Self-absorbed Ca doublet lines for stand-off quantitative analysis by laser induced breakdown spectroscopy

Abstract

Abstract Laser induced breakdown spectroscopy (LIBS) is one of the promising techniques for stand-off detection of element composition. However, it is somewhat limited by quantitative shortage. Absolute line intensity may be influenced by acquisition conditions, environmental variation, and sample surface conditions. Relative intensity may also fluctuate greatly. This study shows that the intensity ratio between Ca II doublet emission lines (393.37 nm and 396.85 nm) is stable, and changes with Ca concentration (or Ca atoms count within the laser spot). This is due to differences in self-absorption between the two transitions. A theoretical calibration shows a linear section for low species density and quadratic section for high species density. Experimental results confirm the linear section after density correction of CaO pellets. However, an equipment factor should be considered for numerical calibration in different laboratories. For Ca-containing samples, quantitative analysis could be based on the detected Ca spectrum. Ca is also shown to be suitable as an internal standard reference to determine other elemental concentration, such as Mg.