Effect of the position of the external magnetic field applied to a glow discharge plasma on the coherent forward scattering spectra in the Faraday configuration

The coherent forward scattering (CFS) spectra of the Ar I 842.5 nm and O I 844.6 nm lines in a radio-frequency (RF) plasma were measured. The CFS spectrometer used was equipped with a movable permanent ring magnet in the Faraday configuration and a diode laser source. The CFS signal was mainly generated near the maximum external magnetic field applied. When the ring magnet was moved toward the RF-powered electrode of the glow discharge tube, the analytical curves of the excited argon atoms in the lower state of the Ar I 842.5 nm transition became nonlinear because these atoms were depleted under the partial Ar pressure (0.04 Torr (5.3 Pa) or less). When the ring magnet was moved toward the grounded electrode, no depletion of the excited Ar atoms was observed, resulting in linear analytical curves. Similar depletion of the excited atoms in the lower state of the O I 844.6 nm transition was also observed at the RF-powered electrode.