In infrared optical system, changes of the reflective index will result in a decrease in imaging quality. Therefore, athermalized treatment is necessary. Chalcogenide glasses (As40Se60) are the ideal material for thermal aberration correction in infrared optical systems, which have excellent infrared optical properties, especially the transmission performance and temperature characteristics. However, thermal deformation is inevitable for chalcogenide glasses in the coating process, which is a major cause of quality deterioration. In this paper, a deep cryogenic treatment with a series of specific parameters is carried out and a comparative experiment is conducted. The result shows that the thermal stability of chalcogenide glass in the coating process is improved markedly after deep cryogenic treatment. The thermal deformation of the optical surface is reduced and the surface accuracy is controllable.
ZnSe is widely used in infrared optical systems because of the good optical characteristics in 0.5~22μm and the good processability. Physical Vapor Deposition(PVD) of ZnSe is good at no pollution in production process, lower price, etc. Infrared optical parts should be made by single point diamond turning or single point diamond fly-cutting after the experimental investigation of the ultra-precision turning capability of PVD ZnSe. The orthogonal experiment of ultra-precision turning PVD ZnSe was done at first, then the smooth turning surface and the rough turning surface were observed by metallographic microscope and 3D profilometer, and the mechanism of the defects on the turning surface was discussed. The result shows: the quality of ultra-precision turning surface of PVD ZnSe was restricted by the grain size and the distribution of the grain which could easily cause the variegated macula at the grain size, rising the spindle speed, reducing the feed rate and reducing the cut depth could make the quality of ultra-precision turning surface better and reduce the roughness Ra value lower, the roughness Ra value of the smooth turning surface was reached 3~4nm which is enough to the infrared optical image systems currently by using the optimization of parameters.
Microscopic morphology and XRD spectra of Hot Press(HP) ZnS powders and fractrues were tested. Preliminary analysis of the turning characters of HP ZnS was got by associating with the characters of HP ZnS and the processing mechanism of hard and brittle materials. Orthogonal experiment of 3 factors and 3 levers was taken by setting roughness Ra value index of the turning surface, and more analyses of the ultra-precision turning characters of HP ZnS were got by associating with the 3D microscopic morphology of CVD ZnSe ultra-precision turning surface and HP ZnS polishing surface. How to get the lower Ra value was discussed at last. The research shows: the primary removal mechanism of HP ZnS is powder removal; HP ZnS can get good ultra-precision turning surface which Ra value is lower than 10nm; to get the Ra value of the turning surface lower than 4nm, speed of main spindle, blunt edge radius, and the corner radius must be optimized because of the polycrystalline structure of the HP ZnS.
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