Skrodzki P J, Burger M, Jovanovic I
Department of Nuclear Engineering and Radiological Sciences, University of Michigan, Ann Arbor, MI, 48109, USA.
Center for Ultrafast Optical Science, University of Michigan, Ann Arbor, MI, 48109, USA.
Sci Rep. 2017 Oct 6;7(1):12740. doi: 10.1038/s41598-017-13188-4.
High-peak-power fs-laser filaments offer unique characteristics attractive to remote sensing via techniques such as remote laser-induced breakdown spectroscopy (R-LIBS). The dynamics of several ablation mechanisms following the interaction between a filament and a solid determines the emission strength and reproducibility of target plasma, which is of relevance for R-LIBS applications. We investigate the space- and time-resolved dynamics of ionic and atomic emission from copper as well as the surrounding atmosphere in order to understand limitations of fs-filament-ablation for standoff energy delivery. Furthermore, we probe the shock front produced from filament-target interaction using time-resolved shadowgraphy and infer laser-material coupling efficiencies for both single and multiple filament regimes through analysis of shock expansion with the Sedov model for point detonation. The results provide insight into plasma structure for the range of peak powers up to 30 times the critical power for filamentation P . Despite the stochastic nucleation of multiple filaments at peak-powers greater than 16 P , emission of ionic and neutral species increases with pump beam intensity, and short-lived nitrogen emission originating from the ambient is consistently observed. Ultimately, results suggest favorable scaling of emission intensity from target species on the laser pump energy, furthering the prospects for use of filament-solid interactions for remote sensing.
高峰值功率飞秒激光丝具有独特的特性，通过诸如远程激光诱导击穿光谱法（R-LIBS）等技术，对遥感具有吸引力。飞秒激光丝与固体相互作用后，几种烧蚀机制的动力学决定了目标等离子体的发射强度和可重复性，这与R-LIBS应用相关。我们研究了铜以及周围大气中离子和原子发射的空间和时间分辨动力学，以了解飞秒激光丝烧蚀在远距离能量传输方面的局限性。此外，我们使用时间分辨阴影成像技术探测了激光丝与目标相互作用产生的激波前沿，并通过用塞多夫点爆炸模型分析激波扩展，推断了单丝和多丝模式下的激光与材料耦合效率。研究结果为峰值功率高达成丝临界功率P 30倍范围内的等离子体结构提供了见解。尽管在峰值功率大于16P 时会随机形成多根激光丝，但离子和中性物种的发射会随着泵浦光束强度的增加而增加，并且始终能观察到源自周围环境的短暂氮发射。最终，研究结果表明目标物种的发射强度与激光泵浦能量具有良好的比例关系，这进一步推动了利用激光丝与固体的相互作用进行遥感的前景。
