B. W. James* and B. C. Zhang

School of Physics, A28, University of Sydney, NSW 2006, Australia
B.James@physics.usyd.edu.au

Langmuir probes are not suitable for measuring potentials in sheath regions close to electrodes as they cause significant perturbation of the discharge; furthermore, simple probe theory, which assumes a thermal electron velocity distribution, is not applicable.

Spectroscopic techniques for measuring electric fields in discharges are based upon the Stark effect. While measurements based upon passive emission are possible [1], practical techniques use laser induced fluorescence (LIF) as it provides not only significantly improved signal levels but also a high level of spatial resolution.

There are two techniques: one is based upon the linear Stark effect experienced by atoms in a Rydberg state [2]; the other upon the fact that Stark mixing of closely spaced states can lead to a forbidden transition becoming partly allowed, to an extent which is dependent upon the magnitude of the perturbing electric field [3,4].

[1] K. Takayama, T. Usui, Y. Kamiura, T. Fujita, T. Oda and K. Kawasaki, Jpn. J. Appl. Phys. 25, L455 (1986)
[2] E.A. Den Hartog, D.A. Doughty and J.E. Lawler, Phys. Rev. A 38, 2471 (1988)
[3] C.A. Moore, G.P. Davis and R.A. Gottcho, Phys. Rev. Lett. 52, 538 (1984)
[4] H. Sakai, K.Takayama, M. Kimura, M. Yamasaki, T. Oda and K. Kawasaki, J. Nucl. Mater. 196-198, 1135 (1992)