Spatially resolved optical emission spectroscopy of a nanosecond pulsed microplasma jet

Recent interests in non-equilibrium microplasma jets for biomedical applications have motivated fundamental studies of these plasmas. This work presents a spectroscopic study of a 500 micrometer-in-width helium microplasma jet that was generated in ambient air with a single needle electrode powered by 4 kV, 5 ns pulses at 500 Hz. Each HV pulse supplied 0.4 mJ of energy per pulse. These pulse characteristics provided a unique set of plasma conditions for spectroscopic evaluation, as the physical and chemical processes that take place within the plasma channel are highly dependent on the HV pulse characteristics. Optical emission profiles were collected at wavelengths that ranged from 200 nm up to 800 nm with a spectral resolution of approximately 0.02 nm. The experimental results identified and yielded information on the optical emission profiles of He*, O*, OH*, N₂* and N₂⁺* as a function of axial position along the jet channel. Evaluation of the optical emission spectrum provided information on the relative emission intensities for each excited species along with rotational, vibrational, and electronic temperatures. These results provide fundamental information needed to understand the complex chemical and physical phenomena occurring in plasma jets.