Minimally destructive analysis of aluminum alloys by resonance-enhanced laser-induced plasma spectroscopy

Aluminum alloys were analyzed for minor components and trace impurities using double pulse resonance-enhanced laser-induced plasma spectroscopy. The first laser pulse at 532 nm ablated the sample. The second laser pulse at 396.15 nm resonantly excited the Al atoms to rekindle the plasma plume. Emissions from Mg, Cu, Si, and Na were observed. At laser energies below the damage threshold, the analyte emissions were already orders of magnitude above the background noise. Nonresonant probes of comparable sensitivity would melt and deform the sample surface. Because of the lower etch rate of resonant probes, depth profiling at nanometer resolution was possible. Using this method, the variation of [Na] with depth was measured for high-purity samples. In contrast, nonresonant probes required 5 times the fluence and proportionally poorer resolution. Worse yet, the associated heating and laser remelting modified the [Na] profile.