Temporal and spatial dynamics of a bipolar pulsed plasma at audio frequency

Plasmas have been utilized extensively in various processing applications. Both radio-frequency (rf) and pulsed discharges have been employed by the community. We investigated the two methods of plasma generation and observed interesting differences. Optical emission spectroscopy shows higher-intensity emission in the UV/visible range for the pulsed plasma comparing to the rf plasma at comparable powers. Data suggest that the electron energy is higher for the pulsed plasma leading to higher ionization, resulting in increased ion density and flux. Motivated by this observation and preliminary modeling suggesting that the polarity reversal in the pulsed plasma plays a key role in supporting interesting transport phenomena, experiments were conducted to further investigate the plasma dynamics and temporal evolution during the pulses. Diode laser absorption and laser induced fluorescence (LIF) provide time- and space-resolved measurements of the argon 1S5 metastable concentration (correlated with the plasma E/N), while laser collision-induced fluorescence (LCIF) provides complementary information on the electron density. Plasma-induced emission provides information on the temporal and spatial evolution of the bulk plasma. The various optical data suggest highly asymmetric dynamics characterizing the positive and negative voltage phases of the discharge.