Evolution of Ar metastable atom density with electron density in Ar ICP discharge

Summary form only given. Evolution of metastable argon atom density (1s⁵) with electron density (plasma power) was investigated with Laser Induced Fluorescence (LIF) in Ar ICP discharge. The laser at wavelength 696.5 nm was used to excite 1s⁵ metastable state to 2p² state and measured the fluorescence of 772.4 nm emitted during the decay of 2p² state to 1s³ state. Two distinctive transition behaviors were observed in low and high electron density ranges respectively. The one, an abrupt decrease of metastable density, observed in low electron density range can be explained by the effect of the evolution of electron energy distribution functions during E-H mode transition of ICP discharge¹. The other one observed in high electron density range is also understood by the effect of changes of population and depopulation mechanisms of Ar metastable density². It is suggested that Ar metastable atom density can exhibit various behaviors with electron density due to its intrinsic characteristic — electric dipole radiation forbidden.