无限远前后零位补偿结合的非球面检验

Aspheric Test Combining Front and Back Null Compensation for Infinite Optical Path

利用有限远零位补偿方法检验非球面时,装调环节多,检验精度低。提出了无限远前后零位补偿结合的非球面检验系统,通过在待检镜球心前后位置处各放置一个补偿透镜,使像差在前后区间具有相关性。基于像差理论,对两片补偿透镜的光学参数进行了推导求解,分析了初始参量与归一化数据的关系,再利用光学软件对计算结果进行缩放与优化。在不同的前零位补偿透镜放大率下,设计了四个具有不同曲率半径的凹抛物面镜,并给出了非球面镜的最大口径和最大相对孔径。采用具有1/10口径比的补偿透镜,实现了口径为3.7 m、相对孔径为1/1.2的非球面镜面形检验,面形波前误差峰谷(PV)值优于0.1λ(λ=633 nm)。容差分析结果证明了检验系统的可行性。针对口径为500 mm、相对孔径为1/1的抛物面镜开展了原理实验,从可检验的最大非球面镜口径和实施难度方面对所提方法与常用方案进行了比较,前后零位补偿结合系统的设计面形波前误差PV值为0.061λ,面形波前误差均方根(RMS)值为0.009λ,实现了面形波前误差RMS值优于λ/40的检测精度。前后零位补偿结合的检验系统适用于具有4 m量级大口径、大相对孔径的非球面镜的高精度面形检测。

The aspheric test via finite distance null compensation is limited by too many adjustment factors and low test precision.Here we establish an aspheric test system by integrating front null compensation with back null compensation,in which a compensation lens is used before and after the spherical center of the mirror to be tested and thus the front and back areas show aberration correlation.First,based on the aberration theory,the optical parameters of two compensation lenses are theoretically derived and solved,and the relationship between the initial parameters and the normalized data is analyzed.Then the normalized results are scaled and optimized by the optical design software.Four concave parabolic mirrors with different curvature radii are designed under different magnifications of front null compensation lenses.The maximum aperture and the maximum relative aperture of the aspheric mirror are obtained.The compensation lens with a 1/10 aperture ratio is used to realize the aspheric test of an aspheric mirror with a large aperture of 3.7 m and a large relative aperture of 1/1.2,and the peak-valley(PV)value of the residual wavefront error is superior to 0.1λ(λ=633 nm).The tolerance analysis confirms that the test system is feasible.The principle experiment is conducted for the parabolic mirror with an aperture of 500 mm and a relative aperture of 1/1.The maximum diameter of the aspheric mirror and the difficulty of implementation are compared between the proposed method and the classical configuration.The PV value and the RMS value of the designed wavefront error of the test system combining front and back null compensation is 0.061λand 0.009λ,respectively.The RMS value is superior toλ/40.The test system combining front and back null compensation is suitable for the high-precision test of aspheric surfaces with 4 m large diameter and large relative aperture.