Li Zhigang, Qiu Lirong, Zhao Weiqian, Zhao Qi
Appl Opt. 2016 Jun 20;55(18):4910-6. doi: 10.1364/AO.55.004910.
We propose a new laser multi-reflection differential confocal focal-length measurement (LDCFM) method to meet the requirements of high-precision measurements of long focal lengths. An optical flat and a reflector are placed behind a test lens for reflecting the measuring beam repeatedly. Then, LDCFM uses the property that the null points of differential confocal response curves precisely correspond to the convergence points of the multi-reflected measuring beam to exactly determine the positions of the convergence points accurately. Subsequently, the position variation of the reflector is measured with different reflection times by using a distance-measuring instrument, and thereby the long focal length is measured precisely. Theoretical analyses and preliminary experimental results indicate that the LDCFM method has a relative expanded standard uncertainty (k=2) of 0.04% for the test lens with a focal length of 9.76 m. The LDCFM method can provide a novel approach for high-precision focal-length measurements.
为满足长焦高精度测量的需求，我们提出了一种新的激光多反射差分共焦焦距测量（LDCFM）方法。在被测透镜后方放置一块平面光学元件和一个反射镜，用于多次反射测量光束。然后，LDCFM利用差分共焦响应曲线的零点精确对应多反射测量光束的会聚点这一特性，准确确定会聚点的位置。随后，使用测距仪测量反射镜在不同反射次数下的位置变化，从而精确测量长焦。理论分析和初步实验结果表明，对于焦距为9.76 m的被测透镜，LDCFM方法的相对扩展标准不确定度（k=2）为0.04%。LDCFM方法可为高精度焦距测量提供一种新途径。
