The representative ones are OSO-7 in 1971, Skylab-HAO in 1973, SOHO LASCO-C1 in 1995, STEREO SECCHI-COR1 in 2006, Solar Orbiter-Metis in 2020, and ADITYA-L1 VELC planned for launch in 2022. In the past decades, a number of solar coronagraphs have been developed, and a lot of high-quality imaging and spectroscopic data have been provided. Research on coronal mass ejections (CMEs) is of great significance for exploring the response of different layers of the solar atmosphere to solar eruptions and for providing observation data for space weather forecasting and the safety of the space environment. The ejection of the plasmas has a great impact on the space environment around the Earth. The corona is the outermost layer of the Sun’s atmosphere, extending from the edge of the solar chromosphere to several solar radii, which is composed of thin plasma. The stray-light measurement results for SCI in the laboratory show that the stray-light level can be suppressed to the order of 10 −8 B ⊙ at 2.5 R ⊙ (B ⊙ is the mean brightness of the solar disk) in the white-light (WL) band, which is consistent with the stray-light level obtained by simulation and verifies the modeling and simulation. The scattered stray-light from the primary mirror, including the surface errors, cosmetic defects, and particulate contamination, is analyzed and suppressed, and the corresponding scattering models are established for simulation based on the laboratory testing.

In this study, a stray-light suppression method is adopted for Solar Corona Imager (SCI) which is a dual-waveband internally occulted reflecting coronagraph simultaneously and independently observing the inner corona in the HI Lyman-alpha (121.6 ± 10 nm) line and white-light (700.0 ± 40 nm) wavebands with a field-of-view (FOV) from 1.1 to 2.5 R ⊙ (R ⊙ stands for the mean solar radius).

In order to achieve a clear observation of the ultra-low brightness solar corona and provide a physical basis for forecasting space weather that seriously affects the human living environment, the stray-light suppression level becomes the key factor affecting the development of the coronagraph. 4School of Physics and Optoelectronic Engineering, Xidian University, Xi'an, China.3College of Communication Engineering, Jilin University, Changchun, China.2University of Chinese Academy of Sciences, Beijing, China.1Changchun Institute of Optics, Fine Mechanics and Physics, Chinese Academy of Sciences (CAS), Changchun, China.Guang Zhang 1,2, Yunqi Wang 1, Lingping He 1, Xiaodong Wang 1, Shuai Ren 1,2, Yubo Xuan 3, Fei Liu 4 and Bo Chen 1*

Sun corona in day light