Laser-ablation laser-induced breakdown spectroscopy (LA-LIBS) based on single Nd:YAG laser is used to analyze copper impurity in silver jewellery with enhanced sensitivity and minimal sample ablation. 6-30 folds signal enhancement can be achieved under the re-excitation of the breakdown laser and the spatial resolution is only determined by the ablation laser. 50 ppm limit of detection of copper is achieved when the crater diameter is 17.2 \mu m under current experimental condition. This technique gives higher analysis sensitivity under the same sample ablation in comparison with single pulse (SP) LIBS. It is useful for high sensitive element microanalysis of precious samples.

当聚焦激光束在焦平面上的光强分布为高斯分布时，理论推导了激光能量与激光在样品表面所烧蚀的坑洞半径的关系。以铝箔、铝反射镜和热敏相纸为样品，用显微镜测量出不同能量的脉冲激光在样品表面烧蚀的坑洞半径并通过数值拟合来实现对聚焦激光束的焦点光斑尺寸和样品剥离阈值的同时测量。对于脉宽为15 ns、波长为532 nm的激光，测得铝和热敏相纸的剥离阈值分别为2.5 J/cm2和0.25 J/cm2。光斑尺寸和剥离阈值两个参量的测量误差均约为±10%。该技术能够同时且简便地测量出聚焦激光束焦点的光斑尺寸和样品的剥离阈值，对研究固体与激光相互作用以及评价激光束聚焦的特性有一定的应用价值。