基于衍射理论的分块镜共相位误差的高精度测量

Technique of detecting the piston of segmented mirrors with high accuracy based on diffraction theory

拼接式的分块镜能满足下一代望远镜更大、更轻和可折叠的要求,分块镜共相位误差的高精度检测是望远镜实现超大口径、超高分辨率成像的技术关键。从理论上证明了一个波长范围内,衍射光斑最高峰的峰值位置偏离图像中心位置的距离与共相位误差之间呈线性关系,提出了基于衍射理论的峰值位置法检测分块镜共相位误差的方法。该方法对峰值位置的定位精度要求很高,采用基于高斯拟合的峰值定位方法,在采样点为10个左右、采样间隔为5μm的条件下,定位精度可达到600nm,能够满足定位要求。实验结果表明:该方法能够有效检测分块镜的共相位误差,在一个波长的测量范围内,其测量精度能够达到λ/20。该方法系统简单,测量精度高,适合大型分块镜共相位误差的测量。

Foldable segmented mirrors satisfy the requirement of next generation telescope which requires larger, lighter and foldable. Detecting the piston error between individual segments with high accuracy is critical to avoiding the image degradation due to segments misalignment with large mirrors. It is also critical to realize the grand scale of the segment mirror. The relationship of piston error and the distance of the main peak point of diffractive spot from the center point of image was proved to be linear within one wavelength range. A method to detect the piston error based on the location of the main peak of diffraction theory was presented. The optical system was simple and the measurement accuracy was high. The accuracy of the peak location was required high enough to satisfy the requirement for piston detecting of segmented mirrors. A peak location method based on Gaussian fitting was used and the location accuracy may arrive to 600 nm on the condition of 10 sampling points or so with the sample interval of 5 μm. The experimental results show that it is a valid method to detect the piston error of the segmented mirrors. The measurement accuracy of piston can achieve within one wavelength range.