DETERMINATION OF OPTICAL ANISOTROPY IN CALCITE FROM ULTRAVIOLET TO MIDINFRARED BY GENERALIZED ELLIPSOMETRY

Generalized (Jones matrix) ellipsometry is gaining considerable intere st because of its ability to determine properties of anisotropic sampl es. Herl, the strong uniaxial anisotropy of calcite (calcium carbonate ) was investigated using generalized ellipsometry. The wavelength rang e from 0.73 to 6.5 eV (190 nm to 1.7 mu m) was covered using a standar d variable angle spectroscopic ellipsometer; from 0.089 to 0.68 eV (1. 8-14 mu m), using a similar instrument based on a Fourier transform sp ectrometer, Measurements were made on a single air-calcite interface f or 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 pa rameters of a material model such that the calculated normalized Jones matrix elements best matched the measured ones. Localized spectral re gions of absorption due to the internal vibrational modes of the carbo nate ions were observed in the infrared at energies which differed for the ordinary and extraordinary optical constants. The certainty to wh ich sample properties could be determined was maximized by judicious c hoice of measurement configurations. (C) 1998 Elsevier Science S.A.