Enhancement of molecular formation in fiber-optic laser ablation with a long nanosecond pulsed laser

Abstract

Fiber-optic laser-induced breakdown spectroscopy (LIBS) can be used for on-site chemical analysis in harsh environments with a flexible light delivery system. In this work, the use of a long-pulse laser (100 ns) is proposed for the detection of molecular emission signals, instead of a normal-pulse laser (6 ns). We show a significant enhancement of AlO signals using an aluminum metal target in air. We also elucidate the enhancement mechanism of the AlO formation by measuring species-specific images of the emission from aluminum atoms, oxygen atoms, and AlO molecules in the plasma. The internal structure of the plasma suggests that the formation origin of AlO molecules in the long-pulse-produced plasma is essentially different from that in the normal-pulse-produced plasma. The long-pulse laser causes a rise of the ablation plume and facilitates the flow of oxygen from the ambient air. This is a key factor to enhance the molecular emission signals.