Analysis Of Elements In The Aluminum Alloy With Dual Wavelength LA-LIBS

Elemental analysis based on the emission from Plasma generated by focusing a powerfullaser beam on any material surface is known as Laser-induced BreakdownSpectroscopy(LIBS). The improvement of analytical sensitivity and spatial resolving powerare equally important for the LIBS technique.In this work，the analytical sensitivity of single-pulse LIBS was studied in the first place.A non-polluted thin wood slice was chosen as substrate to absorb water sample and analyzedwith single-pulse LIBS rapidly and sensitively, to overcome the drawbacks of low sensitivityand reproducibility existed in the process of direct analysis of water samples with LIBS. The214.44nm ionic line of cadmium was chosen as analytical line. A calibration curve wasestablished for the purpose of quantitative analysis. The limit of detection of cadmium inwater was determined to be55μg/L and the relative standard deviation of signal in differentmeasurement was less than5%. The time needed for each measurement was less than5minutes. The approach developed here provides a rapid and simple method for monitoring ofcadmium pollution in water environment.However, the physical processes of stripping and breakdown of the sample was notseparated for single-pulse LIBS, and therefore can’t be optimized separately，resulting thecontradiction between high spatial resolving power and high sensitivity. To break through thisbottleneck，we proposed a technical solution named dual-wavelength LA-LIBS to separatethe processes of laser ablation(LA) and the follow-up breakdown of the sample. We injectedthe output of a Nd:YAG laser second harmonic (532nm) light into the surface of samples to beanalyzed vertically to strip out a little while injecting its fundamental frequency (1064nm)from the orthogonal direction of incident light to excite the sample stripped to form alaser-induced plasma. The signal enhancement of Cu、Cr、Mn、Mg in aluminum alloy standardsamples was researched. Compared with single-pulse LIBS，the improvement of signal tonoise ratio(SNR) of the four elements ranged from8times to25times. We also explored theconditions of laser focusing as well as laser energy and figured out the stripping threshold ofthe aluminum alloys was48μJ under certain conditions. With the near-threshold ablation laser,the space resolving power of dual-wavelength LA-LIBS for aluminum alloy standard sampleswas7.5μm. The spatial resolution of this technology was inversely proportional to the energyof ablation laser under the premise of ensuring the analytical sensitivity. The spatial resolutionand spectroscopic sensitivity of dual-wavelength LA-LIBS were significantly improved in comparison with the traditional single-pulse LIBS.