基于多普勒频移调谐的斐索型同步移相干涉测试技术研究

The optical elements with large aperture have found wide applications in many fields of national economy. The interferometric measurements of large optical elements have to be performed at large cavity lengths in some applications. The existed interferometric structures cannot measure the plane optical elements with large aperture at long cavity lengths.To this end, a new technology of simultaneous phase-shifting Fizeau interferometry based on Doppler frequency tuning is proposed in this project. A radial grating is rotated at high speed to realize beam split and frequency shift. And three interferograms are captured simultaneously. The technology doesn’t need polarization modulation. The structure of the system is simple with few optical elements. And it can measure the optical elements with large aperture at long cavity lengths. The testing theory of the proposed simultaneous phase-shifting interferometry is researched. The characters of beam split and frequency shift, the method of grating writing and the control method of rotating grating at high speed are researched. To calibrate phase shifts automaticly when measured at different cavity lengths, a method based on the Fourier transform is researched. To match the spatial positions and correct the distortions of the interferograms, a robust sub-pixel image registration technique based on local phase correlation is researched. The proposed research is an exploration on the new type of simultaneous phase-shifting interferometry. It will offer the technical basis for the realization of the dynamic measurement of the optical elements with large aperture at long cavity lengths.

大口径光学元件在国民经济诸多领域应用广泛，其面形的干涉检测常需在长干涉腔长下进行，目前已有的干涉结构均不能满足大口径平面光学元件在长干涉腔长下的测试需求。为此，本项目提出一种基于多普勒频移调谐的新型斐索型同步移相干涉测试方法，该方法采用高速旋转径向光栅同时实现分光和移相功能，并在瞬间同时采集三幅同步移相干涉图。其特点是无需偏振调制，元件少，简化了系统结构，能够实现大口径光学元件在长腔长下的测量。项目研究提出的同步移相干涉测试方法的测试理论以及光栅分光和频移特性、光栅刻制方法、光栅高速旋转控制方式等关键技术。研究基于时域傅里叶变换的移相量标定方法，实现在不同干涉腔长下测量时移相量的标定。研究基于相位相关的亚像素级位置和形状配准技术，实现干涉图间空间位置的配准和畸变的校正。该项目的研究探索了一种新型同步移相干涉测试技术，为解决我国急需的长腔长下大口径光学元件的动态检测问题提供技术基础。

同步移相干涉测试技术是目前抗振效果最好的干涉测量手段，目前大多数同步移相方案采用了泰曼型结构形式，而斐索型干涉仪由于其共光路的特点，适用于检测平面元件。目前已有的几种斐索型结构都不适合于长干涉腔长下的平面元件的测试，针对长干涉腔长的测试需求，提出一种新的同步移相干涉测试方案。以斐索型移相干涉仪的结构为基础，采用四分之一波片作为参考镜，得到一对正交偏振光。正交偏振光经过棋盘相位光栅后形成不同衍射级次的光线，通过特制的光阑选取(±1,±1)级衍射光，使这四束光线先后通过相位延迟阵列和偏振片获得4幅移相量依次为π/2的干涉图。从干涉系统、分光系统、移相系统和数据采集系统几个方面设计并研制了该方案的关键器件并搭建了实验装置。在此方案基础上，提出了一种利用针孔线偏振器实现点衍射的准共光路同步移相干涉方案和实验装置，干涉系统采用了环形光路，可以同时获得偏振方向正交的参考光和测试光，实现准共光路的点衍射干涉仪设计。通过相位光栅和相位延迟阵列实现了偏振同步移相，减小了环境振动等因素对干涉测试的影响。.项目还研究了干涉图像的位置配准方法，设计实现了两种干涉图位置配准算法：基于Hough变换的圆检测方法以及相位相关方法。前者以圆域干涉背景图为对象，通过域值分割、Canny边缘检测算子获得干涉背景图的轮廓，最后由Hough变换拟合出圆斑方程，以四幅干涉背景图的圆心坐标作为配准依据；后者同样以干涉背景图为对象，运用相位相关算法计算出四幅干涉背景图的相对平移量，以此作为配准依据。两种算法均通过实验验证其可靠性和精确性。.在斐索同步移相干涉仪中对平面元件进行了测量，将波面测量结果与ZYGO干涉仪的测量结果比较，得到面形的峰谷值相差0.004λ，均方根误差值相差0.001λ。实验结果表明，该方案相比泰曼型同步移相干涉测量方案可以简化系统结构，减小系统误差，并且更易装校，适合用于长干涉腔长下平面元件的测量，并且能有效减小干涉测量中振动带来的影响。