Effects of pulse energy ratios on plasma characteristics of dual-pulse fiber-optic laser-induced breakdown spectroscopy

Laser-induced plasmas of dual-pulse fiber-optic laser-induced breakdown spectroscopy with different pulse energy ratios are studied by using the optical emission spectroscopy(OES)and fast imaging.The energy of the two laser pulses is independently adjusted within 0–30 m J with the total energy fixed at 30 m J.The inter-pulse delay remains 450 ns constantly.As the energy share of the first pulse increases,a similar bimodal variation trend of line intensities is observed.The two peaks are obtained at the point where the first pulse is half or twice of the second one,and the maximum spectral enhancement is at the first peak.The bimodal variation trend is induced by the change in the dominated mechanism of dual-pulse excitation with the trough between the two peaks caused by the weak coupling between the two mechanisms.By increasing the first pulse energy,there is a transition from the ablation enhancement dominance near the first peak to the plasma reheating dominance near the second peak.The calculations of plasma temperature and electron number density are consistent with the bimodal trend,which have the values of 17024.47 K,2.75×10^(17)cm;and 12215.93 K,1.17×10^(17)cm;at a time delay of 550 ns.In addition,the difference between the two peaks decreases with time delay.With the increase in the first pulse energy share,the plasma morphology undergoes a transformation from hemispherical to shiny-dot and to oblate-cylinder structure during the second laser irradiation from the recorded images by using an intensified charge-coupled device(ICCD)camera.Correspondingly,the peak expansion distance of the plasma front first decreases significantly from 1.99 mm in the single-pulse case to 1.34 mm at 12/18(dominated by ablation enhancement)and then increases slightly with increasing the plasma reheating effect.The variations in plasma dynamics verify that the change of pulse energy ratios leads to a transformation in the dual-pulse excitation mechanism.

Amorphous NiMo_(3)S_(13)/nickel foam integrated anode for lithium-ion batteries

Although crystalline anode materials with long-range ordered lattice structure are in favor of facilitating the electron transfer,their structures are easily disrupted during long-term cycling due to the continuous embedding/de-embedding of lithium ions.In contrast,the amorphous materials have abundant defects and lithium ion storage sites,refl ecting a superior reaction kinetics and long-term cycling stability.Here,we synthesize an integrated hybrid anode by in-situ loading amorphous NiMo_(3)S_(13)nanosheets on nickel foam substrate.Benefi ting from the introduction of Ni^(2+)that amorphizes the molybdenumsulfur clusters,the assembled lithium ion battery based on the integrated NiMo_(3)S_(13)/nickel foam anode delivers a specifi c capacity up to 1659 mA·h·g^(−1)at a current density of 0.6 A·g^(−1)and exhibits superior rate/cycling performance.