One of the important prerequisites to produce high-quality laser-related optical coatings is knowledge of accurate optical constants of layer materials and substrates as well as mechanical/environmental properties of the layers. It is important to have reliable dispersion of refractive indices and extinction coefficients in broadband spectral ranges from 0.4 µm to 12-15 µm. Careful optical and non-optical characterization of Ge, YbF3, ZnS, LaF3 films as well as ZnSe and Ge substrates were planned and performed by the AMO group ofthe Laboratory of Attosecond Physics (LAP). A number of measurement devices of the LAP-team were used for this study, namely, Lambda 950 spectrophotometer and universal reflectance accessory; infrared spectrometer Vertex 70, Stylus Profiler, and an industrial atomic force microscope from Fries Research and Technology GmbH.
Abstract: Thin films of Ge, ZnS, YbF3, and LaF3 produced using e-beam evaporation on ZnSe and Ge substrates were characterized in the range 0.4-12 µm. It was found that Sellmeier model provides the best fit for refractive indices of ZnSe substrate, ZnS, and LaF3 films; Cauchy model – for YbF3. Optical constants of Ge substrate, Ge film as well as extinction coefficients of ZnS, YbF3, LaF3, and ZnSe substrate are presented in the frame of a non-parametric model. For extinction coefficient of ZnS, exponential model is applicable. Stresses in Ge, ZnS, YbF3, and LaF3 were estimated equal to (-50) MPa, (-400) MPa, 140 MPa and 380 MPa, respectively. Surface roughness does not exceed 5 nm for all films and substrates.
Original publication: »Characterization of e-beam evaporated Ge, YbF3, ZnS, and LaF3 thin films for laser-oriented coatings« (Applied Optics 59, A40 (2019))
