Determination of Optical Constants from Reflection Bands Using Dispersion Relations

Abstract

A detailed study has been made of the Robinson and Price (Kramers—Kronig) method for determining optical constants from reflection data collected in regions of strong absorption. This method depends upon the fact that the phase shift at any given frequency can be expressed as an integral involving the reflectivity at all frequencies (0 to ∞). Although in practice reflectivity data are ordinarily available only in the immediate vicinity of a reflection band, a method is presented which can be accurately applied to that situation. The circumstances under which this procedure will be valid are outlined, and some differences from previous methods will be indicated. The following two experimental situations have been considered assuming that the reflectivities have been measured at normal incidence: (1) the sample is not covered by a window, (2) the sample is covered by a window whose (constant) refractive index is greater than the zero frequency refractive index of the sample.