Abstract
Dynamical properties of argon plasma jet at atmospheric pressure driven by microwave pulses with high repetition rate and fast rise time are investigated using time-resolved optical emission measurements in combination with fast imaging. Spectroscopic measurements reveal an emission burst at the pulse rise including electron continuum emission, hydroxyl molecular lines, and a large overshoot of argon atomic lines. The latter can be interpreted as a transient increase in electron temperature supported by a numerical simulation. At the pulse off, an afterglow burst of argon lines is observed with a time scale much faster than the conventional afterglow in low pressure discharges. The afterglow burst indicates dissociative recombination of argon dimer ions and generation of excited argon species, implying that the afterglow phenomenon can be used to optimize the pulse operation. Compared to continuous wave operation, the time-averaged emissions of Ar* and OH radical are enhanced by about 60% and 30%, respectively, in the pulsed microwave operation, suggesting more efficient generation of reactive species.
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