Determination of optical anisotropy in calcite from ultraviolet to mid-infrared by generalized ellipsometry

Abstract

Generalized (Jones matrix) ellipsometry is gaining considerable interest because of its ability to determine properties of anisotropic samples. Here, the strong uniaxial anisotropy of calcite (calcium carbonate) was investigated using generalized ellipsometry. The wavelength range from 0.73 to 6.5 eV (190 nm to 1.7 μm) was covered using a standard variable angle spectroscopic ellipsometer; from 0.089 to 0.68 eV (1.8–14 μm), using a similar instrument based on a Fourier transform spectrometer. Measurements were made on a single air–calcite interface for which the optic axis lay nominally in the plane of the surface. To determine the optical constants and orientation of cut, both the angle of incidence and rotation of the sample about its surface normal were varied. Properties of the sample were arrived at by optimizing the parameters of a material model such that the calculated normalized Jones matrix elements best matched the measured ones. Localized spectral regions of absorption due to the internal vibrational modes of the carbonate ions were observed in the infrared at energies which differed for the ordinary and extraordinary optical constants. The certainty to which sample properties could be determined was maximized by judicious choice of measurement configurations.