China has started to develop its geostationary meteorological satellites and associated ground application systems since the 1980s. In the past 20 years, 6 FY-2 satellites were launched and put into application. About 10 years ago, China had planned to develop a new generation geostationary satellite, and the first one, named FY-4A, was launched on December 11, 2016. The Advanced Radiation Imager, one of the observing instruments onboard FY-4A meteorological satellite, has 14 optical channels with the spectral range cover from 0.45µm to 13.8µm. Five kinds of optical coating components, including high reflectance mirrors, dichroic beam splitters, lens, optical windows and bandpass filters, are used to construct the complex optical system. Metal and dielectric thin film materials are selected to design and fabricate these optical coatings. The spectrum measurement, reliability tests and simulated space environment tests are carried out, respectively. The images received by ground station indicate that optical coatings are competent to the application of Advanced Radiation Imager.
As a high refractive index material, silicon is widely used for infrared thin-film coatings. However, the absorption of silicon films is relatively high, especially in the near infrared region with wavelengths less than 1.8µm. In this paper, we investigated the effect of post-deposition annealing on the microstructure and optical properties of silicon films. Silicon films were deposited by electron beam evaporation and then annealed in air within the temperature range from 200 to 600 °C. The films were characterized by X-ray diffraction(XRD), Raman spectroscopy, electronic-spin resonance(ESR), and optical transmittance measurement, respectively. The optical constants of the films were obtained by the simulation of transmission spectra. It was found that all the silicon films maintained amorphous in microstructure, but, with the increase of temperature, the amorphous network order was improved on both short-range and medium-range scales. When samples being annealed at 400°C, the defect density decreased to the minimum, about one fifth of the as-deposited samples. Meanwhile, extinction coefficient also fell to the minimum, and then increased by rising the annealing temperature further. These results showed that post-deposition annealing could reduce optical absorption of silicon films remarkably in the near infrared region, so as to improve the optical performance of the silicon films.
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