Inhomogeneities in the shape of the He 504.7 nm line excited in a hollow cathode discharge

The profile of the He 504.7 nm line emitted in the negative glow of a hollow cathode discharge is analyzed as a function of the distance from the emitting volume to the cathode axis. The value of the discharge current varied within the range of 10 to 30 mA, the helium pressure being 0.4 to 1.5 torr. A dependence was found of the Voigt parameter on the location of the emitting volume. The simultaneous recording of two line shapes, emitted from different regions of the discharge, enables us to observe a shift deltaν of the line centre observed off-axis compared with the line emitted along the axis. The electric field intensity at the periphery, 6 mm off-axis, is evaluated on the assumption that Stark broadening is the cause of deltaν. (author)