Line plasma versus point plasma VUV LIBS for the detection of carbon in steel: a comparative study

Steel impacts a variety of industries such as construction, automotive and ship building. The physical properties of steel (e.g., hardness, weldability) are significantly affected by the concentration of carbon. Hence, accurate determination of carbon content in steel has been, and still is, an active field of research. Laser induced breakdown spectroscopy (LIBS), has been extensively used applied to measure the concentration of carbon in steel. Specifically, vacuum-ultraviolet (VUV) LIBS is a favourable technique for detection of light elements. In this work, a line plasma, as opposed to the more commonly used point like plasma plume, is explored to systematically investigate its effect on the limit of detection for carbon in steel. In addition, the effect of moving the target surface and cylindrical lens focus with respect the optic axis of the spectrometer is studied. The presence of a fore slit, between the plasma and entrance slit of the spectrometer, provides a degree of space resolution, by allowing radiation from a specific slice of the plasma plume to enter the spectrometer. Importantly, the experimental findings suggest a significant improvement in the relative limit of detection, by a factor of six, over the more usual point-like plasmas.