Resonance-enhanced laser-induced breakdown spectroscopy: How the beam profile of the ablation laser and the interception geometry and energy of the reheating laser affect analytical performance

Resonance-enhanced laser induced breakdown spectroscopy (RELIBS) could improve the sensitivity of conventional laser induced breakdown spectroscopy (LIBS) by orders of magnitude. In order to exploit this analytical technique, we aim at establishing RELIBS as a minimally destructive and ultra sensitive analytical tool. For that purpose, three effects were investigated. The first is laser beam profile effect. Beam profiles of varying uniformity were used and their effects on LIBS and RELIBS were studied. Significant improvement in sensitivity was demonstrated when uniform profile was used. The second effect is the interception orientation of the dye laser beam. The laser plume was intercepted both longitudinally (anti-parallel to the target surface normal) and transversely. Transverse interception of the dye laser beam was found to deliver higher detection sensitivity due to a reduction in the background noise. Moreover, transverse interception prevented further ablation of the sample by the dye laser and thereby allowed the investigation of the third effect, the dye laser energy effect. Marked RELIBS signal enhancement and better precision were found when higher dye laser energy was used. By optimizing these three effects, the overall improvement in RELIBS sensitivity was more than an order of magnitude. A mass LOD of about 100 amol for Mg was demonstrated. For comparable sensitivity, LIBS analysis had to be ten times more destructive. Also, sub-monolayer of oxides grown on laser-cleaned aluminum surfaces was detected by monitoring the AlO emissions of rekindled plumes. The molecular emissions were not detectable with LIBS, no matter how destructive.