Kautz Elizabeth J, Yeak Jeremy, Bernacki Bruce E, Phillips Mark C, Harilal Sivanandan S
Pacific Northwest National Laboratory, Richland, WA 99352, USA.
Opticslah, LLC, Albuquerque, NM 87106, USA.
Phys Chem Chem Phys. 2020 Apr 29;22(16):8304-8314. doi: 10.1039/d0cp00078g.
Laser ablation in conjunction with optical emission spectroscopy is a potential non-contact, stand-off detection method for all elements in the periodic table and certain isotopes such as radionuclides. Currently, significant development efforts are on-going to use ultrafast laser filaments for remote detection of materials. The application of filaments is of particular interest in extending the range of stand-off capability associated with elemental and isotopic detection via laser-induced breakdown spectroscopy. In this study, we characterize the expansion dynamics and chemical evolution of filament-produced uranium (U) plasmas. Laser filaments are generated in the laboratory by loosely focusing 35 femtosecond (fs), 6 milli Joule (mJ) pulses in air. Time-resolved, two-dimensional plume and spectral imaging was performed to study hydrodynamics and evolution of U atomic and UO molecular emission in filament-produced U plasmas. Our results highlight that filament ablation of U plasmas gives a cylindrical plume morphology with an appearance of plume splitting into slow and fast moving components at later times of its evolution. Emission from the slow-moving component shows no distinct spectral features (i.e. broadband-like) and is contributed in part by nanoparticles generated during ultrafast laser ablation. Additionally, we find U atoms and U oxide molecules (i.e. UO, UxOy) co-exist in the filament produced plasma, which can be attributed to the generation of low-temperature plasma conditions during filament ablation.
激光烧蚀结合光发射光谱法是一种潜在的非接触式、远距离检测方法，可用于检测元素周期表中的所有元素以及某些同位素，如放射性核素。目前，人们正在大力开展研究，以利用超快激光细丝进行材料的远程检测。细丝的应用对于扩展与通过激光诱导击穿光谱法进行元素和同位素检测相关的远距离检测能力范围尤为重要。在本研究中，我们对细丝产生的铀（U）等离子体的膨胀动力学和化学演化进行了表征。通过在空气中松散聚焦35飞秒（fs）、6毫焦（mJ）的脉冲，在实验室中产生激光细丝。进行了时间分辨的二维羽流和光谱成像，以研究细丝产生的U等离子体中U原子和UO分子发射的流体动力学和演化。我们的结果表明，U等离子体的细丝烧蚀产生了圆柱形羽流形态，在其演化后期，羽流似乎分裂为慢速和快速移动的成分。慢速移动成分的发射没有明显的光谱特征（即类似宽带），部分是由超快激光烧蚀过程中产生的纳米颗粒造成的。此外，我们发现细丝产生的等离子体中U原子和U氧化物分子（即UO、UxOy）共存，这可归因于细丝烧蚀过程中产生的低温等离子体条件。
