多次放电的激光诱导击穿光谱信号增强

激光诱导击穿光谱技术(LIBS)是一种广泛应用于科学和工程方面的元素分析技术。LIBS测量一些微量元素时存在探测极限高的不足，因此增强LIBS信号强度，降低元素探测极限，对扩展其应用范围有着重要的意义。为了实现LIBS光谱信号的增强，提出多次放电增强激光诱导击穿光谱方法，并以固体铝合金材料为例进行了光谱信号强度增强的研究。实验发现，激光作用在铝合金材料上烧蚀样品产生等离子体并溅射到样品上方高压放电电极所在区域，该区域在等离子体产生之后50 μs之内均可以诱导高压电极放电。因此采用高频脉冲电源可以实现一次LIBS产生的等离子体诱导电极多次放电。多次放电会对等离子体进行多次激发，同时多次放电对等离子的加热作用会延缓等离子体冷却速率从而延长等离子体的持续时间，两者共同作用可以增强LIBS光谱信号强度，进而降低LIBS对微量元素的探测极限。使用频率为100 kHz的高频直流脉冲电源，利用数字延迟脉冲发生器同步激光与高压电源，在激光过后3.6 μs触发高压放电，一次LIBS产生的等离子体可以诱导电极5次放电，即对等离子体进行5次激发和加热。利用光谱仪对5次放电等离子体光谱进行积分测量。实验结果表明：使用多次放电增强之后，等离子体持续时间得到大幅延长，光谱信号强度得到大幅增强，其中，Mg Ⅱ (~279 nm)的信号强度可以增强约48倍，Al Ⅱ (~358 nm)的信号强度可以增强约72倍，微量元素Mn Ⅰ (~403 nm)的信号强度增强约6.3倍，微量元素Cu Ⅰ (~403 nm) 的信号强度增强约8.3倍。Mn Ⅰ (~403 nm)和Cu Ⅰ (~403 nm) 的探测极限分别降低为LIBS单次放电的1/6和1/8。多次放电增强激光诱导击穿光谱方法很好地增强了LIBS的光谱信号强度，降低了对微量元素的探测极限，扩展了LIBS技术的应用范围。该方法有潜力应用到贵重物品、稀有材料及文物的鉴定之中。

Multiple Discharges-Enhanced Laser-Induced Breakdown Spectroscopy

Laser-induced breakdown spectroscopy (LIBS) is an elemental analysis technique widely used throughout science and engineering. A limitation of LIBS is the low analytical sensitivity for trace elements. Therefore, it is of great significance to enhance the signal intensity and reduce the detection limit of LIBS. To enhance LIBS signals, here we propose a method, multiple discharges-enhanced LIBS. The measurements were performed on a solid aluminum alloy. A nanosecond laser was focused on the alloy to generate plasma. The plasma was sputtered into the air between the two discharge electrodes, which triggered the discharge. Multiple discharges were generated by using a high-frequency discharge power source. The multiple discharges excite, heat the plasma and extend the plasma duration, thereby enhancing the signal intensity. Here, a direct current pulse power source with a frequency of 100 kHz was used, and five discharges occurred after each laser-induced breakdown. We show that compared with LIBS, the plasma duration is extended by approximately 50 μs. Multiple discharges-enhanced LIBS increases the signal intensity of Mg Ⅱ (at ~279 nm) by about 48 times; Al Ⅱ (at ~358 nm), 72 times; trace element Mn Ⅰ (at ~403 nm), 6.3 times; trace element Cu Ⅰ (at ~403 nm), 8.3 times. The detection limit of Mn Ⅰ (at ~403 nm) is reduced by a factor of 6; Cu, 8. Multiple discharges-enhanced LIBS dramatically enhances the signal intensity and improves the detection limit of LIBS, and it expands the applications of LIBS. This method has the potential to be applied to the identifications of valuables, rare materials and cultural relics.