光学元件表面缺陷散射光成像数值模拟研究

Numerical Simulation Research on Scattering Light Imaging of Surface Defects of Optical Components

对于精密光学元件表面微米亚微米量级的表面缺陷,光在缺陷处会产生强烈的衍射和散射效应,其在像面的分布情况不能简单地使用几何光学进行解释。采用时域有限差分方法(FDTD)建立了光学元件截面为三角形、矩形的表面缺陷的电磁理论模型,模拟仿真得到了缺陷附近区域及像面的散射光分布情况。并使用电子束曝光、反应离子束刻蚀工艺制作了矩形截面的缺陷样本板,对样本缺陷进行了散射成像实验,得到了暗场图像的灰度分布情况,并与理论仿真结果进行了比对。实验中得到的表面缺陷的像面光强分布情况与理论模拟基本吻合,为光学元件的加工制造和缺陷检测的尺度标定提供了理论依据和参考。

Strong diffraction and scattering effects can be caused by micro or sub-micro scaled surface defects of optical components. The distribution of scattering light on the image plane can not be explained simply by geometrical optical theories. The electromagnetic model of triangle-shaped and rectangular surface defects is built by using finite difference time domain（FDTD） method. The distributions of scattering light in the near-field region and on the image plane are simulated. The scattering imaging experiment of sample defects is also performed. The sample defects are rectangular and fabricated by electron beam exposure and ion beam etching. The gray distributions in dark-field images are compared with intensity distribution of scattering light on the image plane and show a good consistency. The results provide significant theoretical references for defect calibration in optical manufacturing and testing.