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Abstract: Single point diamond face flycutting technique is widely applied to fabricate potassium dihydrogen phosphate (KDP) crystals because of their characteristics of softness, brittleness, deliquescence and anisotropy. This paper studies the feasibility of machining KDP crystals through spiral turning method based on the ductile cutting mechanism of brittle materials. The spiral scratch method is employed to analyze various conditions of achieving brittle–ductile transition in different cutting directions where the critical depth of cut is obtained. The cutting forces and surface formation processes within different cutting parameters are discussed and the parameters ensuring full-aperture ductile turning are acquired. White light interferometer and Atomic Force Microscope (AFM) are used to evaluate the coherence of machined surface qualities in different cutting directions. The results indicate that the critical depth of cut varies from cutting directions significantly and fluctuates from about 200nm to 1000nm under the experimental condition. Cutting forces display periodical variation with the change of cutting direction and the periodical trend blurs, even ultimately disappears, with the decrease of the cutting parameters. Root-Mean-Square (RMS) value of the fabricated surface roughness fluctuates from 1.3nm to 1.7nm on the whole surface with no distinct anisotropic distribution of the surface morphology according to the results observed by AFM. Compared with face flycutting method, spiral turning method has capability to generate complex surface profiles such as aspheric or freeform surfaces and can also be used to compensate the deformation error of KDP crystals caused by vacuum suction during fabrication. [Copyright &y& Elsevier]

As the thickness of the adhesive layer between the mirror and the actuator decreases and the performance requirements of the unimorph deformable mirror (DM) increase, stricter control on the adhesive layer thickness and Young’s modulus is necessary. In this paper, a finite element model (FEM) for the unimorph DM with an adhesive layer is obtained. Based on the model, the influence of adhesive layer thickness and Young’s modulus on the deformation is studied. Also their influence on the adhesive’s maximum shear stress is analyzed. In the meantime, the design principles of the adhesive layer thickness and Young’s modulus are established with the restrictions of shear failure and the maximum displacement. As a result, different adhesive Young’s modulus has corresponding requirements for the upper and lower thicknesses (<20 μm) to obtain 85% maximum displacement. Then, DMs with four different mirror thicknesses are fabricated for verification experiments. The experiments results can be matched with the simulation results. Finally, the thickness in the spin coating process of adhesive layer is explored. The adhesive layer thickness can be controlled within 12.1 μm, and the deviation of uniformity is better than ±2%. [ABSTRACT FROM AUTHOR]