Abstract

CaF₂ film is the most common used low index IR coating material due to its wide transmission band (0.2-10 μm) and low water solubility. However, CaF₂ thin film deposited by conventional thermal evaporation processes at an ambient temperature typically has inferior optical, structural, mechanical, and chemical properties compared with the bulk materials, which is attributed to the moisture absorption due to the columnar structure and low packing density. These problems can be remedied by energetic ion bombardments and by addition of TiO₂.^1,2 It has been shown that CaF₂-TiO₂ composite films with TiO₂ contents ≧ 10 at.% prepared by reactive ion-assisted codeposition (IAD) do offer the potential of improving performance, whereas the UV and IR transmission bands decrease with increasing TiO₂ contents.² The aim of this paper is to study the optical, structural, and mechanical properties of CaF₂-rich CaF₂-TiO₂ composite films with TiO₂ contents ≦ 10 at.% prepared by reactive ion-assisted codeposition (IAD). A practical application using this composite film, which has the superior optical, structural, and mechanical properties, as a low index coating material for mid-wave IR dichroic filter is presented.

© 1998 Optical Society of America