Effect of gas temperature on composition concentration measurements by laser-induced breakdown spectroscopy

Abstract

Laser-induced Breakdown Spectroscopy (LIBS) is widely applied to the quantitative measurement of gas composition concentrations. However, studies on the effect of gas temperature on LIBS are still lacking. Here, we investigated the effect of gas temperature on LIBS in terms of composition measurements in an air flow field. The air flow field was heated using a resistance wire to different gas temperatures ranging from 300–930 K in a heating tube. We evaluated the effect of gas temperature on the ratio of spectral line pairs, which is typically used for the calibrations of LIBS measurements. The variations in gas temperature change the ratio of spectral line pairs, which ultimately affects the accuracy of LIBS measurements. Further, the effect of gas temperature on the accuracy of LIBS measurements with different acquisition strategies was compared. The effects of gate width and delay time were investigated. An optimized acquisition strategy was proposed to reduce the effect of gas temperature on LIBS measurements. For LIBS measurements in gas flow fields, the effect of gas temperature on LIBS measurements can be reduced by using a large gate width and a suitable long delay time. The optimized acquisition strategy uses long-time averaging after an appropriate delay time to reduce the effect of gas temperature on plasma parameters. Finally, higher laser energy also helps to reduce the effect of gas temperature on LIBS measurements. In this paper, the LIBS measurement error caused by increasing the gas temperature from 300 K to 930 K is about 5%, roughly 0.8% per 100 K, with the optimized acquisition strategy. This paper can provide some help for LIBS measurements in gas samples with temperature variations.