Exploiting LIBS to analyze selected rocks and to determine their surface hardness based on the diagnostics of laser-induced plasma

The present work introduces a detailed investigation to discriminate between some types of igneous and sedimentary rocks. The used experimental setup was a conventional single-pulse nanosecond system with a neodymium YAG laser at two excitation wavelengths, 1064 nm, and 355 nm. The laser-induced emission spectra of the rock samples were normalized to the irradiance for both utilized laser wavelengths to compensate for the different laser pulse energies used. The surface hardness values of the studied samples were spectroscopically determined via the intensity ratios of the ionic-to-atomic spectral lines of iron in the rock samples. Besides, the laser-induced plasma parameters, namely the plasma temperature and the electron density, were calculated from the obtained spectral data. It is found that the plasma temperature, in the infrared-laser case, was higher than that of the ultraviolet laser while the electron density values were the opposite. Multivariate statistical analysis of the spectroscopic data using the principal component analysis technique revealed the possibility of discrimination between different types of rocks. Furthermore, the laser-induced breakdown spectroscopy results have been validated by comparison to the results of the energy-dispersive X-ray analysis for the same samples.