Oral Presentation

Fabrication & testing the primary mirror of Beijing Normal University 1.93m optical telescope

Author(s): Contributors: Yi Zheng, Xiang Jiang, Xinnan Li, Ying Li, Bin Liang, Song-feng Kou, Xiangqun Cui, Bozhong Gu, Chen Xu, Bo Ji, Yujun Sha

Presenter: Yi Zheng (中国科学院南京天文光学技术研究所)

The BNU 1.93m optical telescope is supposed to get the first light in 2024. The successful finish of its iconic primary mirror in August 2023 has taken a big stride forward to the goal. Here, the paper introduces the technical progresses achieved in fabrication and testing. First, we introduce the optical design and the history of the forty-year-old 1.9m low expansion blank. Then the well-designed support mechanics are presented, which laid solid foundation for the later process. The proper use of multiple tools, including active stress lap and computer controlled small tool not only greatly accelerates the process, but guarantees the good quality of the final surface. When error is large, we perform in situ test, using a new developed profilometer, for the mirror. In final polishing, a vertical tower is constructed for optical test which greatly mitigates the inference by air turbulence. We confidently believe that with the technologies obtained, we can finish 2-6m large aspherical reflector efficiently.