The spatial resolution of nanosecond laser-induced plasma spectroscopy in gases

Abstract

For spectral techniques, one of the most critical parameters is spatial resolution. The spatial resolution of nanosecond laser-induced breakdown spectroscopy (ns LIBS) in gases, however, has not been thoroughly studied, and no clear conclusion has been reached. Here, we measured the one-dimensional spectra of ns LIBS at the boundary of two parallel gas flows, i.e., oxygen and nitrogen, with high temporal and spatial resolution. We found that firstly, the plasma expands rapidly even after the laser pulse, and accordingly, the ions generated during the laser pulse also expand; secondly, as the plasma continues to grow after the laser pulse, it will engulf and ionize the surrounding gases, which also contributes to the LIBS signal. Hence, we believe that strictly speaking, the spatial resolution of ns LIBS in gases is the size of the plasma at the point in time when LIBS is measured.