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

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.