Post-production characterization of double-sided ZnS/YbF3 mid-infrared thin-film optical elements

Development of modern mid-infrared laser applications requires high-quality optical elements operating in the broadband spectral ranges from visible to 15 um. ZnS/YbF3 coatings on ZnSe substrates are perspective candidates for such elements since these thin-film materials and the substrate are transparent in this region and provide sufficient refractive index contrast. Experiments demonstrate that spectra of ZnS/YbF3 multilayers on ZnSe and glass substrates are shifted with respect to each other significantly. This issue plays a key role in the monitoring concept of YbF3/ZnS-coatings since typically the monitoring is conducted on a glass, and the final optical elements are on the ZnSe substrates. The study reports sophisticated experiments on the deposition of ZnS layers, its in-depth analysis on different substrates, and innovative reverse engineering of double-sided ZnS/YbF3 optical elements in the spectral ranges from 400 nm to 12 um. The results can be interesting for optical coating and laser engineers.