System Design And Stray Light Suppression Of Three-disk Externally Occulted Coronagraph

Solar activities are closely related to the earth’s environment and human living environment,and in serious cases,they will cause great harm to aerospace,navigation systems,communications,electricity,etc.,causing severe weather in solar-terrestrial space.In recent years,through the study and observation of the corona and coronal mass ejection（CME）,it has been found that the consequences of coronal mass ejection are no less than solar flares.The coronagraph is the main instrument for observing the corona and coronal mass ejection,which is of great significance for predicting the severe space weather of the Earth and solar-terrestrial space and studying the influence of the sun’s magnetic field.In this thesis,a three-disk externally occulted coronagraph has been developed to image the corona and corona polarization.The field of view is 12～75R_⊙@1AU,36～225R_⊙@3AU,±20°,the resolution is 1.2’,the wavelength is 630nm-730nm,the F number is 4,the focal length is 38mm,and at the Nyquist frequency of 37lp/mm,the transfer function（MTF）is greater than 0.6.The three-disk externally occulted coronagraph developed in this thesis increases the difficulty of stray light suppression of coronagraph due to its large field of view,so the principle and method of stray light suppression of the three-disk externally occulted coronagraph were deeply studied.Firstly,according to the working principle of the coronagraph,the optical design and imaging quality evaluation of the coronagraph system were completed,and the imaging quality inspection was carried out by designing experiments.Secondly,according to the pointing accuracy requirements of the coronagraph,the solar alignment system of the coronagraph was designed,and the alignment accuracy was experimentally verified on the basis of the principle of image processing algorithm.Then,the stray light sources of the coronagraph system were theoretically analyzed,which were classified according to different propagation methods,mainly divided into three categories:direct solar light,edge diffracted light and scattered stray light.Different mechanical structures were used to suppress these stray light sources,and the simulation software was used to simulate each stray light source and mechanical structure,and the suppression effect of stray light was verified theoretically.Finally,the evaluation criterion for the suppression level of stray light in the coronagraph is proposed,a stray light detection device was set up in the laboratory,and a comparative experimental verification of whether there is an suppression structure was carried out,and the suppression effect of each suppression structure can be observed more intuitively.A detection method for the total stray light suppression level of the coronagraph was proposed,and the actual total stray light level of the coronagraph system was experimentally detected.The experimental results show that the total stray light suppression level of the coronagraph reaches the order of 10^-13,which meets the requirements of the stray light suppression level of the coronagraph system.