Varshni,Y.P. and Lam,C.S.: 1974, J.Roy.Astron.Soc.Canada, 68, 264.

In the plasma-laser star model for QSOs (Varshni, 1973a, 1973b, 1974a, 1974b) the line 4686 very likely arises due to laser action in the n=4 to 3 transition in He II. Extensive calculations of population densities in hydrogenic ion plasmas are carried out for a grid of ne (electron density), Te (electron temperature) and n(1) (density of the groundstate atoms) values on the basis of the collisional-radiative model (Bates, Kingston and McWhirter: 1962 Proc.Roy.Soc., A267, 297, Drawin: 1969 Zs.Physik, 225, 470). The region in which the population inversion is most intense for 4686 is identified and the bearing of the result on the atmospheres of the quasars 3C 48, 4C 09.31, PKS 2059+034 and 4C 37.43 and also of Of stars is discussed.

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