多磨头数控抛光对大口径离轴抛物面镜中频误差的抑制

Restraining mid-spatial-frequency error of large-size off-axis parabolic mirrors by multi-tool NC polishing

大口径非球面光学元件的面形中频误差对光路中的光斑扩散函数精度以及高能激光的能量散射有着直接的影响,针对该问题,提出一种计算机控制的多磨头组合抛光技术,用于对非球面元件中频误差的有效控制。对半刚性抛光盘抛光过程进行了力学有限元分析,并基于Bridging模型对半刚性抛光盘抛光过程进行了理论模拟,对其贴合特性进行了研究分析。实验结果表明:采用多磨头组合抛光的技术能够有效改善大尺寸非球面元件的面形中频误差,加工的两件φ460 mm离轴抛物面元件面形PSD1值相对于之前降低了近70%,达到2.835nm,并且PV小于0.16λ(632.8nm),RMS小于0.02λ。

The mid-spatial-frequency error（MSFR）of large aperture aspherical optical elements have a direct influence on the precision of the beam diffusion function and the energy scattering of the high energy laser.To solve this problem,we put forward a kind of multi-tool NC polishing technology of computer controlled optical surfacing（CCOS）for effective suppression of MSFR.The polishing process of semi-rigid polishing tool is analyzed by finite element methods,and the polishing process is theoretically simulated based on Bridging model.The experimental results show that the MSFR of large aperture aspherical optical elements can be effectively reduced by multi-tool polishing technology.The wavefront PSD1 value of specific spatial frequency has been restrained effectively.For the two finished φ460 mm elements,the wavefront PSD1 value has a 70% descend down to 2.835 nm.Besides,the PV value is less than 0.16λ（632.8 nm）and the RMS value is less than 0.02λ.