ИСТИНА

Laser-induced breakdown spectroscopy (LIBS) is a versatile technique capable of analysing a wide range of unique specimens, from samples analysed on ocean floor and Mars, from molten metal to radioactive waste. However, in many cases, appropriate certified reference materials may not be available for calibration. Under the assumption of optically thin plasma subject to local thermodynamic equilibrium (LTE), Boltzmann plot analysis, also referred to as calibration-free (CF) LIBS analysis [1], can be used. However, fulfilling all the necessary requirements can be challenging, with extreme conditions such as open space or deep sea further complicating the calibration process. Assuming a uniform plasma under local thermodynamic equilibrium, it is possible to synthesise a spectrum for a given elemental composition, temperature, electron density, and other conditions [2]. Multiparametric optimization can be used to fit the model to the experimental data, with the relative elemental concentrations and plasma conditions serving as variables. A gradient-free optimisation method has been chosen for this task. The model was tested on metallic and non-metallic multicomponent samples, with various shapes of the loss function considered to account for analytical lines of different intensities and highlight different detail of the spectra. The stability of the solution was verified through repeated runs with randomly-chosen initial parameters. It has been shown that the homogeneous plasma model is sufficient to predict several elements with lines in narrow spectral regions, while a multi-zone model with different temperatures and electron densities provides the best results for the full spectra, although the accuracy is lower. Our algorithm was employed to fit several Curiosity ChemCam and Mars 2020 Perseverance SuperCam spectra, yielding the composition of the studied object. [1] A. Ciucci, M. Corsi, V. Palleschi, S. Rastelli, A. Salvetti, E. Tognoni, Applied Spectroscopy, 53(8), 960-964 (1999) [2] S. M. Zaytsev, A. M. Popov, T. A. Labutin, Spectrochimica Acta, Part A, 158, 105632 (2019).