Optical Data of Rough-Surfaced Ceramics: Infrared Specular and Diffuse Reflectance versus Spectra Simulation

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Abstract
Infrared reflection of strongly absorbing as well as scattering samples was studied. The optical functions of sintered alumina ceramics were derived with the use of the Kramers-Kronig transformation to reconstruct the phase shift under the assumption of a semi-infinite sample with an ideal plane and, in any scale, a smooth surface. In order to validate this procedure and to optimize measuring parameters, the results were compared to their simulated counterparts. Starting from the dielectric functions of monocrystalline Al2O3, the optical response of the sample was calculated by taking into account the polycrystallinity of the bulk and the roughness of the surface; eventually the spectra of specular reflectance were simulated on this basis for different angles of incidence. It turned out that the comparably simple evaluation procedure is well suited in spite of the rough surface and is particularly reliable in the case of large angles of incidence whereby scattering is minimized. Some characteristics of this diffusely reflected component are discussed.