Cascade Fluorescences from Laser-Excited Lithium Atoms Immersed in a Static Electric Field for Plasma Diagnostics

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Abstract
The Stark effect on a laser-pumped Li atom to the 42D or 42F level was studied by the observation of two cascade fluorescences of 610.4 nm (32D→22P) and 323.3 nm (32P→22S) under a static electric field in order to develop a spectroscopic measurement of the static or quasi-static electric fields in plasmas with a combined technique of Li-beam probing and laser-induced fluorescence (LIF). The excitation spectra and field dependencies of both lines were obtained and found to agree with the theoretical values obtained by solving the rate equations. It was also shown that a method for exciting the forbidden transition from 22P to 42F is so sensitive as to make it possible to measure an electric field as weak as ∼ 100 V/cm. A practical method that is applicable to plasma devices is described, and the effect of the electron density on LIF is also discussed.