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Plasma emission of liquid benzene (C 6 H 6 ) and carbon disulfide (CS 2 ) have been studied by using the laser-induced breakdown spectroscopy (LIBS) technique in air. Atomic lines of carbon, hydrogen, sulfur, nitrogen, and oxygen and molecular emissions of CN and C 2 have been identified. The formation mechanism of C 2 and CN molecules has been discussed. The combustion process and high mole fraction of hydrogen in benzene caused a decreasing atomic line intensity of oxygen and an increasing atomic line intensity of hydrogen with respect to the CS 2 and air. Additionally, more intense CN molecular bands and weak nitrogen atomic lines in the C 6 H 6 spectrum compared to CS 2 have been observed. Furthermore, molecular emissions of C 2 have not been observed in the CS 2 spectrum. The electron temperature and vibrational temperature have been calculated from the atomic lines and molecular band intensity, respectively. Finally, the validity of the local thermodynamic equilibrium (LTE) assumption in this experiment has been shown.

In this paper, the influence of heating and cooling samples on the optical emission spectra and plasma parameters of laser-induced breakdown spectroscopy for Titanium 64, Inconel 718 super alloys, and Aluminum 6061 alloy is investigated. Samples are uniformly heated up to approximately 200°C and cooled down to -78°C by an external heater and liquid nitrogen, respectively. Variations of plasma parameters like electron temperature and electron density with sample temperature are determined by using Boltzmann plot and Stark broadening methods, respectively. Heating the samples improves LIBS signal strength and broadens the width of the spectrum. On the other hand, cooling alloys causes fluctuations in the LIBS signal and decrease it to some extent, and some of the spectral peaks diminish. In addition, our results show that electron temperature and electron density depend on the sample temperature variations.

A new setup for spatially resolved laser-induced breakdown spectroscopy (SR-LIBS) is used for the first time to analyze methane-air diffusion flames. Using this configuration, background continuum emission is reduced, signal-to-background noise ratio is increased up to eight times, and spatial resolution is enhanced. The local equivalence ratio is also quantitatively estimated and the width of the secondary combustion region at a specified height above the burner is determined for two different methane flow rates. Furthermore, the threshold energy for spark formation is measured for regions inside and outside the flame. The results show that threshold energy is larger at the secondary combustion region, near the border of the flame, than inside the flame.

The effect of self-absorption was investigated on the estimation of surface hardness of Fe-Cr-Ni metallic alloys by the laser-induced breakdown spectroscopy (LIBS) technique. For this purpose, the linear relationship between the ratio of chromium ionic to atomic line intensities (CrII/CrI) and surface hardness was studied, both before and after correcting the self-absorption effect. The correlation coefficient significantly increased from 47% to 90% after self-absorption correction. The results showed the measurements of surface hardness using LIBS can be more accurate and valid by correcting the self-absorption effect.