Making aspherical lens by thin film deposition coated under vacuum

摘要

AbstractAn aspherical lens is made by a thin-film coating technique. A special mask is placed between the evaporation source and the substrate that is to be coated as an aspheric. The design principle of the mask is completely described. The final surface is tested by an interferometric double path auto-collimation measuring method. Less than 0.05λ rms of a wave (632.8 nm) of aberrations is achieved without much trial and error. The static mask is described and analysed by simulations of the film thickness theory, based on the assumption that atoms and molecules emitted by the source travel in straight lines to the substrates, which rotate about the central axis during films deposition. The design method can be practically used for all optical coatings produced by vacuum deposition. The solution of a mask shape is unique for a stationary set of coating parameters. A set of coating parameters include the height of the apex of the dome above the source, the curvature radius of the dome, the distance from the source to the rotation axis of the dome, the emissive characteristics of the source which modify the cosine law of the surface source, the form and area of the source. The static mask designed by this method can be used for correction optical element’s aberrations. Dioxide silicon thin film was evaporated with 6 µm thickness on BK7 optical glass and fused quartz optical glass for apherization refractive optical elements. The SiO2film was tested for stability and environmental durability, it achieved good sticking and passed the test without peeling or cracking.