Optical dispersion and selective reflection, with application to infra-red natural frequencies

Abstract

1. In a previous paper I gave a comparison of the maxima of absorption and reflection as deduced from optical dispersion formulæ of various types. Exact equations, together with approximate solutions, were found for the maxima of k and nk and for the minima and maxim of n . The maximum of reflection was found by numerical and graphical methods in certain cases, both in the ultra-violet and in the infra-red; in particular, for rock-salt it was shown that available dispersion formulæ agreed in indicating a maximum of selective reflection at about 52 μ , provided the formulæ were properly interpreted. The infra-red frequencies of substances like rock-salt of special interest in view of the various methods now available for estimating them from the point of view of crystal structure. The frequencies so calculated have generally been identified with the frequencies of the residual rays in the same region. For instance, Born, using the dynamics of a simple crystal lattice, compared the natural wave-length with the maximum of selective reflection as given by residual rays; later, allowance was made for the difference between these wave-lengths, and an approximate formula given by Försterling was used in making the correction.