A novel design of a rf afterglow source of the oxygen forbidden lines at 630.0 and 557.7 nm for use in thermospheric dynamics studies is presented. With a repetitive discharge–afterglow excitation cycle, the source yields adequate afterglow intensities of the OI lines that are sufficiently free of background continuum for use in Fabry–Perot interferometer measurements of spectral line profiles. These lines provide accurate zero-velocity references in Fabry–Perot determinations of Doppler shifts in the OI thermospheric lines. The design considerations for the rf source are described, together with its preparation and filling by an ultrahigh-vacuum gas-handling system. Examples are given of the source’s output spectrum, as measured by a grating spectrometer, and its spectral line profiles, as determined by a Fabry–Perot interferometer. Comparative interferometry between the OI afterglow source lines and nearby (within ∼0.01–0.02-nm) lines from hollow-cathode sources illustrates the means of establishing secondary reference sources in cases in which the primary OI afterglow source is not available.
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