Crystallographic orientation of uniaxial calcite and dolomite determined using reflection generalized ellipsometry

Using the two-modulator generalized ellipsometry microscope (2-MGEM), it is shown that it is possible to determine the direction of the optic axis of crystallites of the high birefringence materials calcite and dolomite. 2-MGEM measurements are performed in reflection at near-normal incidence, so sample preparation requires only an optically polished surface. For uniaxial materials, the 2-MGEM measures the direction of the fast axis and the diattenuation, which can then be related to the tilt angle of the optic axis with respect to the surface normal once the maximum diattenuation is known. The optical resolution of the present instrument is 4-6 μm, and areas as large as 1 cm² can be measured without distortion. Additionally, the 2-MGEM measures the depolarization, which is a measure of the quality of the data. Using this information, an optical pole figure can be determined. The 2-MGEM results are compared with electron backscatter diffraction (EBSD) measurements on the same samples. Additional standard spectroscopic generalized ellipsometry measurements at a large angle of incidence were performed on single crystal calcite and dolomite to determine the spectroscopic ordinary and extraordinary refractive indices from 220 nm to 850 nm from which the maximum diattenuation can be determined.