Emission enhancement of underwater collinear dual-pulse laser-induced breakdown spectroscopy with the second pulse defocused

Abstract

Axial focusing arrangement effects on collinear dual-pulse laser-induced breakdown spectroscopy (DP-LIBS) in a bulk solution were investigated by spectra and fast images. By properly defocusing the second laser pulse beyond the first laser formed bubble (LFB), brighter and larger plasmas could be produced due to higher breakdown efficiency and higher expansion efficiency. It is attributed to a distinct mechanism of underwater DP-LIBS that the plasma mostly forms at the bubble-water interface and then expands into the gaseous LFB. The results show that optimization of the axial focusing arrangement in underwater collinear DP-LIBS enables significant emission enhancements with relatively low laser energies.