大口径离轴非球面碳化硅反射镜的加工

Fabrication of Large Off-Axis Aspheric Silicon Carbide Mirror

为了研制出高质量光学表面的离轴非球面碳化硅反射镜，提出一套包括铣磨成型、研磨、粗抛光、表面改性以及精密抛光等工序的完备的离轴非球面碳化硅反射镜加工工艺规范。采用Ultrasonic 100^-5数控加工机床直接将Φ600 mm碳化硅反射镜铣磨成离轴非球面，铣磨后反射镜面形精度的峰谷（PV）值为17.17 μm。利用计算机控制光学表面成型（CCOS）技术对离轴非球面碳化硅反射镜进行研磨和粗抛光，使其面形精度的均方根（RMS）值达到0.102λ（λ=0.6328 μm）。采用离子束辅助沉积（IBAD）表面改性技术在粗抛光后离轴非球面碳化硅反射镜表面镀制一层厚度约10 μm的硅改性层，并利用先进的离子束抛光（IBF）技术对表面改性离轴非球面碳化硅反射镜进行精密抛光。最终离轴非球面碳化硅反射镜的面形精度和表面粗糙度的RMS值分别达到0.018λ和0.6968 nm。加工结果表明提出的加工工艺规范完备，适用于离轴非球面碳化硅反射镜的加工。

In order to manufacture off-axis aspheric silicon carbide （SiC） mirror with high quality optical surface, a perfect process specification for fabricating off-axis aspheric SiC mirror, including milling, grinding, rough polishing, surface modification and precise polishing, is presented. Ultrasonic 100^-5 computer-controlled machine is put to use for milling Φ600 mm SiC mirror to off-axis aspheric surface directly. After milling, peak valley （PV） value of the figure accuracy of the mirror is 17.17 μm. The off-axis aspheric SiC mirror is grinded and rough polished by computer-controlled optical surfacing （CCOS）, and root mean square value of the figure accuracy of off-axis aspheric SiC mirror is 0.102λ （λ=0.6328 μm）. A silicon modification layer with thickness of about 10 μm is coated on off-axis aspheric SiC mirror by ion beam assisted deposition （IBAD）, and the surface modified off-axis aspheric SiC mirror is precisely polished by advanced ion beam figuring （IBF）. At last, root mean square values of the figure accuracy and roughness of off-axis aspheric SiC mirror are 0.018λ and 0.6968 nm, respectively. Experimental results indicate that the process specification is suit for fabricating off-axis aspheric SiC mirror.