Measurement of Intensity and Polarization of HeI Forbidden Lines for Diagnostics of Electric Field in a Plasma

Abstract

Intensity of the HeI 491.1 nm (4 1 P→2 1 P) forbidden line due to the Stark effect, with respect to the HeI 396.5 nm (4 1 P→2 1 S) allowed line, was measured to obtain radial distribution of the electric field in a hollow cathode discharge. The polarization of the lines was also observed to show a capability of detecting the field direction in plasmas. The measured electric field distribution satisfactorily yielded the cathode fall potential, and the polarization was well in agreement with the theoretical prediction. The experiment demonstrated that field strength as low as 250 V/cm could be accurately measured using the present line pair.