Reflection spectroscopy for anisotropic materials: Direct determination of phase differences; validity of Fresnel formulas

Abstract

The reflectance of an anisotropic crystal is generally a tensor quantity even at normal incidence. Phase differences among the tensor components can be obtained from polarized reflectance measurements. A simple method for doing so is described and tested here. Possible applications of phase-difference information range from checking Kramers-Kronig evaluations of absolute phases to substituting for the Kramers-Kronig procedure. In addition, the following is proved, subject to some simple assumptions: If reflection extinction directions exist, the standard Fresnel equations may be used to derive optical constants ($n$'s and $k$'s), regardless of the anisotropy of the crystal. Moreover, extinction directions come in perpendicular pairs.