为瞬态测量大口径光学元件波前，提出一种基于斜入射结构的近红外反射式错位点衍射干涉原理的Φ400 mm瞬态波前检测方法。该方案将待测光分成两束互相错位的参考光与测试光，从而在干涉图中引入高线性载频，采集到对比度良好的干涉图后，利用傅里叶变换相位解调法从单幅干涉图中提取待测波前相位，实现瞬态波前动态测量。实验光路总长近20 m，极易受气流的影响，且由于气流干扰随时间变化，该系统本身可以看作是大口径光学元件瞬态波前发生与检测装置。测试结果与SID4 波前传感器比较，波前均方根（RMS）小于1/50 λ，可知所提方法可以实现大口径瞬态波前的高分辨率与高精度检测。

In order to measure the instantaneous wavefront of large aperture optical elements, a method based on the structure of oblique incidence of reflective shearing point diffraction interferometer is proposed. A lateral displacement between the reference wavefront and the test wavefront is formed after passing this structure. The shear of two beams introduces linear spatial carrier frequency to the point diffraction interferogram. After receiving a good contrast interferogram, wavefront phase is retrieved by Fourier transform ( FT) automatically to realize the dynamic measurement of instantaneous wavefront. The optical path is up to 20 m, so the air current is a significance factor to the result. Besides, because of the air current, the system itself can be seen as a instantaneous wavefront happening and measurement of large aperture optical elements. The results indicate that the root mean square value is in accord with that acquired by SID4 wavefront sensor (less than 1/50λ),so about the repeated accuracy. The method proposed can be applied in high resolution and accuracy measurement of instantaneous wavefront.