Study On Ultra-precision Turning Methods And Processes Of Freeform Optics Of Brittle Materials

The high performance optical elements/systems are the ’’eyes’ ’ of acquiring the information.Elements with optical freeform surfaces using brittle materials are playing a significant role in some optical wavelength ranges.However,it requires both high accuracy and surface integrity in machining freeform optics of brittle materials.The final optical performance highly depends on the form accuracy and surface damage.Till date,it remains a problem to solve how to employ ultra-precision cutting on freeform optics for brittle materials which possesses high accuracy,high quality and high performance.Such issue has become the limitation of popularizing freeform optics and developing relevant technical fields.It requires highly accurate machining in freeform optical elements,such as high performance infrared lenses,irregular aperture freeform mirrors/lenses and microlens array on brittle materials,while the excellent surface quality and surface uniformity should also be guaranteed to achieve outstanding optical performance.Due to the lack of basic foundation in processing technique for machining optical elements on brittle materials,and the ignorance of highly efficient machining of freeform optics,there exist difficulties in improving the performance and functional effects of brittle materials.This research is focused on the highly efficient generation of freeform optics on brittle materials using ultra-precision cutting,including the design,characterization,machining,measuring and evaluation.The main contents are listed as follows:(1)The characterization of surface integrity in machining brittle materials and the surface generation of freeform optics are investigated.A characterizing model is established to quantify the surface and subsurface deformation of brittle materials using Raman spectroscopy.The machining constraints of ultra-precision cutting is understood to guide the machining of freeform optics,wherein the concept of nonrotational degree is proposed to introduce a condition that the freeform optics is nearrotational in fast tool servo turning,whose tool path generation is discussed.(2)The effects on machining-induced surface damage of single point diamond turning on monocrystalline germanium are investigated to obtain the processing technology of fast tool servo turning on near-rotational optical element.Near-rotational infrared lenses are designed and analyzed.The surface quality and o ptical function are measured and evaluated,achieving the manufacture of high performance infrared lenses with near-rotational form.(3)The highly efficient machining of freeform optics with irregular aperture is studied.Surface decomposition and reconstruction are realized in non-circular region by selecting the profile,where the optimization is calculated according to the nonrotational degree.The regular of fast tool servo machining accuracy is investigated in the view of kinematical performance.The effects of tool marks on optical diffraction are studied.A modified off-axis turning approach is proposed to improve the reflective effect in freeform optics with high-aspect-ratio aperture.(4)The cutting strategy is researched to generate microlens array on brittle materials with highly uniform surface quality.A green processing approach is proposed to produce optical elements with brittle material mold core instead of nickel plating on steel to avoid the chemical pollution.A segmental machining with smoothing delivery to tool path is proposed to machine microlens array on plane and cylindrical substrates with high stability,so that a highly uniform surface quality is achieved.Finally,an optical field camera is developed to realize large-depth-of-field imaging using the microlens array machined.