Pulsed microwave excited (2.45 GHz) argon plasmas generated by a slot antenna type plasma source are investigated by various diagnostic tools. Through the combined use of time-resolved planar optical emission spectroscopy (TPOES), microwave interferometry (MWI) and Langmuir probes the temporal behaviour of the electron density, n e (t), and effective electron temperature, T e (t), for the pulse frequency range of 0.2-20 kHz are measured. Additionally, from TPOES maps of Ar * and Ar + , the qualitative spatially and time-resolved electron temperature distribution is derived. The n e (t) and T e (t) rise and decay times are almost constant throughout the examined frequency range. A n e (t) rise time of 1 ms and a decay time of 0.6 ms is derived from probe and MWI data at 5 Pa. A T e (t) rise time between 5 and 10 µs and a decay time between 50 µs and 80 µs is derived from TPOES and probe measurements at 5 Pa. The maximum time-averaged electron density, ne , at 5 Pa is obtained at a pulse frequency f of 200 Hz. With increasing pressure and power the pulse frequency f at which a maximum of ne is reached decreases to f ≈ 50 Hz. The temporal n e (t) and T e (t) behaviour for the investigated pressure range is described by a simple set of equations based on the 'Global Model' of pulsed plasmas. It can be concluded that the electron loss rate ν loss controls both the rise and decay times of n e (t). The ν loss is in the first order a function of the plasma system dimensions and geometry. The decay of T e (t) depends on ν loss and the losses due to inelastic scattering.
The downstream zone of a new type of plasma source was investigated. Microwave power is fed to the plasma by an annular waveguide ring with slotted line radiators on the inner side. In a pure oxygen plasma the conditions for the generation of atomic oxygen were studied by laser-induced fluorescence. Excitation from the ground state is achieved by two-photon absorption (3p 3P1,2,0←2p 3P2,1,0 transitions) of 226 nm laser radiation. Fluorescence is observed at 845 nm. From the Doppler-broadened absorption line profile a temperature of 350 K is determined. A rate equation model combined with a measurement of laser properties and a calibration of the detection system by Raman scattering in hydrogen gas enabled an absolute calculation of the atomic oxygen ground state density. In the downstream zone values in the range of 1013–1014 cm−3 are obtained. The scaling of the atomic oxygen density with external parameters was investigated.
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