Imaging of atomic oxygen in a microwave excited oxygen plasma with two-dimensional optical emission spectroscopy

The density distribution of atomic oxygen was investigated in a pure oxygen microwave discharge. Plasma is excited by use of a circular waveguide with slot antenna. Two-dimensional maps of the O((3)p P-3) to O(3s S-3(0)) emission line intensity have been obtained using planar optical emission spectroscopy imaging (FOES). The dependence on operating parameters of the plasma source has been studied. With increasing pressure the atomic oxygen homogeneity degrades. At pressures below 20 Pa the oxygen density is nearly homogeneous due to the greater diffusion length. Absolute ground state concentration of atomic oxygen has been measured at a downstream position by two-photon laser-induced fluorescence (LIF). Values in the range of 10(13)-10(14) cm(-3) are obtained. Comparing FOES to LIF results the POPS signals must be corrected for line-of-sight path integration. If this is taken into account then LIF and FOES measurements show a good correlation between atomic ground state and excited oxygen for pressures up to 50 Pa. (C) 1997 Elsevier Science S.A.