激光频率对激光诱导等离子体特性的影响

摘要

激光诱导击穿光谱(LIBS)技术是难熔、难溶物质成分分析的重要方法之一,而实验过程中激光的输出频率、能量、功率密度以及聚焦位置等都明显的影响等离子体的特性,从而影响定量分析的精确度.实验采用土壤标样为分析样品,以Fe、Ti、Sr、Al元素为分析元素,纳秒Nd:YAG激光器为激光光源,通过改变激光输出频率(1~20 Hz),研究了激光输出频率对等离子体的光谱信背比(SNR)、温度、谱线自吸以及信号稳定性的影响.研究结果表明,在其他实验条件不变的情况下,随着激光输出频率的增大等离子体的光谱信背比、等离子体温度都明显升高,自吸现象加重;激光输出频率为1、5、10、20 Hz时Fe I 363.360 nm谱线强度的相对标准偏差(RSD)分别为7.16%、7.89%、14.89%、11.85%,信号的稳定性随激光输出频率的增大呈下降趋势.结果表明重复频率能够影响等离子体的谱线质量,针对不同含量的元素分析,应选择合适的激光输出频率.%Laser-induced breakdown spectroscopy (LIBS) is one of important methods for the composition analysis of refractory and insoluble materials.The plasma characteristics are greatly affected by the output frequency, energy, power density and focus position of laser in tests, thus influencing the accuracy of quantitative analysis.The certified reference material of soil was used as sample with Fe, Ti, Sr and Al as analysis elements and Nanosecond Nd:YAG laser device as laser light source.The laser output frequency was changed in range of 1-20 Hz, and its effect on spectrum signal-to-noise ratio (SNR), temperature, spectral line self-absorption and signal stability of plasma was investigated.The results indicated that, when other experimental conditions were fixed, the spectrum signal-to-noise ratio and temperature of plasma obviously increased with the increase of laser output frequency, while the self-absorption effect became aggravated.The relative standard deviation (RSD) of the spectral intensity of Fe I 363.360 nm was 7.16%, 7.89%, 14.89% and 11.85% when the laser output frequency was 1, 5, 10 and 20 Hz, respectively.The stability of signal showed deceasing trend with the increase of laser output frequency.The results showed that the spectral line quality of plasma could be affected by the repetition frequency.The proper laser output frequency should be selected for the analysis of elements with different contents.