Index of Refraction of Helium in the Shielding Approximation

Abstract

We have calculated the index of refraction of the helium isoelectronic sequence at low frequencies using the shielding approximation. When compared with experiment for helium, the accuracy is found to be comparable to that typical of the shielding approximation for static properties, about 10%. In an Appendix we extend Brillouin's theorem to time-dependent problems.