Develop Of Ultra Wide-band Dichroic Filter Coatings

This article bases on a certain project. Ultra wide-band dichroic filter coatings which need to reflect0.6-0.9μm&1.06μm(TV and laser band) and transmit7.5-10.5μm(infrared band) are deposited on the substrate of Germanium. Because of this dochroic filter coatings cover the ultra wide-band of0.6-10.5μm, so at the beginning we carefully calculate and analyze the refractive index dispersion and physical thickness of two selected materials-ZnS and YbF3. Calculating is running by OptiLayer film design software. The physical thickness of calculated is used to adjust the tooling factor of the XTC/2thin film deposition controller, and the refractive index dispersion is used to design the ultra wide-band dichroic filter coatings.At the thin film design process, two approaches are used to satisfy the target. One is start with three formula stack coatings which can satisfy the reflected zone, then add new layers and optimize the transmitting zone only. Another is used the auto optimize function of the film design software to create the film design which can satisfy the target. Both of the approaches have their advantages and disadvantages. The former uses separation design, so the sensitivity relation between the layers thickness and the reflectance or the transmittance is separate. It is easily to control the thickness of the layers and adjust during post processing. But the total thickness of the layers is thick. The latter’s structure make the reflectance or the transmittance affected possibly by each layer of the design, so it is harder to adjust during post processing. But the total thickness of the layers can be controlled.The coatings are deposited by ZZSX-800vacuum depositing equipment. The materials are evaporated by heating with electronic beam source, and assisted with Hall ion source. The samples are tested by Lambda900spectrophotometer at the wavelength between0.6-1.1μm and Magna-IR750spectrophotometer at the wavelength between7.5-10.5μm. Through calculation and analysis, the ultra wide-band dichroic filter coatings we made satisfy design requirements.