Abstract
Fabricating micro-structures on optical materials has received great interest in recent years. In this work, micro-grooving experiments were performed on polycrystalline zinc selenide (ZnSe) to investigate the feasibility of surface micro-structuring on polycrystalline soft-brittle material by diamond turning. A photosensitive resin was coated on the workpiece before cutting, and it was found that the coating was effective in suppressing brittle fractures at the edges of the grooves. The effect of tool feed rate in groove depth direction was examined. Results showed that the defect morphology on the groove surface was affected by the tool feed rate. The crystallographic orientation of grains around the groove was characterized by electron backscatter diffraction (EBSD), and it was found that the formation of defects was strongly dependent on the angle of groove surface with respect to the cleavage plane of grain. The stress distribution of the micro-grooving process was investigated by the finite element method. Results showed that the location of tensile stresses in the coated workpiece was farther from the edge of the groove compared with that in the uncoated workpiece, verifying the experimental result that brittle fractures were suppressed by the resin coating.
Highlights
Many optical crystals, for example, potassium dihydrogen phosphate (KDP) [1], calcium fluoride (CaF2 ) [2], zinc sulphide (ZnS), and zinc selenide (ZnSe) [3], have relatively low hardness and high brittleness, which makes them very difficult to machine in a ductile mode
Commercial optical elements are usually made of polycrystalline materials, for example polycrystalline zinc selenide (p-ZnSe), due to lower cost compared to single crystal materials
A chemical vapor deposited (CVD) ZnSe wafer was used as workpiece
Summary
For example, potassium dihydrogen phosphate (KDP) [1], calcium fluoride (CaF2 ) [2], zinc sulphide (ZnS), and zinc selenide (ZnSe) [3], have relatively low hardness and high brittleness, which makes them very difficult to machine in a ductile mode. All grains have various crystal orientations, which makes it difficult to achieve uniformly smooth surfaces by machining. Fabrication of micro-structure on material surface attracted considerable attention because it can offer unique functions for optical components, such as enhancement of sensitivity [5], increased field of view [6], and miniaturisation of components [7]. Creating micro-structure on polycrystalline soft-brittle materials is of great importance for optics applications
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