Temporally-Resolved Emission Spectroscopic Diagnostics of the Atmospheric Pressure Glow Discharge in Helium

Temporally-resolved spectroscopic diagnostics of dielectric barrier discharges (DBDs) in atmospheric-pressure helium was carried out to study the discharge mechanism. Using an intensified charge-coupled device (ICCD) and a grating spectrometer, we obtained the emission spectra of homogeneous discharges and presented them in 3D graphs. We also studied the time variation of typical emissions from He, O and first negative bands of N ⁺ ₂ . The results showed that the spectral lines do not develop synchronously as N ⁺ ₂ (B² Σ _u +X ² Σ ⁺ _g , 0∼0, λ=391.4 nm) and N ⁺ ₂ (B ₂ Σ ⁺ _u → X ²Σ ⁺ _g, 0∼1, λ=427.8 nm) appear earlier and last for a longer time than He (3 ³ S ₁ → 2 ³ P ₁, λ=706.5 nm) and O (3 ⁵ P→3 ⁵ S, λ=777.4 nm). A certain number of He metastables produced in the initial stage of discharge. Even between adjacent pulses, the emissions from N ⁺ ₂ can still keep certain intensities while those from He and O extinguish. Since long-lifetime He metastables are produced and exist in the discharging space, it is the Penning ionization that keeps the long decay of N ⁺ ₂ emissions.