OPTICAL-CONSTANTS OF SAPPHIRE (ALPHA-AL2O3) SINGLE-CRYSTALS

Spectroscopic ellipsometry has been used to measure the dielectric functions of synthetic sapphire (α-Al2O3) single crystals. The measurements have been made on the (112̄0) surfaces of sapphire in the near-infrared-near-ultraviolet spectral region (1.2-5.4 eV) at room temperature. These data and the literature values are used for the modeling of the optical constants of sapphire crystals over the 0-30 eV photon-energy range. By using damped harmonic oscillators as a basis of the model, the causality, linearity, reality, and Kramers-Kronig requirements, compulsory properties of the dielectric function ε(E)=ε1(E) +iε2(E), can be satisfied automatically. It is found that the damped harmonic oscillator model provides satisfactory fits to the experimental ε2(E), but does not yield good fits to ε1(E) in the higher-photon-energy region (E≳7 eV). As a byproduct of this analysis, we obtain the static and high-frequency dielectric constants of sapphire crystals as ε∞=3.064 and εs=8.90 for the ordinary ray (E⊥c) and ε∞=3.038 and εs=11.11 for the extraordinary ray (E∥c), respectively. © 1994 American Institute of Physics.