The preparation and characterization of a reference mirror of protected aluminum (Al) is reported. The mirror is made of 50–60-nm-thick Al film, coated with several-nanometer-thick Al2O3 and 30-nm-thick film of AlN. The mirror characterization is based on reliable and precise reflectance measurements relative to a silicon- (Si-) wafer reference mirror. The simple phenomenological Drude–Lorentz model is applied for modeling the dispersion relations n(λ) and k(λ) of the Al film. The reflection of the protected Al mirror is determined in the 400–800-nm spectral range with accuracy better than 0.01 for p- and s-polarized light at angles of incidence from 0° to 70°. The accuracy has been confirmed with an evaporated thin silver film with known n(λ), k(λ), and d derived by photometric measurements at normal light incidence.
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