Causality calculations in reflection spectroscopy

Abstract

A new method is presented for obtaining intrinsic absorption spectra (i.e., index of refraction and extinction coefficient versus wavelength) from reflection spectra of stratified media, which usually are complicated by substrate absorption, thin-layer interference patterns, etc. A typical application is to obtain intrinsic absorption spectra of an organic monolayer chemisorbed on the surface of a very thin metal film, which is in turn supported by a bulk substrate. The basis of the method is the proven causality of a special reflection function that we introduce, and the application of the transformation of Peterson and Knight to this function. The method is general, and has been found to give accurate results for various multiphase systems without restriction as to number of phases, angle of incidence, or polarization. While the method is valid for general stratified media, its accuracy depends upon the information content of the particular reflection spectrum taken. The sensitivity available can be calculated and the adjustable optical parameters chosen accordingly.