离子束加工中全频段误差的演变

Evolution of Full Band Errors in Ion Beam Processing

在空间光学、光刻物镜、惯性约束聚变及强光系统等领域的高精密光学元件制造过程中,采用基于小磨头抛光原理的修形技术,虽然能有效去除面形低频误差,但对中高频误差难以修正。为了达到有效控制全频段误差的目的,文章以直径420mm的非球面为样件,在离子束抛光机床上进行不同频段误差的修形收敛试验。针对光学元件面形误差在不同频段的特性,以面形误差频段均方根及梯度均方根指标作为评价参数,分析各频段误差产生的原因,探索离子束工艺参数及其他因素与各频段误差间的对应关系。通过4轮离子束迭代加工后,样件全频段面形误差均方根值从34.973nm收敛到6.025nm,梯度均方根值由0.091λ/cm收敛到0.061λ/cm(λ=632.8nm)。试验结果表明:通过优化离子束的工艺参数,可显著提升光学元件的全频段面形精度,实现频段误差在不同评价参数下的同步收敛。频段均方根及梯度均方根指标可作为评价全频段面形误差变化的标准,对光学加工具有参考价值。

In the manufacturing process of high-precision optical components in the fields of space optics,lithography objective lens,inertial confinement fusion(ICF),strong light system and others,the shape modification technology based on the principle of small grinding head polishing can effectively remove the low-frequency surface shape error,but it is difficult to correct the medium and high-frequency errors.In order to effectively control the whole frequency range error,this paper takes the aspheric surface with diameter of420 mm as the sample,and carries out the shape modification convergence test of different frequency band errors on the ion beam polishing machine tool.According to the characteristics of the surface shape error of optical elements in different frequency bands,the root mean square(RMS) and gradient root mean square(GRMS) of the surface error frequency band are used as evaluation parameters to analyze the causes of the error in each frequency band,and to explore the corresponding relationship between the process parameters of ion beam and other factors and the errors of each frequency band.After four rounds of ion beam iterative processing,the RMS value of the full band surface shape error of the sample piece converges from 34.973 nm to6.025 nm,and the GRMS value converges from 0.091λ/cm to 0.061λ/cm(λ=632.8 nm).The experimental results show that:by optimizing the process parameters of ion beam,the shape accuracy of optical elements in full frequency band can be significantly improved,and the synchronous convergence of frequency band error under different evaluation parameters can be realized.The RMS and GRMS indexes can be used as the standards to evaluate the change of surface shape error in the whole frequency band,which has guiding significance for optical processing.