Spatiotemporally resolved Ar (1s5) metastable measurements in a streamer-like He/Ar atmospheric pressure plasma jet

We have applied diode laser absorption spectroscopy to measure the line-integrated Ar (1s5) metastable column density in a streamer-like atmospheric pressure plasma jet with a 5% Ar to He gas flow driven by a 20 ns rise time, positive unipolar voltage pulse. The stability of this source enabled us to isolate Ar (1s5) production separately from the streamer head, a region of enhanced production near the anode, and renewed production in the residual streamer channel, which continued up to 1 µs after the discharge was initiated. Over the first 4 mm from the capillary tip, Ar (1s5) production was dominated by processes occurring behind the streamer head with a combined column density as high as 1012 cm−2. Where the residual streamer channel production was significant, the Ar (1s5) column density remained > 1011 cm−2 up to 10 µs after the discharge was initiated. This timescale is significantly longer than has been reported to date of He (23 S 1) measured in a pure He plasma jet and Ar (1s5) in a pure Ar plasma jet using different configurations. The longer effective lifetime of Ar (1s5) in the He/Ar plasma jet significantly extended the timescale for afterglow plasma chemistry.