单脉冲和再加热正交双脉冲激光诱导击穿光谱对比研究

摘要

为了提高激光诱导击穿光谱技术(LIBS)的检测灵敏度和辐射光谱特性,采用再加热正交双脉冲结构对样品中的4种元素Fe,Pb,Ca和Mg以及含有不同浓度重金属元素Cr的土壤样品进行分析.研究了4条特征谱线FeⅠ:404.581 nm,PbⅠ:405.78 nm,CaⅠ:422.67 nm和MgⅠ:518.361 nm的光谱强度和信背比随两激光脉冲之间时间间隔的变化关系,获得了两激光脉冲之间最佳的时间间隔为1.0 μs.在单脉冲和双脉冲条件下,得到了4条特征谱线FeⅠ:404.581 nm,PbⅠ:405.78 nm,CaⅠ:422.67 nm和MgⅠ:518.361 nm光谱强度的增强倍数分别为2.23,2.31,2.42和2.10;分析了特征谱线FeⅠ:404.581 nm和CaⅠ:422.67 nm谱线强度随时间的演化特性以及4条特征谱线信背比随光谱采集延时的变化关系,双脉冲能有效延长光谱强度的衰减时间以及提高特征谱线的信背比;比较分析了等离子体温度和电子密度随时间的演化特性,在双脉冲条件下,等离子体温度最大升高了730 K,电子密度最大增加了1.8×1016 cm-3.单脉冲和双脉冲条件下获得重金属元素Cr的检测限分别为38和20 μg·g-1,再加热正交双脉冲技术使元素检测限下降近2倍.以上结果表明:再加热正交双脉冲能有效地提升L IBS技术的检测灵敏度和光谱特性,为进一步降低元素的检测限提供了有效的方法.%In order to improve the detection sensitivity and spectral characteristic of las er-induced breakdown spectroscopy (LIBS),re-heating orthogonal dual-pulse c o nfiguration is adopted to analyze Fe,Pb,Ca and Mg contained in the sample an d soil sample contained different concentrations of heavy mental Cr.Variation relationship between spectral intensity,signal-to-background(SBR) of four c haracteristic spectral lines FeⅠ:404.581 nm,PbⅠ:405.78 nm,CaⅠ:422.67 nm and MgⅠ:518.361 nm and time interval of two laser pulses is discusse d,the best time interval of two laser pulses is obtained 1.0 μs.In the con dition of single pulse and dual-pulse,the enhancement factor of spectral inte nsity of four characteristic spectral lines FeⅠ:404.581 nm,PbⅠ:405.78 nm,CaⅠ:422.67 nm and MgⅠ:518.361 nm is respectively 2.23,2.31,2.42 and 2.10;The time evolution characteristic of spectral intensity of char acteristic spectral lines FeⅠ:404.581 nm and CaⅠ:422.67 nm is considered,and also the variation relationship between spectral acquisition delay time a nd SBR of four characteristic spectral lines,dual-pulse can prolong decay tim e of spectral intensity and improve the SBR of characteristic spectral lines;t ime evolution characteristic of plasma temperature and electron density is compa red in the condition of single pulse and dual-pulse,maximum elevation of plas ma temperature is found to be 730 K,and the maximum increase of electron densi ty is 1.8×1016 cm-3.The limits of detection of heavy mental Cr ar e obtained 38 and 20 μg·g-1 respectively in condition of single and doub le pulse,limit of detection of Cr is reduced approximately 2 times by the cond ition of re-heating orthogonal dual pulse.Results above indicate that re-hea ting orthogonal dual-pulse can improve detection sensibility and spectral chara cteristic of LIBS technique,which provides an effective method for decreasing the limit of detection of elements.