装夹方式及预紧力对透镜像差特性的影响规律

高精度光刻物镜中的光学透镜在自身重力以及装夹预紧力的作用下,面形会发生变化,从而会对光学系统各种像差造成影响。在考虑透镜自重的情况下,研究了镜片夹紧方式及夹紧力对其像差的影响规律。分别在镜片顶面和侧面施加2～6点均布、均匀载荷,且每种加载情况下夹紧力线性增大,通过有限元仿真计算出各种受力情况下的镜面变形;将变形量数据用66项标准Zernike多项式进行拟合,分析载荷均布点数以及载荷力大小对透镜像差的影响。分析结果表明:各种加载工况下透镜像差中的重要影响项皆为平移、离焦、球差和n-foil(n为均布载荷点数);重要影响项所对应Zernike多项式的系数变化与夹紧力变化呈线性关系。分析结果为补偿透镜像差提供了依据,并能指导像差校正的透镜设计。

Influence of Mounting Method & Pre-load on Lens Aberration

The surface deformation of high-accuracy photolithographic objective lens under gravity and assembling force has significant influence on lens optical aberration. Considering the gravity, the influence of mounting method and pre-load on lens optical aberration is analyzed. The forces are evenly applied on two to six equally distributed points on lens top and side respectively, and the force increases linearly under the load cases. Lens surface deformation under each load case is calculated by finite element analysis, and the deformation data is fitted using the standard Zernike polynomials of 66 terms, so that the effecting law of the number of load points and the magnitude of force on lens aberration can be analyzed. The results show that the main aberrations of lens under every load case are piston, defocus, spherical aberration and n foil with n being the number of load point. The relation between the standard Zernike polynomial coefficients of lens and the assembling force is linear. It supplies a basis for compensating lens aberration, and it can be served as a guideline for lens design used for eliminating optical system aberration.