CSigma graphs: A new approach for plasma characterization in laser-induced breakdown spectroscopy

Abstract

a b s t r a c tA generalization of curves of growth called CSigma (Cσ) graphs, which allows including several lines of various elements in the same ionization state at different concentrations, is proposed for laser-induced breakdown spectroscopy (LIBS) experiments. The method relies on the Boltzmann, Saha and radiative transfer equations for plasmas in local thermodynamic equilibrium. Cσ graphs are based on the calculation of a line cross section σ l for each of the experimental data, starting from the atomic data of the line, the temperature and the electron density. A model of homogeneous plasma, applied separately for neutral atoms and ions, is used. A limit of validity is established for this model. Experimental Cσ graphs have been obtained using fused glass samples containing Fe, Mn, Mg, Si and Cr. By fitting experimental Cσ graphs to calculated curves, the LIBS system becomes characterized by a set of four parameters βA, Nl, T, N e , different for neutral atoms and ions. Starting from this characterization, the intensity and selfabsorption of a given spectral line of an element at a certain concentration may be predicted, provided that its atomic data are known and the limit of validity is not exceeded.

Calibration Methods of Laser-Induced Breakdown Spectroscopy

“…A number of researchers have made some modifications to the CF-LIBS algorithm, such as self-absorption [89,90]. In recent years, several research groups [91][92][93][94] began using standard samples to improve the accuracy of the nonstandard analysis. Cavalcanti et al [92] presented and used one-point-calibration CF-LIBS to analyze a set of copper-based samples.…”

Quantitative analysis by laser-induced breakdown spectroscopy based on generalized curves of growth

“…The theoretical framework leading to Cσ graphs is described in detail in our previous work [19]. Here, the main definitions and equations are recalled for clarity.…”

“…This result was in agreement with that deduced previously [18] from the local and spatially-integrated characterization of a laser-induced plasma: as a result of plasma inhomogeneity, different apparent temperatures are obtained in spatially-integrated measurements from the Boltzmann plots of neutral atoms and ions. In a recent work [19], we have introduced a generalization of curves of growth called Cσ graphs, which allow including several lines of various elements at different concentrations. In agreement with our previous results [17,18], different Cσ graphs corresponding to distinct apparent parameters need to be constructed for neutral atoms and ions.…”

“…Then, the complex inhomogeneous character of the laser-induced plasma is addressed using a model limit. In [19], Cσ graphs are proposed as a tool for characterization of laser-induced plasmas. In the present work, we present a method for quantitative analysis by LIBS, based on the use of Cσ graphs (Cσ-LIBS).…”

Novel Applications of Laser-Induced Breakdown Spectroscopy

“…Tests of the method with glass beads after calibration with known samples achieved accuracy for Fe, Ca, and Mn in slag samples better than 10% over a range of concentrations. 19,20 Laser-Induced Breakdown Spectroscopy and Molecular Features Molecular features seen in LIBS experiments have been the source of curiosity since their first observation. Although LIBS in general is focused on the collection and analytical use of atomic emission spectra, molecular signals have been used in a wide range of analyses, including explosives detection, identification of polymers, and even the evaluation of motor oil.…”