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Tomography of Optical Emission Line Intensities of a Radio-Frequency Magnetron Discharge

Volume 51, Number 9 (Sept. 1997) Page 1340-1345

Debal, F.; Wautelet, M.; Dauchot, J.P.; Hecq, M.

An experimental setup for spectroscopic optical tomography of glow discharges is presented. It combines a fiber-optics system with a monochromator coupled to a charge-coupled device (CCD) camera. The light emitted by the discharge is sent to the input of 10 optical fibers through a collimating system. The outputs of these optical fibers are coupled to the entrance slit of a monochromator. The CCD camera is in the output slit. This arrangement allowed us to acquire 10 spectra simultaneously, each being associated with a small zone of the discharge. By translation of the optical fibers, the whole discharge was studied. The data were then analyzed by means of a tomographic reconstruction program in order to obtain the three-dimensional spectroscopic optical tomography, for a large number of lines. This experimental setup was used to deduce the three-dimensional optical emission of various lines of a radio-frequency (rf)-powered magnetron discharge. The discharge deals with an aluminum base alloy cathode, sputtered by Ar. Emission lines corresponding to the cathode (Al: 394.4- and 396.2-nm lines) and the gas discharge (Ar: 763.5 nm-line) were considered. The threedimensional emission profiles, I ( r , Z ), of the lines were measured; r is the distance from the center of the cathode, and Z is the distance from the cathode. I ( r , Z ) profiles are different for the Al and Ar lines. The effects of the electrical power and the pressure were also studied. It was found that the corresponding I ( r , Z ) profiles behave differently with the pressure. In order to compare the results, I ( r , Z ) was fitted with an empirical analytical mathematical function, with parameters depending on pressure. At high pressure, the shape of I ( r , Z ) for the Al line tends towards the shape of the Ar line.