Double-pulse laser ablation sampling: Enhancement of analyte emission by a second laser pulse at 213nm

For the purpose of devising methods for minimally destructive multi-element analysis, we compare the performance of a 266nm–213nm double-pulse scheme against that of the single 266nm pulse scheme. The first laser pulse at 266nm ablates a mica sample. Ten ns later, the second pulse at 213nm and 64mJcm−2 orthogonally intercepts the gas plume to enhance the analyte signal. Emissions from aluminum, silicon, magnesium and sodium are simultaneously observed. At low 266nm laser fluence when only sub-ng of sample mass is removed, the signal enhancement by the 213nm pulse is especially apparent. The minimum detectable amount of aluminum is about 24fmol; it will be a hundred times higher if the sample is analyzed by the 266nm pulse alone. The minimum detectable mass for the other analytes is also reduced by about two orders of magnitude when the second pulse at 213nm is introduced. The spectral and temporal properties of the enhanced signal are consistent with the mechanism of ultra-violet laser excited atomic fluorescence of dense plumes.