Temporal and spatial resolved optical emission behaviors of a cold atmospheric pressure plasma jet

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The propagation behavior of cold atmospheric pressure plasma jets has recently attracted lots of attention. In this paper, a cold He plasma jet generated by a single plasma electrode jet device is studied. The spatial-temporal resolved optical emission spectroscopy measurements are presented. It is found that the emission intensity of the He 706.5 nm line of the plasma behaves similarly both inside the syringe and in the surrounding air (plasma plume). It decreases monotonously, which is different from the emission lines, such as N₂ 337.1 nm line, N₂⁺ 391.4 nm line, and O 777.3 nm line. For the discharge inside the syringe, the emission intensity of the He 706.5 nm line decays more rapidly than that of the other three spectral lines mentioned above. The N₂ 337.1 nm line behaves a similar time evolution with the discharge current. For the N₂⁺ 391.4 nm line and the atomic O 777.3 nm line, both of them decay slower than that of the He 706.5 nm and the N₂ 337.1 nm. When the plasma plume propagates further away from the nozzle, the temporal behaviors of the emission intensities of the four lines tend to be similar gradually. Besides, it is found that, when the size of the plasma bullet appears biggest, the propagation velocity of the bullet achieves its highest value while the emission intensity of the N₂⁺ 391.4 nm line reaches its maximum. Detailed analysis shows that the Penning effect between the metastable state He_m and the air molecules may play a significant role in the propagation of the plasma bullet in the open air. ©2009 American Institute of Physics