Analysis And Suppression Of The Stray Light In The Inner-occulted Coronagraph

Coronagraph is an attachment for viewing the corona of the sun.The observation of the corona can help solve many difficulties existing in current solar physics research,and can also be used for monitoring and forecasting of the space environment.Therefore,the construction of the coronagraph is of great significance in both science and application.In this thesis,an internal-occulted coronagraph is designed with a field of view of 1.05~1.5 R_?,which corresponding to±16.8~24',and an aperture of 70 mm,a F/#of 17.5,and an optical total length of 2182.4 mm.The angle resolution of which is 3.75?,and the passband is 530.3±0.2 nm,such that it can perform narrow-band imaging of the emission line of Fe XIV ions in the corona.The brightness of the corona is extremely weak in visible band,which is only about one-millionth of that of the solar photosphere.In order to view the structure of the corona under such a strong background,the instrument must have an high performance of the stray light suppression.The main research content of this thesis is the stray light suppression technology in the inner-occulted coronagraph and is divided into the following parts:Firstly,the propagation properties and theoretical intensity distribution of various stray light inside the instrument are simulated by the methods of ray tracing,Gabor transformation or Monte carlo analysis,and the suppression structures were designed based on these results.Secondly,a stray light detection system was established in the laboratory,by which the actual stray light of the coronagraph was tested,and the effectiveness of each suppression structure was verified.The result indicates that the intensity of the stray light on the detector is 7.84×10~-66 B_?at inner region and 4.86×10~-66 B_?at outer region,which B_?means the average brightness of the solar photosphere.Then,the parameters of a tunable narrow-band birefringent filter were determined according to the method for observing the corona emission line,and the initial structure of the filter was designed.Finally,the external observing experiment was carried out with this coronagraph,and the brightness images of the E-corona were successfully obtained.This instrument will be the first coronagraph system domestically developed in China.