| Abstract: | Laser ablation is a useful source of particles for chemical analysis by inductively coupled mass spectroscopy in many applications. Optimum particle transport and ionization requires particles with sizes in the range 0.1-2 7m. Significant questions remain as to the mechanisms behind particle production by laser ablation. In this work, we collect and observe particles produced from single-crystal sodium nitrate during irradiation at 1.06 7m as a function of fluence and explore the possibility that laser-induced fracture may produce suitable particles. At fluences between 3 and 4 J/cm2, single laser pulses incident on cleaved samples produce large numbers of fracture particles as a result of the fracture of undercut cleavage steps. Polished samples, lacking cleavage steps, yield few, if any, particles. As the fluence is raised to 5 J/cm2, a small breakdown plume is observed and large melted droplets (~10 7m in diameter) are produced from both cleaved and polished targets, presumably by spallation of a thick melted layer. Particle generation by fracture has the potential to produce particles whose composition closely matches the local sample composition. |
