采用飞秒激光成丝-纳秒脉冲激光诱导击穿光谱技术(Filament-ns DP-LIBS)对土壤中重金属铅元素进行了定量分析。利用飞秒激光等离子体丝烧蚀含铅土壤样品, 向外喷射低密度的土壤粒子源, 经脉冲间隔Δt后, 纳秒脉冲激光再烧蚀低密度土壤粒子, 实现等离子体发射光谱强度增强, 谱线宽度压缩, 降低土壤中重金属铅元素的最小检测限。实验结果表明, 相比飞秒激光等离子体丝诱导击穿光谱技术(FIBS), 在飞秒-纳秒脉冲间隔Δt=10 μs条件时, PbI405.78 nm光谱增强因子为9.66, 谱线宽度从3.66×10-10m压缩至2.74×10-10m, 提高了LIBS光谱分辨率。FIBS和Filament-ns DP-LIBS条件下定标曲线的线性相关系数R2分别为0.982和0.994。FIBS条件下的RSD和LOD值分别为7.37%和65.86 mg/kg, Filament-ns DP-LIBS条件下的RSD和LOD值分别为3.27%和24.39 mg/kg。研究结果表明, Filament-ns DP-LIBS技术可以降低土壤重金属的最小检测限, 提高LIBS的检测灵敏度。

In this study, quantitative analysis of heavy metal lead in soil was conducted by femtosecond laser-filament-laser-induced breakdown spectroscopy (Filament-ns DP-LIBS). First, a femtosecond laser plasma wire was used to ablate the lead-containing soil sample, and a low-density soil particle source was sprayed outward. Then, following interpulse delay time Δt, another nanosecond laser beam was used to re-ablate the low-density soil particle source to enhance spectral intensity, compress spectral line width, improve the experimental repeatability of LIBS, and reduce the Limit of Detection (LOD) of heavy metal lead in the soil. Experimental results show that when compared to the results of the Filament-induced Breakdown Spectroscopy (FIBS), the enhancement factor of Pb I 405.78 nm for the Filament-ns DP-LIBS with an interpulse delay time of 10 μs is 9.66, and the spectral line width is reduced from 3.66×10-10 m to 2.74×10-10m, which improves the LIBS spectral resolution. With the FIBS and Filament-ns DP-LIBS, the linear correlation coefficients R2 of calibration curves are 0.982 and 0.994, respectively. The RSD and LOD values with the FIBS and Filament-ns DP-LIBS are 7.37% and 65.86 mg/kg and 3.27% and 24.39 mg/kg, respectively. The results thus reveal that the Filament-ns DP-LIBS can reduce the minimum detection limit of soil heavy metals and improve the detection sensitivity of LIBS.