为实现同步辐射用光学元件面形的绝对检测，发展了镜面旋转对称三平板检测法。该方法将菲佐干涉法检测到的波前函数关于y轴分解成镜面对称部分与镜面非对称部分，再利用N次旋转取平均值消除镜面非对称部分，从而通过计算获得待测平面的绝对面形分布。推导了镜面旋转对称法检测矩形平面镜面形的公式，应用该方法设计了高精度矩形平面镜的测试实验，并进行了误差分析。实验结果表明，与传统三平板绝对测量方法相比较，两种方法在高度轮廓误差和斜率误差方面的计算结果都符合较好，其对比后的残差均方根(RMS)值分别为λ/500(λ=632.8 nm)与0.93 μrad。

A modified method based on mirror rotational symmetry is developed to determine the absolute flatness deviations of optical elements in synchrotron radiation. The novel method is described in terms of functions that are symmetric or antisymmetric with respect to reflections at y axis. Absolute deviations of three flats can be obtained when mirror asymmetric errors are removed by N-position rotation average method. The formulas are derived for measuring the absolute surface error of the rectangular flat, and experiments on high accuracy rectangular flat are performed to verify the method. Compared with the measurement results obtained by Zygo′s three-flat application, our method is calibrated to an accuracy of better than λ/500 (λ=632.8 nm) root mean square (RMS) on height and 0.93 μrad RMS on slope error. The theoretical derivation, experimental results, and error analysis are presented.