提高土壤重金属污染物的激光诱导击穿光谱探测灵敏度研究

Laser-induced breakdown spectroscopy (LIBS) is a rapid, in situ and multi-element analytical technique based on the analysis of the spectral emission from laser-induced plasma. It is known that the effects of the LIBS spectral broadening and wavelength shift can result in misinterpretation of trace elements, which further reduces the detection sensitivity of LIBS. In this project, we propose a pre-plasma from soil generated by femtosecond laser filaments in air to be the sample which is analyzed by using nanosecond LIBS. Due to the intensity clamping effect of the laser filaments, the generated pre-plasma provides a stable particle source which simultaneously has a higher electron temperature and lower electron density compared with nanosecond laser induced plasma. The analysis of the filament induced pre-plasma by using LIBS can suppress the spectral line width, enhance its intensity, and as a result, LIBS spectra with a higher spectral resolution and single-to-noise ratio can be obtained. The detection sensitivity of LIBS can be essentially improved. Based on this method (laser filament and nanosecond DP-LIBS), the heavy metal elements in soil will be quantitatively analyzed by using internal standard calibration method. Furthermore, the mechanisms of LIBS spectral intensity enhancement and detection sensitivity improvement will be revealed, which provides a scientific and technical basis for in situ and rapid analysis of heavy metal elements in soil.

激光诱导击穿光谱技术（LIBS）是通过测量物质等离子体发射光谱的一种快速、原位和多种痕量元素同时准确探测的光谱技术。土壤中痕量元素较多，由于LIBS光谱存在谱线加宽和谱线漂移，造成LIBS谱线重叠，出现元素错认问题，LIBS的检测灵敏度降低。本课题拟利用具有“强度锁定机制”的飞秒激光等离子体丝烧蚀样品获得稳定的低密度土壤粒子源，作为纳秒LIBS的研究对象，产生具有高电子温度和低电子密度的等离子体，压缩LIBS谱线宽度，增强谱线强度，获得高光谱分辨率和信噪比的LIBS光谱，从而提高LIBS的检测灵敏度。在此基础上采用内标法对土壤重金属污染元素进行快速精确探测。通过本课题研究，给出土壤重金属污染元素飞秒激光等离子体丝--纳秒激光DP-LIBS的谱线增强机理，分析提高LIBS灵敏度检测机理，为最终开展土壤重金属污染物原位快速探测应用奠定基础。

激光诱导击穿光谱（Laser-induced breakdown spectroscopy，LIBS）方法具有快速、原位、多元素同时检测、样品处理简单、远距离、非接触检测等优点，已广泛应用于农业、采矿业、制造业、电力热力生产业、餐饮业等领域。鉴于飞秒激光等离子体丝—纳秒激光脉冲诱导击穿光谱技术在土壤重金属污染物探测方面具有较大的发展潜力和应用前景，项目利用具有“强度锁定机制”的飞秒激光等离子体丝烧蚀样品获得稳定的低密度土壤粒子源，作为纳秒LIBS的研究对象，产生具有高电子温度和低电子密度的等离子体，获得高光谱分辨率和信噪比的LIBS光谱，提高LIBS的检测灵敏度。在此基础上采用内标法对土壤重金属污染元素进行快速精确探测。（1）开展了飞秒激光成丝诱导击穿光谱动力学研究，利用飞秒激光成丝“强度钳制”特性，克服了激光烧蚀靶材焦距的限制，减弱了靶材表面不平整等因素对光谱稳定性的影响，提高了光谱稳定性。（2）研究了飞秒激光烧蚀土壤低密度气溶胶颗粒的动态演化过程，基于filment/ns双脉冲技术得到具有高电子温度和低电子密度的等离子体，增强光谱强度，压缩了谱线宽度，提高了LIBS光谱探测灵敏度。（3）开展了飞秒/纳秒双脉冲作用激光诱导击穿光谱技术参数优化研究，得到了双脉冲不同间隔下的光谱强度、线性相关系数、均方根误差、检测限等参数对脉冲间延迟时间有很强的依赖性。（4）开展了长春市不同地理区域的土壤重金属元素定量与定性分析研究，基于LIBS技术能够有效地对土壤重金属成分定量分析，从而快速对污染做出判断。