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Past because of restriction of the craft, the method of the thermal evaporation can't realizes that double waveband light enter infrared optical window at the same time in the band of 3um to 5um and 8um to 12um. In order to complete the light signal collection in Infrared thermal imaging system, we have to design two light roads for this optical system. Along with the development of science, the design bring many inconvenience for the application and development of Infrared thermal imaging system. For changing this kind of status, we researched a kind of optical thin film that have capabilities in double wavelength light entering into same window together. In our study, crystal germanium was used as the substrate, zinc sulphide(ZnS) and germanium (Ge) are used as double waveband infrared optical window thin-film materials, otherwise, the A of special thin-film material was used to design coating, it was constructed by evaporating two of fluoride material at same time. End-Hall ion source was used to assist the e-beam evaporation to deposit ZnS.
Two surfaces were deposited by different thin film. Because of getting in touch with the environment direct, the outward appearance should have high strength and anti-fogging. We sacrificed a part of spectral energy, adopted the sulphur zinc and germanium to design the layers. Then, antireflection coating of three-layer had designed with Michael's software. Ultimately, we obtained a suitable thin film. Because inside surface was sealed completely in system, and did not touch with environment around it direct, it needn't be a kind of hard material. For increasing the transmittance values of thin film, ZnS was used as the middle-index material, for the high-index, Ge is used. And for low-index, we selected the A of special thin-film material as low-index layer. It made the transmittance of infrared optical window turned higher. Then, antireflection coating of Four-layer had designed with Michael's software. We chose different temperature to heat the substrate, while two of thin films were deposited. At last, Double Waveband Infrared Optical Window were completed.
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