Characterization of the self-reversal phenomenon of Ag resonant lines in laser-induced breakdown spectroscopy experiments

In this work, we analyzed the phenomenon of self-reversal (SR) of spectral lines in Laser-Induced Breakdown Spectroscopy (LIBS) spectra through the study of the temporal evolution of self-reversed emission lines in neutral and ionized silver, using different laser energies and lens-to-target distances. In these experiments, the characteristic dip of self-reversed lines corresponding to resonant transitions begins to form on the bremsstrahlung continuum within 20 ns after the laser-induced breakdown. The dip generated in the initial moments presents an inverted Lorentzian shape and, at later times, gradually acquires a Gaussian profile. Additionally, we found that the self-reversal phenomenon in silver can occur in all transitions whose lower levels are below 6 eV and whose transition probabilities exceed 10 8 s −1 . The SR depends weakly on the laser pulse energy but is strongly influenced by the lens-to-target distance. It is possible to minimize the effect by adjusting this distance. The formation of craters on the target also favors the appearance of self-reversal. We propose a model to explain all the observed characteristics of the self-reversal phenomenon in this work, based on the interaction of Ag atoms and ions ejected by the plasma with the shock wave generated during the breakdown process. • Minimizing self-reversal effects requires precise adjustment of the lens-to-target distance. • Crater formation contributes to self-reversal, though to a lesser extent. • Initially, the self-reversed dip follows an inverted Lorentzian profile, with its full width at half maximum (FWHM) decreasing over time until it transitions to an inverted Gaussian. • Self-reversal generation is influenced by temperature and electron density gradients, as well as a shock wave that creates a low-pressure zone within the plasma.