Abstract

As well known, the propagation of an electromagnetic field inside matter is described by the complex index of refraction n = 1-δ+iβ, where δ and β account respectively for phase retardation and absorption. δ and β are related by the Kramers-Kronig relationships, which theoretically, permits calculating δ(λ) from experimental determination of β(λ) [1]. Practically, however, the method gives questionable results near absorption edges, mainly because only discrete absorption data can be obtained in a finite wavelength range and some assumptions on the material structure must be introduced. More direct methods exist, based on reflectivity measurements [2-5]. Again, assumptions on the material structure must be introduced, which makes the results questionable near absorption edges. In all cases, the influence of β significantly limits the accuracy of the determination of δ. In addition, it is often found that the index values depends strongly on the conditions of deposition of materials. Such methods, which often make use of composite stacks, are therefore not well adapted.

© 1994 Optical Society of America