as stains of reddish-brown, brown or yellowish color, generally of small dimensions, with sharp or irregular edges, most of which, if excited with UV light, show fluorescence. The formation mechanisms of foxed areas have been studied since 1935, however, despite more recent intensive research there are still no conclusive results. Some authors found evidence of bacterial or fungal growth in some foxed areas sometimes associated with the presence of iron. We decided to focus our attention on the influence of the different iron valence in the formation of stains in the paper. For this reason we artificially induced the formation of foxing by adding to the paper small, known quantities of iron (III) and iron (II) ions. We prepared aqueous solutions of ferric chloride and ferrous sulfate at three different concentrations and we always used the same quantity of each solution (5 μl) to obtain a foxing stain. Part of the paper samples was artificially aged in a climatic chamber at 80 °C, 65% relative humidity for 15 days and part was submitted to aging for the same period at ambient temperatures under UV light at 240 nm. All papers were then analyzed for stain diameter, chromaticity coordinates, fluorescence under UV illumination, water content in the paper and in the spots, carbonyl content and then examined with infrared spectroscopy, X-ray fluorescence spectrometry and laser induced breakdown spectroscopy. Infrared spectra were collected in transmittance from potassium bromide pellets or directly in reflectance under microscope; X-ray fluorescence analysis were carried out using an X-ray microbeam (350 μm beam spot; W X-ray tube) and LIBS analysis with Nd:YAG laser coupled with a Czerny-Turner spectrometer. As a result it is stated that the foxing phenomenon is related to a strong oxidation of the cellulose chain. Concerning the color coordinates there are no great differences between samples treated with iron (III) and iron (II). Carbonyl content, on the contrary, varies for the two sets of samples, especially in relation with the kind of aging. μ-XRF and LIBS measurements show a relationship between iron valence and calcium ion displacement in the foxed areas.

Observation of different mass removal regimes during the laser ablation of an aluminium target in air

The mass removal mechanisms occurring during the ablation of an aluminium target, induced by a Nd:YAG laser at λ = 1064 nm in air, were investigated in the fluence range between 1.5 and 840 J cm−2. The spectroscopic analysis of the plasma emission allowed the calculation of the plasma thermodynamic parameters and an estimation of its atomized mass. Conversely, microscopic analysis of the craters allowed the calculation of the hole volume and the quantification of the material accumulated in the rim around it, as well as a qualitative inspection of the craters profile and appearance. The trends of line intensity, of the atomized plasma mass and of the crater volumes with laser fluence suggest the identification of four laser fluence ranges, where a different role of background gas is played and different mass removal mechanisms seem to occur. A complex picture is drawn where vaporization, melt displacement, melt expulsion and phase explosion take place at different laser fluences.