Research Of The Key Techniques Of White Light Coronagraph

Coronal is the outermost layer of the solar atmosphere, which ranges from chromosphere across several sun radius. In a broad sense, our earth environment is a part of coronal. Drastic coronal activities(such as, sun wind, coronal mass ejections(CMEs) and so on) have great effect on earth and the solar-terrestrial space. Coronagraph is an instrument, which is used for coronal observation under the situation without total solar eclipse. Based on the main index proposed in the “Kua Fu Mission”, the first externally occulter white light coronagraph has been domestically designed and finished in this thesis. Then a series of experiment about coronagraph stray light suppression around the coronagraph were carried out. The proposed prototype of coronagraph optical system works at wavelength of 650nm~750 nm, with a field of view of ±2.5-15 R⊙(R⊙ represents a radius of the sun, which is about 16 ’), an effective aperture of 30 mm, an effective focal length of 200 mm, and has a resolution of 14 sec/pixel.Compared with the chromosphere light, the brightness of coronal is extremely weaker and just amount to 10-6 of the sun average intensity. Hence, the main problem is to suppress the stray light. Accoding the different of formation mechanism,coronagraph stray light can be divided into five categories: the straight light of the sun, the diffraction caused by the aperture, the stray light caused by twice reflection of objective surfaces, the stray light caused by the problems of lens machining accuracy, and the stray light caused by the flaws of optical material. And the main reasons were discussed in the five stray lights, respectively. Moreover, the generation of twice reflection ghost image was analyzed by using the ASAP. And, the suppression effect about the heat rejective mirror, the field stop used for block the diffraction of entrance window, and the internal occulter used for weaken the diffraction of external occulter were analyzed by using Trace Pro. In addition, the vignetting issues of externally occulter coronagraph is analyzed and simulated. Finally, the relationship between the value of vignetting and the field of view and the two-dimension equal vignetting function were obtained.In order to have a deep study on the method of the coronagraph stray light suppression, experiments corresponding to the different stray light were designed, and the suppression effect was observed. The result shows that the suppression method of coronagraph stray light is practical and effective, and the stray light have a good restrain. At last, the overall stray light level of the coronagraph is tested and the stray light can reach 10-9B⊙(B⊙ is the brightness of the sun).