腔体约束和纳米粒子共同作用下的激光诱导击穿光谱时间演化特性

Time Evolution Characteristics of Laser-Induced Breakdown Spectroscopy under Combined Action of Cavity Confinement and Nanoparticles

激光诱导击穿光谱(LIBS)技术是近二十几年发展起来的一种新型材料识别及定量分析技术,它具有操作简单、迅速、可多元素同步检测、对样品几乎无损耗等优点。传统的LIBS技术发射光谱谱线强度弱,导致检测精度低。在样品表面施加腔体约束或者沉积纳米颗粒可以大幅地增强等离子体发射光谱强度,同时检测精度以及定量分析时的准确度均可以得到有效提高。而等离子体的存活时间十分短暂,通常在1~10μs之间。采集时间延迟过短会连同背景噪声一同采集,采集延迟时间过长则有可能导致采集到的光谱强度低,因此选择合适的采集延迟时间来获取光谱数据至关重要。为了研究腔体约束和纳米粒子共同作用下激光诱导击穿光谱时间演化问题,对烧蚀合金样品产生的等离子体,采集延迟时间为0.5~5μs时等离子体时间分辨光谱。选择NiⅡ221.65 nm, CⅠ193.09 nm作为目标研究谱线,分析采集延迟时间变化对谱线强度、增强因子、信噪比等参数的影响。实验结果表明:在未加约束,腔体约束激光诱导击穿光谱(cavity confinement LIBS,CC-LIBS)、纳米粒子增强激光诱导击穿光谱(nanoparticle enhancement LIBS,NELIBS)以及两种情况共同作用下,随着采集延迟时间的增加,光谱强度均依次降低;在施加腔体约束时,采集延迟时间大于2μs后谱线强度变得很低;当表面沉积纳米粒子时,采集延迟时间大于3μs仍可以收集到可观数量的等离子体。当采集延迟时间为1μs时,双重作用下的增强因子最高,可达2.1。而当有腔体约束参与时,在采集延迟时间大于3μs后光谱强度比未加约束时更低;当只有纳米颗粒沉积时,信噪比最优,达到9.52;双重作用下信噪比的变化趋势与只有腔体约束时的变化趋势基本相同。纳米颗粒在整个采集延迟时间范围内都有助于检测样品中微量元素,而腔体约束在延迟时间大时对微量元素的检测起抑制作用。

Laser-induced breakdown spectroscopy(LIBS) is a new material identification and quantitative analysis technology developed in the past twenty years, which has unique features including the simplicity of method, being rapid, simultaneous multi-element detection and being non-destructive to sample. The traditional LIBS technology has a weak emission line spectrum, resulting in poor detection accuracy. Applying cavity confinement or depositing nanoparticles on the surface of the sample can significantly enhance the intensity of plasma emission spectrum, and the accuracy of detection and quantitative analysis can be effectively improved. However, the survival time of plasma is very short, usually between 1 and 10 μs. The acquisition time delay is too short and will be collected together with the background noise, while the acquisition delay time is too long, the acquired spectral intensity may be low, so it is important to choose the appropriate acquisition delay time for obtaining spectral data. Focusing on the time evolution of LIBS under the action of cavity confinement and nanoparticles, the alloy samples were used to generate plasma, and the time-resolved spectra of plasma at the acquisition delay time from 0.5 to 5 μs were collected. Ni Ⅱ 221.65 nm and CⅠ 193.09 nm were selected as the target lines, and the changes of spectral line intensity, enhancement factor and signal-to-noise ratio(SNR) were analyzed. Experimental results showed that under the unconfinement, cavity-confinement laser-induced breakdown spectroscopy(CC-LIBS), nanoparticle-enhanced laser-induced spectroscopy(NELIBS) and the above two cases worked together, as the acquisition delay time increased, the spectral intensity decreased in turn. When the cavity confinement was applied, the intensity of spectral line became very low after the acquisition delay time was greater than 2 μs. When nanoparticles were deposited on the surface, a considerable amount of plasma could still be collected even if the acquisition delay time was greater than 3 μs. When the acquisition delay time was 1 us, the enhancement factor under dual action was the highest, reaching 2.1. When cavity confinement was involved, the spectral intensity was lower than that without confinement after the acquisition delay time was greater than 3 μs. When only the nanoparticles were deposited, the SNR was optimal, reaching 9.52. Under the condition of dual constraints, the trend of SNR was basically the same as that with only cavity confinement. Nanoparticles are helpful for the detection of trace elements in samples in the whole acquisition delay time range, while cavity confinement inhibits the detection of trace elements when the acquisition delay time is large.