Experimental Study of Stark Broadening of the Allowed and Forbidden Transitions 23P-43D, 4 3F (λ=4471.5 Å, λ=4470 Å) in Neutral Helium

Abstract

Measurements were made of the profile of the Hel 4471.5 Å line and its forbidden component at λ = 4469.9 Å, emitted from an afterglow plasma of electron densities in the range 2.2 × 10¹⁴ to 1.5 × 10¹⁵ cm^-3. The various quantities which define position and form of the profile have been compared with the theoretical calculations of Griem and of Barnard et al. It has been found that the wavelength shifts of the individual components and, thus, the peak separation are slightly smaller than predicted by theory, whereas the intensity in the valley between the two components is found to be slightly larger than the theoretical values. The peak intensity of the forbidden component is smaller than given by theory but not as small as found by D. D. Burgess and C. J. Cairns. At low electron densities the intensity of the forbidden component is proportional to the square of the normal field strength F₀ of the electric microfield. At higher electron densities the intensity increases proportionally to F₀ in agreement with the transition from quadratic to linear Stark effect at higher electric field strengths. The measurements show that the influence of the ion dynamics on the line profile is probably not as large as assumed by D. D. Burgess. The measurements show that the position of the intensity minimum between allowed and forbidden component is shifted towards the allowed component when the temperature decreases.