Contents lists available at ScienceDirect Spectrochimica Acta Part B journal homepage: www.elsevier.com/locate/sab Determination of the Stark broadening coefcients of tantalum emission lines by time-independent Extended C-sigma method ☆ Francesco Poggialini a,b , Beatrice Campanella a , Rashida Jafer c , Stefano Legnaioli a , Fausto Bredice d , Simona Raneri a , Vincenzo Palleschi a,⁎ a Applied and Laser Spectroscopy Laboratory, Institute of Chemistry of Organometallic Compounds, Via G. Moruzzi, 1, Pisa, Italy b Scuola Normale Superiore, Piazza dei Cavalieri 7, Pisa, Italy. c Department of Physics, Faculty of Science, King Abdul Aziz University, 21589 Jeddah, Saudi Arabia d Centro de Investigaciones Ópticas, P.O. Box 3 C. P.1897 Gonnet, La Plata, Argentina ARTICLE INFO Keywords: Tantalum LIBS Stark broadening Self-absorption Extended C-sigma ABSTRACT In this paper we introduce a new time-independent Extended C-sigma approach for the analysis of Laser Induced Breakdown Spectroscopy (LIBS) spectra and apply it to the determination of the Stark broadening coefcient of several neutral and ionic emission lines of tantalum. The method proposed is based on the recently introduced Extended C-sigma procedure and exploits the spectral information extracted from LIBS spectra acquired at diferent delay times after the laser pulse for building a time-independent Extended C-sigma curve. The method intrinsically includes in the calculation the efects of self-absorption, which is one of the main sources of in- determination in LIBS applications to the determination of spectroscopic fundamental parameters, such as transition probabilities and Stark broadening coefcients. 1. Introduction Tantalum is a transition metal (atomic number 73), mainly obtained from Columbite-Tantalites (Coltan) mineral, which has many uses in the industry of electronic devices [1]; moreover, its chemical and physical characteristics can be used in industrial alloys characterized by high hardness that are good candidates as Plasma Facing Components (PFCs) in next generation fusion reactors (International Thermonuclear Experimental Reactor - ITER) [2–4]. Since several years, the Laser-In- duced Breakdown Technique has been proposed as a viable method for geochemical research of tantalum-rich rocks [5,6] for the mining in- dustry. At the same time, several proposals for the use of LIBS (and Calibration-Free LIBS [7]) have been presented for on-line diagnostics of PFCs in nuclear power research [8,9]; in spite of that, the studies on tantalum by LIBS are quite limited and many fundamental parameters for quantitative analysis, such as transition probabilities and Stark broadening coefcients, are not precisely known. To the best of our knowledge, no information is available in the literature about the Stark broadening coefcients of Tantalum lines. In ref. [10], the authors calculated the electron number density of a tantalum plasma from the Stark broadening of ambient gas emission lines, while in ref. [4] the authors did not try to measure the Stark coefcients, because the spectral resolution of their spectrometer was too low for measuring the Stark width of the tantalum lines. In this paper, we will present a new method for measuring plasma fundamental parameters, such as tran- sition probabilities and Stark coefcients, which exploits the spectral information obtained from time-resolved analysis of a tantalum LIBS plasma to build a time-independent Extended (TIE) C-sigma curve [11]. The principles of the method are presented in the following Section. 2. Principles of the method The spectroscopic analysis of laser-induced plasmas can provide useful information about some fundamental plasma parameters, such as transition probabilities [12–15] and Stark broadening coefcients [16–18]. The procedure seems to be straightforward since, in the ap- proximation of optically thin [19], homogeneous plasma in Local Thermal Equilibrium [20], the transition probability of a line emitted by a given element may be obtained by simply comparing the measured line intensity with that of an emission line of the same species, whose transition probability is known: https://doi.org/10.1016/j.sab.2020.105829 Received 30 January 2020; Accepted 17 March 2020 ☆ Selected Paper from the 10th Euro-Mediterranean Symposium on Laser-Induced Breakdown Spectroscopy (EMSLIBS 2019) held in Brno, Czech Republic, 8–13th September 2019. ⁎ Corresponding author. E-mail address: vincenzo.palleschi@cnr.it (V. Palleschi). Spectrochimica Acta Part B 167 (2020) 105829 Available online 19 March 2020 0584-8547/ © 2020 Elsevier B.V. All rights reserved. T