Sheta Sahar, Afgan Muhammad Sher, Jiacen Liu, Gu Weilun, Hou Zongyu, Wang Zhe
State Key Lab of Power Systems, Department of Energy and Power Engineering, Tsinghua University, Beijing 100084, China.
ACS Omega. 2020 Nov 17;5(47):30425-30435. doi: 10.1021/acsomega.0c03636. eCollection 2020 Dec 1.
Repeatability is of utmost importance as it is directly linked to measurement accuracy and precision of a technique and affects its cost, utility, and commercialization. The present paper contributes to explain enhanced repeatability of the femtosecond laser-induced breakdown spectroscopy (fs-LIBS) technique, remarkably significant for its industrial applications and instrumental size reduction. A fs-laser with 7 mJ pulse energy was focused to create a transient titanium plasma, and a high-resolution spectrometer was used to study time-resolved spectra and single-shot drilling sampling repeatability. Time-resolved spectroscopy study at a delay time interval of 0-1600 ns showed 200-400 ns as the optimum delay time zone for data acquisition with 2-4% line intensity RSDs. Plasma temperature RSDs were <1.8% for the investigated delay interval and reached 0.5% at 200 ns where the temperature recorded a maximum value of 22,000 K. Electron density reached 5.7 × 10 cm at 200 ns, and RSDs were <3% with the least fluctuation of 0.7%. Shot-to-shot RSDs were 3.5-5% at 15-30 drilling shot intervals for line intensities, <2% for plasma temperature, and <6.5% for electron density. Using an uncertainty propagation formula, total number density RSDs were calculated to be 1.9-5.3% for 50 single-shot drilling scenarios. Considering physics behind results, fs-plasmas are "stable ablation sources" due to their electrostatic formation mechanisms and confined hydrodynamic evolution. The fs-laser opens up new directions for LIBS applications where accuracy is significantly enhanced.
可重复性至关重要，因为它与技术的测量准确性和精度直接相关，并会影响其成本、实用性和商业化。本文有助于解释飞秒激光诱导击穿光谱技术（fs-LIBS）的增强可重复性，这对于其工业应用和仪器尺寸减小具有显著意义。聚焦一个脉冲能量为7 mJ的飞秒激光以产生瞬态钛等离子体，并使用高分辨率光谱仪研究时间分辨光谱和单次钻孔采样的可重复性。在0 - 1600 ns的延迟时间间隔进行的时间分辨光谱研究表明，200 - 400 ns是数据采集的最佳延迟时间区域，谱线强度相对标准偏差（RSD）为2 - 4%。在所研究的延迟间隔内，等离子体温度RSD小于1.8%，在200 ns时达到0.5%，此时温度记录最大值为22000 K。电子密度在200 ns时达到5.7×10 cm，RSD小于3%，波动最小为0.7%。对于谱线强度，在15 - 30次钻孔射击间隔下，逐次射击RSD为3.5 - 5%，等离子体温度RSD小于2%，电子密度RSD小于6.5%。使用不确定度传播公式，对于50种单次钻孔情况，计算出总粒子数密度RSD为1.9 - 5.3%。考虑到结果背后的物理原理，飞秒等离子体由于其静电形成机制和受限的流体动力学演化，是“稳定的烧蚀源”。飞秒激光为LIBS应用开辟了新方向，在这些应用中精度得到了显著提高。
