激光诱导击穿光谱实验装置的参数优化研究

摘要

为了使激光诱导击穿光谱(LIBS)实验装置中的多个关键参数达到最优化设置,以便更好地服务于煤质分析,实验中对这些参数与煤粉等离子体中待测元素发射谱线信噪比间的关系进行了详细研究,并根据信噪比大小来进行最优化参数的选择.实验结果表明,对于本LIBS实验装置,其最优化参数设置是将激光脉冲能量设为120 mJ·Pulse-1,光谱仪的曝光延迟时间设为200 ns,激光聚焦点位于样品表面以下3～5mm,样品池转速设为2.7 r·min-1,并在激光出射光路中放置中心频率为1 064 nm的窄带滤波片和中心孔径为1.5mm的光阑.优化后的LIBS实验装置对煤粉中C元素测量的标准偏差(SD)由6.7％降至1.6％,对其他微量元素测量的相对标准偏差(RSD)由28％降至10％,测量精度得到了较大提高.%For a better application of laser-induced breakdown spectroscopy (LIBS) to coal quality analysis, it is necessary to optimize the key parameters of the experimental LIBS-based device. The relationships between the key parameters and the signal-to-noise ratios (S/N) of the elemental emission lines in the plasma spectrum of the pulverized coal were studied, according to which the optimal parameters can be selected. Experimental results indicate that the optimal settings for our LIBS-based device are laser pulse energy=120 mj · Pulse-1, delay time of spectrometer=200 ns, laser focal point be located 3~5 mm underneath the sample surface, rotation speed of sample cell=2. 7 rev · Min-1, a narrow-band filter with center frequency of 1064 nm and a diaphragm with center hole diameter of 1. 5 mm be placed in the path of the laser beam. Quantitative analysis results of pulverized coal show that, by using the optimal LIBS-based device, the standard deviation (SD) of C has been reduced from 6. 7% to 1. 6%, while the relative standard deviation (RSD) of other trace elements has been reduced from 28% to 10%. As a result, the accuracy has been improved greatly.