Microchip laser ablation of metals: investigation of the ablation process in view of its application to laser-induced breakdown spectroscopy

Abstract

Metal ablation with a short pulse, low energy microchip laser was investigated with respect to its application to laser induced breakdown spectroscopy (LIBS). Target surface modifications and crater parameters as a function of laser pulse properties were studied. The effect of the laser pulse is limited to the focal spot, but surface modification by the laser-induced plasma can extend several micrometers beyond the focal spot depending on the target’s thermal properties. Mass removal per shot was found to depend upon the heat of fusion of the target, while appreciable plasma emission was observed only at high pulse energies. Plasma composition and emission intensity can change significantly with the surface properties, requiring a fresh, flat surface to be exposed to each laser pulse. Increasing the temperature of the target resulted in a corresponding increase in plasma emission due to an increased mass removal per laser shot: however, selective ablation was not observed at temperatures up to 550 °C. Fractionation was observed at low laser irradiances and inside deep craters, but it was minimal compared with the results reported for other laser ablation systems. Characteristics such as precision in the mass removal process, well-defined crater parameters, and good spatial resolution make the Powerchip laser an attractive laser sampling tool.