Studies On Dual-wavelength Laser-ablation Laser-induced Breakdown Spectroscopy With High Spatial Resolution

To resolve the contradiction between spatial resolution and spectral analysis sensitivityexisted in single-pulse laser-induced breakdown spectroscopy (SP-LIBS), some criticaltechniques in orthogonal dual-wavelength dual-pulse laser-ablation laser-induced breakdownspectroscopy (LA-LIBS) and elemental analysis of copper in different samples with thistechnique have been studied in this thesis.First, in order to carry out the LA-LIBS experimental studies based on single Nd:YAGlaser,1064nm laser pulses were delivered with silica fiber with large core diameter. Thecoupling between laser beam and fiber, collimation of the output laser beam and there-focusing of the collimated laser beam were studied experimentally. Laser pulse with15mJ pulse energy was delivered with50m silica fiber with800μm diameter and0.39numerical apertures and250ns time delay was realized. Significant improvement of thesignal to background ratio of copper atomic emission at324.75nm for copper alloy wasachieved in LA-LIBS in comparison with that in SP-LIBS.The laser ablation threshold of copper was also first measured with LA-LIBS. For532nm laser with12ns pulse width, the laser ablation threshold of copper was measured to be0.64±0.06J/cm2. This technique is very useful for studying interaction of laser and mattersand for careful pulse energy selection in LA-LIBS in order to achieve high spatial resolution.Copper impurity in silver jewellry was also analyzed with orthogonal dual-wavelengthdual-pulse LA-LIBS with short inter-pulse time delay based on single Nd:YAG laser. Thelimit of detection of copper was determined to be42ppm while the crater diameter was lessthan25μm. The relative standard deviation was less than5%. The possibility of realizingmicroanalysis with orthogonal dual-wavelength dual-pulse LA-LIBS base on single Nd:YAGlaser was demonstrated.The technique of orthogonal dual-wavelength dual-pulse LA-LIBS has high spectralanalytical sensitivity under the condition of minimal sample ablation. It is especially useful for elemental analysis of precious samples or microanalysis with high spatial resolution andcan be potentially used in different fields.