Design And Deposited Technology Of Solar Blind Ultraviolet Bandpass Filter

The target of this paper is to prepare a high performance solar blind ultraviolet bandpass filter. It takes advantage of optical film system design theory, Opti Layer software, OPTUS-700 electron beam vacuum deposition equipment and a variety of modern physical analysis methods to study systematically from the design of film system, deposited technology, preparation and characterization of sample aspects.According to technical characteristics and the development status of ultraviolet bandpass filter in the domestic and foreign, the design scheme that main film system and assistant film system are on both sides of the ultraviolet fused silica substrate were determined. Hf O2 was selected as high refractive index material, Mg F2 was selected as low refractive index material. The membrane system was obtained through the design and optimization. Calculation shows, the dielectric film of solar blind ultraviolet bandpass filter that was designed has a very high transmittance in 240-280 nm, and the width and transmittance of cutoff band meet the design requirements.After determining the appropriate process parameters, such as deposition rate and vacuum degree, etc. The relationships between optical properties and microstructure of two kinds of thin films, Hf O2 and Mg F2, which were deposited at different temperatures, were study mainly. Hf O2 thin films are amorphous when the deposited temperatures were below 150℃, and then the temperature reached 150℃, the crystallization tendency appears. With the deposited temperature increasing, the degree of crystallization increases, grain size decreases. At the same time, the filling density increases and the refractive indices increase along with that, the extreme values of transmittance at central wavelength decrease. The stoichiometric ratio of Hf O2 thin film mismatchs seriously with the increase of the temperature, the absorption loss in ultraviolet band and the extinction coefficient increases. Mg F2 thin films are tetragonal structure which the particles on surface are spire column, with the increase of the temperature, grains grow gradually, surface roughness increases, which lead to the scattering loss increasing and transmittance decreasing.Through the analysis of above results and considering the optical properties and microstructure of two kinds of optical film, 200℃ was determined as the best deposited temperature. According to the design scheme, the solar blind ultraviolet filter was prepared by using appropriate deposited technology. The result shows, the average transmittance of the filter is 50%, the width and transmittance of cutoff band are close to design scheme, and the filter has excellent optical stability and mechanical properties.