Excitation Mechanism of H, He, C, and F Atoms in Metal-Assisted Atmospheric Helium Gas Plasma Induced by Transversely Excited Atmospheric-Pressure CO₂ Laser Bombardment

Abstract

To clarify the excitation mechanism of hydrogen in transversely excited atmospheric-pressure (TEA) CO2 laser-induced helium gas plasma, atomic emission characteristics of H, C, F, and He were studied using a Teflon sheet (thickness of 2 mm) attached to a metal subtarget. The TEA CO2 laser (750 mJ, 200 ns) was focused on the Teflon sheet in the surrounding He gas at 1 atm. Atomic emissions of H, C, F, and He occurred with a long lifetime, a narrow spectrum width, and a low-background spectrum. The correlation emission intensity curves of H–He and F–He indicated a parabolic functions. To explain the emission characteristics, we offered a model in which helium metastable atoms (He*) play an important role in the excitation processes; namely, atoms collide with helium metastable atoms (He*) to be ionized by the Penning effect, and then recombine with electrons to produce excited states, from which atomic emissions occur.

High sensitivity hydrogen analysis in zircaloy-4 using helium-assisted excitation laser-induced breakdown spectroscopy

“…In our previous studies 1 , 2 , 29 , 39 , 40 , we have proved that He* atoms also contribute to the excitation of He itself because He emission continues for a long time and because the excitation energy of He is considerably higher than that of other elements, including Li, Al, and Pb. It is assumed that in the He gas plasma, He* atoms are ionized because of collisions with each other via the Penning effect, as shown in Eq.…”

“…He gas plasma can only be formed at a low pressure if the laser beam is focused and hits a certain sub-target. The intensities of He I 587.6 nm and He I 667.8 nm, which are related to the He* atoms, change depending on the type of sub-target 1 , 2 , 23 – 29 . In this study, we varied the sub-target material from metals to inorganic compounds and found that LiF yields He I 587.6 nm and He I 667.8 nm emission lines with the maximum intensity.…”

H–D Analysis Employing Energy Transfer from Metastable Excited-State He in Double-Pulse LIBS with Low-Pressure He Gas

“…Both compounds can be easily transported in disguise for dangerous abuses. Therefore, the detection of D is important to prevent nuclear terrorism in the future. − …”

Direct evidence of mismatching effect on H emission in laser-induced atmospheric helium gas plasma

“…Thereafter, the helium emission takes place through the recombination process with the electrons. 25 In the meantime, the hydrogen atoms are also excited and leading to the emission observed. The slow component of the helium emission on the other hand is probably due to the fact that helium in its metastable excited state is re-excited by interaction with the strong shock wave plasma.…”