Optical and Mechanical Characteristics of Mixed composition Infared Thin Films — Zinc Selenide - Cryolite & Magnesium Fluoride Thorium Fluoride Systems

Mixed composition optical thin films have been found to possess some optical and mechanical properties that are superior to those of single material films. This makes these mixed composition films attractive for use in multilayer thin film optical coatings for the near infared region (2-10 μ), because not too many suitable single material films are available for use in multilayer optical coalings for this region. In this paper, we have investigated two mixed composition optical thin film systems.... zime selenide-cryolite and magnesium floride-thorium fluoride. Mixed composition thin films of ZnSe-cryolite and of MgF2 - ThF4 have been evaporated by thermal evaporation from mixtures of the constituents in different proportions by weight, from a single source. The films are characterised for their optical properties (refractive index, extinction coefficient and IR transmittance), mechanical properties (inlrinstic stress and surface morphology) and crystalline / amorphous structure. It is found that these mixed composition films have tailorahle refractive indices, good IR transmittance, low intrinsic stress (for certain compositions) and smooth surface morphology. This makes them useful for incorporation in multilayer thin film optical coatings used in the near infrared region (2-10 μ).