Determining Infrared Optical Constants For Dolomite Using Single Angle Reflectance And Spectroscopic Ellipsometry
The optical constants, namely the real (n) and imaginary (k) parts of the complex refractive index, are of interest to generate the infrared (IR) spectra of liquid and solid materials in different morphologies. To obtain n/k, however, most materials are typically not found in the monolithic forms necessary to easily measure n/k, and thus require the use of other methods such as pressing powders to form planar, specularly-reflective pellets. In this work dolomite crystals are measured using fixed-angle IR reflectance spectroscopy in both 1) a monolithic form with the crystal fixed in epoxy and polished, and 2) a pressed-pellet form of the powder of the same mineral. First results for the two methods are compared. It was found that the measured reflectance can vary by as much as a factor of two between the dolomite crystals and the pressed powder forms. For the two-sample preparation approaches the preliminary spectra are compared and the implications and limitations of each method for determining the optical constants of given materials are discussed. Comparison to literature data suggest that polarization effects likely account for the differing amplitude results for reflectance (and hence the k-vectors): Dolomite is biaxial with significantly differing optical constants for the ordinary and extraordinary rays; the pressed pellet method measures an ensemble of microcrystals in randomly oriented positions, whereas the single crystal maintains just one orientation relative to the optical axis.
C. E. Lonergan et al., "Determining Infrared Optical Constants For Dolomite Using Single Angle Reflectance And Spectroscopic Ellipsometry," Proceedings of SPIE - The International Society for Optical Engineering, vol. 12116, article no. 1211607, Society of Photo-optical Instrumentation Engineers, Jan 2022.
The definitive version is available at https://doi.org/10.1117/12.2618920
Materials Science and Engineering
Keywords and Phrases
complex refractive index; dolomite; ellipsometry; optical constants; single-angle reflectance spectroscopy
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01 Jan 2022