# Laser-Induced Breakdown Spectroscopy for Determination of Spectral Fundamental Parameters
## 5 Experimental Determination of Spectral Parameters by LIBS
### Determination of Stark Broadening Coefficients
Plasmas were produced by laser ablation with a Nd:YAG laser on a Sn-Pb alloy (with a Pb content of about 0.5%) and lead target (99.99% purity) in an argon atmosphere. The author reported that self-absorption was lower than 3% [73] and 1% [74] for the most intense lines in the LIBS spectra, respectively. In 2011, the experimental determination of the Stark width for 21 Fe II lines with wavelengths in the range 260-300 nm [75] and 26 Fe II lines in the range 230-260 nm [76] was done. The plasmas were generated from a set of Fe-Cu alloys (iron contents in the range 0.5 wt%-25 wt%) [75] and Fe-Cu/Fe-Ni samples [76], respectively. In these papers, the error due to self-absorption was estimated by authors to be lower than 10%. [PERSON] et al. [78] measured experimentally, in 2012, the Stark coefficients of 6 lines of Si II during pulsed laser ablation of a pure silicon target. A check of the temperature gradient along the radius of the plasma using an Abel inversion did not detect any inhomogeneity, and no self-absorption effects were detected. In 2013, [PERSON] et al. [79] estimated the Stark widths of 53 Ni II lines by laser ablation of Ni-Cu and Ni-Al alloys with a wide range of nickel concentrations. The authors used the curve-of-growth methodology on sample sets with different nickel concentrations to evaluate and reduce the effects of self-absorption. The error caused by self-absorption was estimated around 10%. [PERSON] et al. [80] investigated by LIBS a ZnO target in air, to determine the Stark broadening of the atomic Zn I line at 636.2 nm. The self-absorption effects were evaluated using the method proposed by [PERSON] el al. [54]. The Stark widths of 3 Mg I and 1 Mg II lines were determined by [PERSON] et al. [81] in a LIBS experiment on powder mixture of Al\({}_{2}\)O\({}_{3}\), Li\({}_{2}\)CO\({}_{3}\) and MgCO\({}_{3}\) sample. The authors aimed to reduce the Mg concentration in the sample to avoid strong self-absorption of the studied Mg I and Mg II lines. In 2014, [PERSON] et al. [82,83] determined the Stark widths of 36 Fe II and 27 Ni II [82] and 5 Fe II and 8 Ni II spectral lines [83], respectively. In these two papers, several samples were investigated; fused glass samples with Fe\({}_{2}\)O\({}_{3}\) and NiO oxides in powder form in the first [82] and Fe-Cu alloy and a Fe\({}_{2}\)O\({}_{3}\) fused glass in the second study [83]. The effect of self-absorption on the Stark widths, gave an error of the Stark coefficients lower than 10%, according to the authors. Stark widths and shifts of 11 Ca II lines were determined the same year by [PERSON] et al. [84]. LIBS plasmas were generated by laser ablation of fused glass samples with different calcium concentrations, from 0.005 to 1 percent, prepared from pure calcium carbonate. The authors found that the self-absorption affected the Stark width determination with errors lower than 10%. In another contribution [PERSON] et al. [95] calculated 83 Stark widths and 49 shifts of Cr II lines. LIBS measurements were done on three fused glass samples prepared from pure chromium oxide with chromium atomic concentrations of 0.05, 0.1 and 0.2 percent. The error caused by neglecting self-absorption was estimated to be around 10%. [PERSON] et al. [85] in 2014 determined by LIBS the Stark broadening coefficient for 4 Al II lines. The electron number density was obtained through the measurement of the FWHM of the hydrogen Balmer alpha line. The author used the method of spatial Abel inversion to deal with the nonhomogeneity of the laser-plasma. The effect of self-absorption was calculated using the duplicating mirror method. [PERSON] and [PERSON] [86] reported in 2016 the first measurements of Stark broadening widths of W I lines (426.9 nm, 429.4 nm and 430.2 nm) as a function of the electron number density. The authors found a linear relation between W I Stark widths and electron number density. The authors calculated the electron number density values from the Stark broadening of a C II line at 426.7 nm in nanosecond laser-induced tungsten carbide plasmas.