532和1 064 nm激光的水下LIBS探测对比研究

海洋是国家可持续发展的战略要地，迫切需要海洋探测技术的快速发展，光谱类的化学传感器由于具有原位、非接触和长期探测的优势日益成为研究热点。为了将激光诱导击穿光谱（LIBS）技术应用于海洋原位探测，采用532和1 064 nm波长激光在能量分别为3和40 mj附近进行烧蚀，对比实验研究了532和1 064 nm激光作用下的LIBS击穿特性，并重点探讨了水下激光传输距离对LIBS信号的影响。结果显示，采用1 064 nm的激光能够获得更高的谱线强度和信背比，以及更长的等离子体寿命，但LIBS信号稳定性较差;受水体对不同波长激光能量衰减不同的影响，在水下传输距离2～5 cm范围内，随着1 064 nm激光能量的衰减LIBS信号衰减也很明显，而位于海水“透射窗口”的532 nm的激光LIBS信号基本保持不变。为今后LIBS海洋原位探测系统的开发提供了有价值的设计依据。

Comparative Investigation of Underwater-LIBS Using 532 and 1 064 nm Lase rs

With the hope of applying laser induced breakdown spectroscopy (LIBS) to the ocean applications, the laser energy at 532 and 1 064 nm wavelength with 3 and 40 mj respectively was used, which was near their breakdown threshold. Extensive experimental investigations of LIBS from CaCl₂ water solution were carried out in this paper using different laser wavelengths of 532 and 1 064 nm. The obtained results show that compared with the 532 nm laser, the 1 064 nm laser can induce the plasma in water with higher emission intensity and longer lifetime, while the reproducibility of LIBS signal under 1 064 nm laser is poorer. On the other hand, due to the different attenuation ratios of 532 and 1 064 nm laser energies in water, the LIBS signal of 1 064 nm laser decreases a lot within the transmission distance range 2～5 cm, while LIBS signal of 532 nm remains the same, because that the wavelength of 532 nm lies in the "transmission window" of the water solution. This study will provide valuable design considerations for the development of LIBS-sea system in near future.