Silicon carbide has good physical, mechanical and thermal properties, it has been widely used in aerospace field in recent years. In order to meet the requirements of optical performance of space remote sensor, silicon carbide surface is usually treated by surface modification technology for further implement requirements, this process is called modification. There are two ways of modification: PVD and CVD, the purpose is to cover the surface voids of silicon carbide with a modified layer, reducing surface roughness and suppression of surface scattering, improving imaging quality of optical system, improvement of resolution, reducing the loss of light energy .Now, modification technology is mature, but there are still risks in the modification process, there are also corresponding processing risks in the optical polishing process after modification. In order to investigate the influence to pitted reaction bonded SiC (RB-SiC) without SiC or Si cladding layer, 10nmCr, 10nmTi, 10nmGe and100nm Ag films are deposited using thermal evaporation method. The research results show that Ge can decrease the roughness of RB-SiC surface and has preferable smoothing effect of silver thin film comparing to that of Cr and Ti. This article through the research, a method of direct application of non-modified silicon carbide substrates in production practice is explored. The essence is to utilize the growth characteristics of materials, complete growth in the hole, achieve the purpose of filling holes, then the surface roughness is reduced and the surface scattering is suppressed.
Nowadays, optical elements are often shared in order to improve compactness of optical system and edge filter is one of the core parts. For same spectral system, when half convergence light incidents on edge filter, Sagittal and meridian will have different incident angle range, which cause different polarization characterization for the two directions and is harmful to the optical system’ MTF. In order to improve image quality, all factors affecting MTF are analyzed. When light incidents on edge filter, the difference between P and S polarization’s reflection phase can cause MTF drop. The design process of edge filter is optimized. Optical spectrum and reflection phase are optimized together. The variation is kept in a certain range for reflection phase of P and S polarization when edge filer attains spectrum requirement. The newly designed edge filter is sticked to optical system and carried out simulation. The calculation results showed that the newly designed edge filter has little effect on MTF. Ion-assisted e-beam evaporation method is used to deposit edge filter multilayer and the measurement result is in good accordance with that of the design. We think that a new design method is raised for design wide-incident angle and low polarization aberration edge filter.
With the development of remote sensing technology, the short working wavelength has been extended to 400nm in many current international spatial optical remote sensors. However, the reflectance in the wavelength range from 400nm to 450nm cannot meet the requirement for silver-based mirror. In order to solve this issue, SiO<sub>2</sub> and Ta<sub>2</sub>O<sub>5</sub> used as reflectivity enhancement layers are deposited on the silver layer. Simultaneously, the two dielectric films also protect the metallic silver film to from corroding in complicated environment. During the deposition process of Ta<sub>2</sub>O<sub>5</sub> dielectric coating material, oxygen partial pressure, anode voltage and current of the ion source are optimized to get higher refractive index. The values of stress of the SiO<sub>2</sub> layer and theTa<sub>2</sub>O<sub>5</sub> layer are analyzed to get the adhesive coatings by the Stony formula and the process parameters of SiO<sub>2</sub> dielectric coating material are obtained. The optical constants of these two dielectric films are established by using the Cauchy dispersion formula and the incoherent reflective theory, and then the thicknesses of them are optimized by simplex algorithm. SiO<sub>2</sub> layer and Ta<sub>2</sub>O<sub>5</sub> layer are sequentially deposited on the silver layer. The measurement results show that the average reflectivity of the wavelength ranges 400nm-450nm and 400nm-900nm reaches over 95% and 98%, respectively. The reflectivity enhanced silver-based mirror also passes the adhesion test according to relevant technique requirements.
Silicon carbide, as a new reflector material, its excellent physical and chemical properties has been widely recognized by the industry. In order to make SiC mirror better used in space optical system, we used digital coating equipment during its coating process. By using ion-assisted electron evaporation method, we got a complete metal reflective film system on the surface of finely polished silicon carbide mirror. After automated coating process, by adjusting the coating parameters during the process, the surface roughness of silicon carbide improved from 7.8 nm to 5.1 nm, and the average optical reflectance of the surface reached 95% from visible to near-infrared. The metal reflective film system kept well after annealing and firmness test. As a result, the work of this paper will provide an important reference for high-precision coating process on large diameter SiC mirror.