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La caracterización isotópica y elemental de los meteoritos de Marte ha permitido determinar la cronología de los procesos de formación del planeta y avanzar en la comprensión de su evolución biogeoquímica e hidrológica. Los meteoritos más abundantes son las rocas de origen ígneo, como las shergottitas. Los estudios petrológicos y geoquímicos previos del meteorito Northwest Africa 2975 (NWA 2975), revelaron que se trata de una roca volcánica de grano medio, entre subofítica y granular, compuesta predominantemente por piroxenos (57,3 vol.%) y plagioclasa (38,3 vol. %) completamente enmascarados con fases opacas (2,7 vol.%) y fosfatos (1,7 vol.%) [1]. El instrumento SuperCam a bordo del rover Perseverance (misión MARS 2020 de la NASA) está equipado con técnicas atómicas y moleculares (incluyendo LIBS y Raman) para la detección y análisis a distancia de muestras geológicas en la superficie del Planeta Rojo. La capacidad de estas técnicas se ha demostrado ampliamente en la caracterización de rocas, minerales y suelos en varias misiones espaciales. En el presente trabajo, se analizó un fragmento del meteorito NWA 2975 mediante un sistema de micro-LIBS con el objetivo de revelar su composición química elemental. Debido a la heterogeneidad intrínseca de la muestra, se analizaron diferentes posiciones de su superficie. El análisis cuantitativo de los elementos principales (Si, Al, Fe, Mg, Mn, Ca y O) y de otros elementos menores se llevó a cabo utilizando la metodología Calibration-Free [2]. Los resultados sugieren la presencia de piroxenos como principal componente mineral en las posiciones inspeccionadas, aunque también se pueden encontrar otras fases minerales como la plagioclasa. La información extraída del análisis LIBS se ha comparado con la de fluorescencia de rayos X (XRF) y la espectroscopia Raman. El uso combinado de diferentes técnicas espectroscópicas ha permitido obtener una mejor interpretación de los resultados composicionales. Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech.

Laser Induced Breakdown Spectroscopy (LIBS) is an appealing technique tostudy laser-induced plasmas (LIPs) both from the basic diagnostics point of view and for analytical applications. LIPs are complex dynamic systems, expanding at supersonic velocites and undergoing a trasnsition between different plasma regimes. If the Local Thermodynamic Equilibrium (LTE) conditin is valid for such plasmas, several analitical methods can be employed and fast quantitative analyses can be performed on a variety of samples. In the present paper, a discussion about LTE is carried out and an innovative application to tht analysis of the alexandrite genstone is presented. In addition, a study about the influence of plasma parameters on the performance of LTE-based methods is reported for bronze and brass targets.

Laser-induced breakdown spectroscopy (LIBS) is a fast and reliable technique suitable for the simultaneous qualitative and quantitative analysis of major and trace elements in samples of various nature and origin. In last decades, the use of metal accumulator plants, in combination with compost, has become a cheap and sustainable alternative technique to lower soil contamination by toxic heavy metals. In the present work, the LIBS technique has been applied to measure the concentrations of selected elements, including Al, Ca, Cr, Cu, Fe, K, Mg, Mn, Na, Pb, Sr, and Zn, in two composts of different origin and nature and four accumulator plant species (Atriplex halimus, Brassica alba, Brassica napus, and Eruca vesicaria). The plant samples were analyzed either as bulk plant material or as specific organs (i.e. shoots and roots). The concentrations measured by LIBS were assessed by complementary induced coupled plasma-optical emission spectroscopy. The significant correlation found between the data obtained by the two techniques (R=0.732-0.999) supports the feasibility of LIBS for fast screening of major, trace and toxic elements in plant and compost samples. In conclusion, the LIBS technique shows promising for further applications in soil remediation as well as in agriculture.

Laser Induced Breakdown Spectroscopy (LIBS) is an analytical technique based on the optical emission spectroscopy of the plasma generated by high energy laser pulse and solid sample. LIBS allows to perform stand-off and in situ analysis with immediate response and a limit of detection (in the range of mgkg-1), and for these peculiarities is particularly suitable for analysis in the environmental field. In this work is presented a case of study where the elemental analysis of some polluted soils are obtained either with the classical calibration curve (CC) method or with a Local Thermodinamic Equilibrium (LTE)-based Calibration-Free (CF) method, in order to demonstrate the capability of this technique. It is important to underline that the latter methodology does not require the use of preliminary experiments with standard samples and so it does not have any limitation due to the matrix effect. Several polluted soil samples were analyzed by drawing calibration lines to determine the concentration of some trace metals (e.g., Cr, Pb, Cu, Zn, Sr, Ni), as well as those of some major elements (e.g., Fe, Mn, Mg). The elemental concentration (normalized by Fe concentration) was measured with ICP-OES and LIBS techniques respectively. For what concern LIBS measurements, a comparison was done between two different data treatment: the LTE-CF based method and the classical CC method. For some elements a comparison was tried between calibration lines and calibration-free data, in order to validate the latter techniques also for complex matrices such as soils.

In the Laser-Induced Breakdown Spectroscopy (LIBS) technique, the existence of Local Thermodynamic Equilibrium (LTE) is the essential requisite for meaningful application of theoretical Boltzmann–Maxwell and Saha–Eggert expressions that relate fundamental plasma parameters and concentration of analyte species. The most popular criterion reported in the literature dealing with plasma diagnostics, and usually invoked as a proof of the existence of LTE in the plasma, is the McWhirter criterion [R.W.P. McWhirter, in: Eds. R.H. Huddlestone, S.L. Leonard, Plasma Diagnostic Techniques, Academic Press, New York, 1965, pp. 201–264]. However, as pointed out in several papers, this criterion is known to be a necessary but not a sufficient condition to insure LTE. The considerations reported here are meant to briefly review the theoretical analysis underlying the concept of thermodynamic equilibrium and the derivation of the McWhirter criterion, and to critically discuss its application to a transient and non-homogeneous plasma, like that created by a laser pulse on solid targets. Specific examples are given of theoretical expressions involving relaxation times and diffusion coefficients, as well as a discussion of different experimental approaches involving space and timeresolved measurements that could be used to complement a positive result of the calculation of the minimum electron number density required for LTE using the McWhirter formula. It is argued that these approaches will allow a more complete assessment of the existence of LTE and therefore permit a better quantitative result. It is suggested that the mere use of the McWhirter criterion to assess the existence of LTE in laser-induced plasmas should be discontinued.

The Stark broadening of hydrogen Balmer ? line is often measured in Laser-Induced Breakdown Spectroscopy (LIBS) to evaluate the electron number density of the plasma. When measurements are carried out in air, hydrogen atoms are supposedly supplied by the atmosphere. This hypothesis casts some doubts on the validity of hydrogen as an indicator of the conditions in the inner part of the plasma. In this experiment, we acquired spectrally resolved images of a Laser-Induced Breakdown Spectroscopy plasma generated in air on an aluminum target by irradiation with the Nd:YAG fundamental emission. The evolution of the plasma was studied by acquiring images at several delay times. In particular, we imaged the spatial distribution of plasma emitters along the direction orthogonal to the target surface. The spatial distribution of hydrogen emission was compared to the one of the species ablated from the sample. Moreover, electron density and temperature were evaluated in the time- and space-resolved spectra extracted from the images, obtaining thus a picture of the propagation and internal structure of the plasma. The fluid dynamics implications of the plasma expansion were discussed. The z-resolved characterization was compared with the picture of the plasma obtained by processing space-integrated spectra.