Insights into Enhanced Repeatability of Femtosecond Laser-Induced Plasmas

Abstract

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 17 cm −3 at 200 ns, and RSDs were <3% with the least fluctuation of 0.7%. Shotto-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.

Evaluation of femtosecond laser-induced breakdown spectroscopy system as an offline coal analyzer

“…Ultrashort pulse lasers (pulse width < 1 ps) have addressed fundamental changes in the ablation process due to different mechanisms of power dissipation. LIBS, as an analytical technique widely used for solid sampling, benefits by femtosecond lasers as ablation sources and improves its figures of merit with: enhanced repeatability 11 , reduced matrix effects 12 , better depth control and quality crater 13 , and reduction in damage 14 , 15 . At present—to the authors’ knowledge, only two references to date make use of fs-LIBS systems to coal analysis.…”