Optical dispersion: A comparison of the maxima of absorption and selective reflection for certain substances

Abstract

In the comparison of optical dispersion formulæ with experimental results, it is important to consider the meaning of the various constants, and in particular of the natural wave-lengths which occur in them. With the formula in the simple form n 2 - 1 = ƩC 1 /(λ 2 -λ 1 2 ), the quantities λ 1 are the wave-lengths of the natural vibrations and have been identified in practice indiscriminately with the wave-length of maximum absorption or that of selective rejection obtained by the method of residual rays. This interpretation is allowable if the absorption is very small. For a more general type of formula such as (n2-1)/(n2+a)=ƩC 1 /(λ 2 -λ 1 2 )the corresponding wave-length, on a similar argument, for small absorption is a certain wave-length λ 1 ', which is larger than λ 1 ; in a previous paper numerical examples were given of the difference between the wave-lengths λ 1 and λ 1 '. The present paper includes absorption more generally in the formulæ, so as to determine the position of the various maxima more accurately.