随着中长焦距光学元件在光学遥感、高功率激光器和天文望远镜等系统中的广泛应用, 对这类光学元件焦距的高精度测量提出要求。在双光栅干涉焦距测量技术的基础上, 提出了一种新的改进算法。该算法通过Moiré条纹倾斜角度与待测元件焦距之间的函数关系得到焦距计算公式, 并利用入射平面波时Moiré条纹的理想状态优化了该计算公式, 解决了Moiré条纹倾角基准线的确定问题, 提高了Moiré条纹角度求解精度。采用2块周期为20 μm的朗奇光栅搭建了长焦距测量装置。实验测得的透镜焦距为36.690 m, 测量重复精度达0.382‰。

With the wide application of long focal length optical elements in remote-sensing technology, high-power lasers and astronomical telescope systems, the high-precision measurement of such optical elements’ focal length is required. Based on the technique of double-grating interferometry, a new improved algorithm was proposed. This algorithm obtained the focal length calculation formula by the functional relation between the Moiré fringe tilt angle and the focal length of the element to be measured, and optimized the calculation formula by using the ideal state of the Moiré fringe when illuminated by a collimated beam. So the step for determining the Moiré fringe’s baseline can be avoided, and the precision of the Moiré fringe tilt angle can be improved. In the experiment, two Ronchi gratings with period of 20 μm were used to build the measuring system. The measurement result of the test lens is 36.690 m, and the repeatability accuracy is up to 0.382‰.