The refractivity of helium and its measurement by laser interferometry

Abstract

This article covers the historical background to the study of the helium atom by optical methods, and some essential results from the classical and quantum mechanical theory of optical dispersion. A simple undergraduate-level experiment, designed for refractivity measurements by cw laser interferometry, is described, and the ingredients of the theoretical calculation of the refractivity are discussed. It is shown that careful experimental work in this area can yield information that provides a valuable test of the accuracy and completeness of the available oscillator strength data.