Spectra-assisted laser focusing in quantitative analysis of laser-induced breakdown spectroscopy for copper alloys

Laser-induced breakdown spectroscopy (LIBS) is a capable technique for elementary analysis, while LIBS quantitation is still under development. In quantitation, precise laser focusing plays an important role because it ensures the distance between the laser and samples. In the present work, we employed spectral intensity as a direct way to assist laser focusing in LIBS quantitation for copper alloys. It is found that both the air emission and the copper line could be used to determine the position of the sample surface by referencing the intensity maximum. Nevertheless, the fine quantitation was only realized at the position where the air emission (e.g. O (I) 777.4 nm) reached intensity maximum, and also in this way, a repeatable quantitation was successfully achieved even after 120 days. The results suggested that the LIBS quantitation was highly dependent on the focusing position of the laser, and spectra-assisted focusing could be a simple way to find the identical condition for different samples' detection. In the future, this method might be applicable in field measurements for LIBS analysis of solids.