摘要
采用胶粘剂支撑方式的光学平晶在经过离子束抛光后,硅橡胶可能由于温度过高而发生脱胶,导致平晶受力状态发生改变,进而在面形测试结果中引入误差。对此,提出一种脱胶误差分析方法。针对内部气泡和流动趋势这两种典型的脱胶现象,分别构建平晶非均匀支撑的物理模型,并通过有限元法分析单个胶斑变化对平晶面形产生的影响。仿真结果显示:距离平晶工作面最近的胶斑对其面形影响最大,极限状态下可使面形产生近3 nm的峰谷值误差,且脱胶主要影响面形中的像散成分。结合数字图像处理方法,对立式干涉仪参考平晶在迭代加工中产生的面形误差进行解算与校正,依据校正结果指导离子束抛光,最终实现Φ300 mm立式斐索干涉仪在液面基准下的空腔精度优于λ/30。平晶的面形测试通过液面基准法实现。实验结果表明,所提出的脱胶误差分析方法能够有效地指导胶粘剂支撑平晶的迭代加工,保证加工过程的收敛性。
Objective Ion-beam polishing is a high-precision surface shape-modification technique that requires multiple iterations to ensure surface accuracy.Currently,it is widely used for the surface processing of precision optical flats.However,for transmission flats supported by an adhesive,the temperature generated during polishing may exceed the tolerance temperature of the silicone rubber,which may cause the detachment of the silicone.This changes the uniform support state of the transmission flat,which consequently introduces additional deformation to the surface morphology of the flat.Methods The detachment of adhesive spots occurs primarily in two forms:internal bubbles and flow tendencies.Adhesive spots with bubbles are primarily characterized by a decrease in the contact area with the transmission flat,whereas adhesive spots with flow tendencies primarily exhibit a displacement of the mass center position.We constructed a physical model of a non-uniform support by analyzing the change in force on the transmission flat after debonding.Based on the distance between the adhesive spots and the operating surface of the transmission flat,we classified the adhesive spots into three groups and selected one for analysis.The surface error caused by changes in the adhesive spots was simulated via COMSOL Multiphysics using the finite-element method.The direct result of the finite-element simulation is the global topography of the operating surface of the transmission flat,and the error surface was obtained by subtracting the surface topography under a uniform distribution of the adhesive spots.The results show that the adhesive spots nearest to the operating surface of the flat exert the most significant effect on their surface topography(Figs.4 and 7).Additionally,we investigated the variation in the low-frequency morphology under different degrees of adhesive-spot detachment.The results indicate that adhesive-spot detachment exerts the most significant effect on astigmatism(Fig.16).Results and Discussions The liquid-reference method was employed to monitor the iterative ion-beam polishing process of the transmission flat on a Φ300 mm vertical Fizeau interferometer.The initial peak valley(PV) value of the flat surface before polishing is 122.4 nm.After three rounds of iterative polishing,some adhesive spots around the transmission flat are degummed.An appropriate digital image-processing algorithm was applied to the captured onsite images to calculate the reduction in the area and the displacement of the mass center of the detached adhesive spots.The global surface error was estimated based on the condition of the adhesive spots,and the corrected surface was obtained by subtracting the 300-mmaperture error surface from the absolute test result via the liquid reference.Further ion-beam polishing was performed based on the corrected surface.Finally,the accuracy of the transmission flat reaches 20.45 nm,which is better than λ/30,thus validating the effectiveness of the error correction(Fig.14).The results show that the proposed debonding error-correction method can ensure the convergence of ion-beam polishing(Fig.15).Conclusions The Φ300 mm vertical Fizeau interferometer adopted in this study was equipped with a precise temperature control system and an air-floating structure,thus ensuring a constant temperature and vibration isolation in the test environment.Using this device,the repeatability of the liquid surface interference test can reach 0.005 nm(Fig.17).After assembling the polished transmission flat and considering other error sources,such as detection and light sources,the comprehensive uncertainty of the vertical interferometer is 0.99 nm.
作者
李晶晶
郑东晖
刘宇晴
陈磊
徐晨
俞欣怡
Li Jingjing;Zheng Donghui;Liu Yuqing;Chen Lei;Xu Chen;Yu Xinyi(School of Electronic and Optical Engineering,Nanjing University of Science&Technology,Nanjing 210094,Jiangsu,China;Nanjing Institute of Astronomical Optics&Technology,Chinese Academy of Sciences,Nanjing 210042,Jiangsu,China;University of Chinese Academy of Sciences(Nanjing),Nanjing 211135,Jiangsu,China)
出处
《光学学报》
北大核心
2025年第1期79-87,共9页
Acta Optica Sinica
基金
中央高校基本科研业务费专项资金(30923010934)
国家自然科学基金(62005122)
江苏省自然科学基金(BK20200458)。
关键词
测量
干涉测量
液面基准法
离子束迭代抛光
有限元法
面形误差校正
measurement
interferometry
liquid reference method
ion beam iterative polishing
finite element method
topography errorcorrection
