In this paper we report the first observations of dual-pulse laser-induced breakdown spectroscopy (LIBS) signal enhancements by using a pre-ablation spark. In this technique a laser pulse is brought in parallel to the sample surface and focused a few millimeters above it to form an air plasma or air spark. A few microseconds later a second laser pulse, which is focused on the sample, ablates sample material and forms the LIBS plasma from which analyte emission occurs. In this way, large LIBS signal enhancements, 11- to 33-fold, are observed for copper and lead, respectively, relative to the signal in the absence of the air spark. In all cases where enhanced LIBS signals are seen, greatly enhanced sample ablation also occurs.
Dimitra N. Stratis, Kristine L. Eland, and S. Michael Angel, "Dual-Pulse LIBS Using a Pre-ablation Spark for Enhanced Ablation and Emission," Appl. Spectrosc. 54, 1270-1274 (2000)