Detecting Laser-Volatilized Salts with a Miniature 100-GHz Spectrometer
Detecting Laser-Volatilized Salts with a Miniature 100-GHz Spectrometer
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使用微型 100 GHz 光谱仪检测激光挥发盐
DOI：
10.1021/acs.jpca.9b10548
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发表时间：
2020
期刊：
影响因子：
--
通讯作者：
Mazur, Eric
中科院分区：
文献类型：
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作者：
Raymond, Alexander W.;Kelvin Lee, Kin Long;McCarthy, Michael C.;Drouin, Brian J.;Mazur, Eric
旋转跃迁是分子种类（包括同位素体）的独特标识符。本文介绍了使用微型傅里叶变换毫米波 (FTmmW) 腔光谱仪对两种激光挥发盐 NaCl 和 KCl 进行旋转检测，该光谱仪有一天可用于在现场或太空中测量固体成分。这两种盐是太阳系外冰卫星的相关目标，原则上其他分子固体也可以用 FTmmW 仪器进行分析。通过将光谱仪耦合到碰撞冷却激光烧蚀源，（a）我们证明 FTmmW 仪器足够灵敏，可以检测烧蚀产物，（b）我们使用小尺寸的 FTmmW 腔来测量沿载气光束的烧蚀产物信号。我们发现，对于 532 nm 纳秒脉冲，烧蚀分子广泛分散在载气射流中。除了微型光谱仪结果之外，我们还提供了几种旨在表征激光烧蚀过程的补充测量结果。对于 10 至 30 mJ 之间的脉冲能量，消融产物产量线性增加，达到每 30 mJ 脉冲约 1012 个盐分子。使用质谱法，我们在烧蚀的 NaCl、KCl 和 LiCl 的羽流中观察到 Li+、Na+ 和 K+，这意味着挥发材料的解离。我们没有观察到盐离子（例如 NaCl+）。然而，使用 800 nm 飞秒激光脉冲，会产生三原子离子簇 Li2Cl+、Na2Cl+ 和 K2Cl+。最后，我们观察到纳秒脉冲的不完全挥发：一些喷射物是液滴。从这些实验中收集到的关于烧蚀羽流物理的见解应该可以指导激光挥发技术的未来实施。
Rotational transitions are unique identifiers of molecular species, including isotopologues. This article describes the rotational detections of two laser-volatilized salts, NaCl and KCl, made with a miniature Fourier transform millimeter-wave (FTmmW) cavity spectrometer that could one day be used to measure solid composition in the field or in space. The two salts are relevant targets for icy moons in the outer solar system, and in principle, other molecular solids could be analyzed with the FTmmW instrument. By coupling the spectrometer to a collisionally cooling laser ablation source, (a) we demonstrate that the FTmmW instrument is sensitive enough to detect ablation products, and (b) we use the small size of the FTmmW cavity to measure ablation product signal along the carrier gas beam. We find that for 532 nm nanosecond pulses, ablated molecules are widely dispersed in the carrier-gas jet. In addition to the miniature spectrometer results, we present several complementary measurements intended to characterize the laser ablation process. For pulse energies between 10 and 30 mJ, the ablation product yield increases linearly, reaching approximately 1012salt molecules per 30 mJ pulse. Using mass spectrometry, we observe Li+, Na+, and K+in the plumes of ablated NaCl, KCl, and LiCl, which implies dissociation of the volatilized material. We do not observe salt ions (e.g., NaCl+). However, with 800 nm femtosecond laser pulses, the triatomic ion clusters Li2Cl+, Na2Cl+, and K2Cl+are produced. Finally, we observe incomplete volatilization with the nanosecond pulses: some of the ejecta are liquid droplets. The insights about ablation plume physics gleaned from these experiments should guide future implementations of the laser-volatilization technique.